Habit: "A plant's habit is its direction of growth," states Wallace Pill, Ph.D., professor of horticulture at the University of Delaware. "A plant that grows straight up has an 'upright' habit and one that grows along the ground has a 'prostrate' habit. The many variations in between don't have specific names, so the habits of those plants are described in lots of different ways."
Hardy: In most parts of North America, a key question to ask about any perennial plant is "Is it hardy in my climate," which means "Will it survive winter where I live?" In fact, the continent is divided up by the U.S. Department of Agriculture into "hardiness zones" that help cue gardeners to know which plants will survive winter in their climate. Labels accompanying plants sold at nurseries often denote how hardy a plant is: either by zone ("Hardy through zone 6") or by temperature ("Hardy to -26 degrees F").
"A plant that is said to be half-hardy for a particular area is one that will survive most winters, but cannot take the worst winters in that region," explains Wallace Pill, Ph.D., professor of horticulture at the University of Delaware. "If you decide to try growing a half-hardy plant, you'll give it its best chance for survival if you put it in a south-facing site near the house or another windbreak that will give it some protection from the elements."
Heeling in: You get a new tree, shrub, etc., but the place where you want to plant it isn't ready for you to put it in the ground yet. How can you keep the tree (or whatever) healthy until you can plant it? Heel it in! "Just dig out a couple shovelfuls of loose soil in a shady place and put the plant's rootball in the soil and then cover it lightly," explains Sam Benowitz, proprietor of Raintree Nursery in Morton, Washington. "Water those roots occasionally and the plant can stay there for quite a while—weeks, even months. This is what most nurseries do with the plants before they sell them to you."
Humus: This is a term that can mean two different—though similar—things, according to Wayne Honeycutt, Ph.D., a USDA soil scientist working at the University of Maine. "To some people, humus means any organic matter like leaves or wood chips," Dr. Honeycutt elaborates. "Other people use humus to mean organic matter that has decomposed to the degree that it is no longer distinguishable from the soil itself." The difference between those definitions becomes important when gardeners are advised to add humus to their soil—should you mix in fresh organic matter like chopped leaves or grass clippings or decomposed organic matter, better known as compost? "I believe that adding fresh material stimulates activity of the microbes in the soil and that has lots of beneficial effects for your plants and the soil," Dr. Honeycutt avers, "so mix in fresh organic matter when you plant."
Hybrid: Many new varieties are created when plant breeders combine the characteristics of two different plants into a new one by taking the pollen from one plant and using it to pollinate the other, which in turn produces seeds for a new generation. The plants that grow from those "cross-pollinated" seeds are called "hybrids."
"When the two parent plants have been bred for consistency—so that they will reliably have the same traits each time they're grown—the next generation are called 'F1 hybrids' and they are uniform, too," explains Dennis Stimart, Ph.D., a professor of plant genetics and physiology at the University of Wisconsin. "However, the seeds produced by the F1 hybrids will not grow into a next generation that is uniform—if you save the F1 hybrid's seeds and plant them, the F2 generation may have lots of undesirable traits."
Inflorescence: For such a big word, inflorescence (in-FLOOR-es-sense) has a very simple meaning. It is the way to describe a flower that is made up of many flowers, like you see on hyacinths or hydrangeas. "You sometimes hear people using inflorescence more broadly to mean just 'flower,'" notes Gus De Hertogh, Ph.D., professor of horticulture at North Carolina State University, "but the specific definition of the multi-flowered blossom is more accurate."
Loam: Soil that contains silt, sand and clay—the major components of well-balanced soil—is called "loam." The ideal proportions of those components for gardening, notes Wayne Honeycutt, Ph.D., a USDA soil scientist at the University of Maine, are 30 to 50 percent sand, 30 to 50 percent silt and the remainder as clay. "That balance is ideal," he explains, "because in those proportions the soil holds water well but is loose enough for the roots to penetrate the soil easily." Allow us to state the obvious and point out that "sandy loam" has more sand and "clay loam" has more clay—just wanted to be sure that was clear.
Naturalize: You want bulbs that keep coming back for many years and that multiply themselves? Then you want those that "naturalize" in your climate, Kim Tyson of the Netherlands Bulb Co. in Easton, Pennsylvania, tells us. "A bulb that adapts well to the kind of soil you have, your winter and summer temperatures and the amount of light it gets will naturalize in your area," Tyson explains. "Those differ from one place to the next. Most daffodils, for instance, naturalize in the Northeast, but they don't in Florida because it doesn't get cold enough for them in the winter," she continues, "but it gets too cold in the Northeast for paper-whites [a close relative of daffodils], which will naturalize in most parts of the Southeast."
N-P-K: Pop quiz! Remember back in high school chemistry class when you had to learn the Periodic Table of Elements? Each element had a letter or two for a symbol that scientists use as shorthand to write out formulas. So, what did the letters N, P and K represent? You're right, N=nitrogen, P=phosphorus and K=potassium! Give yourself a gold star.
Now, why are we testing your memory of that long-forgotten class when talking about gardening? Because those three elements, N, P and K, are the major nutrients most garden plants require for healthy, productive growth—in varying proportions, depending on the plant and what stage of its development it has reached. And when you look at a bag or bottle of store-bought fertilizer, it will have an N-P-K rating on it that is typically expressed as a ratio, like 2-1-2, which means there are two parts each of nitrogen and potassium to one part of phosphorus.
Perennial: In contrast to annuals and biennials (see the definitions above), perennials live longer than two years, even through frozen winters. "Some, like columbines, are short-lived perennials that come back for only three or four years," explains Dennis Stimart, Ph.D., a professor of plant genetics and physiology at the University of Wisconsin; "others, such as peonies, come up for decades" even though they look like they've died back in the winter. "And some plants that we think of as annuals, like ornamental peppers, are really perennials in their native climates," he adds, "but we treat them like annuals because they don't survive winters in the North." Petiole: The part of a leaf's stalk between the bottom of the leaf and the plant's main stem is called the petiole (PET-ee-ole). "It is a vascular conduit between the plants' roots and its leaves," notes Richard Racusen, Ph.D., professor of plant biology at the University of Maryland. "Like humans, plants have two types of tubing that serve different purposes. Both of those reach the leaves through the petiole."
Pinch back: Mom always said that if your sister pinches you, you should not pinch her back, but many gardeners know that pinching back some plants helps direct their growth. "The most common reason for pinching back a plant is to make it bushier," states Wallace Pill, Ph.D., professor of horticulture at the University of Delaware. "When you pinch back the top of certain plants, they will grow more lateral branches and thus become bushier."
Pinching back is easy to do—all you need are a thumb and forefinger and the resolve to trim your plants for their own good. Just get a solid grip with your fingers on the stems you're going to pinch back and firmly pull them off. "If you're advised to do a soft pinch, pull off about a half inch," clarifies Dr. Pill. "For a hard pinch pull off a whole inch."
When should you pinch back a flowering plant? "Before the plant has committed to flowering," he answers. "For example, gardeners often pinch back chrysanthemums in midsummer so the plant will get grow more lateral branches that will produce more flowers. But once the days become shorter mums will form flower buds and it is too late for pinching back to do any good—all of the plant's energy at that point will be devoted to filling out those buds and opening them into flowers."
Pollination: Let's talk about sex—flower sex, that is. Flowers contain a plant's reproductive organs, which include the anthers and the stigma. For the plant to produce seed—which is how most plants reproduce—the tiny dust-like grains of pollen contained in the anthers (or male organs) must reach the stigma, where they burst open and release sperm that fertilize the eggs within the ovary (the female organ). Fertilized (or pollinated) eggs grow up to become seeds.
Some types of plants are self-fertile, meaning that the eggs that they produce can be pollinated by their own pollen; others have distinct male and female flowers, and you must grow both to get seed. The majority of plants, however, have flowers with both types of organs yet still grow best when they are cross-fertilized with pollen from another nearby plant of the same species. The pollen in those cases gets from the anthers of one plant to the stigma of another carried either by the wind (anemophilous pollination) or by insects (entomophilious pollination). Flowering plants are generally pollinated by bees, butterflies and moths, which are attracted by the sight and scent of flowers.
Self-seeding: Annuals and biennials that produce and drop seeds where they are growing, which then sprout and grow into full-grown plants themselves are "self-seeding," explains Nona Koivula of All-America Selections in Chicago. Hollyhocks, for example, self-seed so efficiently that you might think they are perennials because they keep growing in the same place year after year; in fact, they are biennials that drop seed which stays dormant through the winter and comes up the following spring in the same place. Unfortunately, many of the peskiest annual weeds like dandelions are efficient self-seeders, too—if you want to get rid of them for good, you have to pull these weeds before they develop their seeds and drop them where they will germinate the next year.
Soil pH: You can find out all you need to know about your soil's pH with a simple soil test—which you can perform with a kit you buy or you can get from a soil laboratory. (Lab tests are inexpensive and give you lots of other worthwhile information about your soil.) The result of the pH test will be a number: if that number is below 7, your soil is acidic; if it is above 7, the soil is alkaline. What that tells you is how hospitable your soil is to specific plants. Some, like azaleas, prefer acidic (often referred to as "sour") soil; others, like cool-season grasses, grow best in alkaline (or "sweet") soil. Many like the soil close to the neutral pH of 7.
You can alter your pH by adding lime to acidic soil or sulfur to alkaline soil. Or you can just add compost! "A soil's pH seems to be less important to plants when the soil is rich in organic matter—the plants still grow well even if the pH isn't quite what they prefer," elaborates Elaine Ingham, Ph.D., an associate professor of soil ecology at Oregon State University. "Unless the pH is extreme in one direction, you're better off adding compost to the soil than trying to balance the pH with other amendments."
Sport: Most of the new plant varieties that find their way into nurseries and garden centers are the result of years of careful breeding and selection of the best specimens from trials. But sometimes that marvelous creator known as Accident can bypass all the years of work when a plant develops a new and desirable trait as the result of a spontaneous mutation in its cells. If that trait remains within new plants grown either from its seed or from a piece of the original plant, the new plants get a new name and are known as "sports." A sport will be identical to the original in every way except the one trait.
Stolon: Plants that don't reproduce by seed often spread by stolons, or underground stems on which new plants grow. Zoysiagrass is a familiar plant that reproduces by stolons; many weeds do, too. When pulling these weeds, you must be sure to get all the stolons as well as the roots and leaves.
Sucker: "A sucker is a bud that forms and grows into a branch in the crotch between another branch and the main stem," says Richard Racusen, Ph.D., professor of plant biology at the University of Maryland, "and it can crowd out the original branch if left to grow." That's why you hear (or read) advice suggesting that you remove the suckers from trees and other plants.
Taproot: The first root that many plants put down when they germinate grows straight down into the soil and is like a stem that all the other roots grow from—this root is called the "taproot" and its like a major artery in the human body. When transplanting, take care not to break the taproot or you severely hamper the plant's chances of surviving the move.
Tissue culture: When scientists and nurseries want to reproduce a lot of one plant very quickly and inexpensively, they can take a piece of that plant—literally, a few cells—and grow them in a laboratory into replicas of the original plant. That process of reproducing a plant in the laboratory is known as "tissue culture" and it's "a valuable tool for researchers and other plant people," insists Dennis Stimart, Ph.D., a professor of plant genetics and physiology at the University of Wisconsin. "However, the plants that come out of tissue culture can be unreliable," he adds, declining to give specific examples for fear of making home gardeners overreact to them. For our part, we've heard gardeners express frustration about the reliability of tissue cultured plants such as hostas (they turn out different rather than identical to the varieties they came from) and so we can recommend that you look for conventionally reproduced plants whenever possible, which Dr. Stimart does not disagree with.
Triploid/tetraploid: Your average plant has two sets of chromosomes. To enhance certain qualities in some species, scientists have bred triploids (which have three sets of chromosomes) and tetraploids (four sets of chromosomes), reveals Dennis Stimart, Ph.D., a professor of plant genetics and physiology at the University of Wisconsin. What do gardeners need to know about triploids and tetraploids? "Triploids are typically sterile," so they don't produce viable seed, answers Dr. Stimart. "The flowers on tetraploids are generally bigger than those on other varieties of that species, but there are fewer of them and the plant generally grows slower than the types with two sets of chromosomes."
Variegated: Leaves that have different colors are variegated—"if those different colors are genetically induced and not caused by pests, diseases or nutritional deficiencies," adds Wallace Pill, Ph.D., professor of horticulture at the University of Delaware. Variegation is most often white or yellow, but it can also be bluish or reddish, depending on the plant. Those colors can change due to light or soil conditions; some plants outgrow the variegation altogether.