We’ve probably all lost seedlings to damping-off disease. Nascent stems, healthy only the day before, suddenly appear pinched and broken, never to recover. When lesions appear further down the stem at the soil line, it is called collar rot.
Collar rot gets its name because of the lesions that form a collar around where the root system meets the stem. In embryonic plants, this area between the first root (radicle) and the first stem (hypocotyl) is called the collet. In more mature plants, this area is called the crown.
Vulnerable stems and seedlings
In the case of both damping-off disease and collar rot, pathogens enter delicate new stems as they emerge from the earth, scratched by soil particles. These tiny wounds provide points of entry. Insect and herbivore feeding, garden tools, and rubbing due to overcrowding and improper pruning can also create these wounds. Wounds heal quickly, but sometimes pathogens get in. When they do, problems begin.
Collar rot symptoms
As fungi, bacteria, and other pathogens enter a plant, lesions start forming in a band, or collar, around the lower portion of the main stem. At the same time, vascular bundles become blocked and the disease-causing agents begin multiplying.
Collar rot pathogens
Collar rot looks similar to damping-off disease because the same pathogen may be responsible. Collar rot can also be a symptom of several other infections. Trees infected with fireblight tend to be more susceptible to collar rot, but we don’t know why. As you can see, collar rot isn’t a specific disease. Instead, it is a symptom of attack by several different pathogens:
Collar rot prevention
Collar rot occurs in gardens and containers where the soil is infected. You can prevent the infections that cause collar rot with these tips:
I hope collar rot never occurs in your garden.
We breathe oxygen in and exhale carbon dioxide. Plants are just the opposite. Well, mostly. Of course, there’s a lot more to it than that.
The origin of oxygen
Most of the Earth’s oxygen was first produced by bacteria during the Great Oxygenation Event some 2.3 billion years ago. This was before plants existed. The bacteria responsible for originally oxygenating our world are called cyanobacteria. More commonly known as blue-green algae, cyanobacteria can perform photosynthesis. I suppose we could say that the oxygen we breathe started out as algae farts.
Oxygen is the third most abundant element in the universe. We now have a lot of it here on Earth, though the numbers can vary. Oxygen currently makes up more than 20% of our atmosphere. You may be surprised to learn, as I was, that oxygen, in the form of oxides, makes up nearly half of the Earth’s crust and nearly 90% of our oceans. Oxides are molecules made up of at least one oxygen atom which is bound to some other element.
Binding is common in the world of oxygen (O). Two oxygen atoms tied together form the dioxygen (O2) found in our atmosphere. Add two hydrogen atoms to an oxygen atom and we get water (H20). Add two oxygen atoms to a carbon atom and you get carbon dioxide (CO2). But I digress.
We’ve all heard how trees provide us with oxygen, but that’s not as true as we once believed. We now know that 50-80% of the oxygen we breathe comes from marine plants and plant-like organisms. So the majority of our oxygen comes from plankton. Also, plants only produce oxygen when they are performing photosynthesis. At night, plants are using rather than producing, oxygen.
Plant respiration takes place through leaves, tree roots, outer stem cells, and root hairs. And respiration is more than just breathing. Respiration refers to any process within a living thing that uses a gas exchange to generate or release energy. When a plant is actively producing energy from light, carbon dioxide is inhaled and converted into sugar, and oxygen is exhaled. This is called the Krebs Cycle. Oxygen molecules are also used to break the sugars into usable bits. This is called oxidization.
Some plants reduce the amount of oxygen available to neighboring plants using tannins in a type of chemical warfare known as allelopathy.
Oxygen and decomposition
If your compost pile doesn’t have enough oxygen present, it will turn into a stinky, rotten mess, or nothing will happen at all. The microorganisms responsible for decomposition breathe air and drink water just as we do. This is why it is important to flip and moisten your compost pile regularly for it to break down into usable bits for your plants.
Oxygen in the soil
Dissolved oxygen in the soil is critical for healthy plants. Soil that contains a lot of dissolved oxygen tends to produce plants with significantly larger root systems. Larger root systems mean healthier, more productive plants. Pumping oxygen into your garden soil probably isn’t on your to-do list. But there are two things you can do to increase the amount of oxygen and other helpful gases in your soil: improve drainage and reduce soil compaction.
I hope that you will breathe deeply and enjoy the changing scents of your garden as we move through the seasons. And remember to give that compost pile a turn.
Underneath the cover of growing plants, leaf litter, and crawling insects is a layer of dark, nutrient-rich topsoil. Below that is something else entirely.
We are all familiar with the importance of topsoil and how it helps our plants grow, but the subsoil layer is also very important to plant health. Do you know what is in yours?
What is in subsoil?
Subsoil is mainly weathered rocks and clay. It contains little if any organic matter, so it is often lighter in color than the soil above it. But this doesn’t mean it has nothing to offer your plants. This is where gypsum, silica, and clay particles filter down and collect. The clay found in subsoil has been used throughout human history to make adobe. It is also the material of choice in wattle and daub fencing. But clay isn’t the only thing that collects in the subsoil.
Aluminum, calcium, iron, magnesium, and other nutrients accumulate in the subsoil, as well. If there is a lot of iron present, the subsoil layer will have a more brown or reddish tint. Because these minerals are often moved by percolating or illuviated water, it is also called the illuvial horizon. The subsoil layer often has a distinct soil structure from the layers above and below.
How do plants use subsoil?
All of a plant’s early growth takes place in the topsoil layer, where nutrients, helpful microorganisms, and water are in abundance in most cases. After that initial growth, many roots move into the subsoil. The subsoil provides anchorage, food, and water. Tucked into the spaces between the minerals and tiny rocks that make up subsoil are pockets of water and mineral nutrients. Water held in the subsoil is protected from evaporation. When topsoil is dry, water can still be found in subsoil.
In the photos below, each block represents one square foot of soil.
Subsoil, erosion, and compaction
Rototilling, construction, and heavy traffic can strip away topsoil, exposing the subsoil. Because subsoil does not contain the same organic matter, microorganisms, and root systems that hold topsoil in place, erosion occurs at a much higher rate. Those actions can also lead to the creation of a hardpan layer that blocks air, water, and roots almost completely.
Compacted soil interferes with plant growth, drainage, and overall soil health. It is often corrected by aeration and deep-rooted cover crops. Compacted subsoil can be detrimental to plant health for many years. One study found that a compacted subsoil layer affected plant growth for nearly 20 years after the compaction occurred. Correcting subsoil compaction is expensive and difficult. Unfortunately, it is also very common in gardens due to home construction. This is why we are all required to conduct perc tests when buying a home. If water can’t percolate down and away, your home might find itself down the river after a particularly bad rain. [In the past, contaminated soil was used to create an artificial subsoil layer for home construction. Luckily, those days are behind us.]
You can protect your soil and plants by being judicious about rototilling, creating paths, and avoiding walking on wet soil. Subsoil can be converted to topsoil by adding substantial amounts of aged manure, compost, green manure, and time.
What’s in your subsoil?
If you have a soil sampling tool, you can use that to collect a sample of both the topsoil and subsoil layers. Or, you can use a trowel or shovel. You will need to dig down a foot or two. Look for changes in both color and texture. You can take a sample of subsoil and send it out to a lab for testing, or you can test its texture for yourself. You can also test your subsoil’s permeability at home. These home tests won’t tell you which nutrients are present, however.
Take a look at your subsoil and tell us what you find in the comments. Extra points for fossils and treasures!
Writing yesterday’s post on soil horizons, I ran across a couple of unfamiliar words. Marl was one of them. Here’s what I’ve learned about marl.
The word marl comes to us from the late 19th century. It is short for marbled. Rather than being as hard as your favorite cat’s eye or aggie marble, marl is a porous, relatively soft mudstone. And it contains many of the nutrients your plants love.
The lower cliffs of Dover and much of New Jersey contain marl.
Marl forms as carbonate-rich clay mud and silt are blended with algae that loves alkaline waters. The carbonate is from the dead shells of water-dwelling organisms and the calcified algae. Originally the term marl only referred to freshwater formations. We now know that marl occurs in saltwater too.
Types of marl
Marl contains 65–35% carbonate and 35–65% clay, depending on the type. It can be blue, green, sand-colored, or red. Marl contains calcium, iron, phosphorus, potash, silicic acid, and sulfur. It also contains magnesium, but only a little. Magnesium deficiencies are common in fields treated with marl.
Soil is fundamental to the health and productivity of your plants. Healthy soil supports healthy plants. But there’s more to soil than meets the eye
You’ve heard a lot about topsoil and maybe some about bedrock, but what about the layers in between?
The layers of soil under your feet have developed over eons of glaciation, erosion, flooding, and thousands of other circumstances of pedogenesis. Underneath it all is your soil’s foundation, or bedrock. Of course, if you go deep enough you’ll reach the molten core, but that only affects gardeners in places like Hawaii. For most of us, it is only the top few feet that dictate the health of our plants. There are several different layers and those layers are called horizons.
There are different classes of thought on soil horizons. Some groups define these layers by the soil texture, while others prefer sorting them by use. Keep in mind that not all soils have all these layers. And some soils have astounding numbers of layers.
Topsoil (O, A, and E horizons)
Topsoil refers to the uppermost 5-10” of soil. It has the highest concentration of organic matter and microorganisms. The majority of your plants’ roots can be found in topsoil. It is divided into three different layers. The organic surface layer, or O horizon, is where we find plant litter. In areas with waterlogged peat areas, we have the P horizon. Under that, we have the surface soil or A horizon. In some cases, leaching (or eluviation) can cause certain minerals to create a separate, lighter-colored layer between the topsoil and subsoil. This lighter layer is called the E horizon and it often contains a lot of silica.
Subsoil (B horizon)
While not as rich in organic matter as topsoil, the subsoil layer is where many minerals accumulate. This is especially true of aluminum, clay minerals, iron oxides, and some organic bits. The subsoil layer is commonly reddish-brown due to its iron content and it often has a distinctly different soil structure than the horizons above it. The subsoil layer is often overlooked, which is unfortunate since all garden plant roots make their way to this layer. When the topsoil and subsoil have gone through the same soil-forming conditions, the combined areas are called the solum.
Substratum (C horizon)
The substratum layer consists of partially weathered rocks that have not been affected by the conditions that created the layers above. It contains a lot of calcium carbonate and other soluble minerals and tends to be a lighter color than the layers above. This layer is often created by flooding and landslides.
Bedrock (R horizon)
Unlike horizon C’s rocks and boulders, which you can dig up, the bedrock layer is massive layers of rock that make up more of what we consider the earth’s crust.
Limnic soil (L horizon) occurs as a result of aquatic life. It contains the diatomaceous earth, sedimentary peat, and marl left behind when lakes and oceans dry up. You can also have a fluid or frozen water layer (W horizon) or man-made layers that block roots (M horizon).
The next time you pass a construction site or look at an image of the Grand Canyon, take a closer look at all those layers and think about how they might affect plant roots. The closer you look, the more there is to see.
How does fog affect your plants? Let’s find out.
First, what is fog?
Fog is the low-flying equivalent of stratus clouds. It contains tiny droplets of water and ice crystals that have formed through condensation. This condensation occurs when the difference between air temperature and the dew point is less than 4.5°F (2.5°C). Dew point is the temperature that ambient air must reach to become saturated with water. When that point is reached, water particles start collecting around any dust, ice, pollen, or salt in the air.
Unlike mist, which we can see through, fog tends to be harder to see through. Technically, fog reduces visibility to less than 0.62 miles, but who’s counting? There are several different types of fog, but I’ll leave that to you to explore. Let’s find out what all this moisture in the air does to our garden plants.
Fog diffuses sunlight, much the way smoke from fires does. [See Yellow Sky Days] Instead of simply shining downward, light particles get bounced around, allowing photosynthesis to occur in places where it normally might not. Of course, if there’s too much fog, photosynthesis is significantly reduced.
Periods of fog often cause discoloration, stunting, and even wilting in crops such as wheat. These responses are temporary and they often disappear once the sky clears.
Extended periods of moisture often increase the likelihood of disease. Bacterial head rot, black scurf, black spot, cucurbit scab, russeting, sooty blotch and flyspeck, and tomato gray wall are more likely in areas with frequent fog.
Foggy days are a good time to apply insecticidal soaps to manage cabbage aphids and other pests. And dormant oils are best applied just after a period of fog. Fog reduces topsoil drying, acts as a protective blanket during cold weather, and slows evapotranspiration, reducing the need for irrigation.
If you’ve never heard Eddie Izzard’s hysterical description of fog, check out his Dressed to Kill video. It cracks me up every time.
With leaves falling from trees and swirling around our feet, today seemed like a good day to talk about leaf scars.
When I say leaf scars, I am not referring to the ravages of battle or bad decisions. Instead, leaf scars occur naturally whenever a leaf falls from a tree. The information they ‘leave’ behind may surprise you. [Sorry, I couldn’t resist.]
What are leaf scars?
Leaf scars are the marks left behind on a twig after a leaf falls off. It is where the petiole, or leaf stem, was attached to the stem. As long as photosynthesis is taking place, the connection between leaf and stem is usually pretty strong. It has to be. Leaves flutter in the breeze, are battered by raindrops and send sugars produced through photosynthesis into the vascular bundle. But then things change.
At some point, a leaf becomes more of a burden than a sugar factory. In the world of plants, the process of getting rid of unwanted body parts is called abscission. Abscission can occur because of seasonal changes, or in response to conditions such as drought, shade tree decline, disease, or natural aging. That natural aging is called senescence.
Whatever the cause, plants try to pull as many resources from leaves as possible before dropping them. This is why leaves change color in autumn. Once a leaf has been sucked dry, the petiole softens, and a protective barrier starts forming between the petiole and the twig. This area is called the abscission layer. After the leaf falls, the wound is covered by a protective corky material, leaving us with a leaf scar.
If you look closely at a leaf scar, you may see tiny holes arranged in a pattern. This area is called a bundle scar, and it is the torn vascular bundle. Buds often form just above leaf scars, and they leave scars of their own. They are called bud scars.
Problems with leaf scars
In some cases, diseases can take hold in leaf scars. Olive knot is one of several bacterial diseases that start this way. European apple canker is a fungal disease that can enter through leaf scars. Any time there is an opening, there is a risk of disease. That being said, you need to resist the urge to seal up plant wounds artificially. In most cases, this results in moisture being trapped against the wound. This slows the natural healing process and increases the risk of disease and rot.
Botanists and plant aficionados use leaf scars to learn more about plants. Plants with small leaf scars tend to have small leaves. Plants with large, curved leaf scars tend to have bigger leaves. This is because a curved attachment can support more weight. Leaf scars can be brown, green, or red, depending on the species. They can be flat or rounded. In some cases, hairs can be seen around the leaf scar.
If you have a mystery tree, you may be able to use its leaf scars to help identify its family ties.
Mid-November may feel like an odd time to be talking about caterpillars, but the delayed dormant period is a good time to start managing obliquebanded leafrollers before they have a chance to damage your fruit trees and it's good to be prepared.
Damage caused by obliquebanded leafrollers
Obliquebanded leafrollers (Choristoneura rosaceana) cause different types of damage: their leafrolling behavior reduces photosynthesis; fruit feeding sets the stage for brown rot and deformed fruit, and early stem-feeding can significantly reduce crop size. These pests are primarily attracted to members of the rose family, specifically cherry, pistachio, and plum trees. They have also feed on apple, chestnut, hazelnut, pear, and stone pine trees, as well as blueberries, cane fruits, strawberry plants, and sunflowers. Several popular ornamentals also host these pests.
Obliquebanded leafroller description
Obliquebanded leafroller adults are light- to reddish-brown moths with a unique squarish back end and something of a ridge just behind the head (thorax). They are a mottled tan to brown with wide, offset (oblique) bands of alternating color. The wingspan ranges from 3.0 to 5.5 inches across, with the females being significantly bigger than the males. If you were to get your hands on one of these moths, you would be able to see that the forewings tend to be much darker than the underwings. Obliquebanded leafroller moths look like fruittree leafrollers (Archips argyrospila) and three-lined leafrollers (Pandemis limitata).
Caterpillars are green to yellowish-green with dark heads. [Sorry, I couldn’t find a photo I could use.] They average one inch in length. These garden pests have the unique behavior of crawling backward when disturbed and dropping to the ground with the aid of a silk thread. Left to their own devices, obliquebanded leafrollers, being true to their name, will fold or roll leaves together to create a protective tent while they feed.
Obliquebanded leafroller lifecycle
Masses of 200-900 eggs are laid on the tops of leaves and then covered with a protective wax. They hatch in a week or so. The first instar larvae crawl to safer places, such as the underside of leaves, in buds, or under the calyx of fruit. [The calyx is the protective growth that encases flower buds.] They may also balloon themselves to nearby plants using a silk thread. As these caterpillars go through six instars, they roll leaves around themselves for protection as they feed. Obliquebanded leafrollers overwinter as second-instar caterpillars in crevices of trees, under flower bud scales, and bark. Eventually, they drop to the ground, where they pupate in the soil.
Obliquebanded leafroller management
Most management practices take place in spring and summer. As young caterpillars begin to emerge in spring, you can spray Bacillus thuringiensis on them, followed by spinosad sprays in summer. You can also use pheromone traps to monitor for adult moths.
Assassin bugs, Exochus ichneumon wasps, lacewings, minute pirate bugs, and parasitic Goniozus wasps will attack obliquebanded leafrollers. You can attract these garden helpers by adding insectary plants to your landscape and avoiding the use of broad-spectrum pesticides.
During the delayed dormant period, be sure to spray your trees with the appropriate dormant oil to help control these and other pests. The delayed dormant period is after full dormancy but before the green bud stage. You can also reduce the problems associated with obliquebanded leafrollers by removing water sprouts and thinning fruit properly.
If you’re an early riser like myself, you know that the pre-dawn morning air is softer and sweeter than any other time of day. There are fewer car sounds, and you can hear birds, bees, and rustling leaves. Somehow, standing outside in a quiet morning hour, I feel as though anything is possible. As the day progresses, it becomes more difficult to hear those natural sounds, partly because humanity is noisy and partly because I get busy and forget to listen for them.
Research has shown that natural sounds can reduce pain and improve mood. They even make us kinder and less likely to feel annoyed. So how can you create a soundscape? And how can we add natural sounds to homes? Let’s find out.
It’s no surprise that we plant gardens for fruits, herbs, or vegetables, colorful flowers, or fragrant aromas. We’ve already talked about sensory gardens and scent gardens, but you can create a garden for its sounds, too.
Barriers against noise
Add fencing, hedges, or a tree line to block the sounds of traffic and other distractions. There are other benefits to these noise barriers. Some hedges are fragrant, while others produce food. Ornamental Thuja plicata ‘Atrovirens’ smells like pineapple when crushed. Or you can harvest blueberries from a berry hedge. Just be careful with bamboo. While some varieties can grow very tall rather quickly, they can spread and become invasive. Keep in mind that sound can travel around barriers.
While adding bird feeders is often touted as a good way to attract our avian friends, research is beginning to show that these unnatural food sources are disrupting natural migration patterns and increasing the incidence of bird diseases. Rather than being part of that problem, reach out to your local native plant society. They can help you identify the best plants for attracting native birds and beneficial insects without creating problems. Those native plants often have the added advantage of requiring less effort on your part.
Annual honesty (Lunaria annua) provides lovely flowers in summer and bright fluttering sounds through autumn and winter. Love-in-a-mist (Nigella damascena) provides beautiful flowers and fairy rattles that remain standing for quite some time.
Indoor soundscapes are trickier to create. Unless you open the window, there aren’t any breezes. And you probably don’t want any birds or buzzing insects flitting about in your kitchen. In fact, I was unable to find any advice online aside from adding yet another app to my daily life. No thanks.
As a child, I had a sequence of pet parakeets. I loved them and I like to think that I took good care of them. As an adult, however, I would never put a bird in a cage. Heck, even my chickens had tons of running around room. But now that I live in an apartment high-rise, things have changed. I could do what my upstairs neighbor does and feed the birds to get more bird sounds. Of course, that also means more bird poop on my balcony and it messes with the birds’ natural cycles. That being said, I do have a hummingbird feeder, which brings the sound of their wings to my daily life. I could add a native seed-producing plant to my balcony. I’ll have to check with my local native plant society for that one. Cats and dogs certainly add natural sounds (and love) to your home. A fish tank will add the sound of moving water to your home, but I don't know if fish can love people or not.
Probably the easiest way to add natural sounds to your home is with an indoor tabletop fountain or waterfall. There’s just something about the sound of trickling water that soothes us humans [and drives beavers into a dam-building frenzy]. Most of these tabletop water features are quite small and easy to care for, making them perfect for apartments. You may even be able to grow some watercress in one. I'm not sure if it would work, but it might be fun to try.
Add some natural sounds to your environment for a more relaxed, happy, and healthy day.
Did you know that plants can hear? We’ll talk about that tomorrow.
Nutrient deficiencies (and toxicities) interfere with plant health. And it’s not a simple matter of being present. Soil can be chock full of nutrients. And plants may still be deficient.
The 20 or so minerals used by plants as food exist in soil as ions. Ions are atoms and molecules that have either a positive or negative charge. These cations and anions, respectively, attach themselves to water molecules and are pulled into the plant by root hairs.
Negatively charged clay and organic matter can attract and hold positively charged nutrients, such as calcium and potassium. Clay, in particular, holds onto more water and nutrients than other soil textures. Sometimes, it holds on so tightly that plants cannot access the food they need. Positively charged sand and water hold on to negatively charged particles, such as phosphorus and sulfur.
The ability of a plant to pull nutrients in also depends on soil texture, structure, and pH.
Nutrient deficiencies and soil composition
We describe soil by its texture (size) and structure (arrangement). Soil texture can be large (sand), medium (loam), or incredibly small (clay). Soil texture determines how well it drains. It also impacts which nutrients are easy for plants to absorb.
Soil structure describes the way minerals clump together with microbes, earthworms, and organic matter. Spaces, called macropores and micropores, occur within and between these particles. Compacted soil makes it difficult for plant roots to get to their food. Sandy soil often allows water and nutrients to drain away before plants can get to them.
Soil pH ranges from 0 to 14, with lower numbers indicating acidity and higher numbers indicating alkalinity. More nutrients are available, and there is more microbial activity when soil pH is between 6.0 and 7.0. Most plants can survive in soil pH from 5.2 to 7.8, but each species has a narrower range that allows them to thrive. As plants absorb these anions and cations, the soil pH changes ever so slightly. Too much or too little of certain minerals in the soil may interfere with nutrient availability. You may want to look at Mulder’s Chart for a more detailed explanation.
Without the necessary nutrients, plants cannot thrive. But too much of a good thing can be a bad thing, too. If there is a lot of a specific nutrient in your soil, plants may take what they need, or they may eat themselves to death. It depends on the nutrient and the plant species.
In my old yard, the soil was compacted clay with a severe iron deficiency. Since plants use iron to help them absorb several other nutrients, it didn’t matter that the previous owner kept adding a balanced fertilizer. As soon as the plants used up the iron, there ended up being too much of everything else.
So, how do you know if there’s a deficiency, and what can you do about it?
Is your soil deficient?
The only way to know if your soil is deficient is with a lab-based soil test. Over-the-counter tests look great, but they cannot provide accurate information. Luckily, laboratory soil tests are not expensive. They cost about the same as a large bag of fertilizer and can save you a lot more than that by preventing overfeeding and poor plant health.
All too often, we see what looks like a nutrient deficiency and we apply a nice 10-10-10 fertilizer. At first, everything looks better. But it never lasts. That is because it is the balance of nutrients in the soil that makes all the difference.
Symptoms of deficiency
Nutrient deficiencies often present in specific parts of a plant. This has to do with nutrient mobility and how the plant uses a particular nutrient. Plants can move mobile nutrients, such as nitrogen, to wherever they are needed. Older leaves look poorly as nutrients are pulled away to help with new growth. The opposite is true for “immobile” nutrients, such as calcium. It takes a lot of water for a plant to move these nutrients, so symptoms occur in fruit and new growth. Let’s take a closer look.
Magnesium, nitrogen, phosphorus, and potassium deficiencies are visible on older leaves, or near the bottom of the plant. We see molybdenum and sulfur deficiencies in the whole plant or around the middle. New growth and the tops of plants exhibit boron, calcium, copper, iron, manganese, and zinc deficiencies.
Deficiency symptoms can overlap, making the diagnosis a bit tricky. This table may help.
What can you do to prevent or correct deficiencies?
First, get your soil tested. You can’t know what’s going on without it. Once you have your test results in hand, only add what’s needed. [Feel free to contact me if you need help interpreting your results.]
If your test results indicate that toxicities are present, you can reduce those numbers over time by harvesting as much as possible. You can plant and harvest heavy feeders, such as cereals, melons, or squash, to help reduce excess nutrients.
In some cases, such as potassium deficiencies, the damage to an individual leaf is irreversible, but you can still improve conditions in general, helping the plant recover. The following good practices will help keep your plants healthy and well-fed:
Apical dominance is why trees and many other plants end up tallest in the middle, but there’s more to it than that.
from each branch also grew into a full-sized limb. You can see how convoluted things would get rather quickly. Apical dominance is what keeps that mess from happening.
Apical dominance refers to the way that central stems are dominant over other stems. It also describes why branches are dominant over their twigs. It makes sense. If the twigs were bigger than the branch, it would eventually break. If side branches were bigger than the central trunk, trees and shrubs might not get enough sunlight. Let’s see what makes plants behave this way and learn how we might use this behavior to our advantage in the garden.
Apical dominance and sun exposure
Plants need sunlight to grow. The tallest plants get the most sunlight. By growing upward first and then outward, a plant’s chance of survival is increased. For conifers, which often grow at higher latitudes where sunlight is lower on the horizon, the triangular Christmas tree shape provides the greatest amount of sunlight. For deciduous trees, growing at lower latitudes with more overhead sunlight, the rounded canopy provides the most sun exposure. In both cases, the woody structure supports the leaf canopy that allows for photosynthesis. Photosynthesis is all about sugar production. And, contrary to popular belief, sugar is the reason behind apical dominance.
Apical dominance and terminal buds
The buds at the ends of stems are called terminal or apical buds. This does not mean they are waiting on a visit from hospice. Just the opposite. This is where meristem tissue is found. Meristem tissue is new, undifferentiated life. This is where growth happens. Even though growth is happening at all the buds and twigs along a stem or trunk, the ones at the top and/or ends have priority. We used to think that this happened because of a plant hormone, called auxin, but research has shown that it is the growing tips’ demands for sugar that robs their neighbors of enough sugar to grow equally fast.
If apical buds are removed, lateral buds are free to demand more sugar and grow more quickly. This is where pruning, coppicing, espalier, pollarding, and tree training come in.
Apical dominance and pruning
If you pinch off the central stem of a basil plant, just above a pair of leaves, it will grow to be bushier and produce more delicious leaves.
Imagine, if you will, that every bud on a young tree grew into a full-sized branch, and that each twig If you apply production pruning to your nectarine tree, it will produce significantly more fruit. Different fruit and nut trees benefit from different types of tree training, but the results are the same: healthier, more productive trees.
Espalier uses the same concept but in two dimensions, rather than three. Apical buds are pinched back to stimulate side growth.
Pollarding and coppicing apply the same principle but on different parts of a tree. Coppicing refers to the practice of cutting small trees and shrubs back to ground level regularly to harvest several thin stems that are useful for basket-making, firewood, and wattle-and-daub fencing. Pollarding is the same practice but done higher up in a tree to promote new overhead growth.
How are you putting apical dominance to work in your garden?
Midges and gnats are common names for many different tiny two-winged flies (Diptera) that congregate over birdbaths and soggy areas.
Midges and gnats are found everywhere there is moisture, including the Arctic and Antarctica. Some of them bite, and some of them don’t. The words are used interchangeably, depending on where you live and who you ask.
We have already discussed fungus gnats, but the midge family is huge. To be accurate, most gnats are biting insects in the Nematocera suborder (making them distant cousins to mosquitoes). Midges can be from non-biting, phantom, or biting families. You can see why it gets confusing.
Midge/gnat life cycle
You may have seen swarms of tiny insects over a birdbath or wet soil some summer evenings. These swarms are mating dances that may last for several days. Some of these swarms can get big enough to hear, and they may look like clouds of smoke from a distance. In some cases, roads can become so slick with gnats that accidents occur. These insects may also sun themselves on the side of a house in such numbers that it appears coated.
Many midge adults do not have mouths. They only live long enough to reproduce. After mating, masses of 3,000 to 10,000 eggs are laid on water or wet soil, and the adults die a couple of days later. The eggs sink to the ground and hatch in 2 or 3 days. Larvae look like microscopic grubs and can be green, red, or white. Most midge or gnat larvae spend this stage in water or burrowed into mud. There can be up to 4,000 larvae in a square foot of mud. These larvae feed on algae and other organic matter. At this stage, they are helpers in the decomposition process. After 4 weeks or so, the larvae begin to pupate. Two days later, they emerge as adults, and the cycle continues.
Biting midges (D. Ceratopogonidae) are blood-suckers. Like mosquitoes, these midges need blood to reproduce. This group includes black flies, no-see-ums, and sand flies, which inflict painful bites and can transmit human diseases. Some members of this group also suck the bodily fluids from insects. Many of them also drink nectar. Larval biting midges are sometimes called bloodworms because they contain blood.
Phantom midges (D. Chaoboridae) are also known as glassworms. You can see why
Most phantom midge adults do not eat. Those that do only drink nectar. Phantom midge larvae are rather bizarre in that their antenna have evolved into grasping organs that crush prey and other foods, somewhat similar to the hands of a mantis.
Several midges create galls and damage buds, leaves, or roots. Some of the more common midges, and the plants they damage, include:
When midges damage plants, the first signs will be small discolored areas, general failure to thrive, and wilting. Over time, the effects of midge feeding and burrowing can significantly reduce crop size. It also makes plants susceptible to other pests and diseases.
Removing standing water is always a good idea, and not just because of midges. Mosquitoes can be more than just a summer annoyance. These tips can help manage both midges and mosquitoes:
Interesting fact: chalcid wasps (the ones who give us figs) are midge and gnat predators.
If midges have become patio pests, turn off your lights or get one of those bulbs that claim to not attract insects. [I’m not sure how well they work. Have you had any experience with them? I’d love to hear about it in the comments.]
Some midges are major pollinators of the cocoa tree, so they aren’t all bad. There are also predatory midges. Aphid midges (Aphidoletes aphidimyza) devour aphids, while predaceous gall midges (Feltiella acarisuga) protect your plants against a surprising number of spider mites.
May all your midges be beneficial, and gnats be absent from your landscape.
Most of us are unfamiliar with pawpaws. Even my computer didn’t recognize the word. This is a shame because pawpaws (Asimina triloba) are North America’s biggest edible tree fruits. We don’t see them in stores because they bruise easily and start fermenting as soon as they ripen.
Tagged with a variety of common names such as Indian custard, Hoosier banana, custard apple, and Quaker delight, the word pawpaw is believed to be from the Spanish word for papaya. They are said to taste like a combination of banana, citrus, mango, and pineapple, with a consistency similar to Hachiya persimmon. These North American natives are commonly found from the Great Lakes region south to the Florida panhandle. More often than not, pawpaw trees are completely overlooked, their bounty left for bears, grey foxes, and other wildlife.
I think that it’s time we all knew a little more about these cousins of cherimoya.
Pawpaw tree description
Pawpaws are large shrubs or deciduous trees that can reach 35 feet in height but are commonly much smaller. They tend to form thin-trunked colonies in shady bottomlands, but will not thrive in full shade. They spread using root suckers. Seed reproduction only rarely results in viable trees in the wild. They have large, simple leaves that grow in clusters at the ends of branches. When bruised, the leaves are said to smell similar to green bell peppers.
Pawpaw flowers are reddish-purple and can be 2” across. Because these flowers smell more like carrion than fruit, blowflies and carrion beetles do most of the pollinating
The fruits, which are berries, are large yellowish-green to brown ovals, similar to mango or papaya. They have pale to bright yellow flesh and can be up to 6” long and weigh more than one pound. Each fruit contains several large seeds. Ripe fruits fall from the tree, but you can pick them just before that happens.
How to grow pawpaw trees
Pawpaws can be grown in USDA Hardiness Zones 5—9. While it is easiest to start your tree from root suckers or bare rootstock, you can use seeds that have been kept moist and stratified in cold storage for 2 or 3 months. The problem with seeds is that each seed is genetically different from its parent and siblings, so there’s no way to know for sure what you’ll be getting. On the flip side, root suckers have very few roots, while seedlings started from seeds have substantial taproots that help them get established.
Pawpaws can be grown in containers at first, but will eventually need to be put in the ground to stay healthy and productive. Since fruit is produced on new growth, annual pruning is important. Being deciduous, it is easy to prune pawpaw trees in winter. Pawpaws should be fed in early spring and again in early summer.
Pawpaws prefer slightly acidic, moist soil with good drainage. These trees grow best in sites with strong morning sun and afternoon protection.
Problems with pawpaws
Pawpaws suffer from surprisingly few diseases or pest problems when compared to other orchard fruits. The most common problem faced by pawpaw growers is insufficient pollination. While pawpaw trees have both male and female flowers, they cannot pollinate themselves, so you will need more than one tree. You can improve pollination rates by hand-pollinating. Commercial growers have been known to spray their trees with fish emulsion or hang chicken necks in their trees to attract the appropriate pollinators. I don’t see myself hanging chicken necks in trees. Ever.
But a cluster of low-maintenance pawpaw trees along a back fence sure sounds appealing.
Frogeye leaf spot refers to three different fungal diseases. One attacks soybeans, one infects peppers, and the other prefers your apples. Let’s look at all three, shall we?
Frogeye leaf spot in apples
Frogeye leaf spot in apples is caused by Botryosphaeria obtusa. This pathogen is also responsible for cankers in apples, cranberries, and quince, and dead arm disease in grapevines. Apple leaves infected with frogeye leaf spot develop purple specks that expand into brown spots with purple margins, hence the name. Left to progress, frogeye leaf spot causes black rot in your apples.
The only treatment for frogeye leaf spot in apples is to prune out infected branches, sanitizing your pruners between each cut. Infected plant material should be thrown in the trash and not composted. To prevent this disease from continuing, all fruit should be removed from the tree. As a gardener who loves her fresh apples, this can be a sad fact. Hopefully, those apples are ripe enough to eat and use for applesauce. The fungus won’t hurt you, and you can cut out the bad bits, but this disease can cause significant leaf and crop loss.
Frogeye leaf spot in peppers
Frogeye leaf spot in peppers is caused by Cercospora capsici fungi. Also known as Cercospora leaf spot, this disease infects eggplant and tomatoes, along with peppers. It starts as tiny, grayish-brown spots with dark margins on leaves, petioles, and stems. These spots eventually grow to one-half inch in diameter. If you look at one of those lesions with a hand lens or microscope, you will see tiny black flecks. Those flecks are fungal spores.
Frogeye leaf spot in soybeans
Frogeye leaf spot in soybeans is caused by Cercospora sojina. This disease is found in many parts of the world and has been expanding its range northward from the southern US. Frogeye leaf spot in soybeans causes small, somewhat rounded, or angular reddish-brown to purple lesions on upper leaf surfaces. The interior of these lesions is often grey or tan. As the disease progresses, leaves become tattered and fall off. Pods and stems can also become infected and covered with dark-rimmed lesions with reddish-brown centers. The lesions also produce ethylene gas which increases leaf loss. And nobody wants rotting soybeans.
This disease can occur at any time during a soybean plant’s lifetime and several different stages of the disease may occur at the same time on different plants. The pathogen overwinters as mycelium in the soil, seeds, and plant residue, and remains viable for up to two years.
In each case, frogeye leaf spot is most likely to occur in situations with warm, humid conditions or long rainy seasons. To reduce the chance of frogeye leaf spot occurring in your garden, use these tips:
Fungicides can also be used, but the frogeye leaf spot pathogens have already developed resistance to some of those treatments (strobilurins). As temperatures continue to rise, frogeye leaf spot is expected to become a more common problem.
Three-lined potato beetles are more likely to damage your tomatillos and cape gooseberries than your potatoes, which is why they are also known as tomatillo leaf beetles. But they will cause problems for your tomatoes and potatoes, too. Both adults and larval forms are voracious leaf eaters.
Originally from North and Central America, three-lined potato beetles (Lema daturaphila) are now found in many parts of North America, Australia, and South Africa. Although these pests are relatively rare, so far anyway, they can cause significant damage.
Three-lined potato beetle identification
As their name states, these invasive pests have three black stripes that run lengthwise on their mustard-colored to bright yellow wing covers. They are ¼” long and have an orange head and prothorax with two black spots. The prothorax is the bit just behind the head.
Larvae look like dark gray slugs with black heads and three pairs of prolegs. Three-lined potato beetle larvae have a nasty habit of covering themselves with their excrement to deter predators. I imagine it works. Eggs are oval and orange and laid in clusters on leaves.
Three-lined potato beetles look similar to western corn rootworms (Diabrotica virgifera) and striped cucumber beetles (Acalymma trivittatum), both of which are more likely to be found among your cucurbits and corn. Also, cornworms are smaller than three-lined potato beetles, while cucumber beetles are larger than both. Colorado potato beetles (Leptinotarsa decemlineata) may be found around potatoes and other nightshade plants, but their shape and color are different
Damage caused by three-lined potato beetles
Adults tend to travel and feed by themselves, so the damage they usually cause is minimal. As they eat, they may create holes in leaves, or they may remove entire leaves. The larvae, on the other hand, feed in groups and can cause considerable damage. Like other creatures who have evolved to eat members of the nightshade family, they are immune to the lethal tropane alkaloids found in the leaves of these plants.
All this leaf-feeding means less photosynthesis, weakened plants, and reduced crop size. It also makes plants more susceptible to other pests and several diseases.
Three-lined potato beetle lifecycle
These garden pests overwinter as adults or as pupae in the soil, depending on the local climate. Adults become active in late spring through the summer, laying eggs on host plants. The larvae usually hatch in early summer, though there can be two generations each year.
Three-lined potato beetle management
Hand-picking the caterpillars is your best defense since adults can fly. Simply pluck them from your plants and drop them in a container of soapy water or feed them to your chickens. Row covers can protect plants from three-lined potato beetles, and eliminating weeds in the nightshade family will make your garden less appealing to these pests.
Vampire moths may sound like something out of European folklore, but they exist and they suck blood.
The vampire moth family
Vampire moths have an entire genus of their own with 17 known species. Ten of them drink blood. Originally from Malaysia, the Urals, and southern Europe, Calyptra have expanded their range to include northern Europe, Sweden, and Finland. Due to international shipping and travel and climate change, it is expected that these moths will continue to expand their range. The Canadian owlet or meadow rue owlet moth (Calyptra canadensis) is the only New World member of this group.
Many adult moths do not eat. Some of them do not even have mouths. Those that do often have a surprisingly long, slender straw, called a proboscis. Moths keep their proboscis curled up in a flat, vertical spiral. The proboscis is generally used to drink nectar. The hawk moth has a proboscis that is over one foot long. In the case of the vampire moth, the end of that straw has a serrated edge that is sharp enough to cut through elephant skin. I don’t know how long it is.
Vampire moth diet
Male and female vampire moths eat the nectar of meadow rue and other members of the buttercup family (Thalictrum). They also suck the juices from fruits, such as strawberries. Vampire moth caterpillars feed on leaves.
Unlike mosquitoes, where it is the females who must drink blood to provide for their offspring (obligate), blood-sucking vampire moths are male and they drink blood because they like it (facultative). Some scientists suspect that male vampire moths drink blood for the salt, which they then pass on to the female in their sperm to provide for their offspring. No one knows for sure just yet.
Male vampire moths pierce the skin of vertebrates, including us, to drink blood. They do this by using a proboscis that is divided into two parts. They use a back-and-forth sawing motion to pierce the skin of their victims with these dual tubes.
Once attached, vampire moths are not easily removed and they may remain in place for up to 50 minutes. They do not technically “suck your blood”. Instead, they use their victims’ blood pressure to do that work for them. If you are the victim of a vampire moth, you will not turn into a vampire or a moth, but the site will be red and sore for several hours with an itchy rash. Vampire moths are not believed to carry or spread any diseases.
It is believed that vampire moths evolved from purely fruit-sucking species. I can’t help wondering what my tomato plants are planning…
Ghost ants may be scaring up problems in both your home and your greenhouse. Or, they may be helping you stay healthy.
Thought to have originated in Africa or the Orient, invasive ghost ants (Tapinoma melanocephalum), also known as tramp ants, are now found everywhere. Like other ants, ghost ant farm aphids and other sap-sucking garden pests for their honeydew, protecting them from their natural enemies.
Ghost ant identification
These ants are smaller than most ant species. Workers average only 0.051 to 0.079 inches long, which means you could line up more than a dozen of them across the face of an American dime. They have dark heads and milky white to translucent legs and bodies, hence the name. Ghost ants look similar to pharaoh ants.
If you were to look at ghost ants with a hand lens, you would see that their antennae have 12 segments. When disturbed, ghost ants tend to race around erratically. These ants do not sting, but they do cause problems.
Problems with ghost ants
Ghost ants have a sweet tooth. While they eat many household foods, including greasy foods, they have a strong preference for sweets. They will track down and devour your honey, syrup, cakes, and cookies while indoors and every sweet, juicy fruit and sap-filled stem outside.
Being a tropical species, ghost ants frequently invade and nest in homes, greenhouses, and potted plants. These ants are so small, they can create tiny satellite colonies inside plant stems and in between the books on your shelf. Most ghost ant colonies are significantly larger and are commonly found within the walls of homes and underground. Each colony may have several queens.
While cold weather generally limits the spread of this species, it is now found as far north as Minnesota, New York, and Canada. Apparently, all of our buildings are making life easier for ghost ants. Because ghost ants farm aphids, they also spread disease. These pests are so small that they are proving to be problematic in quarantine greenhouses. They sneak in, feed for a while, and then go elsewhere, taking whatever diseases were present in the greenhouse with them.
Ghost ants aren’t all bad
Ghost ants are scavengers in the garden, eating dead insects and speeding the decomposition process. They also eat the larvae of small beetles, moths, and butterflies. Ghost ants will also put a significant dent in the local two-spotted mite population. In Venezuela, ghost ants eat the eggs of kissing bugs (Rhodnius prolixus). Kissing bugs are vectors for Chagas’ disease, which damages the heart and nervous system.
Ghost ant control
Ants are one of Earth’s most successful species. Controlling them is difficult, and it all starts with cleanliness. If ghost ants are haunting your home, put all foods into airtight containers and wipe up spills right away. Caulk cracks and other points of entry. These pests enjoy a little moisture, too, so eliminate leaks and condensation.
If you can control aphids, whiteflies, and other insects that produce honeydew, ghost ants will find your garden less attractive.
Ant baits are effective against ghost ants. The closer they are placed to the nest, the most effective they will be. Just follow the ant trail. Also, make sure outdoor plants are not touching your house. Those stems make excellent insect highways to your home.
Apparently, if you crush a ghost ant, they smell like rotten coconuts.
Another name for your household ficus tree or weeping fig (Ficus benjamina) is strangler fig.
Strangler figs get their name because their seeds germinate on the branches and trunks of other trees, as well as boulders, buildings, and soil. As roots emerge, they wrap around their host, strangling them.
Strangler figs are not always the bad guys. In many cases, the host tree ends up gaining strength against storms from this exterior structure. I don’t know that the relationship is so benign when they start battling for sunlight.
Most of these trees produce both male and female flowers. Their fruits are inverted inflorescences, called syconia, that have mutualistic relationships with specific wasp species. Leaves are broad and waxy. Strangler fig trees, in particular, are hemiepiphytes.
Unlike most plants, strangler fig roots start out by growing aboveground. This makes them something called hemiepiphytes [hemi-EP-ifits]. Epiphytes are plants that grow on other plants without being parasites. Air plants, many ferns, and orchids are epiphytes.
Strangler fig fruit
Your garden variety fig tree (F. carica) is not a strangler, though they are cousins. Some strangler fig tree fruits are delicious. Some of them are pretty bland. Banyan tree figs taste awful, but they won’t hurt you. Wherever they grow, strangler fig trees are important food sources for native fruit-eating birds who, in turn, spread the seeds near and far.
These trees make very nice house plants. Unless they are native to your region, they do not belong outside because they can easily become invasive and disrupt the local ecosystem.
Note: If your ficus tree keeps dropping its leaves, give it more water and be sure it’s near a sunny window.
Now you know.
Rhizopus head rot is the most common fungal disease of sunflowers, and it can result in losses of up to 100%.
It starts with a tiny wound and ends with the loss of the entire head.
Rhizopus head rot is caused by three different fungi: Rhizopus stolonifer, R. oryzae (syn. R. arrhizus), and R. microsporus. These fungi are everywhere. They are found in the soil and are easily disturbed and spread on the wind. These are the same fungi that cause bread molds, and soft rots in carrots, melons, raspberries, sweet potatoes, and many other crops.
Rhizopus head rot symptoms
The fungal spores that cause Rhizopus head rot first make their way into your lovely sunflowers through wounds caused by birds, hail, rubbing, and head moth and other insect feeding. At first, these wounds look like small holes or dark spots on the back of ripening heads. Those spots start to rot, eventually drying to a dark brown. As the disease progresses, heads dry prematurely, and the interiors take on a shredded appearance.
You can differentiate this disease from others, such as bacterial head rot or Sclerotinia head rot, by the presence of grey threads (mycelium) and tiny black reproductive structures (sporangia) within the shredded tissue.
Rhizopus head rot management
High temperatures and high humidity set the stage for this disease. There isn’t much you can do about those besides avoiding overhead watering. There are no chemical treatments for this condition.
Wound prevention is the best way to prevent this disease from robbing you of all those delicious seeds. That means monitoring for bird and insect damage and possibly staking plants to prevent rubbing. If you live in areas with hail, there isn’t much you can do short of providing your sunflowers with umbrellas.
You can reduce the likelihood of Rhizopus head rot in your sunflowers by removing rouge plants that may harbor the pathogen and insects most likely to feed on sunflowers. While there are no resistant cultivars, sunflower varieties with more upright heads seem to be more susceptible.
Pickleworms! With a name like that, I had to learn more.
Pickleworms (Diaphania nitidalis) are serious pests of squash, cucumbers, melons, and other cucurbits. Mostly found in the southern United States, these pests are poised to expand their range. It can’t hurt to know what to watch for, right?
Pickleworm moths have triangular, iridescent brown wings with white edges and a yellow stripe. When light shines on these wings, they look metallic blue. Their legs and tail segment are white and the tail ends with a tuft of bristles called hairpencils. The wingspan is just a little more than one inch wide.
Caterpillars start out thin and white with black spots. As they grow and feed, they lose those spots and turn more of an opaque green. Spherical to flattened eggs are extremely small. They start out white but turn yellow in a day or so.
These moths are only active at night. Each adult female lays 300 to 400 tiny pickleworm eggs in small clusters on new buds, and flowers, and shoots. These tender plant tissues make the perfect meal for pickleworm caterpillars, who eat voraciously for two weeks, going through five instars. Then they curl themselves up in dead leaves where they pupate for 8 to 10 days and turn copper-colored. There can be up to four generations each year.
Pickleworms cannot handle extreme cold (yet), so winter weather often takes care of the problem for some regions. Pickleworms have several natural predators, such as soldier beetles and ground beetles, but these predators cannot eliminate the problem. Bacillus thuringiensis (Bt) can be used but is only marginally effective because of where these pests feed and hide. Pickleworm moths are not attracted to light and there are no pheromone traps available, so what’s a gardener to do?
Commercial growers facing pickleworm damage must resort to preventative sprays of insecticides. These sprays can also kill the honey bees needed to pollinate cucurbit crops. It’s a dilemma.
If pickleworms are a problem in your garden, you can buy Steinernema carpocapsae. These are parasitic nematodes that love to eat pickleworm larvae. Also, because these moths only fly at night and honeybees generally pollinate during the day, you can cover your cucurbits each evening with row covers and uncover them each morning.
I know it means more work, but those delicious cantaloupes and chocolate zucchini cake are worth protecting. And nobody wants wormy pickles.
You can grow a surprising amount of food in your own yard. Ask me how!
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