Idioblasts are specialized plants cells that are very different from the cells around them.
Most plant cells are grouped together with other, similar cells: leaf cells with leaf cells, root cells with root cells, and so on. Hidden within these normal groupings are cells called idioblasts.
Scientists believe that idioblasts are the precursors to many specialized cells, such as stomata, glands, and guard cells. When idioblast cells divide, they often create daughter cells different from themselves. These mutations have given rise to much of the diversity within the plant world. At the same time, many idioblasts have remained the same over time, providing important functions within a plant. According to Albert Paul Kausch, in his 1985 doctoral thesis, The development, physiology, and function of selected plant calcium oxalate crystal idioblasts, no one really knows how or why idioblasts form.
Most commonly, idioblasts are storage cells. But some idioblasts hold a defensive arsenal of poisons and pointy crystals!
When botanists and scientists talk about idioblasts, they divide them into several groups, depending on function.
Some idioblasts are simply storage cells. They may store pigment, food, waste products, water, resin, latex, oil, or tiny stones of silica (phytolith). Until recently, it was not understood why plants contained silica. Then, some scientists tried growing plants in soil without any silica. Many of these plants flopped over. Mystery solved. Sort of. Then, another group of scientists, led by Fergus P. Massey, proposed that plants evolved to contain silica for more than just structural support. They claim that plants absorb these minerals as a defense mechanism. Massey and his team point out that silica in plants tends to wear down the teeth of those who eat them. There is debate about the truth behind this assumption. You decide.
Idioblasts as manufacturing centers
Other idioblasts do more than just store materials. Some idioblasts actually manufacture important compounds. For example, avocado skins have idioblasts with antifungal properties. Other idioblasts produce mucilage carbohydrates (mucus cells) that store water. Other idioblasts, called phenolic cells produce and store carbolic acid to be used as defensive weapons.
Idioblasts as weapons
While we consider herbivores to be mostly harmless, plants do not share that view. Rooted to one location, and without claws or fangs, plants have to get creative when it comes to defending themselves against grazers and other plant eaters. This is where idioblasts get really interesting. Some idioblasts contain biforine cells. Biforine means having two doors. [Isn’t that a great word?] These cells are oval-shaped with openings at each end. When something (or someone) bites the plant, breaking the cell, crystals of calcium oxalate shoot out, poisoning or irritating the attacker! These oxalates are produced in the vacuoles of the idioblasts. Oxalates are toxic to the plant, too, but the plant protects itself by binding the material up in crystals. These crystals come in many shapes. They may look like a grain of sand, a pencil (styloid), a needle (raphide), or prismatic (isodiametric). Bundles of raphides or prismatics are called a druse.
Plants that use these weapons
Many plant families rely on druses stored in idioblasts for protection. These families include:
Botanists believe that plants also use these calcium oxalate-filled idioblasts to provide structure to the plant, and as a way to store calcium.
This information may not help your grow brighter flowers or more delicious tomatoes, but your mind needs to grow, too! And who can resist a word like idioblast?
Autumn colors are caused by senescence.
Senescence is the life stage of a plant or plant part when its metabolism slows prior to dying.
Our lovely fall colors are caused by a deciduous tree’s inability to maintain chlorophyll levels within its leaves. Chlorophyll, being green and abundant most of the time, masks the other colors that are alway present within a leaf. Shorter days and cooler temperatures trigger the tree to form a layer of cork at the base of each leaf, blocking the flow of water and nutrients and interfering with the leaf’s ability to produce chlorophyll. Eventually, the other colors can shine through. The veins of a leaf are the last part to turn color because it is the last place nutrients were available.
Autumn leaf color and the final days of a flower’s life are examples of developmental senescence. Developmental senescence occurs at the cellular level in all life stages. The seed leaves of a bean plant experience senescence when they wither and fall off. The mature leaves of the same plant will also exhibit senescence when they die. Ultimately, the metabolism of the entire plant will slow to the point of death. In each case, developmental senescence is triggered from within the plant.
Sometimes senescence is not developmental. It can also be induced for laboratory research, or as a result of injury or stress. Water stress can trigger senescence. A large plant with many leaves may be unable to maintain its canopy in a drought. Rather than risk death, it absorbs water and nutrients from outer leaves and then seals them off from the food supply, allowing them to fall away. Sunburn can also cause senescence. As an under-hydrated leaf receives direct sunlight, the cells most damaged slow their metabolism and relinquish their water and nutrients to the surrounding cells.
As seasons change and plants age, you will see many examples of senescence, but the colors of autumn are my favorite!
The Calvin cycle describes what happens to light energy after it has been absorbed into a leaf.
Put on your steampunk magnifying glasses because, today, we are going deep into the molecular level of leaves to learn how they make energy from sunlight.
Also known as the Calvin-Benson cycle, Melvin Calvin won a Nobel Prize in Chemistry for figuring this out. That was in 1961. Until Melvin’s research was complete, everyone thought that photosynthesis consisted of chlorophyll interacting directly with carbon dioxide to create edible organics (sugars) for plants. Instead, his research taught us that light energy causes chlorophyll to trigger plants to produce those organic compounds for themselves!
So, how does photosynthesis work?
Photosynthesis occurs in two steps. The first step is the light dependent reaction. This is when the sunlight is absorbed and transformed. To do this, electrons are torn from water molecules, creating oxygen as a waste product. When this happens, hydrogen (H) is released and used to create two compounds: nicotinamide adenine dinucleotide phosphate (NADPH) and adenosine triphosphate (ATP). The second stage of photosynthesis is the light independent reaction, or the Calvin cycle. This is when the ATP is converted into glucose.
Each stage of the Calvin cycle has its own enzyme. Enzymes are chemical catalysts that trigger change. After light energy has entered a plant through the stoma and been converted into ATP and NADPH, the light-independent (or ‘dark’) aspect of photosynthesis can begin. There are four stages to the Calvin cycle:
For your chemistry buffs, here's the equation and a graphic:
In the illustration above, atoms are represented as black (carbon), white (hydrogen) red (oxygen) and pink (phosphorus).
For the rest of us, try this story for a more memorable form:
Rubio marries Connie. Connie has twins. One twin becomes a cook. The other twin works family business and marries a girl just like mom. And they have twins. And so it goes….
Factors that interrupt the Calvin cycle
Any interruption in photosynthesis leads to chlorosis, or yellowing. Chlorosis can be the result of insufficient light (epinasty), disease, a lack of mycorrhizae, or sunburn. Other factors that interrupt the Calvin cycle include:
If you see chlorosis, it means your plant is starving. By learning about the Calvin cycle, you may be better equipped to figure out what is wrong with your plants. Get growing!
* RuBisCO - ribulose bisphosphate carboxylase/oxygenase; believed to be the most abundant enzyme on Earth (Wikipedia)
Correct overcrowded roots with division. Not the chalkboard variety, but by digging plants up, cutting them apart, and replanting.
Do my plants need dividing?
If production is down among your perennial plants, it may be that the roots have become too crowded. You can fix that with division. Division is a form of asexual propagation used on perennial plants. Annuals and biennial plants do not live long enough to make this method worthwhile. Signs that your perennials need dividing:
Why divide plants?
There are many perennial plants that benefit from dividing every few years. Plants that grow from rhizomes, such as bunch grasses, asparagus, and ginger, can be divided simply by digging up a section of the underground stem and cutting between the established plant and new growth, and planting the cut end someplace else. Many other perennial plants grow from corms and bulbs. These plants reproduce underground by creating offsets and bulbils, respectively. In either case, over time, it gets crowded down there!
Which plants need dividing?
Some plants, peonies and hostas, for example, never need dividing. Others, such as iris, Shasta daisies, and coreopsis should be divided every 2 or 3 years. Daylilies, evening primrose, and bergenia generally need dividing every 5 years or so. Many other garden plants vary in their need for division, depending on soil health, plant age, climate, and more. It’s generally a case of being observant and noticing when the following plants look like they need some breathing room:
When should plants be divided?
Autumn is generally the best time to divide plants. Autumn-blooming plants, such as saffron crocus, should be divided in spring. In both cases, temperatures are neither too hot not too cold, and plants will have time to recover before winter’s chill slows growth to a halt, or the summer sun bakes everything to a crisp.
How to divide perennial plants
Don’t be afraid to try dividing your plants. They will be far healthier and more productive once they reestablish themselves. Follow these steps to divide the perennials in your landscape:
Help your perennial plants reach their full potential by periodically dividing them. By dividing, I transformed my overcrowded, unhealthy, and unhappy Shasta daisy into 15 separate plants that now have room to grow and thrive and bloom!
Thinning young plants gives them the room they need to grow bigger and stronger. And most people have a hard time with this common garden task.
When to thin seedlings?
While most plant thinning occurs in spring, as new tomato, pepper, eggplant, and other seedlings emerge, the Bay Area is lucky to have a second growing season, filled with salad greens, broccoli, and cauliflower, so the need for thinning comes around again each fall.
A difficult task
For many gardeners, the idea of removing perfectly healthy plants does not come easily. Images of lush, ripe tomatoes, peppers, and melons offer so much potential, that we find reasons not to thin our garden plants. Of course, by not thinning, we compromise the health of all the plants. Thinning eliminates competition, leaving plenty of food, water, and sunlight for the remaining plants. This allows them to reach full size and produce larger crops. Proper thinning also provides good air flow, preventing many fungal diseases.
Thinning used to mean yanking unwanted plants out of the ground by their roots. This is no longer the case. Soil science has taught us how important tiny soil microbes are to plant health. Pulling plants out by their roots removes the microbes, as well. This makes it difficult for the remaining plants to get the nutrients they need. Pulling plants out also disturbs the roots left in place, which also slows growth. Instead, thinning is done with pruners or scissors, cutting pants off at ground level. This leaves the remaining root systems undisturbed. Plus, it allows the microbes from the thinned out plant to relocate and assist the plants left in place. Snipped off seedlings can be added to the compost pile or fed to the chickens. Just keep in mind that not all crops are thinned in the same way.
Just how much thinning is needed?
Onions and other root plants need frequent thinning. Other plants, such as leeks and beans, perform better without thinning at all. Large, spreading plants, such as pumpkins, need to be thinned out leaving a single plant every 2 or 3 feet! To understand the best way to thin each type of plant, check your seed packets. That information is usually printed on the label. Use it. They know what they’re talking about. If the seed packet is no longer available, look it up online or ask me in the Comments section. You can often calculate spacing needs based on the expected mature size of each plant.
If you really can’t bring yourself to toss out healthy seedlings, you can always plant individual seeds in peat pots, cell trays, or egg shell halves, or any other item that will hold a small seedling until it can be transplanted. Of course, this method means extra work in other ways, but it does eliminate the need for thinning.
Do your garden plants a favor and don’t procrastinate thinning!
No, we are not talking about those epic childhood battles in the back of the station wagon.
Pinching back is a way to redirect a plant’s growth and nutrients to where they will best be used.
How to pinch back
Take careful aim, tensing thumb and forefinger... Wait, no. That's not what we're talking about here. Pinching your sibling is probably a bad idea. Pinching back your plants can be a good idea. After a young plant has several pairs of true leaves, you can use your thumbnail to severe the stem just above a leaf node. Leaf nodes are the place where leaves grow out of a stem. It is important that you do not damage the tiny buds that are tucked between the leaf and the stem. This space is called the internode and the tiny buds are made of meristem tissue that can grow into new stems. Pinching back stimulates two stems to emerge at the nodes, increasing lateral growth. This doubles the number of stems, making a plant fuller. In only a few days, you will see these buds swell and new stems emerge. You can pinch back these new stems for even bushier growth after they have a few pairs of new leaves. Do not pinch back below where you have already pinched. Plants don’t respond well to that treatment.
Pinching back vs. deadheading
Deadheading refers to the removal of spent blossoms. This is done to stimulate new flowers to grow and the method is very similar to pinching back. In both cases, stems are cut just above leaf nodes, but for slightly different reasons. If a flowering plant believes that it has completed its reproductive cycle, it has little reason to produce more flowers. [Producing flowers is hard work for a plant.] Removing nearly spent blossoms triggers the plant to create new ones. Pinching back is done to stimulate lateral stem growth, rather than specifically for flower production.
Tipping vs. topping
Pinching is generally performed on herbaceous, or soft-stemmed, plants. Pinching back woody plants, such as trees, is called topping and can harm or even kill the plant, unless performed at the proper time of year and in the right way. Topping trees is best left to professional arborists.
Pinching back for structure
Some plants tend to get too tall, falling over just when they are covered with flowers or produce. My borage does this every year. Pinching the central stem slows that upward growth and stimulates growth out toward the sides. Of course, this does mean you get a few less flowers, at first, but it can extend the total growing time, weather permitting. Creating a bushier structure with herbs, such as basil, also gives you far more of the fragrant leaves you grew the plant for in the first place. You can think of pinching back as pruning, only in miniature!
Pinching back for production
Many plants, such as tomatoes, produce far more side shoots than the main stalk can support. That’s why tomato cages are so popular. You can significantly improve fruit quality by pinching back many of these side shoots. Pinching back is also very useful near the end of the growing season. Removing any flowers that will take too long to mature before the first frost dates forces the plant to focus its sugary energy on the remaining fruit.
Don’t be afraid to pinch back new growth on your soft-stemmed plants. You can help them to be healthier and more productive with this simple task. It also gives you an up close and personal look at the health of your garden plants.
Evil hides beneath the calyx, yet you hold it close.
Sorry, I couldn't resist. The calyx is part of a flower. The reason I say ‘evil hides beneath’ is because that is where many fruit rotting fungi hang out.
Calyx as flower part
Calyx is another word for sepal. Sepals are the green petals at the base of a flower that are modified leaves. The calyx is also the green leafy area at the top of a strawberry fruit. Sometimes, the calyx is the same color as its flower. In most cases, once a plant is done with the flower, the calyx is discarded. Tomatillo plants retain the calyx as a thorny protection. In other cases, the calyx begins to grow in earnest after the flower is fertilized, creating a protective bladder-like enclosure. The sepals of Hibiscus sabdariffa turn into an edible accessory fruit.
Calyx as hiding place
Many fungi, such as botrytis cinema, love to hide under the calyx, waiting for a splash of rain or irrigation water to start breeding grey mold and feeding on your berries and other garden produce. Sometimes the calyx falls victim to the very pathogens it protects, along with the fruit, as in the case of stem-end rot. In some cases, such as calyx blight, only the calyx becomes infected and the fruit remains fine.
How many different types of calyx are in your garden?
Ammonium sulfate is a good source of iron for your plants, even though it doesn’t contain any. How can that be? Read on!
Ammonium sulfate (AS) is the oldest form of manufactured nitrogen fertilizer. Chemically, ammonium sulfate [(NH4)2SO4] is a salt that contains 21% nitrogen and 24% sulfur.
What’s in the fertilizer bag?
Most people know that plants use nitrogen to grow. If you buy a 10-pound bag of 5-5-5 fertilizer, that means you are getting 5% of each of the primary nutrients - nitrogen (N), phosphorus (P), and potassium (K). This works out to 1/2 pound of each nutrient and 8-1/2 pounds of filler. If you buy a 10-pound bag of ammonium sulfate, you get 2.10 pounds of nitrogen, 2.40 pounds of sulfur, and 5.5 pounds of filler. Now, don't think that those fillers simply take up space, though sometimes that’s exactly what they do. Mostly, these fillers are sand or granulated limestone. Whether or not those are good for your soil depends on your unique situation. Personally, I prefer less filler and more substance. Also, here in the Bay Area, we generally don’t need anything besides nitrogen for plant growth. My soil had nearly 10 times the optimal amount of phosphorus, twice as much potassium and calcium, and 8 times more magnesium than my plants need, the last time I had it tested. Adding more would be a complete waste of money. My problem was iron. I had less than one-third of the optimal amount. And my plants couldn’t even get to what little there was because of sol pH.
Ammonium sulfate and soil pH
In areas with alkaline soil, sulfur acts as an extremely mild acidifier. If you want to grow acid-loving plants, such as blueberries, artichokes, or potatoes, lowering the soil pH can seriously improve your harvest and the overall health of your plants. Ammonium sulfate has a pH value of 5.5 and the sulfur it contains will provide a tiny bit of help. The real pH reduction occurs when soil microbes convert the ammonium into nitrate, in a process called nitrification. If your soil has a pH of less than 6.0, you should not use ammonium sulfate. Most Bay Area soils are closer to 7.5 (untreated, mine was 7.7). Soil that is too alkaline or too acidic make it difficult for plants to absorb nutrients and thrive.
Ammonium sulfate and food safety
Unlike many fertilizers, which can be dangerous, ammonium sulfate is a food additive. The U.S. Food and Drug Administration lists ammonium sulfate as “generally recognized as safe”. [I still wouldn't eat it out of the fertilizer bag!] It is commonly added to flours and breads to regulate acidity. It is also added to many vaccines, to improve their effectiveness. Ammonium sulfate is hygroscopic, which means it absorbs moisture from the air, so be sure to keep the bag tightly closed.
Applying ammonium sulfate
As with any soil treatment, read the label and follow the directions. Seriously. When applying ammonium sulfate to your lawn or garden, be sure to water or work it into the soil right away. If it sits on top of everything, much of the ammonia (nitrogen) will be lost to the atmosphere.
Ammonium sulfate and iron
So, how can ammonium sulfate provide your plants with iron if it doesn’t contain any? Here’s the rub: soil pH dictates the absorbability of many nutrients. Slightly acidic soil makes it easier for plants to absorb the available iron. Of course, if your soil is low on iron, all the ammonium sulfate in the world won’t help. Get your soil tested so that you KNOW what you are working with. And if you live in an area with alkaline soil, ammonium sulfate can be an excellent way to add nitrogen and reduce soil pH for healthier plants.
Anthers are where pollen is made.
Plant labels often say ‘determinate’ or ‘indeterminate’, but what do those words mean and how do they affect your garden harvest? Let’s find out.
The botanical definitions of determinate and indeterminate tell us the science behind basic growth patterns. Indeterminate growth doesn’t stop. The main stem will just keep on growing. Think giant sequoias and other redwood trees. Indeterminate growth can also refer to sequential flowering that starts at the bottom and on the sides of a plant, and then moves in and up. Determinate growth is finite. It usually means the main stem ends with a flower or other reproductive structure. Flowering among determinate plant varieties starts from the middle and the top and moves downward and outward. So what does this have to do with your seed packet?
Genetic survival and ripe fruit
Keep in mind that all those fruits and vegetables that we love are a plant’s way of passing on genetic information. It’s survival of the species. Different plants solve the problem of genetic survival in different ways. In fact, the range of behaviors and adaptations goes beyond bizarre in some cases, but we will leave those stories for another day. Basically, in nature, some plants spread their bounty out over several weeks or even months (indeterminate), while others seem to ripen everything on the same day (determinate). In some cases, plants can switch from one to the other! Fruit trees tend to reach harvestable conditions on a determinate schedule. An overabundance of ripe fruit may attract more animals which then spread the seeds over a wider area. [I’m guessing.] Plants that spread their harvest out over a longer period of time may be improving their odds at favorable conditions for their offspring. [Still guessing.] Generally speaking, though not as a hard and fast rule, annuals lean toward the determinate side of the fence, while perennials prefer indeterminate growth. Which ever way they go, it’s a classic case of, “What works, is. What doesn’t, isn’t.” Plants that don’t reproduce successfully do not exist for long.
Since the Agricultural Revolution, we have been modifying plants for size, flavor, disease resistance, and time of harvest, among other things. In commercial agriculture, determinate plants are preferred because crops must be harvested by machinery, all at the same time. For the home gardener, 40 pounds of peas coming ready for harvest within the same week might not be such a good thing. [If it happens, you can always freeze or can your bounty.]
Bushes and vines
In the garden, tomatoes, potatoes, cucumbers, strawberries, peas, and beans are just a few of the plants that can be either determinate or indeterminate. Most determinate garden plants are labeled as ‘bush’ variety, though many of them don’t actually grow into bushes. Indeterminate cucumbers, for example, will use tendrils to climb as far as they want and produce the biggest fruit they can. Determinate, or ‘bush’ cucumbers, will still spread out, but they generally stay lower to the ground and will produce a set size fruit. Indeterminate tomatoes will grow as tall as they can and continue to put out flowers throughout the growing season, whereas determinate tomatoes tend to focus their energy into bushier growth and producing their crop of tomatoes pretty much around the same time. This is helpful if you are making and canning your own tomato sauce, but it can be a problem if you prefer all of your tomatoes fresh from the garden.
Some crops, such as peas and beans, can be semi determinate. This means they tend to stop producing at a set point but can be coaxed to continue into a second or even third round of production by regularly harvesting pods as soon as they are produced. Remember, a plant is trying to pass on its genes. If they ‘believe’ they have not succeeded, they will keep trying, in most cases.
Ears: another form of determinism
Ears of corn can also be determinate or indeterminate. In this case, the variable is ear size. Ears of determinate corn will stop growing at a set size, while indeterminate corn has no set size and will reach maturity based on environmental conditions.
Pruning and determinism
Indeterminate plants can be pruned of unwanted shoots to direct growth and nutrients where you want them. Determinate plants, on the other hand, perform better if they are not pruned excessively.
Bottom line: if you want everything to come ripe around the same time, plant determinate varieties. If you prefer an ongoing harvest, plant indeterminate varieties.
Pollinators are animals that carry pollen from flower to flower. This pollen then fertilizes female flowers, allowing plants to produce fruit and seeds.
Without pollinators, we would be in a bad way. The U.S. Dept. of Agriculture tells us, “Of the 100 crop species which provide 90 percent of the world’s food, over 70 crops are pollinated by bees.”
Fruit set failure often means there are not enough pollinators. Today, we will find out who the pollinators are and how to attract more of them to the garden.
How does pollination occur?
Some plants have the ability to self-pollinate. If pollen grains can be moved from the male (anther) to the female (stigma) within the same flower, it is called autogamy. If pollen grains are carried from the anther of one flower to the stigma of another flower, while still on the same plant, it is called geitonogamy. When the pollen must be taken to the stigma of a different plant it is called cross-pollination, xenogamy, or allogamy. In some cases, self-pollination occurs before the flower even opens! This is called cleistogamy, but it has nothing to do with pollinators, so we will leave those flowers to themselves - which is what they seem to prefer anyway.
How do pollinators move pollen?
Even in the case of self-pollinating flowers, something is needed to break the pollen loose from the anther so that it can stick to the stigma. Note for those with allergies: pollen is very sticky. Rubbing or rinsing with water will not remove pollen. Soapy water is needed. So, as pollinators land on a flower, pollen sticks to them. Walking around on a flower knocks pollen loose to fall on the stigma and to stick to the body of the visitor. Next, that visitor flies, walks, or crawls away, carrying that pollen with them. When they visit the next flower, pollen is knocked loose from the anther and the pollinator’s body and the chance of fertilization starts going up. Some pollinators end up looking like Charles Schultz’ Pig-Pen, a walking cluster of pollen grains. Others have evolved with pockets on their legs! Honey bees and other apid bees have a pollen basket, or corbicula, on their legs that hold pollen wetted down with nectar. Other bees have a pollen basket called a scopa, on their abdomen. Whether they carry it on purpose or not, pollinators are drawn to flowers for several reasons.
How flowers attract pollinators
Plants have evolved with specific characteristics that attract the best pollinators for their needs. In some cases, the relationship is very specific. Figs are only pollinated by a fig wasp. No fig wasp - no figs. In most cases, plants go for the hard sell to attract as many pollinators as possible, using several different characteristics:
Installing a wide variety of plants is one of the best ways to attract pollinators.
Who are the pollinators?
There is far more to pollination than just the 1,000 different species of native, mostly non-stinging bees in California (4,000 nationwide; 20,000 worldwide). Bats, flies, moths and butterflies, beetles, birds, wasps, even lizards and monkeys can be pollinators. For that matter, so are we! As we walk through the garden, pollen attaches to our skin and clothing, to be deposited on the next plant we approach. We have also been known to hand-pollinate plants on purpose. More often, pollinators co-evolve in mutually beneficial relationships with their nectar and pollen food sources.
How to attract pollinators
First and foremost, get rid of the toxins that kill these beneficials. Broad spectrum insecticides, herbicides, and pesticides, even when they claim to be safe, should be avoided. They cause too much of an interruption in the normal, natural cycle of things. Yes, it means a few more pests in the garden, but it also means less toxins and more pollinators.
Second, pollinators need fresh water. While you do not want to create mosquito breeding grounds, bird baths, fountains, and other water features make lovely additions to the garden while providing water for pollinators.
Third, you need to provide adequate food and shelter for pollinators. Now, before you go out and buy one of those new fangled bug hotels, know that research does not show they are effective. In fact, these artificial clusters end up being breeding grounds for pests and diseases of pollinators! Most native bees are ground-dwelling, so they wouldn’t use them anyway.
You can certainly install a bat house, but most of the shelter you provide will be the same plants you install to provide pollinators with food. Use these strategies to provide shelter:
Plants that attract pollinators
Plants can be divided according to the pollinators they attract:
Butterflies also benefit from access to your compost pile and a patch of mud. They use the mud as a source of both water and minerals, and they enjoy eating rotten fruit.
Going native through the seasons
Since evolution is a really slow process, one of the best ways to attract a wide variety of pollinators to your garden is to install native plants. Native plants already provide for these beneficial insects and birds. You will also want to ensure that there are flowering plants available throughout the year. Not only will this help the pollinators, it will make your garden and landscape look better! Perennial natives, such as manzanita, make the job of attracting pollinators far easier. Here is a list of some California native plants that attract and provide for pollinators:
Let it go to seed
All too often, we sabotage ourselves at the end of each growing season. Rather that pulling (never pull!) or cutting (better) spent plants, leave them in the ground (best) to go to seed. Not only will this provide for local pollinators, but it can also give you seeds for next year’s crops! I always let things go to seed. Now, as the seasons change, I find lettuce, escarole, cosmos, carrots, and more, growing where I never planted them, but where they can grow without any help from me.
Other causes of low pollination
Sometimes, pollinators are not the problem. Other causes of low pollination rates include:
For region specific planting advice, check out the Pollinator Partnership’s interactive tool. Simply type in your zip code and they provide valuable information about suitable plants that will attract pollinators.
Calcium is a critical plant nutrient commonly found in alkaline soil. But that doesn’t mean your plants can get to it.
Calcium inside plants
We all know that calcium makes for strong bones and teeth. It also helps plants stay healthy. In fact, calcium is critical to plant growth and development. 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.]
Calcium deficiency is often caused by irregular irrigation. Unlike more mobile nutrients, such as nitrogen, calcium does not move around within a plant easily. Once it stops traveling through the xylem, it pretty much stays where it is. This is why calcium deficiency is rarely seen in older plant tissue. Normally, calcium is moved through a plant by evapotranspiration, which uses a lot of water. Calcium deficiency can also occur when there is too much nitrogen in the soil, causing plants to grow faster than they can move the available calcium. When plants do not have enough calcium, you may see stunted growth, leaf curling, dead terminal buds and root tips, leaves with brown spots along the edges that spread toward the center. These damaged areas make it easier for pests and disease to strike. Some crop-specific symptoms of calcium deficiency include:
Drought and minerals
Minerals, such as calcium, are affected by drought in ways that might surprise you. Reduced water supplies often mean we get our tap (irrigation) water from reservoirs that are scraping the bottom of the proverbial barrel. That water already has high salt and mineral contents. The chemical reactions that occur between those salts and plant nutrients can make life difficult for everyone involved. California pistachio growers have found that, by adding more calcium to the soil, they can reduce the amount of salt absorbed by plants. This is not something you should attempt in your garden, because what you just read is an oversimplification of a complex condition. I only use it to point out the amazing balancing act that is going on all the time to get you the foods you love. Another factor that involves drought and calcium is drip irrigation emitters. They tend to get clogged by calcium the same way your coffee maker and iron do. If your region has hard (high mineral content) water, you may want to invest in a filter.
Sources of calcium
Before adding calcium to your soil, it is important to find out what it already contains. Most Bay Area soils contain abundant calcium. The optimal range is 1000-1500 ppm. My laboratory soil test results for calcium were 2705 ppm! A soil test, conducted by a reputable, relatively local lab, is the only way to know for sure. Over-the-counter soil tests are not reliable or accurate enough. If you are growing in the Bay Area (or anywhere there used to be an ocean), there’s probably plenty of calcium already present. If you live east of the Rockies, it’s a different story. Egg shells, agricultural lime, and calcium chloride sprays can be used to replenish depleted soils.
Calcium uptake problems
Let’s assume that your soil has plenty of calcium in it. and that you are watering regularly and properly. There are other problems that can interfere with a plant’s ability to absorb this important nutrient. Excessive potassium (K) is one. Too much magnesium (Mg), sodium (Na), iron (Fe), or ammonium (NH4+) can also slow the uptake of calcium. Soil alkalinity or acidity (pH) also plays a role.
The molecular balancing act that occurs between minerals within your soil and plants is mind-boggling, to say the least. Suffice to say, your average gardener (or gardening blogger) only groks the tip of this iceberg. This is not something to guess about. Get your soil tested. Your plants will thank you.
We’ve all played with sand at some point. There were probably waves crashing in the distance, the smell of tanning lotion and sunscreen mixing with salty air. Sand gets everywhere and it can be used to make some amazing temporary castles and other works of art. It is also a component of soil.
What makes soil?
Soil is a combination of minerals, organic stuff (living and dead), liquids, and gases. The liquids and gasses, mostly air and water, move through large and small spaces called macropores and micropores, respectively. Soil can be mostly clay, mostly silt, mostly sand, or somewhere in between. Clay, silt, and sand classifications are more about particle size than actual material, but here’s the typical breakdown:
[Note: μm stands for micrometer, or micron. One micron equals one one-millionth of a meter.]
Soil texture and nutrient availability
If you live in Florida, you know all too well how difficult it is to keep nutrients and water in your sandy soil. This is because the spaces between the grains of sand are so big. At the other end of the spectrum, clay is made up of flat plates that tend to stick together, holding tightly to water and nutrients and making it difficult for plant roots to move through it. It very few macropores and micropores, which means drainage and aeration are common problems. This is also why it makes such nice pottery.
The Sand-Clay Myth
What is a gardener to do? Our intuition tells us that we can lighten heavy clay soil by adding sand. It sounds right. Sand has plenty of spaces! Putting the two together should give us a nice, happy medium, right? Wrong. Instead, the tiny clay particles fill in all the spaces around the sand grains, creating a soil that is even heavier than before!
Organic mulch to the rescue!
When I say ‘organic mulch’, I am not necessarily saying organic in the OMRI sense, although that is what I use. Organic mulch refers to mulch composed of materials that were or are alive: plants, animals, bugs, manures, that sort of thing. It does not include ground up plastics or other manufactured materials. When you incorporate organic mulch into sandy soil, you provide materials that can bind nutrients and water to the planting bed. The macropores become partially filled with water- and nutrient-retaining compost. When you top dress heavy clay soil with an organic mulch, earthworms, microorganisms, irrigation, and other actions will slowly incorporate chunks of non-clay material below the soil line, creating macropores and micropores for air, water, and plant roots to move through. Top dressing means you just leave the material on top of the soil, rather than digging it in. Digging clay soil is generally not helpful because of the smooth surface left behind by the shovel. When that surface dries, it can be impenetrable.
So, leave the sand at the beach or in your egg timer. If you have clay soil, organic mulch is what you want to use. You may be surprised to learn that sand is a non-renewable resource in high demand, due to our penchant for concrete. Apparently, creating sand take eons and we use a lot of it.
Callus is what plants use instead of bandaids.
What are tree wounds?
Tree wounds can occur on purpose, by pruning, or by accident, from heavy winds or by being overladen with fruit. Most pruning cuts are relatively smooth. Accidental wounds tend to be jagged and the bark may be torn down the trunk. In these cases, the tree will benefit from the branch being cut back to a place where a flat wound is possible. This gets rid of insect hiding places and speeds the healing process for the tree. In both cases, interior tissue is exposed to the elements.
Traditional wound treatment
For decades, people have said that we should protect tree wounds with paint, pastes, and salves, which are generally petroleum based. The idea behind these treatments was that an open wound was vulnerable and that we could ‘help’ our trees by painting the cut surface with tar, asphalt, wound paint, or some other sealant. Instead of providing protection, these treatments actually seal in harmful bacteria and fungi, increasing the chance of disease or decay. Also, there are certain disease-carrying organisms that love to feed on or are otherwise attracted to the sealant!
It ends up, trees already know how to protect themselves. Just as our skin forms a callus in response to hard work and friction, trees create tissue over wounds to protect themselves from pests and diseases. The word ‘callus’ is from the late Middle English Latin word ‘callosus’ which means ‘hard-skinned’. Trees are able to generate their own ‘hard skin’ to cover a wound. If that process is interrupted with oil-based sealants, the internal processes of decay prevention may also be interrupted.
An exception to the rule
One case where wound dressing is a good idea is in regions (like ours) where oak wilt is a problem. If an oak in these areas is damaged or requires pruning, a sealant that contains insecticide and fungicide can prevent loss of the tree.
Why do the flowers keep falling off your tomato, squash, melon, and bean plants, and citrus trees?
This condition is called blossom drop. Blossom drop can be caused by several factors, most of which are perfectly normal. Others, not so much. Generally speaking, unfertilized flowers are kicked to the curb. Here are some species-specific causes of blossom drop.
Citrus June drop
Most citrus trees will produce far more flowers than they could possibly bring to maturity. When the tree decides it has enough fertilized flowers, usually around June, the rest are discarded. It’s nothing to worry about.
Cucurbit blossom drop
The first flowers on your melons, winter or summer squash, and cucumber are generally male. These drop naturally after a brief appearance. If female blossoms start falling off, it is usually because of thrip damage, poor soil fertility, environmental factors, or inadequate pollination. You can attract more bees and other pollinators to your garden by adding yarrow and bee balm. You can also allow onions, carrots, and fennel to go to seed. These plants will all provide pollen and nectar to beneficial insects that should increase pollination rates. If that doesn’t work, you can always try hand-pollinating.
Bean blossom drop
Temperatures over 90°F will cause bean flowers to abort. This can also occur with insufficient irrigation and poor air quality due to smog or fires. If you know your summer temperatures are likely to go over that threshold, try planting beans earlier or later in the season.
Tomato and pepper blossom drop
Tomatoes and peppers often drop their blossoms when environmental conditions are unfavorable. This might mean any of the following:
How to reduce blossom drop
Use these handy tips to reduce blossom drop in your garden:
The good news about blossom drop
Luckily, when environmental conditions cause blossom drop, most plants will simply try again, producing a second crop of blossoms.
Why do healthy plants fail to set fruit?
Your plants look lush and healthy. There are plenty of leaves and blossoms. You’ve been watering and feeding and mulching, just the way you are supposed to, and still not fruit. Why not?
Assuming that your plants are otherwise healthy, not diseased or water stressed, there are several reasons behind fruit set failure. The most common are lack of pollinators, too much heat, not enough light, and the wrong fertilizer.
Lack of pollinators
While many crops, such as tomatoes, are self-fertile, the lack of bees, flies, butterflies and moths, and even wind can reduce the number of fertilized flowers. Unfertilized flowers cannot produce fruit. You can attract more pollinators into your garden and landscape with colorful flowers that offer a variety of landing pads. Plant flowers in clusters, rather than singly, for the best results. You can shake plants very gently to increase pollination rates.
Too hot to fruit
One of the most common reasons why blossoms do not transform into fruit is heat. As temperatures rise, plant life processes slow down. Most spring temperatures are pretty mild, but a few scorching hot days can ruin everything, at least for a while. This is because pollen loses its viability between 85 and 90 ºF. So it won’t matter how many bees stop by for a visit or how healthy your plants are. It simply can’t happen. Luckily, most plants continue to produce flowers beyond the brief heat wave and the pollen in those flowers can produce fruit. Note, hybrid plants tend to be more sensitive to temperature fluctuations.
Most fruiting plants need six to eight hours of sunlight to produce. If growth is leggy and etiolated, it may be that they are not getting enough light.
Fertilizer, a balancing act
All plants need good nutrition to produce fruit. Unhealthy plants simply do not have the resources to produce a decent crop. At the same time, too much nitrogen can lead to excessive vegetative growth, and even blossoms, and still no fruit. Insufficient phosphorous can also cause reduced flowering and fruiting, but that is rarely a problem in the Bay Area. Before adding phosphorous (which we generally have in excess), conduct a reliable soil test (not the OTC variety).
So, if you are watering your plants properly and they are getting enough light, you may simply need to wait out the unfavorable conditions, or you may need to alter your fertilizer applications.
Epinasty refers to the way leaves and stems turn downward when their tops grow faster than their bottoms.
While we all know that many plants move to follow the path of the sun each day (phototropism), sometimes plant movements are more random. These are called nastic movements. Epinasty is a nastic movement. Hyponasty is the opposite of epinasty.
The weight of a heavy flower or fruit is an example of mechanical epinasty. Over time, the upper portion of a stem grows longer and faster as the weight of the fruit or flower pulls downward.
The most common cause of epinasty is ethylene. Ethylene is a gaseous plant hormone that helps fruits ripen. It is also a major survival tactic in cases of flooding, either temporary or permanent. Let me explain. When roots experience flooding, they generate an amino acid that I cannot pronounce, but botanists call it ACC. ACC is the precursor to ethylene. ACC moves up the xylem where it is turned into ethylene gas. This ethylene stimulates roots to create hollow tubes that connect to adventitious roots. These tiny roots and tubes are used to draw oxygen into the plant. Other signs of ethylene exposure include chlorosis, thickening stems, petal loss, and deformed or aborted flowers. Epinasty from ethylene gas is common among plants grown in greenhouses with poorly maintained propane or natural gas heaters.
If your tomato plants are exhibiting downward curling leaves, it may be that the soil needs more time to dry out between waterings.
Everyone knows what berries are, right?
Sweet, juicy summer favorites commonly include strawberries, blueberries, raspberries, and blackberries. Of course, in the world of botany, you'd be wrong on most counts.
What are berries?
Botanically, a berry is “a [simple] fleshy fruit, without a stone, produced from a single flower, containing one ovary.” (Wikipedia) Fruits are the mature ovaries of one or more flowers. When a single ovary is fertilized to produce a fruit, it is called a berry. The fleshy part we find so tasty is made from the pericarp.
Berries that are not berries
With that definition in mind, we learn that strawberries, raspberries, and blackberries are not berries at all. Strawberries are what’s known as ‘accessory’ fruits. The flesh of an accessory fruit is not made from the ovary. Instead, it is a protective growth from surrounding tissue. Blackberries and raspberries are ‘aggregate’ fruits. Aggregate fruits are made from single flowers, but many ovaries that are held together in a cluster. Speaking of clusters, what about grapes?
Fruits that are berries
Yep, grapes are, by definition, berries. In fact, plants that produce berries are called ‘bacciferous’. [I wonder if that name comes from Bacchus, the Roman god of wine.] There are many fruits, other than grapes, that we would never call ‘berries’ even though they are. Consider many of your favorite garden plants. Do they have fruit? Are they from a single ovary? Are they without a stone? It ends up, tomatoes, cucumbers, kiwi, peppers, eggplants, persimmons, pumpkins, and watermelons are all berries! Even coffee beans, allspice, and bananas are berries!
Of course, scientists are still working out the details, but now you can amaze and baffle your friends with your new knowledge about garden plants!
Bite into a cucumber and, instead of crisp deliciousness, you get a bitter taste. What happened?!!?
Fruit can turn bitter for several different reasons. Unfortunately, once a plant produces bitter tasting fruit, you may as well cut it off at ground level and start again, because most of the fruit it will produce from then on will have the same taste. Also, the chemicals that cause the bitterness can make you sick. In extreme cases, they can even kill you. So, what makes fruit turn bitter and how can it be prevented?
Causes of bitter fruit
The bitterness is caused by chemicals, called cucurbitacins, that are always present in the roots, leaves, and stems of these plants. When the plant becomes overly stressed, it increases the production of cucurbitacins, which then make their way into the fruit. Scientists believe these chemicals are intended to discourage feeding by herbivores (and us). Common causes of stress that leads to bitter fruit include:
Steps to prevent bitter fruit
If your cucumbers have started turning bitter, you can still eat much of the fruit, simply by peeling it and tossing the stem end into the compost pile. If it still tastes bitter, compost it. The chemicals will disperse and break down.
Help your cucumbers, melons, and summer squash stay sweet with proper irrigation and a little sun protection.
Temperature impacts every stage of plant growth and fruit production.
We all know that most plant life processes stop when it gets really cold outside, but did you know that the same thing happens when it is hot?
Temperature sweet spots
Each plant species has a minimum, maximum, and optimal temperature range for its different life processes: germination, seedling growth, vegetative growth, and reproductive growth. Some plants, such as peas, lettuce, broccoli, and spinach, prefer cooler weather (60 °F), while squash, melons, peppers, tomatoes and corn prefer hot weather (80 to 90 °F). The normal (phenological) responses to temperature are what make our harvest possible. And sometimes we get 90 °F weather in April.
Plant responses to heat and cold
Just as the symptoms of not enough water look a lot like the symptoms of too much water, plants respond to both temperature extremes in very similar ways. (Their options are limited.) At first, they close the tiny pores, called stoma, on the underside of leaves to retain moisture. If this isn’t sufficient protection, they wilt. Then leaves begin to dry and burn at the tips and edges, and tender new growth can die. Prolonged exposure can lead to twig and branch dieback, or complete loss of the plant.
What happens when it gets too hot?
Excessive heat (above 90 °F) can lead to water stress and sunburn damage. It can also interfere with pollination. Pollen loses its viability at temperatures over 95 °F and seedlings die at 125 °F. While the Bay Area never sees temperatures that high, sunlight reflected off of hot pavement can easily scorch nearby plants. In crops such as corn, a sudden heat wave can reduce your harvest by 80 to 90%! Studies have shown that high temperatures can reduce the amount of time a plant takes to produce fruit, lowering both size and quality. Plants also tend to stay smaller. You cannot control the weather, but there are things you can do before, during, and after planting to help your garden and landscape plants survive temperature extremes.
When water isn’t enough
Deep roots and good health go a long way toward helping a plant protect itself. Shallow root systems dry out quickly and are more sensitive to heat and cold. Watering plants deeply and allowing the soil to dry out between waterings encourages roots to go deeper. And sometimes water isn’t enough. A thick layer of aged compost or other mulching material placed around trees, shrubs, and other plants can stabilize soil temperature and provide a slow-release of nutrients. Just be sure the mulch does not touch the trunk. Avoid using fertilizer when extreme temperatures are expected, and be sure to leave as much leaf cover as possible. Excessive pruning can make plants vulnerable to heat and cold. Artificial protection from the elements can take the form of shade structures, row covers, pergolas, umbrellas, and shade cloth. Blocking even a little sunlight on a hot day can help your plants get through the worst of it without sunburn damage or water stress.
An ounce of prevention
You can eliminate much of the work related to temperature extremes by selecting plants best suited to your microclimate (natives are an easy choice), and place them in locations suitable to their species. And be sure to install plants at a time of year when they will have enough time to develop a strong root system. Finally, have your soil tested by a reputable lab, to find out exactly what you are working with, and continually strive to improve soil structure.
Healthy soil makes healthy plants. Healthy plants can tolerate heat and cold better than plants marginalized by poor soil, insufficient irrigation, or improper care.
I hope this information inspires you to grow more of your own food. You can ask your garden questions on my Home page.