Garden Word of the Day
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Hesperidium is the name given to certain types of fruits.
Hesperidia are berries with a tough, leathery skin that tends to be bitter.
If you cut a hesperidium open, you will see separate compartments, called carpels. Within these carpels, you will see hundreds of tiny, fluid-filled vessels that are made out of specialized hair cells. These vessels are called vesicles.
If you haven’t already guessed, all citrus fruits are that special type of berry, known as hesperidia.
Bud scar may sound like a great punk band name, but knowing how to recognize this tiny bit of plant anatomy can come in handy.
At the tip of most twigs is an area of meristem tissue. This plant tissue can turn into several different types of plant cells. When the tissue grows upward, to continue the trunk of a tree, or a branch stem, it is called apical meristem, or a terminal bud. In this sense, terminal does not mean lying on its death bed. Rather, it refers to the bud at the end of the branch.
As these terminal buds burst forth with new growth, the protective scale normally falls away, leaving a bud scar. Bud scars look like rings around stems and branches of trees and other woody plants. Bud scars are from the terminal bud on a stem. These marks are different from leaf scars. Leaf scars occur at the point of attachment for a leaf, after the leaf has fallen off. Just above a leaf scar, there is usually a lateral bud that can grow into a twig or flower.
Ultimately, the growth of the tree or branch will grow over these scars, but that can take a long time. Until then, you can use the number of bud scars to determine the age of a branch, since each terminal bud indicates one year’s growth.
As a child, I would eat around the center core of my carrots, leaving the darker, sweeter core for last. I didn’t know it then, but that inner core is called the stele.
Vascular plants have both root and stem steles, but they didn't start out that way. Primitive steles were nothing more than a strand of xylem, surrounded by phloem. [Remember, water and minerals ‘rise up the xylem’ from the roots, and manufactures sugars ‘flow down the phloem’ from the leaves. In case you forgot.]
More modern steles may consist of vascular tissue, pith, and pericycle. Pith is the spongy material seen in the center of stems, and the pericycle is a thin layer of tissue between the xylem and the endodermis. There are two major types of stele: protostele and siphonostele.
Protostele describes the more primitive stele, which consists of a strand of xylem, surrounded by phloem. Protosteles may or may not have an endodermis that controls the flow of water. There are three different types of protostele:
Siphonosteles are a little more complex than protosteles. Siphonosteles may have gaps in their vascular tissue in places where leaves are born. These spaces are called leaf gaps. You can think of these leaf gaps as sections cut from a hula hoop and pulled a little apart, making room for leaf tissue to grow through. Siphonosteles also contain pith. If the xylem is found only outside of the pith, it is called ectophloic. If the xylem can be found both within and outside of the pith, it is called amphiphloic. Members of the nightshade family, such as tomatoes and peppers, are amphiphloic. There are three types of amphiphloic steles:
Diseases of the stele include phytophthora root rot, verticillium wilt, black root rot, and crown rot. In each case, prolonged exposure to wet soil creates the conditions needed for pathogens to infect your plants. Maintaining good drainage and soil structure can help prevent these diseases.
So, why would you care what sort of stele your plants have? Besides sounding really smart, being able to look up information about what’s inside a plant stem can help you identify unknown plants.
What's inside your stems?
Every rose has its thorns, right? Well, no. They don’t.
Roses do not have thorns. Roses have prickles. Citrus trees have thorns.
Thorns, prickles, and other spiky bits
Thorns are a type of spinose structure made out of a modified leaf, stem, root, or bud. Many people use the terms bristles, prickles, spines, and thorns interchangeably. Botanically, these terms mean very different things:
So, where bristles are stiff hairs and prickles are hard, spiked skin (neither of which contain plant veins), spines, being modified leaves, and thorns, modified stems, do contain plant veins.
Plants use thorns as a mechanical defense against herbivores (and gardeners). Cacti are far less likely to be eaten when they are covered with hard thorns. And the pollinators who specialize in pollinating these particular types of plants seem to be unaffected by the presence of thorns. In some cases, thorns are also used to shade certain plant varieties, or to provide a layer of insulation.
Home, sweet thorn
Some thorns are hollow. These tiny chambers are called domatia. Plants, such as certain acacia species, produce domatium to provide shelter for beneficial arthropods (insects, spiders, and crustaceans). Similar to galls, which are produced by the resident, rather than the landlord, domatium are the plant’s side of a mutually beneficial relationship, most commonly with ants or mites. Occasionally, thrips may also move into these tiny apartments, but they are generally unhelpful to the plant. The plants that create these thorny thresholds are called myrmecophytes.
While I do not expect any of you to stop calling rose prickles thorns, why not impress your friends with your new-found knowledge?
Wax is made by honey bees to build the comb used to store honey and to protect larvae.
Did you know that plants also make wax?
Nearly all vascular plants manufacture wax. This wax is used as part of the cuticle, or outer layer of the epidermis, of leaves, stems, and even some fruits.
Having a waxy outer layer reduces evaporation, making it easier for plants to hang on to the water they need. It also reduces the chance of abrasion, when plant parts rub against each other. Finally, wax makes it more difficult for pests to attack.
Wax is actually a class of fatty compounds that are insoluble in water and tend to be relatively soft at room temperature. When honey bees are between 12 and 20 days old, they develop a special gland on their belly that converts the sugars in honey into waxy flakes. The flakes are collected by other bees and chewed up before being used to make new comb. [I thought you’d want to know about that.] Plants, however, have neither the organ nor the chewing ability. Instead, plants synthesize wax out of hydrocarbons, made up of fatty acids and long chain alcohols, along with aromatics, ketones, and other chemicals. The chemical make up of a plant’s wax varies by species and geographic location.
Plant wax candles
Carnauba wax, of shiny car and confectionary fame, is a wax made by the Brazilian palm Copernicia prunifera. A lighter colored substitute, ouricury wax, comes from the Brazilian feather palm Syagrus coronata. Several species of native bayberry (Myrica cerifera), also known as wax myrtle, and the succulent stems of candelilla (Euphorbia antisyphilitica), produce so much wax that they were used by Native Americans to make candles. In the case of bayberry, the berries are boiled until the wax separates from the plant material. After it hardens, it is removed from the soup. These candles are still made today, due to the pleasant smell as they burn. Candelilla plants are now endangered and collecting them is forbidden. Other plant waxes include castor wax, rice bran wax, and tallow tree wax.
The next time you look at a leaf or stem, take a closer look and see if wax is part of that plant’s defense system.
Heliotropism refers to a plant’s ability to track the sun’s movement.
For many centuries, it was believed that a plant’s tendency to follow the sun as it crossed the sky was a passive action caused by water loss on the side of the plant exposed to sunlight. Now, we know that there is far more to it than that.
Growing toward sunlight
Instead of passively shrinking to one side as the sun’s harsh rays boil away a plant’s bodily fluids, we now know that plants actively grow toward (or away from) sunlight. [When a plant grows away from sunlight, it is called skototropism.]
Experiments conducted in the 1800’s demonstrated that plants will respond to any type of light: street lights, grow lights, or sunlight. When plants are attracted to this light, it is called phototropism. Phototropism is a function of the hypocotyl, or individual cells found in the same region. Hypocotyls are the embryonic stem found below the seed leaves (cotyledons) and directly above the root. You can easily see examples of phototropism when seedlings first emerge and they don’t get enough sunlight - they become leggy and lean toward whatever light they can. This is phototropism.
In heliotropism, not any old light source will do. It is only radiation from the sun that causes the reaction. And the mechanical causes of these two types of movements are very different.
Mechanics of plant movements
When plants move in response to the position of an external stimulus, it is called a tropic [TRO-pic] movement. If a plant’s movement is independent of the stimuli’s position, it is called a nastic movement. In phototropism, plant hormones (auxins), found in the meristem tissue of leaf and stem tips, photoreceptors, and multiple signaling pathways are used to direct a plant to grow more rapidly toward sunlight. In heliotropism, a structure called the pulvinus is used to direct movement.
The power of pulvinus
The pulvinus is an amazing, fluid-controlled joint found at the base of a plant leaf stem (petiole) or just below a flower.
The pulvinus causes movement by altering fluid pressure in the surrounding plant tissue. These changes in fluid pressure start when sucrose is moved from the phloem into the apoplast. The apoplast is the conjoined spaces between plant cells. As sugar is pumped into the apoplast, potassium ions are pushed out, followed by water molecules. This changes the pressure within the affected cells, causing movement. This is called turgor-mediated heliotropism. But not all heliotropic flowers have a pulvinus. Those that do not are still able to move by permanently expanding individual cells. This is called growth-mediated heliotropism. Pulvini are also used in response to nyctinastic and thigmonastic movements.
Heliotropic flowers face the sun from dawn to dusk. Slowly tracking the sun’s path across the sky, these flowers are believed to use heliotropism as a way to improve pollination, fertilization, and seed development. Heliotropic flowers often have five times as many beneficial insects present, due to the added warmth. [Many tropical flowers exhibit a modified form of heliotropism in which flowers maintain an indirect tracking of the the sun. This is believed to reduce the chance of potential overheating.] Beans, alfalfa, sunflowers, and many other species turn their blooms to follow the sun’s path across the sky each day. But sunflowers only use heliotropism in their early development, in the bud stage. Once a sunflower head emerges, it may track the sun for a short time, as an expression of phototropism, until the flower head reaches full size. The majority of sunflowers found in the northern hemisphere nearly always end up facing east.
Like floral heliotropism, leaf heliotropism is the method by which plants focus their leaves perpendicularly to the sun’s morning rays (diaheliotropism), or parallel to midday sun (paraheliotropism). Diaheliotropism allows leaves to capture the maximum amount of energy from the sun, while paraheliotropism protects plants from overheating and dehydrating.
How do your plants move during the day?
What bottle of wine would be complete without its cork? The same is true of most trees.
Everyone knows that trees and woody shrubs are made of wood, surrounded by bark. But there’s a lot more going on in those outer layers than meets the eye.
The bark you see protecting the living wood of a tree is made up of dead plant cells. This layer is called the rhytidome. The reason these cells are dead is because the cork layer cuts them off from the tree’s resources.
Components of bark
Bark is made up of three basic layers. The inner layer, or phloem, is a living part of a tree’s vascular system. Manufactured sugars ‘flow’ down the phloem to feed the rest of the plant. The middle tissue, or cortex, is made up of porous tissue that stores and transports carbohydrates, tannins, resins, and latex. The outermost layer of bark is called its periderm.
The periderm is also made up of three layers: the cork, cork cambium, and phelloderm. Cork (phellem) is produced by a specialized layer of cambium tissue, known as the cork cambium, or phellogen. This cork cambium layer is only one cell thick and the cells divide in parallel (or periclinally) toward the outside of the tree. In some trees, the cork cambium layer also produces cells towards the inside of the tree. These inner cells are the phelloderm layer.
Function of cork
Cork keeps wine safe from the elements because it is impermeable to gases and water. Because of the cork, your wine stays where it is and (as long as the cork remains intact) will only grow better with time. The cork of a tree also blocks air and water. Cork is able to keep trees and wine safe from the elements, along with insects, bacteria, and fungal disease because it contains suberin. Surberin is a waxy material that creates a protective barrier. This barrier also blocks water and gas exchanges between the outermost layers of the tree killing the epidermis, cortex, and secondary phloem. This is the bark you see.
Trees and shrubs also use cork to cut off an unwanted body part (leaf, diseased twigs, mature fruit) from the rest of the plant. This is called abscission.
Most fruits hang in their own singularity: apples, oranges, and apricots are common examples. Other fruits, such as grapes, form clusters. Still other fruits are formed when a group of flowers merge to create a fruit. Soroses are that type of fruit.
What is fruit?
Fruit is 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). In the case of apples and oranges, one flower produces one fruit. Sometimes, multiple flowers can fuse together to create a fruit. There are three different ways that this can happen:
In nearly every piece of literature you see, pineapples are listed as a common example of sorosis, but this is incorrect. I don’t know why they do this.
How a sorosis fruit develops
If you look at a mulberry flower cluster, you will see several flower buds held tightly together. Each of these individual flowers open up, awaiting pollination.
If you look closely, you can see tiny fruits at the base of each flower. Each of these fertilized fruits will develop around the stem that they emerged from in the first place. This is unlike pineapples, which include the receptacles and flower parts in their fruit development.
Berries vs. soroses
While mulberries may appear to have the same structure as blackberries and raspberries, botanically, they are quite different. Raspberries and other members of Rubus are made up of several drupes (a type of fruit) that are clustered around and attached to a dry thalamus. All of the drupes in a single fruit are made from a single flower. In mulberries, and other soroses, each rounded bit is its own fruit, formed from its own flower.
It won’t make any difference, as you enjoy a fig, some pineapple, or a mulberry, but now you can impress your friends with this fascinating word!
Some garden words are fun to say. Schizocarp [ˈskitsōˌkärp] certainly qualifies.
A schizocarp is a type of dry fruit that splits into single-seeded parts, called mericarps, when ripe. Each mericarp is made from its own carpel. [A carpel is the female reproductive parts of a flower, including an ovary, stigma, and usually a style.] Mericarps can be dehiscent, which means they split open when ripe, or indehiscent, which means they stay closed.
The seeds of carrots, celery, coriander, anise, dill, parsnip, and other umbellifers are all indehiscent schizocarps. Hibiscus (Malvaceae), mallows and cheeseweeds (Malva), false mallows (Malvastrum), and wireweed (Sida acuta) fall in the same category.
Members of the Geranium genus produce dehiscent schizocarps. [These are not the garden variety geraniums, which are another genus altogether (Pelargonium). I know, I know, it gets confusing.] True Geranium species include the cranesbill, horns’ bill and filaree plants that produce needle-shaped schizocarps that twist and gyrate into the soil (and were fun to play with, when we were children).
Maple trees produce winged schizocarps, called samaras.
Unlike the juicy fruits we enjoy each summer, or the dried caryopsis of cereal grains, plants that produce schizocarps have found that procreation works best when each flower produces a number of independent seeds protected by a dried fruit coating.
Now you know.
Plants cannot be green without magnesium, but too much magnesium in the soil can turn plants yellow. How can this be?
Magnesium is essential for plant health. Magnesium stabilizes cell membranes, making plants better able to withstand drought and sunburn. Magnesium is found in enzymes that plants use to metabolize carbohydrates. Most important, magnesium is contained in the chlorophyll molecules that convert the sun’s energy into food. This process, the Calvin Cycle, is what makes photosynthesis possible. Clearly, magnesium is important to plant health. But too much magnesium can interfere with the absorption of other plant nutrients.
Plants use 13 dissolved minerals as food. There are three primary macronutrients (nitrogen, potassium, and phosphorus) and three secondary macronutrients (calcium, sulfur, and magnesium). Plants use large amounts of these macronutrients to grow, thrive, and produce. Seven other nutrients, used in smaller amounts, are called micronutrients. Fertilizers claim to provide all the food your plants need, but it’s not that simple. [Is it ever?]
The chemical interplay, taking place in the soil, that allows plants to absorb nutrients, is a delicate balancing act. Too much, or not enough, of one nutrient can create a domino effect that causes starvation for plants that are surrounded by a banquet of nutrients.
What is magnesium?
Magnesium is an elemental metal. Pure magnesium (Mg) is too stable of a molecule for plants to absorb. The less stable, cation form of magnesium (Mg2+) is a dissolved salt that plants use for food. To be able to attract and hold those positively charged molecules, plants also need negatively charged molecules (anions), such as nitrogen, phosphorus, and sulfur. The ability of soil to perform this balancing act is called its Cation Exchange Capacity (CEC). Without a soil test from a reputable, local lab, you cannot know your soil’s CEC or nutrient levels.
For example: My first soil test found magnesium levels of 798 parts per million (ppm). The ideal range is 50 to 120ppm. Clearly, before I moved in, someone was applying an awful lot of fertilizer. The problem they were probably trying to correct was not insufficient nutrients, but a nutrient imbalance. Without a soil test from a local, reputable lab, you simply do not have enough information.
Base saturation and magnesium
Soil test results also include base saturation figures for potassium, calcium, and magnesium. Base saturation is the percentage of available connections being used. [Think of it as how many grocery bags you can carry in from your car.] The optimal range for magnesium base saturation is 10 to 30%. This means that soil particles, because of their electrical charge, will ideally hold on to 10 to 30% of the magnesium in the soil. It takes the right absorption percentage and the right volume of magnesium in the soil for plants to be healthy.
My soil’s magnesium base saturation was 32%. That sounds close enough to the 10 to 30% optimal range, right? The problem is, with seven times the amount of magnesium needed in the soil, my plants were getting 32% of too much.
Too much magnesium in the soil makes it difficult for plants to absorb calcium and other anion nutrients, which can lead to blossom end rot, bronzing, and many other problems. This is a common problem in areas with alkaline soil. The opposite is true in areas with acidic soil. Insufficient magnesium symptoms look very much like potassium toxicity symptoms: older leaves, at the bottom of the plant, start turning brown, between and alongside the leaf veins, working upward through the plant. Magnesium deficiencies in stone fruits often start out as slightly brown areas along leaf edges (margins) that expand inward, causing cracking, necrosis, and leaf loss. Magnesium deficiency in California is extremely rare.
Stabilizing magnesium levels
Reaching and maintaining ideal mineral levels in soil for healthy plant growth is both science and art - mostly science. To start, get a soil test from a local, reputable lab. Unfortunately, over-the-counter soil tests are not yet accurate enough to be useful. Once you have your results, you can take these other factors into consideration:
Finally, schedule regular soil tests for your garden and landscape. Look at these tests as an annual physical for the living skin of your property. The information in these tests will help you make informed decisions about the magnesium in your soil.
If you pick a dandelion, you will see a viscous, milky white goo come out of the stem. That goo is latex. Exposed to the air, latex coagulates, creating a protective barrier. Plants use latex as a defense against insect feeding. [Slugs will eat leaves drained of latex, but not before.] We use latex in very different ways.
Latex gloves, latex paint, and cosmetic sponges all get their start from latex. So do chewing gum, balloons, adhesives, and opium. The latex collected from the rubber tree is where we get, you guessed it, rubber. [Most latex paint, such as is used in whitewashing, is actually a synthetic latex.] It is estimated that 10% of all flowering plants, angiosperms, contain latex.
Plants that produce latex
There are over 20,000 species of plant that produce latex, occurring in over 40 plant families. Some of the more commonly known latex-producing families include:
Some mushroom, conifer, and fern species also produce latex as a defense mechanism.
Allergic reactions to latex
Because latex contains defensive chemicals, it can be an irritant. Prolonged exposure can lead to an allergic response. Individuals with a latex allergy are at risk for anaphylactic shock and should avoid contact. Some forms of latex can cause blistering of the skin, or blindness, while other plants produce a latex with reduced amounts of the allergen.
As you work in the garden, note which plants exude latex when damaged. And monitor your skin for reactions to this liquid plant defense.
How would you like a garden or landscape filled with plants for free?
Rather than buying seeds and seedlings, digging furrows, rows, and hills, planting and watering those seeds and seedlings, and hoping for the best, you can let nature takes its course and grow a surprising number of self-seeding vegetables, herbs, and flowers without any help from you.
What is self-seeding?
Plants classified as self-seeding are usually annuals or biennials that tend to produce a large number of viable seeds, pods, or capsules. These seeds fall to the ground, where they then start a new crop of the same plants (called volunteers) within the immediate (and not-so-immediate) area, during the next growing season. All this productivity occurs without any human intervention. As an added advantage, self-seeding plants provide more pollen and nectar for local pollinators and other beneficial insects than would otherwise be available, and for a longer period of time.
Self-seeding plant selection and placement
Self-seeding plants come in all shapes, colors, and sizes. Aeoniums, borage, marigolds, nasturtiums, poppies, snapdragons, sunflowers, sweet alyssum, and zinnias and are all self-seeding. Before installing a self-seeding plant, however, be sure to check with your local extension service to make sure it is not an invasive plant. Also, be sure to select a location suitable to long-term growth. You can introduce self-seeding plants into your garden for free simply by tossing a seed head from a mature plant into the area. The seeds will take care of themselves, providing a new crop during the next growing season.
Allowed to follow their natural lifecycle, many popular garden vegetables will bolt and produce hundreds of seeds. While many of these seeds will rot or be eaten by birds and other critters, you will end up with more seedlings than you know what to do with. (Give them to neighbors, family, and friends, Plant It Forward style). A surprising number of vegetable plants readily self-seed, as long as your winters are not too cold:
While these offspring are not always true to their parent plants, especially in the case of hybrids (names that include F1), I have found they are always delicious and edible! Open-pollinated (OP) heirlooms are more likely to look, grow, and taste like their parents.
I have maintained the same four beet plants, two yellow, one white, and one red, for several years, for seed production. As a result, I have beets turning up everywhere! And the parent plants add changing shapes, sizes, and colors throughout the seasons. Endive and several lettuces are now naturalized in my foodscape. By naturalized, I mean that the plants turn up wherever they take hold. At first, they are low-growing mounds of salad deliciousness. Then, in mid-spring, a central stalk appears, drawing the plant upward in a cone shape that ends up bearing lovely blue and white flowers. After the seeds have been dispersed, I cut the plants off at ground level and feed them to my chickens. Next winter, new crops of endive and lettuce appear like clockwork, with no effort on my part. I transplant some of these volunteers to create lovely borders and accent plants. And they don’t cost me a dime.
Many herbs are also self-seeding. Basil, chamomile, chives, cilantro/coriander, dill, fennel, lemon balm, oregano, parsley, and sorrel, are just a few favorite herbs that willful an area without any help from you. Parsley, in particular, is a super seed producer. A single parsley plant can produce the equivalent of 10 seed packets! For free!
The very characteristics that make self-seeding plants so successful can also make them troublesome. Some self-seeding plants can take over an area, much the way mint plants do. Also, if a plant is prone to certain diseases, such as powdery mildew or blight, or susceptible to insects commonly found in your garden, you might need to incorporate crop rotation to break the disease triangle, or insect life cycle. If you really want them, these self-seeding plants are best corralled into containers and deadheaded frequently.
If your self-seeded volunteers turn up in undesirable locations, you can always transplant them into a more suitable or convenient spot, pull them by hand as seedlings, or mow any that turn up in a lawn. If your winters are too cold to allow self-seeding to occur naturally, you can always collect seeds from these abundant producers and use them to start next year’s crops.
Lighten your work load and increase biodiversity in your garden and landscape with self-seeding vegetables and herbs!
When you look at a flower, you probably notice the petals first. Bright colors and brilliant arrangements attract people and pollinators alike. All of those petals together are called the flower’s corolla, or inner perianth. At the base of that corolla, you will sometimes see a green cup shape made up of lobes. The lobes together are called the calyx, or outer perianth. Each lobe, individually, is called a sepal.
Sepals encase a bud before the flower blooms, providing protection. Usually, after the flower blooms, the plant has no use for the sepal and it is allowed to whither. Some flowers retain their sepals, using the cup-like structure for added support for the flower. In some cases, such as oyster plants, the sepals are quite large and they protect the nyctinastic flower during the afternoon and through the night. Tomatillos and groundcherries, however, put their sepals to work as papery outer coverings for their precious fruit. These protective bladders help keep birds and insect pests away.
Like flower petals, sepals are modified leaves. While often smaller than the petals, sepals can be longer and larger. Sepals can look like teeth, ridges, or scales, especially on plants in the grain family, or they can look like leaves or petals. Normally green, they can also be very colorful and may look like petals. When the petals and sepals are too difficult to tell apart, they are called tepals. Flowers with tepals are called petaloid. Tulips and aloe plants are petaloid.
Some sepals are attached or fused to each other (gamosepalous), while others are separate from one another (ploysepalous). When the sepals are fused toward the base, as in the case of legumes and pomegranates, they form a calyx tube. In the rose and myrtle plant families, this structure is called the hypanthium.
Sepal count and plant classification
The number of sepals present can help with plant identification. The number of sepals is called its merosity. Eudicots generally have a merosity of four or five, while monocots and palaeodicots have a merosity of three. If you see a flower with 4 or 8 sepals, you will know that it is a eudicot. If it has 3, 6, or 9 sepals, it is either a monocot or a palaeodicot. If is has 15 sepals, well, you’re on your own.
You can make clones of many favorite plants for free with layering. Layering is a form of vegetative propagation.
Unlike other vegetative propagation methods, such as cuttings and division, layering allows the parent plant to continue providing water and nutrients to their offspring as they develop their own root system. This is because they are still attached!
Strawberry runners are an example of natural propagation by layering. The parent plant sends out runners. Where the nodes touch soil, adventitious roots emerge and a new root system begins to develop. As it does, the parent plant continues to support this newly developing clone. Once the offspring are self-sufficient, the runner stem eventually dries up and falls away. Layering uses the same basic idea by pulling a stem downward until it touches the soil at what would have been a leaf node. Coming into contact with moist soil, the plant reprograms that node to become root tissue.
Many window sill gardens are populated with herbs, such as rosemary, sage, and lavender, that are easily propagated with layering. In some cases, plants are wounded on one side, to stimulate rooting. In other cases, the stem is bent sharply at the point where it touches the ground. The most critical point in layering is that the soil must be kept moist as the new roots grow. If the growing medium dries out, the process fails. In some cases, this process is complete within the first year. In other cases, it can can 3 or 4 years, so be patient. Some people use rooting hormones (auxins) to speed things up.
There are six different types of layering:
Air layering Air layering is used predominantly on thick-stemmed houseplants that have become leggy. It is also used to generate new trees and shrubs, including apple, blueberry, citrus, cashew, cherry, fig, kiwi, pear, pecan, and walnut. Stems are slit just below a node and the slit is pried open. The wound is then wrapped with wet, unmilled sphagnum moss and wrapped with plastic, which is tied in place. When new roots fill the moss, a cut is made below the root ball, separating it from the parent plant and replanted elsewhere.
Compound (serpentine) layering Compound layering is best suited to plants with flexible stems, such as pothos. Stems are bent into rooting medium in a serpentine arrangement that allows several nodes to begin developing their own root system. Again, some people wound the area that ends up below ground to stimulate rooting.
Mound (stool) layering Mound layering, also called stool layering, is used primarily on woody plants to stimulate rooting of new shoots. During the dormant season, the plant is cut back to one inch above ground level. Soil is then mounded over the new shoots as they emerge in spring. This method is best suited for apple and plum rootstocks, and gooseberries.
Simple layering Simple layering consists of bending a stem down to the ground and covering it with soil, leaving the last 6 to 12 inches exposed. This tip is bent into a vertical position and staked in place. Wounding the area that ends up underground can stimulate rooting. This method is best suited for hazelnuts, forsythia, and honeysuckle.
Tip layering Tip layering is a method commonly used on cane fruit, such as blackberries and raspberries. Tip layering consists of digging a small hole, a few inches deep, and putting the tip of a cane into the hole and covering it with soil. At first, the tip will grow downward. Then, it will complete a U-turn in the soil and emerge aboveground. That bend will develop roots, allowing the new plant to be separated from the parent plant in spring and replanted elsewhere.
Trench (etiolation) layering Trench layering, or etiolation layering, is generally used to create fruit tree rootstock and grape vines. In this method, parent plants are planted at a 30 to 40° angle. As new shoots emerge, they are pulled down into shallow trenches, pegged in place, and covered with soil until new roots emerge.
Layering is an easy way to make new plants out of existing favorites, without spending any money!
Achenes are small, one-seeded dry fruits that do not open to release the seed, which means they are indehiscent.
[Pronounced ah-KEEN or eh-KEEN, depending on who you ask.]
Examples of achenes
The tiny bits that you see on the outside of a strawberry are achenes. If you look closely, you will see that each tiny bit is actually a dried fruit that contains a single seed. If those seeds happen to sprout while still attach to the strawberry, it is called vivipary.
Many members of the sunflower family feature achenes. Cardoons, cannabis, caraway, and roses also produce achenes. Some plants, such as the maple tree, produce modified achenes, called samaras. Other plants, such as wheat, barley, and other grains, produce a caryopsis, which is much like an achene, except that the seed coat is stuck to the pericarp. In the same way, each spike of a dandelion is a type of achene known as cypselae.
Scientists are still sorting out the details of this particular mode of seed life. Until recently, the individual seeds from sunflowers were considered achenes, but genetic research may be changing that decision. I’ll keep you posted.
Pea pods are just one example of the protective seed covering we call a pod.
Most legumes and many Brassicas produce a long, dehiscent fruit that contains many seeds. [Dehiscent means that the structure opens spontaneously when its contents are mature.] Vanilla beans come in a pod, as well. But what makes a pod unique in the plant world?
Anatomy of a pod
A pod is made up of two identical long halves (bivalve) that contain seeds. These halves are joined and then split along a seam, called the suture. Legume pods are made from a single carpel, while Brassica pods (siliqua and silicula, depending on the pod dimensions) are made from two carpels
A pod’s purpose
A pod protects the developing seeds. Pods can also perform photosynthesis, providing the seeds with food energy. Scientists have recently learned that pod tissue can recognize when a seed is damaged and relocate resources to where they might be better used. It ends up pods are major players in regulating seed development.
Pod pests and diseases
Plants invest a lot of energy into creating pods to protect their precious cargo. While bean seed beetles and other seed-chewing beetles may gnaw their way inside, and the pod spot (Ascochyta fabae), powdery mildew, and other fungal diseases may try to dissolve the pod, pods tend to be a strong defense for the genetic information they contain.
The pods of beans, okra, peas, radish, and mustard are just a few of the edible pods you may have in your garden. And if you allow any of these plants to go through their complete life cycle, the pod will dry and split open, dispersing seeds where they fall, generating more plants for your foodscape!
Trichome is one of those words you’ve probably never heard before, but you’ve seen what it means your whole life.
Trichomes are plant hairs. Trichome can also refer to plant scales, such as those seen on the outside of pineapples. These hairs or scales can be seen on leaves or stems. Understanding the vocabulary related to trichomes can help you identify unknown plants.
When a plant is covered with hairs, that covering is called an indumentum. The presence of trichomes provides a physical barrier against grazing, as in the case of nettles. In other cases, there is a sticky secretion that traps insects as food.
Anatomy of trichomes
Trichomes can be unicellular or multicellular. Unlike thorns and spines, which grow from shoots and leaves, respectively, trichomes are more similar to root hairs, both being outgrowths from epidural plant cells. Each of these cells, or groups of cells, may turn into thread-like extensions that can be long or short, stiff or soft, straight or curved. Some trichomes are glandular, meaning they secrete fragrant essential oils or toxic histamines. Plants with hairs or scales are called pubescent. If a plant lacks hairs or scales, it is said to be glabrous or glabrate.
Is it true that melons and squash can cross-pollinate? If I plant a lemon tree too close to an orange tree, will the oranges be sour? You’ve heard of cross-pollination, but what does it really mean and do you have to worry about it? Let’s start by reviewing pollination.
Pollination and fertilization
Pollination refers to the act of pollen, the male genetic information (gametophyte), moving from the anther to the (female) stigma. From there, the pollen grain grows a pollen tube, which makes its way down the style to the ovary. Two sperm cells (gametes) then move through this tube to fertilize female gametes. One male gamete fuses with a female gamete to produce an embryo, while the other fuses with a different type of cell, called a polar body, to form the endosperm, which will feed the developing embryo. [You can think of these two much like the yolk and white of an egg, respectively.] Since two fertilizations are actually occurring, it is called double-fertilization, but I digress.
Types of pollination
Pollination can occur one of two ways: self-pollination or cross-pollination. Self-pollinating flowers pollinate themselves. Cross-pollination, or allogamy, refers to the way pollen moves from one plant to another of the same species. Wind and insects, such as honey bees, are the main perpetrators of cross-pollination. Natural cross-pollination can only occur within a species (we will not discuss genetic manipulation at the nano surgery level).
To give you a clearer idea, consider this: Horses breed with horses. Donkeys breed with donkeys. When a female horse breeds with a male donkey, their offspring, a mule, is nearly always infertile. The same is true in the plant world.
This means that zucchini plants can cross-pollinate with pumpkins and other summer squash varieties, but not with melons or cucumbers. This is because squash and pumpkin are both members of the Cucurbita pepo species. In the same way, cucumbers (Cucumis sativus) cannot cross-pollinate with muskmelons (Cucumis melo). Their genetic information doesn’t match up properly.
When cross-pollination within a species does occur, the offspring (seeds) are often useless, but it has no affect on the current season’s fruit or vegetable. The only exception to that rule is sweet corn. When varieties of sweet corn cross-pollinate, the current season’s crop will exhibit characteristics of both species. In nearly all other cases, it is the DNA found in seeds that is altered. If you save seeds for next year’s crop (and I urge you to do so), you will grow plants with characteristics of both parent plants. This is how we get many new cultivars with desirable traits or unique properties. The only way to prevent cross-pollination is to keep crops 100 yards or more apart, which probably isn't realistic in your home garden. You can reduce the chance of cross-pollination by keeping plants as far away from each other as possible.
The science of genetics owes its start to cross-pollination among common pea plants
and a central European monk, named Gregor Mendel, back in the mid-1800’s.
As for those sour oranges, they were probably unripe, irrigated improperly, or victims of the Asian citrus psyllid, not the result of cross-pollination.
Most of us grew up learning about how pollen sticks to bees as they go from flower to flower, collecting nectar and pollinating many common food crops. But that’s not how it works for your tomatoes and peppers. Instead, they use buzz pollination.
Most flowering plants (angiosperms) have male parts, called anthers, that have pollen on the outside, available to all takers. This pollen held in place by its extreme stickiness. [That stickiness is why you need to use soap and water to get pollen off your face and eyelashes, for those of you who are prone to allergies.] This pollen can be knocked loose by busy pollinators and then carried on the wind, or the pollinators find themselves covered with the sticky stuff, as they move from flower to flower, feeding on nectar and collecting pollen.
Dry, dusty pollen
Some flowers don’t have sticky pollen. Instead, they have pollen that is dry and dusty. If that pollen was exposed, it would all be gone with the first breeze, most of it never making it to another flower. Instead, these plants have evolved a specialized type of anther, known as a poricidal anther. Poricidal anthers are tubes with tiny openings at one end, but these openings are too small for bees to use. To make matters worse, these plants generally do not offer nectar, so how do they get pollinated?
Pollination by vibration
Approximately 8% of the world’s flowers are only pollinated when the correct sound wave frequency occurs nearby. When it does, the flower explodes a small dose of pollen into the air, coating whatever is at hand with genetic information and protein-rich food. This is called buzz pollination, or sonication. It gets those names because certain insects that have learned how to buzz at just the right frequency to trigger these plants to share their bounty.
These flowers release pollen at frequencies between 40 to 1000 Hz, depending on the species [You can use a tuning fork or an electric toothbrush to try this for yourself.] Scientists believe this arrangement evolved as a means to ensure that each visiting pollinator carries away a smaller portion of pollen (which they are less likely to drop on their way to the next flower) and that those portions are spread out over a greater number of pollinators, and over a wider time frame, for better odds of procreation. How’s that for evolution?
Not honey bees
Honey bees do not use sonication to get at pollen, but several other bees do. Sweat bees, carpenter bees, and bumblebees all use buzz pollination to get at the pollen held in poricidal anthers. They do this by disconnecting their wings from their flight muscles [I have no idea how they do this!] and vibrating those muscles at just the right frequency. In most cases, this frequency is close to middle C. The force generated during sonication can reach 30 Gs, which is almost more than a human can tolerate!
Which plants use sonication?
You may be surprised to learn that many common garden plants use sonication. Members of the legume and nightshade plant families frequently use buzz pollination to generate the fruits and vegetables we love. In addition to tomatoes and peppers, other edible plants that use buzz pollination include eggplants, potatoes, peas, blueberries, tomatillos, and kiwifruit.
How are your flowers being pollinated?
In the world of plants, crown can mean two very different things.
Like the fancy hat on a monarch’s head, crown can refer to the canopy of a tree. It can also mean the part of a plant slightly above and below the soil line. In both cases, the more you know about them, the better your plants will grow.
Tree top crown
Technically, the crown of a plant refers to everything that is above ground. Most people, however, use the term to describe the outer branches or canopy of a tree. In either case, mature crown size is an important factor when selecting a site for a tree. While most trees don’t mind mingling their branches, there are a few species that exhibit ‘crown shyness’ and will grow in such a way as to keep their distance from the branches of other trees. Tree crowns are classified by their shape. They can be rounded, weeping, funnel-shaped, spreading, pyramidical, oval, or conical.
Leaves that make up the crown are responsible for far more than just photosynthesis. In addition to being the major food manufacturing system of the tree, they also filter out dust and other particles from the air, slow the speed at which raindrops hit the ground, and shade the ground below the tree, stabilizing soil temperatures for the root system. [Seven or eight trees also produce the oxygen you need to breath each year.]
Tree crowns can be reduced moderately using heading cuts. Pruning in this way can lead to increased stem development lower in the tree, which means even more pruning to maintain air flow and sun exposure, while limiting the fruit load to a level that the tree can safely support.
In most cases, these diseases can be prevented with simple cultural practices:
Exceptions to the rule
In some cases, transplants can be replanted deeply enough that the lowest set of leaves end up underground. These leaves should be removed at transplanting time. The nodes where the leaves were are then transformed into root tissue, increasing the availability of water and nutrients found in the soil. This practice is not recommended for most plants. However, tomatoes and peppers, in particular, can increase their yields substantially with this practice. I have heard mention of using the same technique on brassicas, such as cabbage and broccoli, but I could not find any verifiable proof, so I am skeptical until proven otherwise.
As you walk through your garden, be sure to inspect the ground level crowns of your plants for signs of fungal disease and pests. Then, look skyward for a quick check on the overall form of your trees. These quick checks can reduce your workload and protect your plants over the long haul.
You can grow a surprising amount of food in your own yard. Ask me how!
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