This brings me to the most important aspect of foliar feeding: it is a temporary fix for a much larger soil problem.

Instead, select plants suited to your soil and microclimate, get your soil tested periodically, and remain skeptical about too-good-to-be-true advertisements.

Why do soil bacteria matter to gardeners?

Most soil bacteria are valuable members of your team. They provide a huge benefit to your soil and plants. And you need to know what the bad bacteria look like when they start to set up housekeeping. The earlier you break those disease triangles, the faster your can return to harvesting your delicious crops.

Most bacteria are aerobic, which means they need oxygen. This is why turning your compost pile makes everything decompose faster. You are providing the decomposer bacteria with the air they need. If you don’t, the anaerobic, non-air breathing bacteria take over. Those are the ones associated with rot and purification. [Ew!]

Did you know that soil bacteria will consume more water than they can hold, causing their bodies to burst? Yet another argument against over-watering...

While all nutrients are important to plant growth, primary nutrients are used in the greatest amounts. Before you add more fertilizer, however, you need to find out what is already in your soil. Adding too much of a nutrient is just as bad, or worse, than not enough.

The only way to know about the nutrients in your soil is with a lab-based soil test. Over-the-counter soil tests are not accurate enough to be of any use. Soil tests are inexpensive and extremely valuable.

Each of the primary nutrients supports different aspects of plant growth and health. The more you know about what they do for your plants, the better you will be able to spot deficiencies and toxicities.

Nitrogen

Nitrogen is the single most limiting factor in plant growth. Nitrogen is used to make chlorophyll as well as plant enzymes and proteins. Nitrogen is responsible for lush, green, vegetative growth. Without nitrogen, photosynthesis cannot occur. 

Stunting and chlorosis are the two most common signs of insufficient nitrogen. Nitrogen is highly mobile within the soil and in plants. Too much nitrogen can be just as bad as not enough. Excessive nitrogen is seen as darker than normal leaves and more vegetative growth than fruit or flowers. Too much nitrogen can burn plants, and it can cause erratic or reduced budbreak. Too much nitrogen can also stimulate new  growth that may be vulnerable to pests, disease, and injury. ​

Potassium

Potassium (K) is the third primary nutrient and it dictates the size, shape, color, and sugar content (brix) of your fruit crops. It also boosts photosynthesis and respiration, helps plants stay upright, and promotes healthy root systems.

There’s a lot of potassium on Earth, but most of it is unavailable to plants. Plants can only use potassium that is in solution. As plant roots absorb mineral-rich water from the ground, potassium is pulled in and put to work. Potassium, also known as potash, is concentrated in leaves and growing tips. Also found in bat guano and wood ashes, potassium is a highly mobile element.

Potassium deficiencies result in reduced nitrogen absorption and a build up of sugars that can give leaves a burnt appearance. Other signs of potassium deficiency include wilting, brown spotting, and discolored veins. These symptoms move from older/lower growth to higher/newer growth.

Potassium is one nutrient that plants can absorb at levels higher than they can use, in an action called ‘luxury consumption’. If you see a white crust developing on leaf margins (edges), it is the sugar and potassium residue from guttation. 

Nutrient imbalances and high temperatures can interfere with nutrient absorption. Before you toss another bag of fertilizer at your plants, make sure they really need it. The only way to know for sure what your plants are working with is to invest in a soil test from a local, reputable lab. It will save you a lot of money in terms of replacement plants, reduced harvest, unnecessary soil amendments, and chemical treatments.

So just remember: nitrogen promotes lush, green growth, phosphorus helps plants prepare for reproduction, and potassium promotes healthy crops.

​And too much of a good thing can be a bad thing.

Using base saturation numbers

Soil test results will tell you how much of each plant nutrient is present and base saturation percentages. One thing you might see is an excessive amount of a nutrient but a normal base saturation percentage. How is this possible? Again, it goes back to electrical charges. Say you have a ton of calcium, a positively charged mineral, but the calcium base saturation is normal. This happens because other charged particles are also present. They can block the excess bits from connecting with anything. Or, there may not be enough negatively charged soil particles available. You need to use both the actual mineral levels and the base saturation percentages when deciding on whether or not to add fertilizer.

This post is an oversimplification of an extremely complex topic, but it is accurate enough to help you get the most out of your soil test results. Soil tests cost around $25 and are worth every penny.

In the garden, bicarbonates are touted as cure-all treatments of powdery mildew, gray mold, septoria leaf spot, and other fungal diseases, particularly sodium bicarbonate (baking soda) and potassium bicarbonate. The truth is, baking soda is a type of salt and always a bad idea in the garden. Potassium bicarbonate, on the other hand, is an effective organic fungicide. 

But what about ammonium bicarbonate? What are bicarbonates, anyway?

Bicarbonates

In chemistry, the word ‘bicarbonate’ is inaccurate and outdated. It was first coined in 1814 by a chemist who observed that there is twice as much carbon as sodium in sodium bicarbonate. After different types of bicarbonates were identified, with different ratios, the observation became irrelevant, but the habit lives on.

Bicarbonates are the main form of dissolved inorganic carbon in the ocean. In freshwater plants, bicarbonates are released into the water as part of photosynthesis. This can shift the water’s pH to toxic alkaline levels. This continues until nightfall, when photosynthesis stops and respiration releases carbon dioxide, causing pH to return to normal. Bicarbonates commonly act as pH buffers in the human body [plop, plop, fizz, fizz] and in soil. 

Ammonium bicarbonate fertilizer

In the plant world, ammonia means nitrogen. This makes ammonia bicarbonate sound like a good idea as a fertilizer, right? In China, ammonium bicarbonate is used as an inexpensive fertilizer. But, because of its instability, it is being phased out in favor of urea. Also, ammonium bicarbonate is an eye, skin, and lung irritant. If you were to use it (against my advice) be sure to wear protective clothing and a respirator. 

High soil bicarbonate levels commonly occur when soil or irrigation water have a pH of 7.5 or higher. Alkaline soil and irrigation water tend to have lots of bicarbonate and carbonate ions floating around. These ions tend to attach themselves to and transform calcium and magnesium into less soluble forms that are difficult for plants to use. Also, as these minerals are altered, they leave salt behind in your soil. Not good. When these conditions occur, chelated fertilizers should be avoided. The level of bicarbonates in your soil also determines how much acid is needed to acidify the soil. 

If powdery mildew or other fungal diseases are causing problems in your garden, forget the baking soda and ammonium bicarbonate, Instead, space and prune plants for better air flow and apply potassium bicarbonate, Bordeaux mixture, sulfur, fixed copper, or milk. You may also want to apply insecticidal soap (not dish soap) to reduce the spread of disease by ants.

Generally speaking, milk or whey, applied before exposure to powdery mildew does reduce disease incidence. This may be because the benign microorganisms that start growing on the milk make it more difficult for powdery mildew organisms to take hold. Another theory is that the fatty acids contained in milk have antifungal properties. It may be for another reason altogether. We don’t know yet. Note that none of these studies succeeded using nonfat milk. 

Research has also shown that foliar sprays of milk are effective in treating viral diseases, particularly tobacco mosaic and other mosaic diseases on barley, beans, beets, celery, peas, spinach, sunflowers, tomatoes, and zucchini. It is believed that the milk may either deactivate the viruses, or physically isolate them, but no one knows for sure. The milk spray may also prevent aphid attack, thereby reducing the number of aphid-borne viral diseases.

Problems with milk in the garden

The main problem associated with milk in the garden is that there has been very little scientific research conducted. Most of the information available is anecdotal, at best. Besides being expensive, there are three problems you should keep in mind before deciding to use milk in the garden:

1. Rotten milk smells bad.
2. Dried skim milk, in particular, has been shown to induce, rather than prevent, Alternaria leaf spot, black rot, and soft rot on cruciferous crops.
3. Benign fungal organisms that grow on the milk can make your plants unattractive.

How to apply milk

If you decide to use milk to prevent disease, it is recommended that whole milk be sprayed on soil prior to planting and again when insects appear or just prior to when powdery mildew and similar diseases are expected to occur. You can also dump sour milk into your compost pile or around acid-loving plants, such as blueberries.

So, can milk help improve your plant and soil health? Yes, and no. Used as a preventative antifungal, antiviral, antibacterial treatment, milk may reduce disease incidence by 50% to 70% on some plant species.

One question that comes up when gardening is whether you should use organic fertilizer or  inorganic fertilizer.

Whatever their source, certain nutrients are needed for plants to grow and thrive. In many cases, those nutrients are present in the soil. Some times they are not. Without a soil test, you simply cannot know for sure. If a soil test shows there are nutrient deficiencies, you will need to add fertilizer. Should you use organic or inorganic fertilizer?

Inorganic chemicals

“Better living through chemistry” has been the victory cry against countless diseases, inconveniences, and poor crop yields. There is no denying that the introduction of chemical fertilizers, pesticides, herbicides, and insecticides was a boon to farmers around the world. Of course, we now recognize that everything comes at a price and that it is important to weigh the pros and cons of every situation.

The downside of chemical pest killers is that the pests evolve faster than we do and the point is reached, sooner or later, where the pests can handle the poisons but we can't. Inorganic fertilizers, however, are a different story.

One advantage of inorganic gardening is that you know exactly which nutrients are present and at what concentration. The same cannot be said for composted chicken bedding. Also, inorganic fertilizer is generally in a form easiest to use by plants. 

There are also synthetic fertilizers, such as ammonium sulfate, that start out as naturally occurring minerals, which are then processed. These modified minerals are considered acceptable for use in organic gardens.

Organic nutrients

Organic fertilizers come from manure, compost, bone meal, feather meal, and blood meal. Each of these amendments comes from a plant or animal source. Surprisingly, many of these nutrients must be acted upon by microorganisms to convert them into inorganic forms that plants can use. If it is too hot or too cold for microbes to be active, that organic fertilizer may not be as helpful as we might wish.

That being said, organic fertilizers tend to contain a wider variety of nutrients and microorganisms, which may or may not be advantageous for our plants. Believe it or not, there is still a lot we don’t know about plants.

A rose is a rose

As far as your plants are concerned, it doesn’t matter. To a plant, a molecule of nitrogen looks the same, whether it came from a factory or buffalo urine. It really doesn’t matter. The same is true of all plant nutrients. To a plant, the source of the molecule is meaningless. So why do we care one way or the other?

In both cases, too much fertilizer can burn plants, excessive application can lead to run-off and pollution, and their proper use can improve plant health and production. For me, I lean toward the organic side of the fence simply because it makes me feel good. I like the idea of it. Even though I know that, at the molecular level, it doesn’t really matter.

Did you know that the real difference between organic and inorganic is simply the presence (or lack thereof) of a carbon molecule? Nearly all inorganic compounds lack carbon.

Now you know.

Symptoms of molybdenum deficiency

Without molybdenum, leaves turn yellow and die and flowers may fail to form at all. The yellowing is often along leaf margins and downward cupping may also appear. In some cases, leaves develop a whiptail shape, rather than the leaf’s normal wider blade shape. Corn kernels may germinate on the cob prematurely in a last-ditch effort at reproduction. Legumes will have fewer or no root nodules if molybdenum is in short supply.

Again, you don’t know what your plants have access to without an inexpensive, lab-based soil test. Take my word for it, it is worth the effort.

Over-fertilization is an increasingly common problem in home gardens.

It happens all the time. Your plants start out doing so well. Then they lose some of that vigor. You might see chlorosis (yellowing), cupping, less fruit production, or simply a failure to thrive. What is a gardener to do?

The traditional response was to add more fertilizer, manure, or aged compost. And it would work for a while. Then those same symptoms would return, motivating you to add more fertilizer. And more. And more. Until it reaches the point where no matter how much fertilizer you add, your plants are not performing well. They seem more prone to pest infestations and diseases. How can this be?

Balanced plant nutrients

Just as we must eat a balanced diet to stay healthy, plants need access to a balance of nutrients. Plants absorb nutrients at the molecular level as cations and anions. Those are positively and negatively charged particles, respectively. Too many of one charge makes it difficult for plants to absorb what they need. Also, some minerals, such as iron, are critical components of the absorption process of other nutrients. If there aren’t enough of these nutrients or if they are made unavailable due to an imbalance, your plants can starve while sitting at a banquet. Mulder’s chart provides an image of what those nutrient relationships look like.

Toxic nutrients

Too much of a good thing can be a bad thing. In the same way, too much of a nutrient can lead to toxic levels. Phosphorus, for example, is critical to plant growth and photosynthesis. And it binds tightly to soil particles. Phosphorus toxicity can lead to severe stunting. It can also block the absorption of iron and zinc.

Potassium is critical to enzyme reactions and water and mineral movement within a plant, helps prevent diseases, and regulates the rate of photosynthesis. Potassium toxicity causes leaf distortions, chlorosis, and yellowing along leaf margins. Potassium toxicity can cause calcium, nitrogen, and magnesium deficiencies.

Similar problems occur when there is too much of any nutrient. And these excess nutrients often leach into rivers, streams, and groundwater, causing algae blooms that kill fish and create ripples of pollution and threats to biodiversity.

Too much of any nutrient can throw a monkey wrench in the works. Too much of several nutrients can take years to resolve.

Is your soil over-fertilized?

The first step is to get a soil test. You don’t know what is in your soil without a soil test from a reputable lab. Sadly, those colorful over-the-counter soil tests are not accurate enough (yet) to do you any good. Many universities offer inexpensive soil tests. These tests can save time and money and help your plants be healthier.

Below, you can see my soil tests from 2015 and 2019. In 2015, I learned that the property we bought had been over-fertilized for a long time. Phosphorus and magnesium levels were critically high, and there was too much of everything except iron.

Remember what I said about iron and nutrient absorption? Yep, my plants had been sitting at a feast, unable to get more than a nibble. And it showed. The plants in my landscape were prone to fungal disease, borers, and other insects, and none were thriving.

For four years, I thought I was doing better. I added a little iron. I avoided using fertilizers besides blood meal and ammonium sulfate (for nitrogen). But I continued to add aged compost to help aerate my compacted soil. The majority of that compost was plant debris and chicken coop bedding. It ends up that chicken poop contains very high levels of nitrogen, potassium, phosphorus, and calcium. While my plants needed nitrogen, they didn’t need the other nutrients.

How to correct over-fertilization

Looking at my 2019 soil test results, I realized I hadn’t done enough to correct my over-fertilization problem. I had wasted four years in the process. To resolve the nutrient imbalance, I stopped using compost in my garden. Instead, I saved it for raised beds and container plants.

And that’s the cure - stop adding nutrients. The other half of that cure is to remove nutrients by taking plant material out of your yard completely. Instead of grasscycling, bag and remove grass clippings. Or, you can add them to the compost pile or feed them to your chickens. Avoid using the chop and drop method for a while. Add the following heavy feeders to your garden to use up those excess nutrients: asparagus, beans, beets, broccoli, Brussels sprouts, cabbage, carrots, celery, corn, cucumbers, eggplant, garlic, leeks, melons, okra, onions, parsnips, peas, peppers, potatoes, pumpkins, shallots, squash, tomatoes, and turnips. And harvest those crops within an inch of their lives. Take everything they have to give and get it out of your yard.

Armed with more recent soil test results, I added much more iron to help my plants absorb what they needed. And I switched to using wood chip mulch to counteract my compacted soil. These actions will take time to have an effect. To monitor the effectiveness of these new actions, applying more iron and removing more plant material, I will switch to annual soil tests until soil nutrient levels are balanced.

Your garden may have different issues, but only a lab-based soil test can tell you what your plants need.

Gypsum in the garden

Gypsum is made of calcium and sulfur, two nutrients important to plant health. In the early 1800’s, gypsum was considered such a fertilizer miracle that smugglers battled local authorities in what became known as the Plaster War. At that time, gypsum was also known as sulfate of lime or lime sulfate.

Plants use calcium to maintain cell walls.  Calcium in the soil helps build healthy soil structure by binding tiny clay particles into larger clumps called aggregates. Sulfur is an important component of proteins used by plants. As such, gypsum can be beneficial in the garden, but not always.

False claims about gypsum

Like most other quick fixes, many of the claims about gypsum are based in fact, but taken too far.

• Acidification - Normally, elemental sulfur is used to acidify soil as it reacts with water to form sulfuric acid. The sulfate ion in gypsum, however, does not turn into sulfuric acid, so it does not acidify the soil.
• Blossom end rot - This condition is not, as popularly thought, always the result of insufficient calcium in the soil. Very often, it is due to water stress. Adding gypsum will do nothing for your irrigation schedule.
• Drainage - Unless you have clay soil with high salt levels (see below), gypsum will not improve drainage.
• Soil fertility - Beside adding calcium and sulfur, which may or may not be needed, gypsum does nothing for overall soil fertility. Soil fertility is largely a function of its cation exchange capacity (CEC), pH, and organic matter content, not the presence of gypsum.

Applying gypsum unnecessarily can cause leaching of aluminum, iron, lead, manganese, potassium into local lakes, rivers, and underground water stores. It also interferes with the beneficial soil microorganisms responsible for helping plants absorb nutrients. Applying gypsum to sandy soils can slow the transport of copper, phosphorus, and zinc.

Benefits of gypsum

All that being said, there is one situation when gypsum can be helpful in the garden. This only occurs when clay soils contain high levels of salt or, more accurately, sodium. These sodic soils can benefit from gypsum applications, in moderation. High salt levels in clay compound poor drainage, often causing heavy crusts to form. Adding gypsum in this situation allows the calcium to bind to the clay, replacing the salt, which is then leached out of the soil over time through cation exchange. Ultimately, this improves soil structure and drainage and reduces salt levels. Adding gypsum to clay without high sodium levels is a bad idea, as it can make alkaline soils even more alkaline. In most cases, plants need a soil pH of 5.5 to 7.0 to thrive.

Rather than simply adding gypsum because you heard it was a good idea, get your soil tested, determine your soil structure, and mulch everything with coarse wood chips to improve your soil and help your plants grow. If you happen to find a large, fine-grained seam of gypsum, you are in luck. Because that particular form of gypsum is more commonly known as alabaster. Now you know.

What is urea?

Our bodies use urea to excrete nitrogen in our urine. Urea is colorless, odorless, soluble in water, and non-toxic. Urea and urine both contain a lot of nitrogen, and all plants need nitrogen to grow and thrive. Nitrogen is the fundamental building block for chlorophyll and plant enzymes and proteins, including a plant’s DNA. Without nitrogen, photosynthesis cannot occur.

Over 90% of the world’s manufactured urea is used in agriculture as the most concentrated, affordable nitrogen source available to plants. Pure urea has an NPK value of 46-0-0. For comparison, ammonium sulphate has an NPK of 21-0-0, followed by blood meal at 13-1-1. On average, human urine has as NPK value of 18-2-5. This means urine contains 18% nitrogen (N), 2% phosphorus (P), and 5% potassium (K). The potassium and phosphorus found in urine, human or otherwise, are in forms that are quickly absorbed by plants.

Keep in mind that nitrogen, in all its forms, is highly mobile and easily leached into ground water. This causes out of control algae blooms and water pollution. Regardless of where you get your nitrogen, don’t add more than is needed. [Get a soil test before adding anything!]

How urea feeds plants

When urea comes into contact with the soil, specific bacteria convert it into ammonia (NH3), ammonium ions (NH4+), and bicarbonate ions (HCO3−). Other bacteria use the Calvin Cycle to oxidize the ammonia, converting it into nitrites, in a process called nitrification. This makes the ammonium and nitrites readily available to plants. It also acidifies the soil slightly.

Research published in the 2007 American Chemical Society [J. Agric. Food Chem.200755218657-8663] reported that cabbage grown with human urine as a fertilizer grew larger than those fertilized with industrial fertilizer. Those same plants showed less insect damage that their commercially fed counterparts, though unfertilized cabbages showed the least amount of insect damage. The same study demonstrated that urine performed equally well as commercial fertilizers on cucumber and barley crops, without increasing the risk of disease. In each case, there was no noticeable change in the flavor of the food being grown. [So much for those lemons! ] 

In a similar study, published by Cambridge University Press, larger harvests of amaranth were noted on the crops fed with urine. Other studies have found similar results with beets and tomatoes. In fact, beets grown with urine tend to be 10% larger than those grown with commercial fertilizer.

Top dressing your garden with urea or urine just before it rains or irrigating can add a lot of nitrogen to the soil. If you buy a bag of urea, be sure to keep it tightly closed. Nitrogen evaporates rapidly into the atmosphere and urea absorbs water from the air very quickly. Also, you should know that urea can contain biuret, an impurity that can be phytotoxic, or poisonous to plants.
Thank 
Did you know that the average adult in the Western world pees enough in a year to fill three bathtubs? That’s a lot of plant food!

But there’s a catch.

Too much fo a good thing can be a bad thing

There is so much nitrogen in urea and urine that it can prevent seeds from germinating and burn seedlings, roots, leaves, and your lawn. This is especially true if a plant’s moisture content is low. Urine also contains salt, which can dehydrate or kill plants. You know those dead spots in the lawn where Fido relieved himself? That damage is nitrogen and salt burn.

​If you want to use urine to water and feed your garden, it is a good idea to dilute it first. The recommended dilution is one part urine to 2-8 parts water, depending on who you ask. This nutrient rich mix can then be dispersed using a watering can. If you are taking prescription or recreational drugs, you may want to discuss transference with your doctor or local pharmacist first. Chemicals in our water and food supplies is real.

Otherwise, go unzip yourself at the more mature plants in your backyard, such as that lemon tree, or you can contribute some nitrogen and moisture to the compost pile and conserve some tap water.

The soil food web is what makes it possible for plants to grow.

Soil is not simply ground up minerals. We now know that there are gazillions of living things breathing, growing, moving, and reproducing beneath our feet.

Bacteria 

Bacteria are one-celled organisms. They are so tiny that they can enter a plant through a broken hair, or trichome. It is estimated that there is one ton of bacteria in every acre of soil. That’s the weight of two adult cows, or half of your car. A teaspoon of productive soil may contain anywhere between 100 million and 1 billion bacteria.

Most bacteria are decomposers that prefer more tender fare. As they breakdown carbon-based life forms, they make those nutrients available to plants and improve soil structure. Other bacteria are mutualists, which means they work together with plants to everyone’s benefit. This group includes the bacteria which convert atmospheric nitrogen into a form available to plants. Another group of bacteria, called lithotrophs, break down hydrogen, iron, nitrogen, and sulfur compounds, rather than carbon, making those nutrients available to plants. The fourth group of bacteria are pathogens. This group includes Erwinia (fireblight) and Xymomonas diseases, and gall-forming Agrobacterium.

Recent research has shown that a certain soil bacteria, Mycobacterium vaccae, improves mood and reduces stress. See, gardening really is good for you!

Small vertebrates

Small animals, such as  gophers,  moles, rabbits, snakes, and voles are the giants of this microscopic world. As amphibians, birds, mammals, and reptiles scratch at and burrow through the soil, they help reduce compaction. They can also destroy plant roots. While both predators and prey aid in nutrient cycling, some are more beneficial to your garden than others. In my opinion, snakes, lizards, and toads are preferable. That’s just me.

Adding manure to the garden provides a wealth of plant nutrients, right?

Yes, it does! 

It can also make you very, very sick. 

Raw manure

Raw manure should never be applied to the soil while plants are growing. If it is, be sure that the manure does not touch the plants. After manure is applied, plants that come into contact with the soil (lettuces, melons, squash) should not be harvested for 120 days. Crops that do not touch the soil (tomatoes, corn, pole beans) should not be harvested for 90 days. But you can’t wait that long, you say? What about composted manure? At what point does it become safe to use?

Composted manure

Simply allowing manure to sit in a pile until it looks done is not adequate to protect your family’s health against disease. Many pathogens can survive for years in a pile of poo.

Research has shown that manure must be composted for at least 45 days, 15 of which must be at temperatures between 131°F and 170°F, and turned at least 5 times to be safe to use. Assuming it hasn’t been recontaminated by air-dropped bird poop or other pathogens.

How certain are you that those temperatures have been reached? Seriously. If you are using manure in your garden, you need to be out there with a thermometer and a pencil, documenting those temperatures. You can get a soil/compost thermometer for around $10. Compared to trip to the emergency room, it’s worth it.

Manure sources

As many of you already know, I raise chickens for eggs and compost. Poultry manure has a high nitrogen content and, mixed with straw bedding, makes for an excellent soil amendment. I only feed my hens organic laying pellets, organic treats, and mostly organic kitchen waste, so I feel safe using it after it has been properly composted.

Before you accept a truck load of cow or horse manure from the local farm or stable, keep in mind that you have no control over medications being used on those animals, or on any pesticides, herbicides, or other chemicals that were used on their feed and which can pass through their digestive systems. Signs of toxic manure include poor germination rates, seedling death, distorted leaves and fruit, and smaller harvests. Also, horse and cow manure tends to be high in salt, which is fine once in a while, but it can build up to toxic levels if used too frequently.

Many people worry that using manure will make their garden smell bad. Properly aged manure smells more like rich earth. Mushroom compost, as my Gilroy neighbors know, has a much more pungent aroma.

Now you know.

Stop fighting natural cycles

Moving materials around is often unnecessary. Instead, copy the natural cycles that have evolved over millions of years. Simply chop plant material where you find it and drop it on the ground. This saves a lot of time and energy, while still putting all that organic matter to work for you in the garden. Insects, animals, microbes, rain, and foot traffic will move that chopped plant matter into the soil, improving soil structure and adding important nutrients, just as it has since plants arrived on the planet’s surface. No wheelbarrow required.

Benefits of mulch

Mulch, of practically any sort, creates a buffer against erosion and temperature extremes. It also makes weeding a lot easier. While I am a huge proponent of coarse wood chip mulch, you can use the same idea to simplify your spring garden work: trim off bits of plant, chop it where you stand, and let it fall. Using a plant’s own material to create instant mulch puts the nutrients that plant needs to grow and thrive within easy reach. Of course, you should still get your soil tested every 3 to 5 years, to make sure there are no deficiencies or toxicities.

Levels of effort

In one school of thought, the chopped material is simply dropped to the ground after the first snip. This green manure will, over time, break down. Obviously, woody stems will take far longer than green leaves and new growth, but they will break down eventually. Personally, I take a slightly more active role and chop the removed plant parts into smaller pieces, just as I do at the compost pile. ​​​

Recycling plant material

Chopping plant material speeds the decomposition process. Dropping it where you found it puts nutrients back where the plant can reuse them. This is the same idea behind grasscycling, which is when you mow the lawn without the bag attachment, allowing the clippings to fall right back on the lawn. Yes, you will be more likely to track snipped blades of grass around on your shoes for a day or two, but the nutrients and soil structure improvements are worth it. 

Come autumn, when leaves start falling, leave them where they fall, unless they fall on your lawn. In that case, mow them where they fall, or blown them into flower beds and around shrubs and trees, where they will create a winter blanket of protection that is transformed into food in spring.

Some claims are made about plants containing especially high levels of nutrients, making them excellent green manure crops, perfect for chop and drop mulching. These ‘dynamic accumulators’ are mostly hype. The truth is, plants contain a wide variety of elements used to help them grow. Some produce more volume, or biomass, than others. That’s all.

A word of warning

While chopping and dropping is an excellent way to save time while improving soil health, you don’t want to drop heavily diseased or infested plant material where reinfection or re-infestation can occur. By throwing diseased plant material in the trash, you are breaking the disease triangle for that pathogen on your property. In most cases, infestations by insects can be added to your compost pile. In both cases, you can also go ahead and drop everything, allowing natural predators to kill off most of the pests. Most disease pathogens do not last long in green manure, with the exception of fungal diseases, such as peach leaf curl and rust. When those diseases are present, I toss leaves in the trash.

Chop and drop weeding

Unless they have gone to seed or are spread by runners, weeds can be pulled, chopped, and dropped where they are. Weed plants with seeds and those that spread using runners are fed to my chickens, or you can add them to your compost pile. [Compost piles are still great to have for kitchen waste and to process chicken or other animal bedding.

As you move through your garden, pruners at the ready, snip off unwanted stems, spent blooms, and the like, chop them where you stand and let them fall to the ground. If you think it looks messy, you can chop while standing behind the plant instead of in front. In a surprisingly short period of time, you will forget they were even there as natural cycles take hold and transform yard waste into valuable plant food and soil amendments. For free.

Eggshells contain calcium. Plants need calcium. Lack of calcium causes blossom end rot. Therefore, adding eggshells to the garden will prevent blossom end rot and feed my plants, and snails won’t cross a line of broken eggshells, right?

​Wrong.

Manganese toxicities

Plants can absorb too much manganese in acid soils, or under drought conditions. When acid-forming fertilizers, superphosphates (fertilizers made by treating phosphate rock with phosphoric or sulfuric acid) are used, or when nitrate (NO3-) is used as a nitrogen source, those acidic conditions can occur. Manganese is most available to plants when the soil pH is between 5.0 and 6.5. Soils with neutral or alkaline pH slow the solubility of manganese, so toxicities are less likely.
The most common symptoms of too much manganese look a lot like the symptoms of too much boron: 

• darkening of leaf veins, especially on older leaves
• leaf cupping
• older leaves exhibit pale, sunken, irregularly shaped patches of interveinal tissue, with patches closest to leaf margins turning black [these spots are more regularly spaced in boron toxicities]
• minor veins on the underside of leaves may appear black in older leaves
• soybean leaves crinkle and cup downward
• apple stems develop pustules in a condition called apple measles
• watermelon plants may wilt and drop leaves in only days, in a condition called sudden crash
• chlorosis occurs on younger leaves due to an induced iron deficiency

Too much manganese interferes with root growth and causes overall stunting, especially in alfalfa, small grains, and beans.

While magnesium is needed by all living things, too much magnesium can be very, very bad. At high doses, inhaled magnesium can lead to neurological damage called manganism, a condition similar to Parkinson’s disease. If you have to work with manganese, wear protective gear.

How can you use soil test results? You could ask Mulder.

We have learned a lot about plant and soil science in recent decades, but there is a chart that gives us some insight into how the minerals used by plants as food might interact. 

Before we learn how to use this chart, let’s review soil pH and nutrient absorption.

Nutrient absorption 

The 20 or so minerals used by plants as food are found in soil as ions. Ions are atoms and molecules that have either a positive or negative charge. These cations and anions, respectively, attach themselves to water molecules and are pulled into the plant by root hairs. The ability of a plant to pull those nutrients in depends largely on soil pH.

Soil pH

Soil pH ranges from 0 to 14, with lower numbers indicating acidity and higher numbers indicating alkalinity. Using the chart below, you can see that more nutrients are available, and there is greater microbial activity, when soil pH is between 6.0 and 7.0. Most plants can survive in soil pH from 5.2 to 7.8, but the narrower range allows plants to thrive. As anions and cations are pulled out of the soil, the soil pH changes, ever so slightly. This is why too much or too little of certain minerals in the soil may interfere with nutrient availability. This is where Mulder’s Chart comes in.

How to use Mulder’s Chart 

Looking at Mulder's Chart, you can see 11 essential plant nutrients and micronutrients arranged around a circle. Solid and dotted lines connect the nutrients, with arrows heading one way or the other. Solid lines indicate an “antagonistic” relationship, which means high levels of one nutrient leads to a problem absorbing the nutrient being pointed to, while dotted lines indicate a “synergistic” relationship.

For example, according to Mulder’s Chart, high levels of nitrogen may reduce a plant’s ability to absorb boron, copper, and potash, as seen by the solid lines pointing from nitrogen toward the other nutrients. In the same way, high levels of nitrogen may stimulate magnesium uptake, and high levels of molybdenum might stimulate plants into absorbing more nitrogen, as seen by the dotted “synergistic” lines. Like most things in life, though, it isn’t really that simple.

Soil chemistry

Until you have a soil test from a reputable laboratory, you cannot know what is in your soil. Soil test results provide an amazing snapshot of what is really going on “down there”. Your soil test results will include individual measurements of several plant nutrients, as well as a cation exchange capacity rating, which describes a soil's ability to hold nutrients.

According to Linda Chalker-Scott, associate professor of horticulture and extension specialist at Washington State University, “It makes sense from a strictly chemical point of view, but soils are also biological. Plants exude organic acids from their roots. Mycorrhizae can mobilize "immobile" nutrients. I find these types of charts way too simplistic for real world conditions.”

While there is certainly a limit to its usefulness, I do encourage you to apply Mulder’s Chart to your soil test results and compare those results to what you are seeing in your garden. It may give you an idea of where problems may be occurring, or it might just be a fun way to review your soil test.

Boron toxicity

Boron toxicity occurs when boron levels are at or above 1.8 ppm. Too much boron negatively impacts plant metabolism, and it reduces root and shoot development, chlorophyll production, rates of photosynthesis, and the lignin and suberin needed for structure and protection.

Toxic levels of boron can often be identified by looking at plant leaves. Too much boron will appear as either necrosis (death) or chlorosis (yellowing) of leaf tips and edges (margins). These damaged areas are believed to occur because the overabundance of boron interferes with several life processes, all at the same time. Unfortunately, these are the same symptoms as caused by magnesium deficiencies. [Can you say laboratory soil test?]

Adding extra boron is easy, when more is needed. Getting rid of excess boron requires more effort in the form of improved drainage through the addition of more organic material. Obviously, this takes time.

​Boron deficiency

Insufficient or unavailable boron in the soil is the world’s most widespread micronutrient deficiency. It is a common problem in soils with low levels of organic matter (<1.5%). Boron deficiencies lead to reduced crop size and quality but symptoms can vary, depending on the crop:

• Apples may display ‘water core’, areas that look frozen
• Cabbages will have hollow areas in stems and distorted leaves
• Cauliflower will show rough areas on stems, leafstalks and midribs, and brown patches on underdeveloped curds
• Celeriac will envelop brown heart rot
• Celery stalks will crack, showing reddish brown internal areas
• Corn and soybeans will exhibit incomplete pollination
• Pears will have hard brown flecks in the skin and new shoots will dieback in spring
• Rutabagas and turnips show gray or brown concentric rings inside roots
• Strawberries will be stunted and pale, with small yellowed, puckered leaves

Too much, too little, or no way for plants to get to the boron they need can all cause problems. Getting a laboratory soil test is the only way to know what’s eating your plants, or rather, what your plants are eating.

Plant nutrition

There are 16 chemical elements critical to plant health. Depending on how much is needed, they are labeled as micronutrients (tiny amounts) or macronutrients (large amounts). Macronutrients are further divided between primary and secondary nutrients. Primary nutrients are the NPK of fertilizer bags. Plants use nitrogen, phosphorus, and potassium more than any other plant food, which is why they are the ones most often needing replacement. They are the rice and beans of a plant’s diet. Secondary nutrients, calcium, magnesium, and sulfur, rarely need to be supplemented, but they are very important to plant health. Micronutrients include boron, copper, iron, chloride, manganese, molybdenum, and zinc. [These used to be called trace elements.]

If you count up all those nutrients, you will only find 13. That is because plants also have non-mineral nutrients. These non-mineral nutrients are hydrogen, oxygen, and carbon. All of these nutrients work together to provide your plants with the energy and materials needed to grow. Some of those nutrients are mobile, while others are immobile.

Nutrient mobility

Highly mobile nutrients go where they are needed within a plant. Nitrogen, potassium, phosphorus, magnesium, chloride, and molybdenum are all mobile plant nutrients. All the other nutrients are considered immobile because they stay where they were initially placed. Problems with mobile nutrients tend to appear in older leaves, while problems with immobile nutrients are seen in new growth. This is important to know because it can help you narrow down deficiencies and toxicities.

What is in your soil?

Before we take a closer look at each of these important factors to plant health, let me remind you that you cannot know what nutrients are in your soil without a soil test from a reputable lab. I wish those colorful plastic tubes from the store could do the job accurately, but they can’t. Not yet, anyway. Contact a local soil test lab and find out what you are working with. Not knowing the facts can lead to toxic levels of these nutrients, which can backfire. [For a hysterical read about the effects of too much fertilizer, check out Don Mitchell’s Moving/Living/Growing Up Country series.]

Just because your plants are not thriving does not mean they need to be fed. All too often, plant problems are caused by inhospitable soil conditions, unhealthy roots, irrigation problems, pests, or disease.

So, let’s see what each of these nutrients do for your plants:

Primary macronutrients

• Nitrogen (N) is the single most critical plant food. It is part of the chlorophyll used in photosynthesis for rapid leaf growth. Nitrogen is abundant in our atmosphere, but only legumes can convert atmospheric nitrogen into a usable form. Nitrogen can occur in ammonia (more alkaline) or nitrate (more acidic) forms.
• Phosphorus (P) stimulates root, fruit, and flower growth, and is used in photosynthesis.
• Potassium (K) is used in stem and cell growth, to fight disease, and improve fruit quality.

Secondary Macronutrients

• Calcium (Ca) is used to build cell walls, and to move other nutrients around.
• Magnesium (Mg) is essential for photosynthesis and it activates plant enzymes.
• Sulphur (S) is used to create amino acids for root and seed production.

Micronutrients

• Boron (B) is used to make cell walls, to reproduce, and in sugar and carbohydrate production.
• Chlorine (Cl) aids plant metabolism during photosynthesis. It is necessary for osmosis and fluid balance within plants. Too much chloride (common in areas with hard water) can interfere with nitrogen absorption.
• Cobalt (Co) is used by legumes in nitrogen fixing.
• Copper (Cu) is used to make reproductive enzymes, to metabolize proteins, and to help plant roots eat and breathe.
• Iron (Fe) is essential in the production of chlorophyll and moving electrons around within the plant. Iron is also used in enzyme functions that help your plants absorb many other nutrients.
• Manganese (Mn) activates plant enzymes that breakdown carbohydrates and nitrogen into usable bits.
• Molybdenum (Mo) helps plants use nitrogen by working with certain enzymes.
• Nickel (Ni) is used in nitrogen processing and disease protection.
• Selenium (Se) is believed to stimulate plant growth and to counteract stress, pests, and disease.
• Silicon (Si) is used by plants to build cell walls and to improve plant health and productivity.
• Sodium (Na) is needed at low levels to stimulate growth, maintain water balance, and improve fruit flavor.
• Vanadium (V) is used by some plants as a substitute for molybdenum.
• Zinc (Zn) helps plants breakdown carbohydrates, regulate sugar consumption, and activates enzymes.

Non-mineral nutrients

• Carbon (C) is used by plants as energy, structural building blocks of starches, proteins, and cellulose, and in photosynthesis.
• Hydrogen (H) impacts soil pH and is used in photosynthesis and respiration, and to build sugar molecules.
• Oxygen (O) is used in respiration and, when combined with hydrogen to make water, in building and moving molecules within the plant.

Not enough of a plant nutrient, or too much, can cause problems. The tricky part comes in when the balance of nutrients is out of whack.

Nutrient interactions

A man named Mulder created a chart that shows us the interactions between plant nutrients. While there are limits to the usefulness of this overly simplistic view, it can help you understand what might be happening to your plants.

According to Mulder's Chart, synergistic elements help each other to be absorbed by plants, while antagonistic elements get in each other’s way. Using the chart above, you can see that proper levels of potassium help plants absorb iron and manganese, but too much potassium interferes with a plant’s ability to absorb boron, calcium, magnesium, nitrogen, and phosphorus. This interference can take the form of competition for space on water molecules, or it can alter soil pH, making some nutrients unavailable.

Plant food and soil pH

Soil pH ranges from 0 to 14, with lower numbers indicating acidity and higher numbers indicating alkalinity. Using the chart below, you can see that more nutrients are available, and there is greater microbe activity, when soil pH is between 6.0 and 7.0. Most plants can survive in soil pH from 5.2 to 7.8, but the narrower range allows plants to thrive. This is because the minerals used as food are ions. Ions are atoms and molecules that have a positive or negative charge. These cations and anions, respectively, attach themselves to water molecules and are pulled into the plant by root hairs. The wrong soil pH can cut your plants off from a bounty of nutrients.

Soil is given a cation exchange capacity rating to describe its ability to hold nutrients. [Did you know that root hairs knock cations (unbalanced atoms or molecules) loose with a hydrogen canon? Stay tuned for more on that!]

How to feed your plants

While there is no chemical difference between nitrogen from compost and nitrogen formulated in a lab, I prefer feeding my plants with composted yard and kitchen scraps and chicken bedding. Not only does this mix have excellent nutrients, it also improves soil structure. If you decide fertilizer really is necessary: READ THE BAG. Seriously. Federal law requires that important information is printed on the container and for good reason. Follow directions carefully and wash your hands when you’re done.

What are your plants hungry for?

Plants that are struggling need more fertilizer, right?

It makes sense. Your plants were doing fine, growing and thriving. Then, they started to decline. Leaves lost their color and fell off, stems lost their vigor, and flowers started looking like pale comparisons of their former selves. So, you add fertilizer and the plants look better. For a while. Then the decline returns. You add more fertilizer. And the cycle continues.

While you may think you are feeding your plants a healthy diet, what is more likely to be happening is toxic levels of some nutrients are building up in the soil, causing more complex problems. Excluding disease, insect attack, or improper soil pH, adding more fertilizer makes sense, on the surface. Except when it doesn’t, because sometimes that’s the last thing you should do. While there are certainly cases in which adding an all-purpose (hopefully organic) fertilizer is a good idea, more often than not, nutrient-based problems are more about imbalances and nutrient mobility.

Nutrient imbalances

Before we look at nutrient mobility, we need to understand a little bit about nutrient imbalances. In technical terms, this is called the cation exchange capacity. Put simply, cation exchange capacity (CEC) is a measurement of how many positively charged minerals can be held by the surface of a soil particle. Clay and organic material tends to be negatively charged, while many plant nutrients are positively charged. Mineral ions that are negatively charged are held in suspension, in water. These charged ions act like magnets. If the electrical charges are out of balance, plants cannot absorb the nutrients they need. This is why adding even more of an unnecessary nutrient can make matters worse, rather than better. In some cases, nutrients may already be inside your plant, but not where they are needed. This is where nutrient mobility comes in.

Plant nutrients and mobility

Plants absorb fourteen mineral nutrients from the soil. These nutrients are divided into macronutrients and micronutrients. Plants need large amounts of the macronutrients and small amounts of the micronutrients. Don’t be fooled, however. Just because a small amount is needed, doesn’t mean it is unimportant. As in the case of iron, insufficient levels can cripple a plant’s ability to absorb and use many other nutrients.

​Mobile nutrients

When a nutrient is considered mobile, it moves around inside a plant easily. Nitrogen is a highly mobile nutrient. Nitrogen deficiencies can be seen when nitrogen is pulled from older leaves, causing chlorosis (yellowing), to feed newer leaves. Other highly mobile plant nutrients include phosphorus, potassium, magnesium, chlorine, molybdenum, and nickel. When any of these nutrients become deficient, the symptoms will appear in older growth first.

Immobile nutrients

Other nutrients are not easily moved once they are incorporated into a plant. In most cases, these nutrients stay where they are first dropped off, usually at growing points. This is great for as long as there is a steady supply of those nutrients. It takes a lot of water to move them around inside a plant. This is why blossom end rot isn’t really caused by a simple calcium deficiency. Instead, it is caused by insufficient calcium and insufficient water, which is needed by the plant to move the calcium where it is needed when it is initially absorbed. Other immobile nutrients include sulfur, boron, copper, iron, manganese, and zinc. Deficiencies of immobile nutrients are more likely to appear in newer growth.

What nutrients are in your soil?

I’ve said it before and I’ll say it again: you don’t know what is in your soil without a soil test from a reputable, local lab. I wish I could say that those cute, over-the-counter soil tests were effective, but they aren’t. Not yet, anyway. Find a soil test lab on your side of the Rocky Mountains and send them a sample. That is the ONLY way to know what nutrients are available to your plants. 

What are you feeding your plants?

Magnesium levels

​Too much magnesium in the soil makes it difficult for plants to absorb calcium and other anion nutrients, which can lead to blossom end rot, bronzing, and many other problems. This is a common problem in areas with alkaline soil. The opposite is true in areas with acidic soil. Insufficient magnesium symptoms look very much like potassium toxicity symptoms: older leaves, at the bottom of the plant, start turning brown, between and alongside the leaf veins, working upward through the plant. Magnesium deficiencies in stone fruits often start out as slightly brown areas along leaf edges (margins) that expand inward, causing cracking, necrosis, and leaf loss. Magnesium deficiency in California is extremely rare.

Stabilizing magnesium levels

Reaching and maintaining ideal mineral levels in soil for healthy plant growth is both science and art - mostly science. To start, get a soil test from a local, reputable lab. Unfortunately, over-the-counter soil tests are not yet accurate enough to be useful. Once you have your results, you can take these other factors into consideration:

• Local water supply Irrigation water that is more alkaline, such as we have in San Jose, California, tends to make calcium and magnesium less soluble, and harder for plants to absorb. This is because of carbonate and bicarbonate ions in the soil. The chemical transformation between these molecules also tends to leave salts behind.
• Soil pH Acidifying alkaline soil with ammonium sulfate or sulfur can help reduce the number of ions (Residual Sodium Carbonates) that make magnesium more available to your plants. If you have acidic soil, wood ashes can be a good source of magnesium and other plant nutrients.
• Soil structure Compacted soil makes it difficult for plant roots to access nutrients. Overly loose (sandy) soil cannot hold nutrients long enough for roots to find them. Incorporating organic matter as a top dressing will improve soil structure and soil health, leading to healthier plants.
• Compost Applying compost, mulch, and green manure are good ways to add magnesium and other plant nutrients to your soil.

Finally, schedule regular soil tests for your garden and landscape. Look at these tests as an annual physical for the living skin of your property. The information in these tests will help you make informed decisions about the magnesium in your soil.

You may see the word chelated [ˈkēlāted] on bags of fertilizer, but what does that mean, and how can it help (or harm) your garden?

Advertisers make many claims about chelated fertilizer. They say it will help your plants thrive and reduce chlorosis by making more soil nutrients available to plants. In some cases, chelates hold onto ions that pathogens need to growth, thereby reducing their population. These claims are all accurate, mostly.

What they don’t tell you is that the effectiveness of chelated products depends entirely on soil pH and that many chelated products are rather toxic to both the environment and to soil microorganisms. Before adding chelated fertilizers to your food crops, let’s find out what’s really going on, shall we?

The chemistry of chelation

Chelates (or ligands) are organic molecules (chemically speaking) that attach themselves to metal minerals found in the soil. The word ‘chelate’ comes from the Greek word for lobster’s claw (chelé). This word describes the claw-like mechanism that surrounds a metal nutrient and ‘complexes’ the mineral. This prevents the mineral from being oxidized or precipitated. Once a mineral is complexed, it is held until a root hair is reached. Then the mineral is released and absorbed by the root hair, and the chelate goes in search of another mineral. [Try wrapping your brain all of those actions taking place around the roots of all your plants… it’s mind boggling!]

Metal minerals as plant food

Metal micronutrients, such as copper (Cu), iron (Fe), magnesium (Mg), manganese (Mn), and zinc (Zn), are important food for your plants. But plants can only use these metals when they are in the form of water soluble ions. Very often, these molecules attach themselves to oxygen molecules and become oxidized, or hydroxide ions (OH-) to be precipitated. This makes them unavailable to plants. Both oxygen and hydroxide ions are abundant in the soil. When metal nutrient molecules become chelated, they can be absorbed and used by plants. In fact, plants produce some of their own chelates. This must mean chelation is a good thing, right? Well, not always.

The power of pH

If your soil has a pH greater than 6.5, chelated fertilizer can provide plants with the nutrients they need in low quality soil without risking eutrophication. [Eutrophication refers to the condition of too many nutrients ending up in bodies of water due to urban drool and runoff, which leads to dense plant growth and animal death due to lack of oxygen. It’s not pretty.] Did you know that different minerals become unavailable at different soil pH levels?

No simple answers​

Here is where I have my biggest concern about chelated products. All too often, people see plants not growing well, so they add fertilizer. The plants don’t improve fast enough, so more fertilizer is added. This cycle can continue indefinitely because the lack of all those nutrients isn’t the problem. Very often soil structure and soil health are the problem. It could be a lack of soil microorganisms, or the incorrect choice of plants for a certain microclimate. Frequently, the lack of a single nutrient, usually iron on the West Coast and calcium on the East Coast, can make all the other nutrients unavailable. Without soil test results from a reputable, local lab, there is no way of knowing what your soil needs.

Before adding chelated fertilizers, you need to recognize that there’s much more to this situation than the Quick Fix claims. According to a report published by the University of Florida Extension Office, you need to take into account soil pH, your soil’s bicarbonate content, and the specific plant species when deciding whether or not to use chelated products. Bicarbonate levels? What does that mean? Bicarbonates are ions that precipitate (attach to) calcium, leaving salt behind. If your soil or irrigation water have a pH of 7.5 or higher, you can safely assume that the bicarbonate levels are higher than is good for your plants.

Are you sure you know what you’re doing? It’s not nearly as simple as advertisers make it out to be. [Is it ever?] And where do those chelates come from?

Chelate sources

Chelated products normally include ingredients such as DTPA, EDDHA, and EDTA. Since iron is the most commonly chelated mineral, we will look at the effects of those ingredients on soil health and iron absorption:

• DTPA  DTPA is effective up to a soil pH of 7.5 and it is less likely to bind to calcium, rather than iron.
• EDDHA  EDDHA is effective up to a soil pH of 11, and it is the most expensive form.
• EDTA  EDTA is the most commonly used ingredient in chelated products. It is only effective in acidic soil (pH < 7.0) and it binds with calcium more readily than iron. EDTA is difficult for soil microbes to break down and can be toxic to those beneficial microbes. EDTA also binds to toxic heavy metals, making those minerals equally available to plants and part of our food system. EDTA is also used in manufacturing and is source of pollution. [Are you sure you want to add that to your soil?]

Not all bad

There are times when the use of chelated fertilizers make sense, if used judiciously. For example, chelated iron helps you grow acid-loving plants, such as blueberries, in alkaline soil. Start by selecting the best form of chelate for your soil pH. You can avoid soil-based problems by using foliar (leaf) applications of chelated products, once you are certain of the need for them. You can also increase the number of naturally occurring chelates (and improve soil health) by adding more organic material in your soil. This is done by top dressing the soil with aged compost or mulching with clean wood chips.

Just remember, quick fixes that sound too good to be true are usually far more complex and risky than they are made out to be.

Zinc absorption

Unlike many other plant nutrients, which are freely absorbed in solution, zinc is only available to plants in a positively charged form (Zn2+) that must be carried in on specialized transporter proteins. Zinc, on its own, cannot cross cell membranes. Once a plant absorbs a zinc molecule, it is mostly immobile. This means that signs of zinc deficiency usually show up on newer growth.

Symptoms of zinc deficiency

Zinc deficiencies are very rare, east of the Rocky Mountains. Alkaline soil and too much phosphorus, such as we have in the Bay Area, can make it difficult for your plants to absorb zinc and copper. Zinc deficiencies are more commonly seen in containerized plants. Symptoms of zinc deficiency include bronzing, twig dieback, and chlorosis. That chlorosis often presents as yellowing between young leaf veins and general bleaching that does not reach leaf edges (margins) or midribs. The bleaching may also look like yellow or white stripes between the veins of upper (newer) leaves. Zinc deficient leaves may also roll or curl, and may be smaller than normal.

Copper deficiencies look very much the same, to the untrained eye, so the only way to really know what is wrong is to submit a soil test to a local, reputable lab for analysis. [If you thought your DNA report was fascinating, you’re going to love reading your soil test results!]

Too much zinc

Just as too much phosphorus can make iron and copper unreachable for your plants, too much zinc can bind with iron, making nearly all the other nutrients unavailable. Signs of zinc toxicity, no surprise, look identical to iron deficiency. Zinc toxicity is normally seen in areas with widespread mining or industry and is characterized by severely stunted growth, transplant failure, and wilting. Dark blotches may be seen on older leaves and red areas on vines, petioles, and along margins (edges) and veins.

Before adding fertilizer, you really need to have your soil tested. And those cute little over-the-counter kits are not able to give you the information you need.

Zinc sulfate

Zinc sulfate is a compound used by commercial almond growers in autumn to force trees to drop all of their leaves. These leaves are then collected and destroyed. This is done to reduce the chance of bacterial spot on almonds. This is not something for home orchardists to use without training.

Preventing zinc problems

Soils with insufficient organic matter are more likely to have nutrient imbalances. This means heavy clay soil, improper soil pH, too much calcium carbonate, and poor soil structure can all contribute to zinc and other plant nutrient problems. The best way to prevent or counteract these problems is to develop healthy soil by composting, mulching, and sprinkling some coffee grounds around.

Research is showing us that malnourished soil results in foods with lowered nutrient values. When you start talking about feeding 7 billion people, that can be a real problem.

Feed the soil in your garden and landscape properly, so that it can feed you!