We've assembled this glossary of 37 gardening terms you're likely to encounter at garden centers and in catalogs, and defined them in our usual accurate yet crystal clear, gardener-friendly way.
Annual: This type of plant has its complete life cycle, beginning from a seed and producing new seed for a succeeding generation, during a single season and then dies at the end of that season. Marigolds and zinnias are annuals many of us have grown.
Biennial: It takes this type of plant two seasons to go from seed to seed, like hollyhocks and foxglove, develop roots and leaves during their first growing season and then grow flowers and set seed during the second year. Biennial plants die at the end of their second season.
Bracts: On most of the plants we grow for their appearance (rather than for food or fiber), the blossom—the part of the plant that contains its reproductive organs—is the main attraction. But on certain plants it is the colorful leaves surrounding the flower that attract us. Those leaves are called "bracts." The most familiar example of this is on the poinsettia, notes Gus De Hertogh, Ph.D., professor of horticulture at North Carolina State University. "The little yellow, egg-like things in the center of those colorful leaves are the flowers on the poinsettia," he elaborates. "But those colorful leaves known as bracts are what we grow them for."
Bulbs: "Any plant with an enlarged underground storage organ can be called a 'flowering bulb,'" says Gus De Hertogh, Ph.D., professor of horticulture at North Carolina State University. But botanists and others who are sticklers for detail do distinguish between bulbs, corms, rhizomes, tubers, tuberous roots and hypocotyls—all of which produce geophytes, or plants with (here we go again) enlarged underground storage organs. What is being stored? "The nutrients the plant needs to grow each year," Dr. De Hertogh answers. "After a flowering bulb finishes blooming for the year, its energy is devoted to storing those nutrients for the next season in the bulb." That's why you must let the leaves stay on tulips, daffodils, lilies and other flowering bulbs after they're done blooming; if you cut off the leaves, the bulbs have no way to collect sunlight and convert it into food for next year's blooms.
A bulb, strictly speaking, has enlarged scales where most of those nutrients are stored and a small basal plate, which is where the next season's roots and shoots are. A corm is just the opposite: it has small scales and the nutrients are stored in the enlarged basal plate. Rhizomes and tubers are two different types of enlarged stems, which store the nutrients. Tuberous roots are (no surprise) enlarged roots serving as storage organs. A hypocotyl is like an oversized seed, where the nutrients are stored in enlarged cotyledons.
Cotyledon: Seeds of all sizes contain the nutrients they need to get growing—those nutrients are stored inside the cotyledon (pronounced cot-el-LEE-dun), which are wrapped around the embryo within the seed. "In many plants, the cotyledon opens up to form transitionary leaves—the small, rounded leaves you see when the seed has first sprouted--which then fall off after the plant has developed more permanent leaves," observes Richard Racusen, Ph.D., professor of plant biology at the University of Maryland. "But in all plants that grow from seeds, the cotyledon's critical role is as the structure that stores the nutrients the plant uses to germinate."
Crown: Simply put, a plant's crown is the spot where its roots and stems meet. If you get a plant, like an astible or a peony, that comes with the recommendation to "bury the crown," be sure to completely cover the roots with soil, but leave some of the stems poking up through the soil, advises Gus De Hertogh, Ph.D., professor of horticulture at North Carolina State University.
Cultivar: The quick answer to the question "What is a cultivar?" is to say that it's the proper term for what we usually refer to as a "variety." Now, what exactly is a variety? "A plant that has been selected or bred to have a specific trait or traits different from other members of its species and that has been given a unique name," responds Nona Koivula, executive director of All-America Selections, an organization that coordinates annual trials of new cultivars and then awards its AAS designation to the winners of those trials.
An example might be the best way to make the concept of cultivars clear: 'Elizabeth Taylor' and 'Ingrid Bergman' are names of hybrid tea roses you may see at a nursery or in a catalog. They have similarly shaped canes and flowers, but Elizabeth Taylor's blossoms are deep pink while Ingrid Bergman's are dark red. Both are hybrid tea rose cultivars. Names of cultivars are typically designated with single quotations marks ('Elizabeth Taylor').
Deadhead: When an annual plant finishes making seed for the season, it will stop flowering (one of the steps in the seed-making process; see entry on "Pollination") because it has completed its biological mission of reproducing. You can keep the plant blooming longer by plucking off flowers that have passed their prime in appearance but have not yet produced finished seed. Removing those aging flowers is what we (and other people) mean when we recommend that you deadhead the plant.
Direct-seed: This is the most basic act of gardening—planting seeds outside right where you want them to grow. Flowers like sunflowers and nasturtiums are almost always direct-seeded because they come up so quickly and reliably from seeds you sow that there's no need to transplant seedlings into your garden that were started indoors.
Dividing: You can make two or more plants from one by dividing it, or breaking it into several pieces. Dividing is frequently recommended for certain perennials (see entry entitled "perennial"), like hostas, that have grown too large for their site; if you just want more plants to grow yourself or to share, you can divide almost any perennial that has grown large enough and developed sufficient roots to sustain several plants. "The key to dividing successfully is to make sure that each piece has some top growth and some roots," advises Scott Stiles, horticulturist at Raintree Nursery in Morton, Washington. "And the best time to do it is when it will put the least amount of stress on the plant—that, generally, is when the plant is dormant," Stiles adds.
"Double" flowers: It's all in the petals. Single flowers are like daisies—they have one row of petals around the blossom's center. Double flowers have a second (in some cases third, fourth or more) row of petals completely overlapping the first row; if the secondary petals don't overlap the first layer completely, the flower is called "semi-double."
Foliage: This is simply a way of referring to a plant's leaves. And when we talk about foliage plants, we mean plants that are grown primarily for the appearance of their leaves, like coleus or dusty miller.
Genus/species: Back in the 1700s, a Swedish botanist named Linnaeus devised a system of classifying plants using Latin names so that scientists all over the world could communicate with each other without the confusion caused by using common names that vary from place to place. Today's gardeners benefit from that same system, because when you get information about a plant using its botanical name—which is its genus and species names—you can be sure you're talking about the the exact plant you want. You can think of a plant's genus as its family—actually, in scientific taxonomy family is a broader classification than genus, but for the purposes of our explanation the concept of the genus as the family is very sensible.
So, for example, lilies belong to the genus Lilium, and within that genus there are thousands of relatives called species, like Lilium tigrinum (commonly known as the Tiger lily) and Lilium longiflorum (sometimes called the Trumpet lily). They are all lilies, but they differ somewhat in color, height of the plant, etc. Plants that belong to the same genus will have many similar characteristics, but those in the same species will have even more in common. Within each species there can be many cultivars, or what we call varieties (see entry on "cultivars" above); plants of the same variety will have virtually identical traits.
Grafting: The process of splicing parts of two or more plants together to make one plant is known as grafting. The reasons for making these botanical Frankensteins is to get desirable characteristics from each of the original plants into the resulting plant. Many of the most beautiful roses, for instance, have roots that are susceptible to diseases or cannot survive cold winters, but gardeners can still grow those roses because nurseries graft the attractive tops of the bushes onto more durable roots. And you don't need to be a mad scientist to do this yourself—the techniques are simple, you don't need special tools to do it and if you choose compatible plants the prospects for success are very high.
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.