Sometimes plants grow in ways you might not expect.
Instead of a nice round stem, you see a flattened ribbon shape. Rather than a regular flower, you get undulating folds. In flowers, it is called cockscomb or cresting. Wherever it happens, it is called fasciation.
Fasciation is a relatively rare physiological disorder that can create some beautiful mutations. It can occur anywhere on a plant, but stems and flowers are the most commonly seen examples.
How does fasciation occur?
In normal plant development, growing tips (apical meristems) focus all their resources on a single point, creating straight or cylindrical stems and flowers. Fasciation elongates the apical meristem, creating a ribbon-like growth. The Latin fascia means band.
In some cases, these distortions can create unique bends, twists, odd angles, or unusual clusters of growth that look like a witch's broom. Flowers and leaves growing on these distorted stems may be smaller, more abundant, or have other unique characteristics.
One rare form of fasciation, ring fasciation, has a ring-shaped growing point that creates hollow tubes.
What causes fasciation?
Plant hormone imbalances, genetic mutations, environmental conditions, or disease can all result in fasciation. It can also occur for no apparent reason. Possible environmental factors include chemical overspray or exposure, mite or other insect infestation, and certain fungi. Exposure to cold and frost can also cause fasciation. Fasciation is not contagious unless caused by bacteria.
Plants affected by fasciation
Milkweed, nasturtiums, geraniums, dandelions, and ferns may all exhibit fasciation. It also occurs in fruits and vegetables, such as asparagus and broccoli.
Some plants are prized and propagated simply because of their fasciation.
Galls are like warts or tumors in the plant world.
Not really. Galls are neither warts nor tumors, but that’s how many of them appear. The word gall comes from the Latin galla, for oak-apple. Oak apples are not fruits. They are a plant’s reaction to the presence of a foreign substance.
The study of plant galls is called cecidology [see-SID-ology]. Most commonly associated with baseball-sized knobs seen on oak trees, galls come in all sizes and can occur on many different plants.
Galls are swellings that occur in response to invasion. That invasion may be in the form of bacteria, fungi, insect larvae, eriophyid mites, nematodes, other pests, and even other plants. Mistletoe is one example of a gall-forming plant. Unlike fungal cankers, which involve plant tissue death, galls, fungal or otherwise, are cases of extra tissue growth.
Galls are nearly always woody knobs that may occur anywhere on a plant. Galls may be simple, with a single chamber (unilocular), or highly complex, with multiple pockets (plurilocular). Galls can also look like a sphere, a saucer, pineapples, pinecones, pouches, pods, or fantastic, tiny red spikes. It just depends on the host plant and the cause of the gall.
Where they occur and how they look inside can tell you a lot about what caused them.
If you cut a gall open, you will see distinctly arranged vascular tissues, depending on the cause of the gall, and an enlarged cambium layer. These distortions interfere with the flow of water and nutrients, leading to wilting and stunting. Or, you may see a large, open area, perfect for use as a larval nursery, with no noticeable impact on the host plant.
Insect, mite, and nematode galls
When insects invade a plant, they build galls. These galls can act as food or shelter for insects. They are not the same as the plant-produced domatia (tiny apartments) found in some thorns for beneficial insects. Insects inject chemicals (pseudo plant hormones) into host plants, triggering gall formation. Often, eggs are laid in these galls, providing developing larvae with food and protection. Gall wasps, sawflies, gall flies, scale insects, some aphid species, weevils, psyllids, and gall midges can all cause insect galls, but it is nearly always gall wasps or gall midges.
Nematodes are microscopic round soil worms that can cause small galls on roots. Root knot nematodes are one such pest. These galls are made up entirely of plant tissue, unlike fungal and bacterial galls, which incorporate fungal or bacterial tissues, respectively. Insect galls may also house interlopers, technically called inquilines.
When a fungus infects a plant, it grows alongside plant cells, creating swollen areas that can develop into galls. Several varieties of rust can cause galls to form. When these galls form on conifers, as in the case of cedar apple rust, they look like glutinous fingers called telial horns.
Fungal galls on other types of leaves tend to look more spherical.
Bacterial and viral galls
Bacterial and viral galls develop because the bacteria or virus reprograms plant cells into producing more bacteria, viruses, or other supportive cells. Galls at or just below the soil level are nearly always crown gall. Crown gall is a bacterial disease that can occur on blackberries, sunflowers, grapes, and roses, along with almond, apple, apricot, cherry, and pear trees.
Galls on roots may mean clubroot, a disease caused by parasites known as Phytomyxea. On the other hand, root galls may also indicate the presence of beneficial, nitrogen fixing Rhizobium bacteria. Galls have long been used in leather tanning, to make ink, and as astringents. Most galls contain high levels of tannic acid and resin. There are even a few edible galls, corn smut being the most notable. Sometimes, what looks like a gall is herbicide overspray.
New and undifferentiated plant cells are most vulnerable to gall formation. Spring is a good time to monitor plants for signs of galls. Once gall development begins, the tissues have been reprogrammed and cannot return to normal.
In a word, you can’t. Insect and mite galls rarely harm plants, and you can’t control these pests completely, anyway. Once they are inside the plant, there is nothing you can spray or apply that will reach them. Anyway, the gall is already in place.
Fungal and bacterial galls may be prevented or reduced with fungicide treatments if you can time it perfectly. Or not.
If you are galled by galls, remove them with a sharp knife. Otherwise, recognize that galls are just another amazing aspect of playing with plants.
The truth about nuts may surprise you.
While you probably already know that peanuts are not nuts (they’re legumes), many of the other foods you have come to know as nuts are not true nuts at all. Let’s begin by learning the botanical definition of nuts.
True nuts are hard-shelled, inedible pods that hold both the fruit and the seed of a plant. These pods do not open of their own accord, which means they are indehiscent. The pod, or shell, of a nut is made from the ovary wall, which hardens over time. Hazelnuts, chestnuts, and acorns are true nuts. So are kola nuts, which gives “cola” soft drinks their signature flavor.
[Did you know that small nuts are called ‘nutlets”? To me, that sounds like the perfect name for a little chihuahua.]
So, when is a nut not a nut?
A nut is not a nut when it is a fruit seed. Fruit seeds can be angiosperm, drupe, or gymnosperm seeds:
These not-nut nuts are commonly referred to as culinary nuts.
[Did you know that cashews are the seeds of an accessory fruit, which means they share characteristics with strawberries and poison ivy. Isn’t botany amazing?]
Of course, you can call any of these delicious morsels "nuts" whenever you want to. True nut or culinary nut, many of these yummy snacks find their way into our gardens and foodscapes. Which ones are you growing?
Bronzing your baby's shoes is one thing; bronzing in the garden indicates a problem.
What is bronzing?
Bronzing refers to how some leaves or fruit turn purplish or bronze-colored due to mineral imbalances, pest feeding, chemicals, environmental conditions, or disease. Bronzed leaves are often smaller, and damaged areas cannot perform photosynthesis. Bronzing damage may look similar to sunburn damage, except that sunburned leaves tend to turn gray rather than bronze. Bronzed fruit has a dry, rough texture.
Too much or too little of certain minerals can cause bronzing. Regularly adding organic material to your garden soil helps minimize mineral imbalances. But it’s still a good idea to know what to look for when scouting your foodscape:
Chlorine deficiency – More likely in sandy soils, symptoms include bronzing, stunting, necrosis, chlorosis, and wilting.
Copper deficiency – Copper deficiencies are rare. When they occur, they make trees look more like shrubs than trees. Bronzing, shoot, twig and needle dieback, and witches’ broom are common symptoms.
Iron toxicity – Iron toxicity often appears as bronzing and reddish spots. These symptoms are from iron oxidizing the chlorophyll used in photosynthesis. In areas with heavy clay soil, insufficient iron is more likely.
[Did you know that rice farmers rate their plant varieties using leaf bronzing scores (LBS)? They rank rice varieties according to their ability to tolerate excessive iron in the soil.]
Manganese deficiency – Manganese is an immobile nutrient, so deficiencies are seen in younger leaves first. Manganese deficiencies look very similar to iron (Fe), magnesium (Mg), and nitrogen (N) deficiencies, with interveinal chlorosis and bronzing. Brown specks may also be visible.
Sodium toxicity – Too much sodium can cause severe chlorosis, bronzing, and leaf drop. Stunting and other water stress symptoms are also common.
Zinc deficiency – Rare in most areas, zinc deficiencies appear as twig dieback (necrosis), yellowing (chlorosis), and leaf bronzing, often caused by too much phosphorus in the soil. Zinc deficiencies are more common in container plants.
As pests feed, leaf and fruit bronzing may occur. Most of these pests are sap-suckers:
Damage can occur when herbicides, pesticides, and fungicides are incorrectly applied. Also, the wind can carry herbicides and other chemicals from neighboring gardens and yards that may cause leaf bronzing. Bronzing, necrosis, interveinal chlorosis, desiccation, and distorted growth may indicate chemical misuse or overspray.
Air pollution often causes high ozone (O3) levels in the atmosphere. Ozone, combined with high temperatures and bright sunlight, can cause purple-brown discoloration, or bronzing, on the upper surface of leaves. Bean plants are especially vulnerable to air pollution.
Many plant diseases include bronzing as a symptom. These include spotted tomato wilt (carried by thrips), phomopsis stem canker in sunflowers, alfalfa mosaic, cotton root rot, and blueberry bronze leaf curl.
Use bronzing as a clue when you walk through your garden. The brownish or purplish discoloration of bronzing is a clear sign that something is amiss.
There’s a lot more to wind than meets the eye.
You may not see it, but gentle breezes and wailing typhoons carry insect pheromones, fungal spores, viruses, and bacteria. Gentle breezes help plants develop stronger stems, and gale-force winds can rip trees from the ground.
Seedling development is a function of sunlight, moisture, temperature, and wind. Being blown around stimulates the stem to be stronger. Botanists call this action thigmomorphogenesis. Plants grown in greenhouses, without any wind, are gently knocked around by a machine that helps prevent the plants from becoming too tall and spindly.
Note: While most pollen is too sticky to be affected by wind, wind is the primary mechanism for pollination of corn plants.
Pollen is too sticky to wipe or rub off your eyelashes, so don’t try.
You can damage your cornea. Believe me. It takes soap and water.
Wind dries plants out. Plants exposed to a lot of wind need more water than their protected brethren. Wind can also speed up erosion. Ground covers and mulch reduce that erosion. During heavy winds, you may want to move containerized plants next to a fence or wall to prevent breakage.
Protect tall plants against wind damage with stakes, tree supports, and tomato cages. Wind damage can be in the form of branches flailing around and tearing holes in leaves and branches rubbing together. Wind damage provides pathogens with a way in. And hot summer winds can lead to blossom drop and fruit set failure.
Strong winds can rip heavily laden branches or overly large limbs from a tree, leaving jagged wounds. You can help these trees recover quickly by cutting the tear to make it a flat surface, close to the trunk, but not too close. Do not cut into the branch collar. And you do not need to paint the wound. Instead, allow the tree to protect itself. It will grow a callus over the area. You may, later on, need to provide the callus with sunburn protection.
Diseases on the breezes
Disease-causing pathogens are usually microscopic. As such, they can catch a free ride on every breeze that blows through. [I wonder if that would make it a case of phoresy…] In any case, several diseases can arrive in your garden in the wind. Gray mold (Botrytis cinerea) is always present. That is why rotting fruit gets that gray fuzz so quickly. It’s everywhere.
Mummy berry spores blow into your garden on the wind. So do chemical oversprays. The chances of ringspot on Brussels sprout skyrockets after a windy day, and citrus blast often occurs right after periods of wind-driven rain. You can reduce the likelihood of citrus blast by providing citrus trees with some wind protection.
Wind protection can take many forms. It may be a fence, a hedge, or a row cover.. You can protect plants from wind by installing them close to your house. Pineapple guava, mature blueberry bushes, and many fruit and nut trees can provide a windbreak. Portable cold frames can protect smaller plants against cold winter winds.
When spring comes around, wind can mess up a plant trying to get established in a new location (ecesis). The wind is one of the main reasons for taking the time to harden off plants started in protected areas. And when you start planting those tiny seeds, such as lettuce, you can often lose most of your crop to the wind. They simply blow away. [You may want to check your neighbor’s yard for all that lettuce and endive you planted last year…] And all those delicate seedlings that emerge can be protected from the wind with a moistened layer of vermiculite. Or, you can cover them with a plastic gallon jug (cloche) with the bottom cut out. Just be sure to bury the edges or weigh down the jug enough to prevent it from blowing away, too!
Finally, I wanted to share this with you. While researching wind and its impact on plants, I learned that there are three types of wind in the universe:
I never knew that our planet outgassed anything. So, now you know. Our planet farts into outer space.
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 gray 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?
Epinasty refers to how leaves and stems turn downward when their tops grow faster than their bottoms.
While many plants move to follow the sun's path each day (phototropism), sometimes plant movements are more random. These are called nastic movements. Epinasty is a nastic movement.
Herbicide overspray can cause severe epinasty. This crazy growth occurs because many popular herbicides are synthetic auxins (plant hormones) designed to drive a plant to grow itself to death.
[If your tomato plants are exhibiting downward curling leaves, it may be that the soil needs more time to dry out between waterings.]
When roots experience flooding, they generate an amino acid that I cannot pronounce, but botanists call ACC. ACC is the ethylene precursor. ACC moves up the xylem, where it converts to ethylene gas. This ethylene stimulates roots to create hollow tubes that connect to adventitious roots. These structures 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.
Fruit. We all know what fruit is, right? Well, maybe not.
There are vegetables that we call fruits, nuts that are fruits, and fruits that are not fruits at all! Before we get started, let’s look at why plants go to all the trouble to produce fruit in the first place.
How fruit benefits a plant
In the world of plants, reproduction is the name of the game. Characteristics that evolve to promote the likelihood of a plant surviving are passed on to the next generation. Fruit is one of those characteristics. Creating fruit takes a lot of energy from a plant. But the fruit we eat has evolved to protect, disperse, and feed the seeds within. As the fruit ripens and falls, the fruit provides protection and nutrients. Fruit also encourages birds, animals, and people to spread seeds farther than the plant could do alone.
Depending on who you ask, fruits can be several different things. The simple tomato provides a classic example:
For something to be a botanical fruit, it must be the fertilized ovary of a flowering plant (angiosperm). After pollination and fertilization occur, two new structures are produced: seeds (fertilized ovules) and pericarp (thickened ovary walls). There are three different types of pericarp tissue: exocarp (outer skin), mesocarp (flesh), and endocarp (inner layer). The dominant pericarp tissue can become hard, as with nuts, or fleshy, as we see in peaches and avocados. In some cases, we eat the pericarp. In others, we eat the seed. When we eat the pericarp, we call it a fruit. Sometimes.
Like most things in life, the more we learn, the less simple anything is. Fruit is no exception. Fruits can be simple, multiple, or aggregate. Rather than going too far down that rabbit hole, let me summarize by saying simple fruits, such as apples and tomatoes, develop from a single ovary. Pineapples and figs are multiple fruits, which form when separate flowers cluster together. Aggregate fruits, such as raspberries and blackberries, are clusters of multiple ovaries from the same flower. Make sense? But wait! There's more! To start, simple fruits are also classified as either dry or fleshy.
Dry simple fruits
Dry simple fruits are not the shriveled backpacking fare variety. Dry fruits are made up of dead cells that either split open (dehiscent) or stay closed (indehiscent). Dehiscent fruits include hazelnuts, walnuts, pecans, sunflowers, corn, and wheat. Indehiscent fruits include beans and peas and other legumes, dill, poppies, and even cotton!
You might think you are finally in familiar territory, but that might be a mistake. The world of plant classification has been home to some bitter battles, and recent DNA analysis has turned many assumptions upside down. The fundamental categories of fleshy fruit are drupes, berries, aggregates, and multiples. Before you jump to any conclusions, check out these definitions for each category:
Nuts as fruits
Nuts are a strange case, when it comes to defining fruit. Some nuts are fruit, and some nuts are seeds. And some nuts, such as peanuts, aren’t nuts at all. Peanuts are legumes, which makes them indehiscent fruits. A ‘true nut’ is a hard-shelled pod that holds both the fruit and the seed, and the fruit does not open. True nuts include hazelnuts, acorns, and chestnuts. The other nuts are actually drupes. Drupes *dupe* us into thinking they are nuts, but they actually have a fleshy outer covering over top of the hard shell. Almonds, walnuts, and pecans are drupes, not nuts. But most of your friends will never believe you.
Accessory fruits and non-fruit fruits
There are also accessory fruits, which are made not just from the ovary, but also from nearby tissues. Common accessory fruits include strawberries, rose hips, apples, and pears. We may as well run the gamut with this one. Rhubarb is considered a fruit, but we only eat the stems, which are technically vegetables.
Getting the best fruits from your garden
Healthy plants produce bigger fruit. Keep your plants healthy with regular inspections for pests and diseases, appropriate watering and feeding, regular pruning, and disposing of mummies as soon as they are seen.
As your fruit starts to ripen, you can make it sweeter by reducing irrigation.
Transplanting young seedlings is a rite of spring for many gardeners. Learn how to transplant your seedlings safely and easily to help them thrive.
Benefits of seed starts
Some plants, such as lettuce, have very tiny seeds that need light to germinate. Planting these directly in the ground often leads to losses due to wind dispersal or rotting under too much soil. Starting these plants in containers makes it easy to monitor them closely and keep the soil moist until the seeds sprout. As seedlings grow, they can become root bound, which means the roots start wrapping around the inner wall of the container. Many store-bought plants are root bound. Before this happens, you can up-pot or transplant those seedlings. Up-potting means moving a seedling from a small container to a slightly larger container. Transplanting means moving the plant to where it will live out its life.
When NOT to transplant
Plants that are fruiting, flowering, infested, or infected should generally not be transplanted. New transplants need to be able to focus on building a strong root system. Also, just as some people are more sensitive than others, some plants do not take kindly to being transplanted. The following plants should be sown directly into the ground whenever possible:
How to transplant seedlings
For many vegetable crops, you can transplant seedlings with the first leaves (cotyledons) below the soil line. Very often, these meristem tissues will transform into root tissues, adding nutrients and vitality to your plants. Once your seedlings are a couple of inches tall, you should prepare their new home, making sure that the soil is loose. The Bay Area’s heavy clay can form an impenetrable barrier to new roots if it is left smooth from a trowel or shovel. Be sure to rough up the edges of the planting hole. Then, follow these steps to successfully transplant your seedlings:
Caring for new transplants
New transplants should be treated gently for a few days. To help a young seedling thrive in its new environment (ecesis), be sure to:
Be sure to use plant markers when transplanting. This will help you recall where everything is!
Chilling hours are the accumulated periods of cold temperatures that allow many fruit and nut trees and shrubs to provide us with their bounty each year.
We are all familiar with the buds and leaves of spring, the prolific growth of summer, and the harvest of autumn, but fruit and nut trees and shrubs (and strawberries!) are working through winter, too. Colder winter temperatures are part of a deciduous tree’s natural lifecycle. In preparation to survive potentially freezing temperatures, many fruiting trees and shrubs produce a hormone that initiates a state of dormancy.
What are chill hours?
Just as many seeds require vernalization (a period of cold temperatures) to germinate, many fruit trees have the same need for hours between 32°F and 45°F each winter, called its chilling requirement. In this temperature range, the growth-inhibiting hormone responsible for dormancy begins to break down, allowing trees and shrubs to produce buds that ultimately become the leaves and flowers of spring. Fruiting trees and shrubs that do not receive enough chilling hours in a year will generate fruit and leaves erratically. Any fruit produced will be lower in both quantity and quality. Also, insufficient chilling hours can extend bloom time, making delicate buds and flowers vulnerable to diseases like fireblight and brown rot.
How are chilling hours calculated?
There are different models used to calculate chilling hours, but they all take the same basic information into account:
The Utah model provides chilling hours, while the Dynamic model provides chilling portions. Whichever model you use will give you a better idea of the best varieties for your microclimate.
How many chill hours do my trees need?
Different species need varying amounts of accumulated chill hours. Within each species, each variety has its own needs, as well. For example, northern varieties of blueberries have chilling requirements of 800 to 1,000 chilling hours, while southern varieties may only need 150 to 200 chilling hours.
Your local chilling hour station
Universities work with the USDA to provide valuable information to farmers and orchardists. You can access this information to learn the cumulative chilling hours in your area. The accuracy of this information will depend on where you live and how far you are from the nearest recording station. Click on the county and town closest to you for historical averages or current season figures for hours below 45°F and those between 32°F and 45°F.
Almonds are a staple crop in California. Part of the reason is most almond varieties only need 200 to 300 chill hours. Northern California receives an average of 800 to 1,500 chill hours, while southern California only gets 100 to 400 chilling hours.
Ultimately, your fruit and nut crop will depend on pollination rates, weather, plant age, soil nutrition and structure, irrigation, and chilling hours. You can get the most out of your fruit and nut trees and shrubs by selecting varieties best suited to your microclimate and the average number of chilling hours each year.
Poinsettias, Amaryllis, and miniature Christmas trees make delightful gifts during the holiday season, but they need special care to last.
Two plants couldn’t be more different than poinsettias and miniature pine trees, and their care is equally diverse. In each case, if these plants are simply set on a countertop and watered occasionally, they will probably never make it to the end of January. Amaryllis plants are often watered to death. Being bulbs, your holiday Amaryllis can last for several years, given the proper care.
Understanding what these popular holiday gifts need to stay healthy can transform them from short-lived hostess tokens to durable members of your garden, landscape, or home interior.
Poinsettias (Euphorbia pulcherrima) are fascinating plants. The bright red blooms we see are bracts or modified leaves. The plant itself is a tree that can reach 13 feet in height! The flowers of poinsettia plants are tiny structures hidden away in pseudo flowers called cyathia. Native to Mexico, poinsettia plants need 12 hours of darkness for at least five days in a row to turn from green to red, in a process called photoperiodism. The slightest exposure to sunlight, street lights, headlights, or table lamps will interfere with this process. Poinsettias need strong morning sunlight and afternoon shade to be healthy. They can be grown outdoors, in warmer regions, as long as they are protected from frost.
Commercially grown poinsettias are infected with a phytoplasma (bacteria) that causes the plant to produce abundant lateral buds, which make the plant grow in a more bushy structure. Poinsettias left on their own have a more open, spindly growth. Poinsettias are susceptible to certain fungal and bacterial diseases, including leaf spot, stem rot, crown gall, anthracnose, blight, black rot, dieback, gray mold, powdery mildew, rust, scab, mosaic, and root-knot nematodes. These tendencies indicate the importance of allowing plants to dry out between waterings and providing good drainage. The University of Vermont Extension provides an excellent way to remember how to care for your poinsettias:
As a member of the spurge family, poinsettias contain latex, which can be an irritant. Contrary to popular belief, poinsettias are not poisonous.
In early fall, as the leaves begin to turn brown, cut the leaves back to 2 inches from the bulb and remove the bulb from the soil. Clean the bulb and place it in the crisper drawer of your refrigerator for 6 weeks. Just be sure there are no apples nearby, as they will sterilize your amaryllis bulb! After 6 weeks in the cooler, bulbs should be returned to the soil about 8 weeks before you would like fresh blooms. This cycle can continue for several years.
Most holiday plants receive too much water, not enough sunlight, and too much heat to make it through the holiday season. Understanding what these popular holiday gifts need to stay healthy can transform them from short-lived hostess tokens to durable members of the garden, landscape, or home interior.
If you slice into a stalk of celery, you will be able to see vascular bundles that carry water, nutrients and hormones throughout the plant. These vascular bundles, or veins, are made up of the xylem and phloem.
The xylem mostly carries water. Xylem is Greek for wood, so an easy way to remember the word meaning is to think “water wood”. The xylem also carries some mineral salts, but that is mostly the job of the phloem. Generally, the xylem is found closer to the center of a stem, while the phloem is closer to the outer edge.
The most interesting thing about the xylem is that it pulls water upward from the ground, against gravity. If you’ve ever picked up a bucket full of water, you know this isn’t always easy. There is some debate about how this actually occurs, but most botanists agree that it has a lot to do with surface tension.
Water molecules like to stick together. As a plant breaths, evapotranspiration occurs, reducing the amount of water in the leaves and stem. The water in the ground in then pulled upward by the water in the above ground portion of the plant. The structure of the xylem helps support the water molecules as they are drawn up.
Xylem vessels are actually made up of elongated cells that are dead. Weird, right? These cells are arranged end to end, with little openings between each cell. There are secondary xylem cells that contain lignin. Lignin is found in cell walls and it is what holds plants upright.
Diseases of the xylem include Fusarium wilt, root rot, damping off, and tomato spotted wilt.
Children's activity: This is crazy easy and the kids seem to really enjoy it. Simply take several celery stalks and place them in separate cups or glasses. To each cup, add some water and a few drops of a specific food coloring. As the stalks pull the water up, they bring the dye too, and the color changes can be striking. (It works faster if you trim the base of each stalk to create fresh openings for the vascular tissue.)
Too much of a good thing can be a bad thing.
And this is especially true when it comes to water in the soil. Over-watering and poor drainage often result in root rot, especially in houseplants. Once root rot occurs, the plant is doomed.
How does root rot occur?
Heavy rains, flooding, and poorly managed sprinklers can lead to water stress just as easily as drought. Water-stressed plants quickly become susceptible to pests and diseases they would usually be able to handle on their own.
A healthy plant breathes through its leaves and roots. When soil is too wet, the macropores and micropores become saturated. These tiny pockets within the soil hold and move water and air. If they are full of water, air can’t get in, and the roots cannot breathe.
At the same time, spores of mold and fungal diseases, such as crown rot, thrive in this soggy environment, replicating exponentially and clogging vascular bundles. When the xylem and phloem are blocked, plants cannot rid themselves of all that excess moisture. And the food from the leaves cannot reach the roots, resulting in death by starvation and asphyxiation.
Symptoms of root rot
There are several types of root rot. The most common are Armillaria root rot, avocado root rot, black root rot, and Fusarium crown and root rot. Their symptoms are very similar.
One sign of root rot is the presence of fungus gnats. These tiny black, flying insects love to eat decomposing organic matter. Wilting is another common symptom of root rot. Leaves may turn red, purple, or yellow. You may also notice darkened areas in the bark at ground level. If you peel the outer bark away, you may see reddish-brown streaks within the inner bark.
Preventing root rot
Since root rot will kill your plants, prevention is paramount. These tips can help:
Water is a precious resource, and there is no sense in wasting it, especially when it threatens the health of your plants. You may be surprised at how little water plants need.
No, it's not a new brand of mouthwash.
Chlorosis is the plant equivalent of a human gasping for air. It is the word used to describe the yellowing or bleaching of leaves frequently caused by insufficient sunlight. Or, it might be too much water or disease. Or it might be pest feeding. Or a nutrient imbalance.
Plants suffering from chlorosis are unable to produce chlorophyll. Since plants need chlorophyll to help them convert sunlight into energy, it’s a significant problem that warrants a closer look without delay.
If you notice chlorosis on any of your plants, consider these possible causes:
When I first bought my home, I sent soil samples to the University of Massachusetts Extension lab. [I think over-the-counter soil tests are a waste of money.] For the price of a bag of fertilizer, I learned exactly what was (and wasn't) in my soil.
My soil test results told me that my soil had a superabundance of every nutrient known to humanity except iron. Since plants use iron to process nearly every other nutrient, the previous owner kept adding more fertilizer whenever her plants started yellowing. As a result, the soil had too many nutrients, interfering with the delicate chemical dance between microorganisms, plant roots, water, and nutrients.
I sprayed my plants with liquid iron and applied ammonium sulfate. Over a few years, I was able to bring the excessive nutrient levels down a bit (which is harder than you might expect) and iron levels up. As a result, chlorosis was less common, my plants were healthier, and I saved money on fertilizer that I didn't need.
As soon as you correct the problem causing chlorosis, your plant's little energy factory will kick right in. Everything should start greening up pretty quickly.
You might be surprised to learn that your plants can get sunburned just as you can. Well, it is a little different, but too much sun can be deadly either way.
Damaged bark blisters and cracks, exposing internal tissue to pests and disease.
You can prevent sunscald by painting tree trunks and exposed branches with a 1:1 dilution of water and white latex paint. Do not use enamel paint because the tree needs to breathe. This whitewashing will help prevent winter sunscald, as well.
Selecting plant varieties suited to your microclimate and placing them well are good ways to avoid sunburn and sunscald. Properly irrigated plants are less likely to be sunburned.
Be sure to water your plants thoroughly this summer (especially on July 4th) to help protect against sunburn, sunscald, and bottle rockets.
You can grow a surprising amount of food in your own yard. Ask me how!
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