Our ‘A’ to ‘Z’ of Gardening Terms

Throughout this site there are links to documents of various file types.
Please contact us if you require this information in a different format.


Browse the full glossary below or select alphabet search above.

abscisic acidA growth-inhibiting hormone.
abscissionThe dropping of leaves, flowers, or fruit by a plant. This can result from natural growth processes (e.g., fruit ripening) or from external factors such as temperature or chemicals.
abscission layerSpecialized cells, usually at the base of a leaf stalk or fruit stem, that trigger both the separation of the leaf or fruit and the development of scar tissue to protect the plant.
absorptionThe intake of water and other materials through root or leaf cells.
accumulated heat unitsThe number of hours in a growing season. Usually calculated at temperatures above 50°F, but can be calculated at other temperatures, depending on the crop. A day’s heat units (above 50°F) are calculated as:
accumulated heat unitsDaily values are then totaled for the season, with values less than zero ignored (but not deducted from the total). [formula = max temp plus minimum temp divided by 2 – 50 in degrees Farenheight]
acid soilSoil with a pH below 7 on a pH scale of 0 to 14. The lower the pH, the more acid the soil. See pH.
actinomorphic flowerA flower possessing radial symmetry. Any cut through the center divides the flower into two equal parts.
active ingredientThe chemical in a pesticide formulation that actually kills the target pest.
additiveA substance that, when added to a pesticide, reduces the surface tension between two unlike materials (e.g., spray droplets and a plant surface), thus improving adherence. Also called an adjuvant or surfactant.
adjuvantSee additive.
adventitiousGrowth not ordinarily expected, usually the result of stress or injury. A plant’s normal growth comes from meristematic tissue, but adventitious growth comes from nonmeristematic tissue.
adventitious budA bud in an unusual place on a plant, often on an internode. This may be the result of an injury. Suckers and water sprouts usually grow from adventitious buds.
adventitious rootA root in an unusual place, often where a branch contacts soil or damp material. A plant cannot be reproduced from cuttings or layering unless adventitious roots develop.
aerationMechanically loosening or puncturing soil to increase permeability to water and air.
aerial rootA root emerging above the soil level.
aerobicActive in the presence of free oxygen.
after-ripeningThe seed maturation process that must be completed before germination can occur.
aggregate fruitA group of small fruits derived from several ovaries within a single flower.
aggregationThe process by which individual particles of sand, silt and clay cluster and bind together to form soil peds.
alkaline soilSoil with a pH above 7 on a pH scale of 0 to 14. The higher the reading, the more alkaline the soil. See pH.
alkaloidA nitrogen-containing compound frequently used as a chemical defense by plants.
allelopathyThe excretion by some plants of compounds from their leaves and/or roots that inhibit the growth of other plants.
ammonium (NH4+)A plant-available form of nitrogen contained in many fertilizers and generated in the soil by the breakdown of organic matter. See nitrogen cycle.
anaerobicActive in the absence of free oxygen.
angiospermA member of a class of plants characterized by the formation of flowers and seeds in fruits.
anionA negatively charged ion. Plant nutrient examples include nitrate (NO3–), phosphate (H2PO4–), and sulfate (SO42-). See cation.
annualA plant that completes its life cycle in one growing season.
annual ringA cylinder of secondary xylem added to the wood in a single growing season.
antherThe pollen-bearing part of a flower’s male sexual organ. The filament supports the anther; together they are referred to as the stamen.
anvil prunerA pruning tool that cuts a branch between one sharpened blade and a flat, anvil-shaped piece of metal. These have a tendency to crush rather than make a smooth cut.
apexThe tip of a stem or root.
apical budA bud at the tip of a stem.
apical dominanceThe inhibition of lateral bud growth by the presence of the hormone auxin in a plant’s terminal bud. Removing the growing tip removes auxin and promotes lateral bud break and subsequent branching, usually directly below the cut.
apical meristemA region of actively dividing cells at the tip of a growing stem or root.
arboretumAn area devoted to specimen plantings of trees and shrubs.
asexual reproductionSee vegetative propagation.
aspectDirection of exposure to sunlight.
assimilationThe building of cell matter from inorganic and organic materials (carbohydrates and sugars).
attractantA material that lures pests.
autotrophic nutritionA form of nutrition in which complex food molecules are produced by photosynthesis from carbon dioxide, water, and minerals.
auxinOne of the best known and most important plant hormones. Most abundantly produced in a plant’s actively growing tips. Generally, stimulates growth by cell division in the tip region and by cell elongation lower down the shoot. Growth of lateral buds is strongly inhibited by the normal concentration of auxin in the growing tip.
available water supplySoil water that is available for plant uptake. Excludes water bound tightly to soil particles.
axilThe upper angle formed by a leaf’s stalk (petiole) and the internodes above it on a stem.
axillary budA bud that forms on an axil.
axillary bud primordiumAn immature axillary bud.
bacillus thuringiensis (Bt)Bacillus thuringiensis (Bt) is a bacterium used as a biological control agent for many insect pests.
bacteriumA single-celled microscopic organism having a cell wall but no chlorophyll. They reproduce by cell division.
balled and burlapped (B&B)A plant dug with soil. The root ball is enclosed with burlap or a synthetic material.
bandTo apply a pesticide or fertilizer in a strip over or along each crop row.
bare-root (BR)A plant with little or no soil around its roots, a common method of selling deciduous plants and small evergreens.
barkAll the tissues, collectively, formed outside the vascular cambium of a woody stem or root.
basal(1) At or near the base of a branch or trunk. (2) At or near a plant’s crown.
basal breakNew growth that develops at the base of a branch or near a plant’s crown.
beneficial insectAn insect that helps gardening efforts. May pollinate flowers, eat harmful insects or parasitize them, or break down plant material in the soil, thereby releasing nutrients. Some insects are both harmful and beneficial. For example, butterflies can be pollinators in their adult form, but destructive in their larval (caterpillar) form.
berryThe fleshy fruit of cane fruits, bush fruits, and strawberries.
biennialA plant that germinates and produces foliage and roots during its first growing season, then produces flowers and seeds and usually dies during its second growing season.
biennial bearingProducing fruit in alternate years.
biosolidsA by-product of wastewater treatment sometimes used as a fertilizer.
bladeThe flattened part of a leaf.
blanchTo exclude light from plants or parts of plants to render them white or tender. Often done to cauliflower, endive, celery, and leeks.
blightRapid, extensive discoloration, wilting, and death of plant tissue.
blotchA blot or spot (usually superficial and irregular in shape) on leaves, shoots, or fruit.
boleSee trunk.
boltingProducing seeds or flowering prematurely, usually due to heat. For example, cool-weather crops such as lettuce bolt during the summer. Leaf crops are discouraged from bolting by removal of flower heads. See deadhead.
bonsaiOne of the fine arts of gardening; growing carefully trained, dwarfed plants in containers selected to harmonize with the plants. Branches are pruned and roots trimmed to create the desired effect.
botanical insecticideAn insecticide, such as rotenone or pyrethrum, derived from a plant. Most botanicals biodegrade quickly. Most, but not all, have low toxicity to mammals.
botrytisA fungal disease promoted by cool, moist weather. Also known as gray mold or fruit rot.
bractA modified leaf, usually small, but sometimes large and brightly colored, growing at the base of a flower or on its stalk. Clearly seen on dogwoods and poinsettias.
brambleA spiny cane bush with berry fruits (e.g., raspberries and blackberries).
branchA subsidiary stem arising from a plant’s main stem or from another branch.
break(1) Any new growth coming from a bud. (2) See bud break.
broadcast(1) To sow seed by scattering it over the soil surface. (2) To apply a pesticide or fertilizer uniformly to an entire, specific area by scattering or spraying it.
broadleaf evergreenA non-needled evergreen.
BTU (British Thermal Unit)Amount of heat required to raise the temperature of 1 pound of water 1°F.
budA small protuberance on a stem or branch, sometimes enclosed in protective scales, containing an undeveloped shoot, leaf, or flower.
bud breakThe resumption of growth by a resting bud.
bud headA swollen or enlarged area where a bud was grafted to a stock.
bud scaleA modified leaf that forms a protective covering for a bud.
bud sportSee mutation.
bud unionThe suture line where a bud or scion was grafted to a stock. Sometimes called the graft union.
buddingThe grafting of a bud onto stock of a different plant. The bud is the scion.
budstickA shoot or twig used as a source of buds for budding.
bulbAn underground storage organ consisting of a thin, flattened stem surrounded by layers of fleshy, dried leaf bases. Roots are attached to the bottom. See corm, tuber, rhizome.
bulbilA small bulb-like organ that sometimes forms in place of flowers.
bulblet(1) An underground bulbil. (2) A tiny bulb produced at the base of a mother bulb.
buttress rootAn enlarged, aboveground root giving support to a tree trunk.
C:N ratioThe ratio of carbon (C) to nitrogen (N) in organic materials. Materials with a high C:N ratio (high in carbon) are good bulking agents in compost piles, while those with a low C:N ratio (high in nitrogen) are good energy sources.
calcium carbonate (CaCO3)A compound found in limestone, ashes, bones, and shells, the primary component of lime.
callusTissue that develops when cambium or other meristematic tissue is wounded.
calorieAmount of heat required to raise the temperature of 1 cubic centimeter of water 1°C.
calyxThe collective term for the sepals (the cup, usually green, between a flower and its stem).
cambiumThe living, growing layer of cells between the xylem and phloem. In woody plants, it is located just beneath the bark.
candelabrumA strong, dominant rose cane with accelerated growth that originates from a bud union and explodes with many blooms.
candleOn a pine tree, new terminal growth from which needles emerge.
caneThe externally woody, internally pithy stem of a bramble or vine.
cankerA localized lesion on a limb or trunk, usually due to disease or injury. Part of the bark or wood appears to be eaten away or is sunken.
canopy(1) The top branches and foliage of a plant. (2) The shape-producing structure of a tree or shrub.
capillary forceThe action by which water molecules bind to the surfaces of soil particles and to each other, thus holding water in fine pores against the force of gravity.
capillary waterWater held in the tiny spaces between soil particles or between plant cells.
capitulum(1) A dense, short, compact cluster of sessile flowers (stalkless and attached directly at the base), as in composite plants or clover. (2) A very dense grouping of flower buds, as in broccoli.
caroteneA orange-yellow pigment located in the chloroplasts.
caterpillarSee larva.
catfacingDisfigurement or malformation of a fruit. Fruits typically affected include tomatoes and strawberries. Although not fully understood, catfacing is thought to be caused by insects or adverse weather during fruit development.
cationA positively charged ion. Plant nutrient examples include calcium (Ca++) and potassium (K+). See anion.
cation exchange capacity (CEC)A soil’s capacity to hold cations as a storehouse of reserve nutrients.
cellThe smallest structure in a plant.
cell wallThe outer covering of a plant cell.
cellular respirationThe chemical breakdown of food substances, resulting in the release of energy.
celluloseA plant substance forming part of the cell wall.
central leader(1) A trunk or stem extending up through the axis of a tree or shrub and clearly emerging at the top. (2) A system of pruning that uses the central leader as a basic component.
cercusA thread-like or sometimes forceps-like tail near the tip of an insect’s abdomen (usually a pair). Plural: cerci.
chelateA complex organic substance that holds micronutrients, usually iron, in a form available for absorption by plants.
chlorophyllThe green pigment in plants. Responsible for trapping light energy for photosynthesis.
chloroplastA specialized component of certain cells. Contains chlorophyll and is responsible for photosynthesis.
chlorosisAn abnormal yellowing of a leaf.
chromosomeA threadlike structure within each living cell which contains the cell’s genetic material.
cladodeA flattened stem performing the function of a leaf, as in a cactus pad.
clayThe smallest type of soil particle (less than 0.002 mm in diameter).
climberA plant that climbs on its own by twining or using gripping pads, tendrils, or some other method to attach itself to a structure or another plant. Plants that must be trained to a support are properly called trailing plants, not climbers.
clocheA plastic, glass, or Plexiglas plant cover used to warm the growing environment or protect plants from frost.
cloneA plant group whose members have all been derived from a single individual through constant propagation by vegetative (asexual) means, e.g. by buds, bulbs, grafts, cuttings, or laboratory tissue culture.
cold compostingA slow composting process that involves simply building a pile and leaving it until it decomposes. This process may take several months or longer. Cold composting does not kill weed seeds or pathogens.
cold frameA plastic-, glass-, or Plexiglas-covered frame that relies on sunlight as a source of heat to warm the growing environment for tender plants.
cold hardeningThe process where plants prepare for low temperatures.
cole cropsA group of vegetables belonging to the cabbage family; plants of the genus Brassica, including cauliflower, broccoli, cabbage, turnips, and brussels sprouts.
coleopteraAn insect family made up of species having horny front wings that fit over their hindwings. Includes beetles and weevils.
collarA swollen area at the base of a branch where it connects to a trunk. Contains special tissue that prevents decay from moving downward from the branch into the trunk. See shoulder ring.
compactionPressure that squeezes soil into layers that resist root penetration and water movement. Often the result of foot or machine traffic.
companion plantingThe practice of growing two or more plants together in the hope that the combination will discourage disease and insect pests.
compatibleDifferent varieties or species that set fruit when cross-pollinated or make a successful graft union when integrated. See pollinizer.
complete flowerA flower having all of the normal flower parts.
complete metamorphosisA type of insect development in which the insect passes through the stages of egg, larva, pupa, and adult. The larva usually is different in form from the adult. See simple metamorphosis.
composite headAn inflorescence composed of many tightly packed, small, ray and disc flowers.
compostThe product created by the breakdown of organic waste under conditions manipulated by humans. Used to improve both the texture and fertility of garden soil. See humus.
compound budMore than one bud on the same side of a node. Usually, unless growth is extremely vigorous, only one of the buds develops, and its branch may have a very sharp angle of attachment. If it is removed, a wider angled shoot usually is formed from the secondary (accessory) bud. Ashes and walnuts are examples of plants that typically have compound buds.
compound leafA leaf in which the blade is divided into separate leaflets.
coniferA cone-bearing tree or shrub, usually evergreen. Pine, spruce, fir, cedar, yew, and juniper are examples.
conkA fungal fruiting structure (e.g., shelf or bracket fungi) formed on rotting woody plants.
contact pesticideA pesticide that kills on contact.
cordon(1) A method of espaliering fruit trees, vines, etc. to horizontal, vertical, or angles wire or wooden supports so maximum surface is exposed to the sun, resulting in maximum fruit production. (2) A branch attached to such a support.
corkThe protective outer tissue of bark.
cork cambiumA layer of cells in the cambium that gives rise to cork.
cormAn underground storage organ consisting of the swollen base of a stem with roots attached to the underside. Crocus and gladiolus are examples of plants that form corms. See bulb, tuber, rhizome.
cormelA small, underdeveloped corm, usually attached to a larger corm. See bulbil and bulblet.
cornicleA short, blunt horn or tube (sometimes button-like) on the top and near the end of an aphid’s abdomen. Emits a waxy liquid that helps protect against enemies.
corollaCollectively, all of a flower’s petals.
cortexCells that make up the primary tissue of roots or stems.
corymbA usually flat-topped flower cluster in which the individual flower stalks grow upward from various points on the main stem to approximately the same level.
cotyledonA seed leaf; the first leaf from a sprouting seed. Monocots have one cotyledon; dicots have two.
cover cropA crop dug into the soil to return valuable organic matter and nitrogen to the soil. Legumes such as clover, cowpeas, and vetch are common cover crops. Also called green manure.
cross-pollinationThe fertilization of an ovary on one plant with pollen from another plant, producing an offspring with a genetic makeup distinct from that of either parent. See pollenizer.
crotch angleThe angle formed between a trunk and a main scaffold limb. The strongest angle is 45° to 60°.
crown(1) Collectively, the branches and foliage of a tree or shrub. (2) The thickened base of a plant’s stem or trunk to which the roots are attached.
cultivarA specially cultivated variety of a plant that most often is reproduced vegetatively. For example, ‘Transparent’ is a cultivar of apple. See variety.
cuticle(1) A relatively impermeable surface layer on the epidermis of leaves and fruits. (2) The outer layer of an insect’s body.
cutin(1) A waxy substance on plant surfaces that tends to make the surface waterproof and can protect leaves from dehydration and disease. (2) A waxy substance on an insect’s cuticle that protects the insect from dehydration.
cuttingA piece of leaf, stem, or root removed from a plant and prompted to develop into a new plant that is genetically identical to the parent plant.
cymeA flower stalk on which the florets start blooming from the top of the stem and progress toward the bottom.
cystThe swollen, egg-containing female body of certain nematodes. Can be seen on the outside of infected roots.
cytokininA plant hormone primarily stimulating cell division.
cytoplasmThe living protoplasm of a cell, excluding the nucleus.
cytoplasmic membraneThe membrane enclosing the cytoplasm.