Foliar feeding refers to feeding plants by spraying nutrients on leaves and fruit.
Normally, plants absorb their mineral nutrients from the surrounding soil through the root system. Nutrients can also be absorbed through the stomata, tiny holes used for gas and moisture regulation, found on leaves and fruit.
Foliar feeding claims
Advertisements claim that foliar feeding is many times more efficient than soil feeding, that it cannot be used incorrectly, it promotes larger, sweeter crops, boosts a plant’s tolerance for heat and cold, increases pest and disease resistance, and even improves a plant’s internal circulation. Wouldn’t that be something? The number and diversity of these claims should raise a warning flag, and with good reason. Most of the claims about foliar feeding are false, but there are situations where foliar feeding is useful.
Foliar feeding research
The claims made about foliar feeding are based on research published in 1957 in which leaves and fruit were shown to be very efficient at absorbing tiny amounts of mineral nutrients in a lab setting. You can read the full report here.
Unlike nutrients absorbed through the root system and transported through the xylem, nutrients absorbed through leaf stomata are more likely to remain in nearby plant tissue. This is especially true for the ‘immobile’ nutrients, such as calcium and magnesium. According to the study, “Phosphorus, choline, sulfur, zinc, copper, manganese, iron, and molybdenum were intermediate [with regards to absorption] with decreasing mobility in the order given.” Potassium and sodium were shown to be the most readily absorbed and highly mobile nutrients.
Again, this research was conducted under laboratory conditions, not out in someone’s garden. As one might expect, results are very different in the field. There are, however, some cases where foliar feeding is a good thing.
Foliar feeding and alkaline soil
Nutrient absorption is helped or hindered by soil chemistry and electrical charges in the soil. One aspect of that chemistry is soil pH. Acidic soil has a pH of less than 7.0 and alkaline soil has a pH greater than 7.0. This is important because alkaline soil is slower to release metallic nutrients, such as iron and manganese. If your soil is deficient in these nutrients, foliar feeding can help in the short-term while you make long-term adjustments to your soil.
The downside to foliar feeding
Simply spraying fertilizer on your plants’ leaves is a good way to burn them. There are too many variables to make foliar feeding something you would want to do all the time with all your plants. Environmental conditions, species characteristics, developmental stages of the plants, varying thicknesses of plant cuticles, and the likelihood of stomata being open or not all contribute to a lot of wasted fertilizer and the potential for harm.
Foliar feeding case in point
For those of you who have been reading The Daily Garden for a while now, you may recall reading about how my first soil test, in 2015, reported extraordinary numbers for all nutrients except iron. This was due to over-fertilizing done by the previous owner. That imbalance made those abundant nutrients largely unavailable to my plants. Also, my soil pH at that time was 7.7 and the soil was badly compacted. Truth be told, it looked and felt like concrete.
At that time, nearly all the plants in my landscape were being damaged by fungal diseases (partly due to badly aimed sprinklers), aphids, borers, scale insects, and what looked like nutrient deficiencies. Of course, the automatic (and incorrect) response would have been to add more fertilizer. Thanks to my lab-based soil test, I had the information I needed to make better decisions.
Secondary plant nutrients are calcium (Ca), magnesium (Mg), and sulfur (S).
The nutrients plants use the most are called primary nutrients. Nitrogen, potassium, and phosphorus are primary nutrients. On the other hand, only tiny amounts of boron, copper, iron, chloride, manganese, molybdenum, and zinc are needed. These micronutrients used to be called trace elements. In the middle are the secondary nutrients. Secondary nutrients rarely need to be supplemented, but they are very important to plant health.
Most soils already contain high enough levels of these secondary nutrients, but you don’t know for sure without a lab-based soil test. The effects of not enough or too much of any one nutrient can create a domino effect that is difficult to diagnose. Simply adding more fertilizer can often makes problems worse, rather than better.
Why are these secondary nutrients important and what are some signs of toxicity or deficiency? Let’s find out!
Plants use calcium to build strong cell walls, to move materials across cell membranes, to grow primary root systems, and to maintain the cation-anion balance. [Cations and anions are electrically charged atoms of minerals that plants use for food.] Optimal levels of calcium range from 1000 to 1500 parts per million (ppm).
Calcium is relatively immobile inside a plant. It takes a lot of water to move a calcium molecule around inside a plant. That’s why blossom end rot is more of an irrigation problem than a calcium deficiency problem. Calcium deficiencies, whether caused by real lack or insufficient irrigation, are rare in nature. When they do occur, they can cause bitter pit in apples, cavity spot in carrots, and leaf tip burn in several different plants.
Too much calcium is also rare, but it can interfere with the absorption of magnesium and potassium, causing deficiencies in those nutrients. Bottom line with calcium: irrigate adequately, regularly and consistently.
Magnesium is essential for plant health. Ideal levels of magnesium range from 50 to 120 ppm. Magnesium stabilizes cell membranes, making plants better able to withstand drought and sunburn. Magnesium is found in enzymes that plants use to metabolize carbohydrates. Most important, magnesium is contained in the chlorophyll molecules that convert the sun’s energy into food. This process, the Calvin Cycle, is what makes photosynthesis possible.
Too much magnesium in the soil makes it difficult for plants to absorb calcium and other 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 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.
Plants use a surprising amount of sulfur. This secondary nutrient is used in making chlorophyll and certain proteins and enzymes. Sulfur is also part of the arrangement between legumes and rhizobia bacteria that allow them to make use of atmospheric nitrogen.
Sulfur deficiency is seen first in new growth. Leaves are pale and growth is spindly. If sulfur levels become toxic, leaves will be smaller than normal and have scorched edges. Sulfur is commonly used as an organic fungicide and to acidify the soil.
Do not use horticultural oil within 2-4 weeks of applying sulfur. Sulfur and horticultural oil are phytotoxic (poisonous to plants) when combined. Also, it is better to use fixed copper, rather than sulfur, on apricot trees.
Your plants may not need as much of these secondary nutrients, but they are just as important to plant health. Get a lab-based soil test to find out what is in your soil.
As fruit trees begin putting out fruit in spring, it is your job to take some of that fruit off.
It may seem counterproductive. Why on earth would I plant a fruit tree only to take the fruit off when it has only just started growing? Why would you want to reduce your crop that way? Read on and find out!
Why thin fruit?
Most fruit trees will produce far more fruit than can be supported or made flavorful. Too much fruit and branches start breaking. Now, the tree doesn’t care how the fruit tastes, as long as it tastes good enough to cause animals to help with seed dispersal. To get the sweetness, size, and shape that we want, we have to intervene. Thinning fruit also helps reduce the likelihood of pests or diseases getting established in the nooks and crannies between fruit. Finally, fruit thinning reduces the chance of your tree taking a year off of production (alternate bearing) out of sheer exhaustion.
How (and when) to thin fruit trees
Different trees have different thinning needs. Generally, the time to thin fruit is dictated by fruit size. Stone fruits are thinned when they reach 3/4 to 1 inch in diameter, while pome fruits can be thinned when they are 1/2 to 1 inch. This is usually in April and May in the Bay Area. You can also predict the time for thinning by noting it 30 to 45 days after full bloom on your calendar. To actually remove the fruit, give it a gentle twist. Sometimes, pruners are needed. Your fruit tree is working very hard at this stage, so be kind. Do not be tempted to thin your fruit trees too early, as this can lead to split fruit later on, especially in peaches. Of course, thinning too late won’t help your fruit become as large as it might have.
Fruit thinning by species
Some trees do not require thinning. These include cherries, figs, citrus, Bartlett pears, pomegranates, and persimmons. You may want to monitor your persimmons tree, however, as a very productive year can lead to breakage. Use this information to determine just how much to thin, depending on tree species:
Natural fruit drop
We are not the only ones who want to protect our fruit tress from breakage due to too much fruit. These trees have evolved to protect themselves with what is erroneously called “June drop”. June drop normally occurs in May in the Bay Area and it refers to a fruit tree dropping many immature fruits. Fruits that are diseased or infested may also drop prematurely.
Don’t be afraid to get up close and personal with your fruit trees in spring. Thinning fruit will ensure a better crop and a healthier tree. Thinning also gives you a chance to see what’s really going on for your fruit trees, allowing you to halt a minor pest invasion before it causes any real damage.
For those of you (like me) who need ways to remember what and how to thin, give this a try:
Spring season of thinning, no need to despair
Help them grow stronger with inches to spare
Small apricots and plums, give them each two to four
Peaches and nectarines, need three inches or more
Then muster the clusters of apples and pears
Save just the biggest, only one or two there
Mutants and mummies and twins all must go
Leave only the best. Now just watch them grow!
Insecticidal soaps are an easy DIY method of pest control in the garden.
People have been using soap sprays for a long time to protect their plants, but the science behind using soap has only begun to demonstrate just how insecticidal soaps work. Current research has shown that spraying soapy water on insects kills them off by:
Before jumping on the insecticidal soap bandwagon, however, you need to understand that not all soaps are created equally and that many soaps are actually detergents that can kill your plants.
Homemade insecticidal soaps
True insecticidal soaps contain potassium salts of fatty acids and are designed specifically for use on plants. These fatty acids are commonly found in fish oil, lard, and olive, palm, coconut and other plant oils. These fatty acids are mixed with potassium hydroxide, which is strongly alkaline, to create soap, much the way fatty acids are mixed with sodium hydroxide to make lye. While potassium salts and sodium salts will both kill insects, sodium salts are toxic to plants. [The same problem occurs when people use baking soda (sodium bicarbonate), rather than potassium bicarbonate, on plants to fight fungal disease. Baking soda is phytotoxic, whereas potassium bicarbonate is not.]
Not all household liquid soaps are safe for use on plants. In fact, I couldn’t find a list of any that are truly safe. Laundry soaps and dry dishwashing detergents are also too harsh to be used on your garden plants. Also, many liquid dishwashing soaps contain bleach, fragrances and colors, and other chemicals that can harm or kill your plants. As tempting as it may be to grab your bottle of dish soap from the kitchen sink, this is not a good idea. [I challenge you to take a close look at the ingredients list on your dishwashing soap and look up any words you don’t know.]
Effectiveness of insecticidal soap
Instead of burning up your plants with detergent, go to the store and buy a bottle of insecticidal soap. It is less expensive that many other pesticides, plus it is less damaging to the environment and other living things. Insecticidal soap that has been properly formulated and applied will kill many common pests, including:
Unfortunately, insecticidal soap can also kill off the larval forms of many beneficial insects, such as ladybugs and lacewings.
How to use insecticidal soap
Insecticidal soap only works when it comes in direct contact with and completely covers an insect pest. Use these tips to safely use insecticidal soap:
Insecticidal soaps have little or no residual effects, so treatments must be repeated regularly until the desired level of control is reached.
So, insecticidal soap isn’t the Quick Fix you might have thought it was before reading this post, but it is effective when used properly.
What happened? Yesterday, your plants looked lovely. Today, several leaves are rolled up, looking like green cigars. What did this, is it a problem, and what can you do?
Leaf roll (or leafroll) is not the newest thing in Burmese take-out. Instead, it is a symptom that can give you clues about what is going on in your garden. Leaf roll can be caused by environmental stresses , viral infections, fungal infection, pests, or herbicide damage.
If you notice leaves starting to roll on any of your plants, start by asking yourself the following questions:
Physiological or environmental causes of leafroll
Environmental or physiological damage is normally visible near the base of a plant first, as leaves cup upward, toward the leaf vein. These leaves tend to thicken and become leathery, while remaining a normal green color, as the plant tries to protect itself. Environmental damage is a common problem when growing members of the nightshade family, such as tomatoes, peppers, and eggplant. Interestingly enough, bush (determinate) varieties are less likely to exhibit leaf roll than vine (indeterminate) varieties. Symptoms of environmental damage can indicate any of these problems:
Some viral diseases can also cause leaf roll. Viruses often enter plant tissue as insect carriers feed. These carriers are normally aphids, mealybugs, and soft scale insects. Leaf roll viruses can also be spread through infected scion wood. Once infected, vascular bundles become clogged as the viruses reproduce in the nutrient-rich phloem. This reduces water and nutrient flow within the plant, causing stunting, delayed maturity, reduced crop size, chlorosis, necrosis, and leaf roll.
Viral infections affect newer leaves first. Leaves cup upwards and turn pale green. They may also have yellow edges, mottling, and veins may look purplish. This color change is due to damage to the phloem. Infected fruit may start rotting from the inside out.
There are three major types of viral leafroll that warrant concern:
Because these viruses can spread rapidly, over relatively great distances, close monitoring and control are in everyone’s best interest. Once a plant is infected with one of the leafroll viruses, it should be removed and destroyed. There is no cure or treatment. When shopping for plants, choose resistant varieties and put them in quarantine when you bring them home. Controlling carrier pests will also help reduce the likelihood of leafroll affecting your garden.
Leaf curl caused by fungal infections can be particularly destructive, since the disease can be carried in by whiteflies. Peach leaf curl, bacterial blast, and botrytis are common examples. Symptoms include:
As aphids, leaf miners, thrips, mites, scale insects, and mealybugs feed on sap, they can cause leaves to curl. Occasionally, a spider may curl a leaf to create a cocoon, but spiders are Good Guys in the garden, so leave them alone. The real pest when it comes to leaf rolling comes from the larva of certain moths. In particular, California has a problem with moths in the tortricid family. These pests can be found in citrus, pear, plum, apple, almond, apricot, raspberries and other cane fruit, quince, and walnut, plus most ornamentals. Light brown apple moths also fall in this category. Pest damage usually includes ragged edges on nearby leaves and tightly rolled nesting leaves. Inspect fruit and nut trees carefully from March through May for signs of these pests.
The ads make herbicides look so safe and helpful, but they are, in my opinion, anything but. Leaching, overspray, rain splash, a sudden breeze, and the failure to breakdown in the soil as advertised can put many other plants at risk. Symptoms of herbicide damage include:
If you notice leaf rolling on your garden or landscape plants, take a closer look to see if you can figure out what is causing this change. Knowing the cause helps you find a solution that allows your plants stay healthy and productive.
Renewal pruning is a method that stimulates new growth while removing unproductive wood or canes.
According to some, renewal pruning refers specifically to plants that produce canes from the root system. I am going to use the broader definition above. The general rule of thumb for renewal pruning is to remove one-third of any older wood each year. These are thinning cuts that take branches back to the main stem or crown, depending on the growth habit. [When making thinning cuts, be sure to avoid damaging the branch collar.] Each species has its own characteristics, which need to be taken into account before you start lopping off branches. Some of the more common approaches to renewal pruning are listed below.
Renewal pruning of currants
Currants produce fruit on spurs that emerge from 2- and 3-year old wood. After that, those limbs are far less productive. Use the following pruning schedule on currants:
Renewal pruning of fruit trees
Fruit and nut trees produce fruit on spurs and on twig tips. Some species only produce fruit on new spurs, while others can use the same spurs for several years. For example, figs, grapes, persimmon, and quince produce fruit on new shoots and one-year old wood. Pears, walnuts, and apples, on the other hand can produce fruit on the same spurs for several years. UC Davis offers a chart of fruiting wood characteristics that can help you decide what to remove and what to leave for another year. Did you know that large, unproductive branches are called bulls? I didn't either.
Renewal pruning of raspberries and blackberries
Some varieties of raspberry and blackberry produce fruit on primocanes. These are fall-bearing varieties that produce the best fruit on first-year canes. While leaving them in place will provide some fruit the following spring, the quality and quantity are usually poor. For these berries, it is better to cut the canes back to ground level in late autumn. This gives the plant time to pull carbohydrates from the leaves down into the crown and root system. These nutrients will be used to grow new canes in spring. Summer-bearing floricanes produce fruit on buds from second-year canes, so removing them at the end of year one would be problematic.
Some trees and shrubs can become so out of control that they risk falling over, severe disease infestation, or they simply look awful. In some (but not all) of these cases, rejuvenation pruning can be used to give them a new start on life. These plants are cut to ground level and allowed to start over from an established root system. Before you try this method, be sure to research the plant to make sure this is an appropriate choice. Cutting back some plants in this way will kill them.
Whole tree pruning
Traditionally, trees that produce fruit in new growth, such as cherries, are pruned by removing selective branches. Another method being studied is whole tree pruning, in which all the major limbs are removed each winter, leaving only 12 to 18 inch nubs. This method is not for the faint of heart, but it is gaining popularity among commercial growers.
Don’t be afraid to prune your trees and shrubs. It is an excellent way to help your plants to stay healthy and productive. As you move around under the canopy or peaking into the center of your shrub, you may even discover a new pest or disease before it gets out of hand!
Nitrogen is the single most limiting factor in plant growth.
There is far more to tell about nitrogen than we have time or space for here, but I hope that this summary will give you a better understanding of what makes nitrogen so important in the garden, and encourage you to learn more.
What is nitrogen?
Nitrogen is an element, like hydrogen or oxygen. The Earth’s atmosphere is 78% nitrogen, but it is in a form that plants cannot use. Nitrogen is the first number you see on a bag of fertilizer. It is the “N” of NPK. Since pure nitrogen boils away at -320 degrees Fahrenheit, you won’t be buying a bag of pure nitrogen at your local garden center. [If you’ve ever had a dermatologist “freeze” off a wart or precancerous area, they are often using nitrogen.]
How plants use nitrogen
Nitrogen is a fundamental building block for chlorophyll and plant enzymes and proteins, including a plant’s DNA. Without nitrogen, photosynthesis cannot occur. Some crops use more nitrogen than others. Cucurbits, such as melons and squash, are relatively light feeders. Heavy feeders include sage, artichoke, potatoes, onions, lemongrass, and corn. If you are growing plants in containers or straw bales, plants should be monitored closely for signs of insufficient nitrogen.
Not enough nitrogen
Stunting and chlorosis are the two most common signs of insufficient nitrogen. Nitrogen is highly mobile within the soil and in plants. Nitrogen deficiencies are frequently seen as a pale area down the middle of each leaf, with older leaves affected first. This happens because the plant pulls nitrogen from older leaves to feed newer leaves. Nitrogen deficiencies in peach and nectarine tend to show as red areas on leaves (where photosynthesis is no longer occurring properly). Nitrogen deficiency and sodium toxicity are common in San Jose, California. Our heavy clay also reduces nitrogen levels in the soil.
Too much nitrogen
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 cold weather, thrips, leaf spot, Verticillium wilt, aphids, and scale. This is why the timing the use of fertilizer is so important.
Types of nitrogen
The Nitrogen Cycle refers to the conversion of atmospheric nitrogen into chemically reactive forms that attach themselves to other elements, creating ammonia or nitrate based fertilizers. Crops that prefer more acidic soil, such as blueberries and potatoes, seem to prefer ammoniacal nitrogen based fertilizers over nitrate based fertilizers. As plants absorb nitrates, they increase the soil pH, making it more alkaline. California soils are already more alkaline than many plants prefer. When plants take up ammonium, the soil becomes more acidic.
Nitrogen - a fleeting plant nutrient
Nitrogen is quickly used up by nearby plants. It also deteriorates rapidly and is leached out of soil by rain. This deterioration is largely a function of moisture and temperature. As temperatures rise, there tends to be less organic matter in soil. As moisture increases, so does organic matter. This is why it is so important in our hot, dry California weather to regularly add compost to our gardens and landscapes.
Native Americans used the Three Sisters Method of growing corn, beans, and squash together. Beans, being a legume, are host to bacteria that convert atmospheric nitrogen into forms usable by plants. Planting them all together provided the corn and squash with extra nitrogen early in their growing season. Some tribes added dead fish or eels when planting, which provided even more nitrogen. Fish emulsion is a mild source of nitrogen. According to study by the Washington State University Extension Office, coffee grounds contain 10% nitrogen after brewing. Blood meal, cottonseed meal, alfalfa meal, and feather meal are all good sources for nitrogen. Urea and urine both provide high levels of nitrogen.
Finally, if you are like many gardeners who plant marigolds to deter pests, you may want to plant them away from any legume crops. It is rumored that the same chemicals that make marigolds beneficial can also interrupt the nitrogen-fixing capabilities of legumes, such as peas and beans, though I have not yet found any scientific proof.
Spinosad is an organic insecticide originally made out of fermented bacteria found in soil where sugarcane was grown. Actually, it was first found in a rum still. Bootleg bacteria, anyone?
Let me start by saying that anything called insecticide, organic or otherwise, is deadly to something. That’s the point, right? Since not all insects are our enemies, that can be a problem. Before we explore the benefits of spinosad, let’s keep in mind that spinosad can be highly toxic to honey bees and other pollinators, under certain conditions. Now let’s find out how it works and how we can use it safely.
How spinosad works
Spinosad works by messing with an insect’s neurological system, creating hyperactivity, tremors, and muscle contractions. Ultimately, the insects go into seizures and then become paralyzed, out of pure exhaustion, and then they die. Insects can be affected by eating or touching this insecticide. Chemically, there are over 20 different natural forms of spinosads and 200 different synthetic forms. These synthetic forms are called spinosyns. The spinosad formulas that you can buy are made from two of the synthetic types, spinosyn A and spinosyn D.
Uses of spinosad
Spinosad is used on a large number of crops, against many types of insects, including:
Safe use of spinosad
According to the University of California Dept. of Agriculture & Natural Resources (UCANR), spinosad has a residual toxicity that can last anywhere between 3 hours to more than 24 hours, depending on application rates and formulation. UCANR recommends using 1.25 to 3 ounces per acre. That sure doesn’t work out to be very much for my little 1/5 acre property! As with any other insecticide, it is probably a good idea to stay out of the area yourself for the same time frame. You know, just in case. Spinosad should not be used within 24 hours of harvesting.
Protecting pollinators from spinosad
Spinosad is sold under several different brand names, including Bull’s Eye, Entrust, Natular, Protector Pro, and Success. To reduce the risk to honey bees and other pollinators:
If you really must use an insecticide, spinosad is probably a better choice than non-organic products that build up in the soil and encourage the evolution of resistant species. Personally, I prefer tolerating a little bit of damage, monitoring regularly, and handpicking the pests I see. It’s not as effective as, say DDT, in the short run, but it serves me best in the long haul.
Hardening off is a process that acclimates new plants and seedlings to your microclimate.
When a plant finds itself in a new environment, it must make several adjustments to all the changes. This is called ecesis. Sudden changes in temperature, sun exposure, and wind can be fatal to plants raised in a greenhouse. Most plants sold commercially are raised in greenhouses. Greenhouses are generally warm, moist, protected areas that allow plants to get a good start. It does not, however, prepare them for the outside world. Many nurseries use equipment that bends the plants over, back and forth, a few times each day, in an effort to mimic the effects of wind. This strengthens the plants through a process called thigmomorphogenesis. It helps, but you can significantly help new plants become acclimated through hardening off.
When to harden off plants
Since all newly acquired plants have the possibility of carrying pests or disease, it is always a good idea to start them off in a protected quarantine area for 40 days. This gives you time to watch the plant for signs of infection or infestation. It also provides an opportunity to see what conditions best help the plant thrive, and it gives you time to carefully decide where in the garden this new plant will go. Depending upon the climate tolerance of the plant species, you may have to wait until it is a couple of weeks before your last frost date before you begin hardening off.
How to harden off plants
Plants should be brought outside for a few hours each day, at first. They should be in a location protected from wind, with filtered or morning sunlight. Increase the amount of time and sunlight by an hour or two each day until they are outside all day. If temperatures allow, plants can now be left outside overnight. If you are growing plants in a cold frame, you can harden them off by opening the frame a little more each day until the lid is no longer needed. Hardened off plants can now be installed in the landscape or garden, with a significantly higher chance of success.
Which plants need hardening off?
Generally speaking, bare root stock does not need hardening off. There are no leaves to dry out or get sunburned. Young blueberry plants, garden sale seedlings, and seeds you have started yourself indoors will all benefit from hardening off.
By gradually getting plants used to your microclimate, they are more likely to thrive.
Don’t let the name scare you off. Bacillus thuringiensis (called “Bt” to make things easier) is a naturally occurring, rod-shaped, pest-killing collection of bacteria found in soil.
In addition to occurring naturally in soil, Bt can be found on leaves, in animal feces, and in flour mills. It is even found living in the gut of the caterpillar stage of some moths and butterflies.
Being a living thing, Bt doesn’t handle extreme heat very well. Because of this, you will only want to buy as much as you will use in a single growing season, and store it in a cool, shady location. One advantage to being easily killed is that it reduces the likelihood of pests developing a resistance, the way they do for many chemical treatments.
Bt is used against a wide variety of garden pests, including whiteflies, budworms, moths, flies and mosquitoes, aphids, beetles, blackflies, leafhoppers, wasps, and sawflies. Unfortunately, Bt can also negatively impact important beneficial insects, such as honey bees and parasitic wasps. (There are no easy solutions…)
Bt reproduces using spores. Now, there are spores that generate plants such as mushrooms, moss, and other eukaryotes. This is a different kind of spore, called an endospore. Endospores are not seeds or embryonic offspring. Inside the endospore, a dormant, bare-bones, reduced version of the original bacteria divides within its cell wall. Then one of these divisions swallows the other one! This behavior allows endospores to remain dormant for hundreds (some say millions) of years without food. Endospores can resist ultraviolet radiation, extreme temperatures (even boiling water), and chemical disinfectants.
Death by bacteria
Bt are 1 µm (micron) wide and 5 µm long. That works out to over 25,000 Bts standing next to each other to cover one inch. If they had feet, that is… Regardless of their diminutive size, MicroWiki describes the [brutal] process of Bt pathology this way:
There are hundreds of strains of Bt, and each one attacks a different type of plant (or animal). Bt is related to the same bacteria that cause anthrax (Bacillus anthracis) and food poisoning (Bacillus cereus), but Bt is believed to be harmless to humans and animals. The European Food Safety Authority approved the use of Bt, but pointed out that many safety claims lack adequate scientific proof. The Organic Materials Review Institute (OMRI) has approved Bacillus thuringiensis for use in organic farming with certain restrictions, including the use of crop rotation, proper sanitation, creating habitat for beneficial insects, and minimal use of Bt treatment. There are 5 subspecies of Bt available in the U.S.:
There are other Bacillus thuringiensis that claim to attack nematodes, flatworms, and mites. These forms are given mind-numbing names like Cry5B, Cry6A, Cry14A, Cry1A, Cry3A, and Cry4A. Unfortunately, research hasn’t shown them to be nearly as effective as advertisements claim, though they do provide some aid. These bacteria are also being used to genetically modify several food crops, including corn.
Bt is used on a wide variety of crops. The short list includes stone fruits, citrus, cruciferous vegetables, apples, artichokes, melons, berries, tomatoes, lettuce, and grapes, just to name a few. But Bt only works on insects when it is ingested. This normally occurs in the larval stage. Eggs and adult insects are generally not affected, so timing is important. Also, Bt degrades quickly in sunlight, so early morning or evening applications are best. These steps can help you get the most out of Bacillus thuringiensis:
You can find Bt at most garden centers. It comes in concentrated form or in a ready-to-spray bottle.
IMPORTANT NOTE: NOT ALL Bt PRODUCTS SOLD AS EFFECTIVE INSECTICIDES CAN ACTUALLY DO THE JOB. BE SURE TO LOOK FOR THE SUBSPECIES LISTED ABOVE.
What kind of plant is that?
Has that ever happen to you?
It happens to me a lot. I will plant seeds in what appears to be the ‘perfect spot’, confident that the location will trigger a memory of what I planted there, except that sometimes it doesn’t. Sometimes, I have no idea what it coming up. In those cases, I have to wait until the plant reaches a recognizable size. That’s fine when it turns out to be what I planted, but it’s a waste of soil, sun, and space when it turns out to be a pesky weed that has choked out the intended resident.
Using plant markers is a handy way to remind yourself of what is planted and where. This can help you take better care of your plants, especially when it comes time for feeding, propagating, or transplanting. Plant markers can also be used as lovely yard art. Here are several ideas for free (or nearly free) plant markers for your garden.
If your family eats popsicles, have them save the sticks. This works best if you create a place for them to collect: a cup, box, planter pot - something convenient. These wooden sticks will not last forever, usually no more than a single growing season, but they are fabricated with the intention of touching food, so I assume they are relatively safe. Popsicle stick plant markers absorb gel pen and marker colors nicely, so you can make them look colorful and easy to read. These plant markers are an excellent choice for seed starting. When the begin to wear out, you can simply toss them into the compost pile.
I used to own a private school, called Children’s Academy, in Virginia. We were on three acres and had a vegetable garden, a butterfly garden, and a wide variety of trees, shrubs, and other plants. I encouraged my students to go out and select a plant, conduct research, and identify it. Whoever identified it first was given the opportunity to select a large rock, paint the common and scientific names of the plant on the rock, and then place it near the plant. The kids seemed to enjoy it (they became a bit competitive about it, at times) and the rocks made beautiful reminders of what was growing around our school. You can do the same thing in your yard, especially for the perennials.
If you have a log or decent sized branch laying around, and a saw, you can cut disks of wood that make lovely plant markers. This requires some effort if you do not have a power saw, but it is certainly do-able. The wood grain looks really nice, without standing out too much, and the edge can be sunk into the soil enough to make it stand up or you can lay them flat.
Yard sales & garden markets
Yard sales and Master Gardener events are excellent sources for low-cost garden tools, and plant markers are no exception. Flatware, old mugs, saucers, and many other durable materials can be had for practically nothing and then painted with plant names.
Give yourself permission to be creative. Heck, go for flamboyant! You can add a touch of your personal creativity to the garden or landscape while making it easier to recall where all of your plants are!
Imagine a world without cabbageworms, leafminers, or whiteflies… Or one without Sudden Oak Death, bacterial spot, or tomato yellow leaf curl…
Such would be our gardens, had quarantines been in place and enforced sufficiently. Alas, it is not to be.
Imported plants that are not adequately inspected, nursery stock that is sold in spite of being infected or infested, and the use of grocery store produce to start a garden are responsible for a profound amount of damage to the environment. According to The Nature Conservancy, invasive species cost the U.S. economy $120 billion each year. The U.S. Forest Service echoes those figures, adding that 81 million acres of American soil are at risk due to these pests and diseases, and that 42% of threatened or endangered species are being pushed out by these invasives. Scale those figures down to the size of your garden and decide for yourself if it is worth the risk.
What is a quarantine?
To quarantine something means to keep it away from everything else, for a period of time, to avoid the spread of disease. In the world of plants, quarantines are used to halt the spread of diseases, pests, and other plants (weeds). In Italian, quarantina means 40 days and that’s where we get the idea behind quarantine. By isolating plants for 40 days, you are more likely to see signs of pests, diseases, or weeds, before exposing all of your other plants.
When to quarantine a plant?
Plants that are new, infected, or infested should be quarantined whenever possible. The easiest case, and the most useful, is when you bring a new plant home. As much as you want to add it to the landscape, 40 days in quarantine can prevent a whole lot of work later on. Plants new to your property can never be guaranteed disease-, pest-, or weed-free. Blithely adding it to your landscape may work out fine, or it may introduce a devastating disease that can stay in the soil for decades, introduce pests that you will have to battle every year forever after, or add even more weeds to your To Pull list. To avoid these risks, you can place new plants in quarantine until they have shown themselves to be safe for your garden or landscape. Containerized plants that develop problems are pretty easy to quarantine. Established plants are a bit more difficult.
How to quarantine
Ideally, new plants should be kept separate from all others for 40 days. This is especially true for houseplants, because there aren’t very many natural predators in your livingroom. This can be done by placing the latest addition in a different room, across the room, or in a clear plastic bag. The bag method is the most effective because it creates a barrier that you can see through. Established plants, such as fruit trees, are difficult, if not impossible to quarantine. In cases such as Citrus Greening, trees must be destroyed. If you suspect an invasive pest or disease in one of your established plants, contact your local County Extension Office for help.
Alternatives to quarantine
Some of us can’t (or won’t) invest 40 days of waiting before adding a new plant to the garden. When this is the case, use these tips to reduce the likelihood of problems:
Government mandated quarantines
In 1912, the Plant Quarantine Act was enacted, giving the U.S. government the right and responsibility of preventing the spread of pests and diseases through nursery stock and other plants. This act evolved into the Plant Protection Act of 2000. If you’ve ever driven across the California state line, you have seen the inspection stations and you may have been required to hand over an apple, a bag of green beans, or a butternut squash before being allowed in. From a visitor’s point of view, this Orwellian treatment may feel extreme, but it’s not. In fact, too many invasive pests and diseases are making their way around the globe because of too few precautions.
Grocery store produce
As tempting as it may be (I know, I’ve done it), do not use grocery store produce to seed your garden. Garlic, onions, and leeks look easy to start from your discards (and they are), but they can also carry fungal diseases that will never go away. Take a look at the current list of current quarantines in California to see some of the other vulnerable crops.
To quarantine or not to quarantine? That is the question. The answer is up to you. As you think it over, consider the fact that many pests can generate a surprising number of offspring pretty quickly. For example, a single aphid can turn into 600 billion descendants in a single season, according to entomologist Stephen A. Marshall.
Forty days of caution, or a lifetime of reactionary treatment.
Ecesis (eh-SEE-sus) is the establishment of a plant in a new habitat.
According to some, ecesis refers to plants becoming newly established in areas that were barren or previously devastated. However you define it, a better understanding of ecesis you to help your plants thrive.
Note: In the past, I have lived in duplexes whose tiny patch of soil was nothing more than a moonscape. Apparently barren, it didn’t take long to create a lush, edible landscape. Before you start, however, you need to know that each time you plant a seed, install a seedling, or transplant an established plant into a different container or location, ecesis is a factor.
Once a plant is established, there is a whole lot more going on than meets the eye:
Moving this plant to a new location, or into a bigger container, is a shock that can slow or halt growth, temporarily or permanently. Soil microorganism must repopulate the area. Roots that are damaged or overly stressed during transplanting mean less water and minerals available to the aboveground portion of the plant. (Ever have a plant wilt on you after transplanting?) Below, you can read about the many factors of ecesis that may impact plants being added to your garden or landscape.
Light and temperature
Significant changes in light and temperature can be devastating, or they can be necessary to a plant’s development. Some plants won’t put out fruit without enough chilling hours. Some seeds won’t germinate without being exposed to fire or ice or other damage to the seed hull. Most plants need a period of acclimation, called hardening off, when moved from one environment to another. Too much sun all at once and tender seedlings can be scorched. For your plants to be the most successful, choose varieties suited to your microclimate, be it a balcony, a farm, or a suburban yard.
Wind and other airs
Plants added to an environment with more wind than they are used to are going to need more water. Wind dries plants out. Wind can also blow containers and tall plants over, risking breakage. Placing containers against walls or tying plants to stakes can help prevent these problems. Insufficient air flow, whether through plant structure and improper pruning, geography, other plants, or fencing can increase the chance of fungal diseases occurring.
Problems with pavement
Plants installed near sidewalks, driveways, and buildings face a unique set of potential problems. The pavement and concrete create a heat sink, exposing plants to much more heat than is good for them. Also, these structures are usually designed to move water away, which means plants may need extra irrigation. And even easier solution is to select plants that can handle a lot of heat and very little water. Container plants grown in dark colored pots face similar problems. The dark color absorbs heat and the limited amount of soil can mean frequent drying out.
From whence they came
Where a plant came from should always be taken into account when installing it someplace new:
Containers If a container plant is being moved into a larger pot, it is a good idea to keep it in the exact same environment, or a slightly more protective version of the same place, until the roots have a chance to recover.
Nurseries Plants grown in nurseries are accustomed to climate-controlled warmth and moisture; they are often infested with aphids and other pests; they may have been sprayed with pesticides, fungicides, or herbicides; they may be carrying diseases or weed seeds. It is a good idea to have a quarantine area for all new plants that reduces stress to them and the chance of infection to established plants.
Soil Seeds started in potting mix and container plants that are used to loose soil will need some help when being transplanted into the ground. This is especially true in the Bay Area, where we mostly have heavy clay soil. If you dig a hole in the ground, be sure to rough up the sides of the hole. Smooth clay is almost as impenetrable as a ceramic pot.
Just as we need a period of time to get used to a new home or job, plants need a little TLC when they are moved into a new environment. Providing this care ensures that the move will be a successful one!
Have you ever seen trees with knobby limbs, bare of all leaves and twigs? It’s called pollarding.
Pollarding is a pruning method that limits the size of trees and shrubs. Unlike shearing, which trims everything past a certain point, pollarding cuts back all new growth. This stimulates regrowth that will bring it back to full size.
Pollarding was first done by the Romans and we still use it today. The word pollarding comes from ‘poll’ which refers to the top of the head (as any horse enthusiast knows). To ‘poll’ someone was to cut their hair. [I wonder if polling at the voting booth came from the same root - asking what is inside someone’s head. It makes sense, but I digress.]
Originally, trees were pollarded to provide food for livestock and fuel for winter fires. [Peasants were allotted a ration of firewood and other materials from the king’s trees in something called an ‘estover’. Pollarding stimulates vigorous upright growth, which turns into straight boards for boats and fence material. Thinner upright stems were also used to make baskets and garden bowers. Pretty smart for 2,000 years ago, eh?
Which trees are pollarded?
Pollarding is not recommended for all types of trees. Many conifers do not handle pruning very well. Their twigs tend to die back to the branch they grew out of, providing entry points for pests and disease. Yew are one exception. Trees that respond well to pollarding are those that tend to send out shoots quickly, a characteristic called ‘epicormic’, including:
When & how to pollard trees & shrubs
Pollarding is normally done annually in late winter. Maple trees are pollarded in summer to avoid bleeding sap. In most cases, each year’s pollard cuts should be just above the previous year’s cuts. Because pollarding large trees involves chainsaws and ladders, this is best left to the professionals. Small trees and shrubs can be pollarded with hand pruners and a tree saw. When evaluating a shrub for pollarding (or other pruning) keep in mind the future desired shape and size as you cut. Where each cut occurs, a mass of new stems will appear.
Advantages of pollarding
In addition to size maintenance, pollarding provides other benefits:
Disadvantages of pollarding
Pollarding is stressful to trees and shrubs and it must be done every year or two, to avoid limb breakage. The sprouts that appear after pollarding are attached weakly to the ‘knob’ and may break off. Mature trees that have not previously been pollarded can be killed by the process if it is done incorrectly. Even healthy trees and shrubs are exposed to pests and diseases after pollarding is done.
Whether you use pollarding or not, now you know what all those knobby looking trees are about!
Benefits of rain barrels
If you live in the Bay Area, you have probably noticed that our water is getting "harder". This is because of the minerals that are being dredged up from the bottom of reservoirs and ground water sources. It's not necessarily a bad thing (unless you are a coffeemaker or an iron), but it doesn't taste as good as it used to. Unlike the water that comes out of our faucets, rain water collected in rain barrels is free of chlorine and other chemicals used to make it potable. Watering container plants and in-ground plants with water from rain barrels means less potable water is being used. If you wash your hair from rain water, you may find that your hair feels softer.
Your average 2700 sq. ft. roof in the Bay Area can collect more than 25,000 gallons of water each year. Most rain barrels are significantly smaller than that, so you will only be able to collect so much before that water has to go someplace else, but it still ends up saving on your water bill.
The down side of rain barrels
As good as rain barrels are at conserving water, there are certain things you should know before you go shopping for your very own Amazing Rain Catcher. Here is what I have learned:
Now, I’m not trying to discourage you. As I said, I have three rain barrels and I use them year round. In the peak of summer, if I have managed my 65-gallon rain barrels properly, they give me a total of 195 gallons of rain water to use on my plants that would have had to come from the taps.
Let me know if you have any questions about rain barrels in the comments section.
If you are planting bare root trees this January, you may need to provide tree supports for the first year or two.
Structural support, or anchor staking, prevents the root ball from moving while the new roots are established. Tree supports hold the young tree by tying it to 2-4 posts with straps. Do not use rope, wire, or hose segments, as these put too much pressure on a narrow area, risking bark damage. Straps spread the pressure out over a wider area, keeping the bark healthy and intact. Since your tree will be growing, be sure to keep the strap around the trunk loose.
Damage caused by tree supports
Tree supports are only needed when a young tree cannot stand on its own or if it is being planted in an area with heavy winds. Also, tree supports should be removed as soon as they are not needed. Too many trees have become structurally unsound or vulnerable to pests or disease because the bark was allowed to grow over the support system. Don’t do this to your tree!
You may be surprised to learn that unnecessarily staking trees can actually hurt them in the long run. Plants grow in response to their environment. They lean toward sunlight and brace themselves against breezes, developing strength as they do so. This is called thigmomorphogenesis. Young trees that are prevented from developing this strength are more prone to breakage as they get bigger.
If you absolutely must provide tree support, it should be installed when the tree is planted, to avoid disturbing or damaging tender root systems. Tree supports should be placed one foot from the tree, with no branches touching.
There is a correct height for tree support ties. Too low and no support is given. Too high and the tree won’t learn how to stabilize itself. To determine the correct height, grasp the trunk of your floppy new tree and gently try to bend it over with the other hand. As you move your hand up the trunk, you will reach a point where the flop ends and the tree bounces back to an upright position. This is the magic spot. Your stakes should only be a few inches taller than this height to avoid damaging new branches as they come in.
The bare branches of January make this an excellent time for pruning.
Winter pruning helps improve the appearance and health of trees, shrubs, and roses. The only exception is apricot and cherry trees, which are susceptible to Eutypa dieback. Apricot and cherry trees are best pruned in the dry months of summer.
Different plants have different pruning needs, but the overall goals are the same: a balanced structure, adequate airflow, and the retention of productive limbs. There are two types of pruning cuts: thinning and heading. Heading cuts control height, while thinning improves air flow and sun exposure. Keep in mind, while pruning, that new growth will head in the direction of the remaining buds.
The first goal of pruning is to remove dead, diseased or crossing branches. Dead and diseased limbs can allow pests and disease easy access into healthy tissue. Crossed branches will rub against each other, causing similar problems. You will also want to trim away branches that are angled too closely together and those that hang downward.
Proper pruning protects people and property
Structural pruning reduces the likelihood of uprooted trees falling on you or your house. Trees with too much weight to one side also risk splitting the trunk and killing the tree. Pruning early in the tree’s life can create a safer, more balanced structure. While the depth and spread of tree roots depends on a number of factors (soil structure, irrigation, variety and age of the tree, and more), pruning can help the root system keep your tree upright. To give you an idea of how much weight we are talking about: an average mature hardwood tree, with a circumference of 100” inches at chest height, weighs nearly 13,000 pounds! Your average commuter car weighs 2,800 pounds - so imagine 4 or 5 cars hitting your roof in a storm to see why good pruning is so important.
How to prune larger branches
Pruning larger branches (those with a diameter of 2" or more), it is important to use multiple cuts to avoid peeling the bark beyond the final cut and damaging the remaining branch.
In drought-prone areas with heavy clay soil, moisture retention is an art that most plants have mastered. This also means fungal diseases can be a real problem. Roses and fruit trees are especially vulnerable to brown spot, rust and fireblight. Pruning for good airflow between twigs and branches can help reduce these diseases. It can also provide sunlight to inner leaves, which translates into more vigorous growth and heavier fruit and flower production.
Too much pruning is bad
Now, as I’ve said before, too much of a good thing can be a bad thing. Excessive pruning can expose interior branches to sunburn. Also, while pruning some or a little can promote new growth, heavy pruning can cause irreparable harm or death to the plant. Before you start pruning, research the specific variety of plant to learn about its natural growth and shape. For example, some trees produce fruit on last year’s growth, while others produce fruit on new growth. There's no sense in cutting off your nose to spite next summer's harvest!
The backyard orchardist will generally want trees that are small enough to make harvesting fruit easier, so you will want to use heading cuts to reduce the height of your trees. Branches that grow vertically tend to be more vegetative, while horizontal branches produce more fruit. Branches growing at 45 to 60-degree angles tend to do both.
When you cut off the end of a vertical branch, phytohormones, such as auxins, will cause the remaining buds will send out new growth horizontally. When you tip a horizontal branch, it will send out new fruiting wood. This is also a way to prevent too much fruit developing and risking a broken branch.
It is always a good idea to remove suckers and water sprouts. Water sprouts are flimsy twigs that quickly grow vertically, directly from the trunk or older branches. Suckers are similar growths that occur at the base of the trunk or from the root system. These growths drain energy from the plant without providing any benefits.
In Mediterranean climates, roses never go completely dormant, but winter is still the best time to prune for better spring and summer blooms. Generally speaking, you will want to remove 1/2 to 2/3 of the existing bush. Remove dead, diseased and crossing branches and then reshape the bush for better airflow. You can learn more about pruning roses at the San Jose Heritage Rose Garden.
When pruning, it is best to cut close to the branch collar without cutting into it. You also want to avoid leaving nubs that interfere with a plant’s ability to heal itself. There is generally no need to apply sealants to pruning cuts. Plants have evolved an effective system for that all on their own.
Finally, be sure to keep your tools sharp and to clean your cutting tools between cuts. Use a household cleaner, such as Lysol. Otherwise, you may be spreading disease to healthy plant tissue.
It can be incredibly rewarding to take before and after photographs of your pruning work. Feel free to share them with us!
Diatomaceous earth, or DE, isn't really earth at all. DE is actually the sedimentary rock formed by countless fossilized diatoms, a crusty little algae.
You can find food grade diatomaceous earth at many garden and feed stores. It can be used to kill pests, dust chickens, or clean your teeth!
Diatomaceous earth is very tiny and it has sharp edges. The edges are too small to hurt humans or chickens, but hard-bodied insects breath through their exoskeleton and DE blocks the insects’ breathing holes. Diatomaceous earth can be used as an insecticide against flea beetles, slugs and snails, mites, aphids, earwigs, and thrips, just to name a few.
You can dust around your house and garden to reduce the number of crawling insects that may be infesting your house or attacking your garden plants. Many grains that you buy in the grocery store contain small amounts of diatomaceous earth, to prevent insects from eating all the grain before you do.
It’s naturally abrasive character makes it an excellent choice as a toothpaste additive and pot scrubber. Chickens love to take dust baths in the stuff, as it helps remove dander, insects, and skin oils.
If you decide to use diatomaceous earth in your garden (or your henhouse), be sure to follow the directions on the package. You really should wear a dust mask and gloves. Use it very sparingly.
No, deficit irrigation doesn't refer to tossing the national budget into the ocean.
Instead, it is a method used by growers to increase the amount of sugar in foods such as tomatoes, basil, pomegranates, and peaches.
Plants have flavor because they contain sugar and volatile chemicals. Aroma plays a major role, as well, but we will leave that for another day. The volatile chemicals that generate flavor are used by plants as defense mechanisms. The pungent taste of many herbs is a perfect example of strong flavors being used to discourage herbivore and insect feeding. As water levels within a plant are reduced, those flavors get stronger. This is where deficit irrigation comes in.
The opposite of dilution
When the water supply is significantly reduced, sugar and flavor molecules become concentrated. More water means less sugar and flavor per plant, while less water means more flavor. It's a simple matter of dilution.
Some crops are bad choices for deficit irrigation. Cucumbers, melons, and other members of the squash family are more likely to turn bitter than better without adequate irrigation. For crops well suited to this practice, there is still a downside. Improperly done, deficit irrigation increases the risk of stunted growth and smaller fruit. Start too early and you end up with fruits and vegetables that are weaker, drier, and not what you were hoping for.
In the case of backyard tomatoes, it's a good idea to significantly reduce watering as the fruit begins to turn red. This way, the size is already reached and flavor is in full production.
Deficit irrigation also helps conserve precious water resources.
Harvesting the fruits of your gardening labor is an often forgotten yet critical aspect of the craft.
When you get down to it, everything plants do is directed towards reproduction. Creating flowers attracts pollinators, pollination creates seeds, and fruit provides seeds with food and protection. As soon as your plants start producing harvestable fruits and flowers, it is very important that you harvest frequently.
By putting your harvesting efforts off for another day, you are giving your plants the message that they have succeeded at reproduction and that no further effort is needed. This means less fruits and vegetables and flowers for you!
Bottom line - harvest every couple of days whenever your garden is producing to ensure maximum production.
You can grow a surprising amount of food in your own yard. Ask me how!
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