ID MGH Glossary (edited for length)

Idaho Master Gardener Program Handbook Glossary. 10th Edition. external arrow

Abscission
The dropping of leaves, flowers, or fruit by a plant. Can result from natural growth processes (e.g., fruit ripening) or from external factors such as temperature or chemicals.
Absorption
The intake of water and other materials through root or leaf cells.
Adventitious bud
A bud that develops in locations where buds usually do not occur. An example would be buds found on root pieces used for propagation; roots do not have buds.
Adventitious root
A root that forms at any place on the plant other than the primary root system.
Aeration
The practice involving removal of cores or turf plugs and soil with the purpose of reducing compaction and improving air flow.
Aerobic
Active in the presence of free oxygen.
Alkaline soil
Soil with pH above 7 on a pH scale of 1 to 14. The higher the reading, the more alkaline the soil. (See also pH.)
Ammonium
A plant-available form of nitrogen contained in many fertilizers and generated in the soil by the breakdown of organic matter.
Anatomy
The study of plant structure.
Angiosperm
Flowering plants. Plants that have a highly evolved reproductive system. Seeds enclosed in an ovary such as a fruit, grain, or pod.
Annual
Plants that grow, mature, flower, produce seed, and die in one season.
Anther
The pollen-bearing part of a flower's male sexual organ. The filament supports the anther; together they are referred to as the stamen.
Apex
The tip of a stem or root.
Apical dominance
The 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 meristem
Area of the plant shoot and root tips where cells actively divide to provide more cells that will expand and develop into the tissues and organs of the plant. Also called shoot meristem.
Arboretum
An area devoted to specimen plantings of trees and shrubs.
Assimilation
Building of cell matter from inorganic (minerals) and organic materials (carbohydrates and sugars).
Auxin
One 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.
Bacillus thuringiensis
A bacterium used as a biological control agent for many insects pests.
Bacterium
A single-celled, microscopic organism having a cell wall but no chlorophyll. Reproduces by cell division.
Balled and burlapped
A plant dug with soil. The root ball is enclosed with burlap or a synthetic material.
Band
To apply a pesticide or fertilizer in a strip over or along each crop row.
Bare-root
A plant with little or no soil around its roots; deciduous plants and small evergreens are commonly sold bare-root.
Basal
(1) At or near the base of a branch or trunk. (2) At or near a plant's crown.
Berry
The fleshy fruit of cane fruits, bush fruits, and strawberries.
Biennial
Plants that take two years, or a part of two years, to complete their life cycle.
Biological insect control
The use of beneficial organisms to control pest insect populations.
Blade
The flat thin part of a leaf.
Bolting
Producing seed or flowering prematurely, usually due to heat. For example, cool-weather crops such as lettuce bolt during summer; leaf crops are discouraged from bolting by removal of flower heads. (See also Deadhead.)
Bonsai
One of the fine arts of horticulture; growing carefully trained, dwarfed plants in containers selected to harmonize with the plants. Branches are pruned and roots trimmed to create the desired effect.
Botany
The science that studies all phases of plant life and growth.
Branch
A subsidiary stem arising from a plant's main stem or from another branch.
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 evergreen
A non-needled evergreen.
Bud
A small protuberance on a stem or branch, sometimes enclosed in protective scales, containing an undeveloped shoot, leaf, or flower.
Budding
A method of asexual plant propagation that unites one bud (attached to a small piece of bark) from the scion to the rootstock.
Bud union
The suture line where a bud or scion was grafted to a stock. Sometimes called a graft union.
Bulb
A below ground stem (for example, in tulip) that is surrounded by fleshy scale-like leaves that contain stored food.
Calcium carbonate
A compound found in limestone, ashes, bones, and shells; the primary component of lime.
Callus
Tissue that forms over the wounds on plants.
Calyx
The entire set of sepals on a flower.
Cambium
A layer of meristematic tissue that produces new phloem on the outside, new xylem on the inside, and is the origin of all secondary growth in plants. The cambium layer forms the annual ring in wood.
Capillary action
The force 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.
Cation
Positively charged ion. Plant nutrient examples include calcium and potassium. (See also Anion.)
Cation exchange capacity (CEC)
A soil's capacity to hold cations as a storehouse of reserve nutrients.
Cell
A structural, functional unit of a plant.
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.
Chelate
A complex organic substance that holds micronutrients, usually iron, in a form available for absorption by plants.
Chlorophyll
The green pigment in plants responsible for trapping light energy for photosynthesis.
Chloroplast
A specialized component of certain cells. Contains chlorophyll and is responsible for photosynthesis.
Chlorosis
Yellowing or whitening of normally green tissue.
Clay
The smallest type of soil particle (less than 0.002 mm in diameter).
Climber
A 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.
Clone
A 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 frame
A plastic-, glass-, or Plexiglas-covered frame or box that relies on sunlight as a source of heat to warm the growing environment for tender plants.
Companion planting
The practice of growing two or more types of plants in combination to discourage disease and insect pests.
Complete fertilizer
A fertilizer that contains all three macronutrients (N, P, K).
Compost
The 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 also Humus.)
Conifer
A cone-bearing tree or shrub, usually evergreen. Pine, spruce, fir, cedar, yew, and juniper are examples.
Cork cambium
On woody plants, the layer of cells that produces bark, or cork, located just below the bark layers.
Corm
A below ground stem that is swollen (for example, in crocus).
Corolla
Part of a flower; all of the petals together.
Cortex cells
Found beneath the epidermis, these cells help move water from the epidermis and are active in food storage.
Cotyledon
A seed leaf, the first leaf from a sprouting seed. Monocots have one cotyledon, dicots have two.
Cover crop
(1) A crop planted to protect the soil from erosion. (2) A crop planted to improve soil structure or organic matter content.
Crop rotation
The practice of growing different types of crops in succession on the same land chiefly to preserve the productive capacity of the soil by easing insect, disease, and weed problems.
Cross-pollination
The fertilization of an ovary on one plant with pollen from another plant, producing an offspring with a genetic makeup distinctly different from that of either parent. (See also Pollenizer.)
Cuticle
(1) A waxy layer on the epidermis on a leaf. (2) The outer layer of an insect's body.
Cutting
One of several forms of asexual propagation.
Damping off
Stem rot near the soil surface leading to either failed seed emergence or to the plant's falling over after emergence.
Day-neutral plant
A cultivar or species capable of flowering without regard to day length. (See also Short-day plant, Long-day plant.)
Deadhead
To remove individual, spent flowers from a plant for the purpose of preventing senescence and prolonging blooming. For effective results, the ovary behind the flower must be removed as well.
Deciduous
A plant that sheds all of its leaves annually.
Decomposers
The microorganisms and invertebrates that accomplish composting.
Determinate
A plant growth habit in which stems stop growing at a certain height and produce a flower cluster at the tip. Determinate tomatoes, for example, are short, early fruiting, have concentrated fruit set, and may not require staking.
Diatomaceous earth
The fossilized remains of diatoms (a type of tiny algae) used to kill insect pests, snails, and slugs.
Dicotyledon
Plants with two seed leaves. Also referred to as dicot.
Differentiation
A change in composition, structure, and function of cells and tissues during growth.
Dioecious
Plants that have male and female flowers occurring on separate plants (e.g., holly).
Disbud
The selective removal of some flower buds so remaining buds receive more of the plant's energy and produce larger, showier flowers. Roses, chrysanthemums, and camellias often are disbudded.
Division
The breaking or cutting apart of a plant's crown for the purpose of producing additional plants, all genetically identical to the parent plant.
DNA
Deoxyribonucleic acid is the genetic information that dictates all cellular processes. DNA is organized into chromosomes and is responsible for all characteristics of the plant.
Dormancy
The annual period when a plant's growth processes greatly slow down.
Dormant
Resting or not growing. A deciduous tree is dormant in the winter.
Dormant bud
A bud formed during a growing season that remains at rest during the following winter or dry season. If it does not expand during the following growing season, it is termed latent.
Double, semidouble
A flower with more than the normal number of petals, sepals, bracts, or florets.
Dripline
An imaginary line on the ground directly beneath the outermost tips of a plant's foliage. Rain tends to drip from leaves onto this line.
Drip zone
The area from the trunk of a tree or shrub to the edge of its canopy. Most, but not all, of a plant's feeder roots are located within this area.
Dwarfed
Restricted plant size without loss of health and vigor.
Emasculate
To remove a flower's anthers.
Embryo
The tiny plant that is formed inside a seed during fertilization. It has two growing points, the radicle (a tiny root) and the plumule (a tiny shoot).
Embryo dormancy
Common in seed of woody perennial plants. A physiological condition in the embryo that prevents it from growing. This type of dormancy can be overcome by stratification.
Endosperm
The food-storage area in a seed that feeds the embryo.
Enzyme
A biological catalyst that aids in conversion of food and other chemical structures from one form to another.
Epidermis (leaf)
The outer cell layers on the top and bottom of the leaf.
Epidermis (root)
The cells that protect the root surface. The epidermis contains the root hairs and is responsible for the absorption of water and minerals dissolved in water.
Epidermis (stem)
In non-woody plants, the outer single layer of surface cells that protects the stem. As in leaves, this layer is usually cutinized, or waxy, and on young stems it has stomata.
Evergreen
A plant that never loses all its foliage at the same time.
Exotic
Non-native
Fallow
To keep land unplanted during one or more growing seasons.
Feeder roots
Fine roots and root branches with a large absorbing area (root hairs). Responsible for taking up the majority of a plant's water and nutrients from the soil.
Fertility (soil)
The presence of minerals necessary for plant life.
Fertilization
(1) The fusion of male and female germ cells following pollination. (2) The addition of plant nutrients to the environment around a plant.
Fertilizer
Any substance added to the soil (or sprayed on plants) to supply those elements required in plant nutrition.
Fertilizer analysis
The amount of nitrogen, phosphorus (as P2O5), and potassium (as K2O) in a fertilizer expressed as a percentage of total fertilizer weight. Nitrogen (N) is always listed first, phosphorus (P) second, and potassium (K) third.
Fibrous root
A root system that branches in all directions, often directly from the plant's crown, rather than branching in a hierarchical fashion from a central root. (See also Taproot.)
Filament
The stalk supporting a flower's anthers.
Flower bud
A type of bud that produces one or more flowers.
Foliar fertilization/feeding
Fertilization of a plant by applying diluted soluble fertilizer, such as fish emulsion or kelp, directly to the leaves.
Fruit
The enlarged ovary that develops after fertilization occurs.
Fungus
A plant organism that lacks chlorophyll, reproduces via spores, and usually has filamentous growth. Examples are molds, yeasts, and mushrooms.
Gall
A growth on plant stems or leaves caused by abnormal cell growth stimulated by the feeding of some insects (e.g., aphids) or by viral, fungal, or bacterial infection or genetic abnormality.
Genus
A subdivision of family in the classification of plants. Plants of the same genus share similarities mostly in flower characteristics and genetics. Plants in one genus usually cannot breed with plants of another genus.
Genetically modified
A plant or animal that has had genetic material introduced to its genome from other organisms through artificial means.
Geotropism
The turning or curving of a plant's parts in response to gravity. A root growing downward is an example. Geotropism is controlled largely by the hormone auxin.
Germination
The processes that begin after planting a seed that lead to the growth of a new plant.
Girdling
The damaging, cutting, removing, or clamping of cambium all the way around a trunk or branch. Sometimes, girdling is done deliberately to kill an unwanted tree, but often it results from feeding by insects or rodents. Wires and ties used to support a tree can cause girdling, as can string trimmers.
Grafting
A method of asexual plant propagation that joins plant parts so they will grow as one plant.
Groundcover
Plants used for holding soil, controlling weeds, and providing leaf texture.
Growing season
The period between the beginning of growth in the spring and the cessation of growth in the fall.
Growth regulator
A compound applied to a plant to alter its growth in a specific way. May be a natural or synthetic substance. (See also Hormone.)
Guard cells
Cells on either side of each stoma. They swell to open the stoma and shrink to close it.
Gymnosperm
Plants that have seed not enclosed in an ovary (e.g., conifers).
Hardening off
(1) The process of gradually exposing seedlings started indoors to outdoor conditions before transplanting. (2) The process of gradual preparation for winter weather.
Hardpan
An impervious layer of soil or rock that prevents root growth and downward drainage of water.
Hardy
Frost or freeze tolerant. In horticulture, this term does not mean tough or resistant to insect pests or disease.
Head
(1) To cut off part of a shoot or limb rather than remove it completely at a branch point. (2) The part of a tree from which the main scaffold limbs originate.
Heartwood
The central cylinder, often dark colored, of xylem tissue in a woody stem.
Herbaceous
A soft, pliable, usually barkless shoot or plant. Distinct from stiff, woody growth.
Herbaceous perennial
A plant that dies back in the winter and regrows from the crown in spring.
Herbicide
A chemical used to kill undesirable plants.
Hormone
A naturally occurring compound that alters plant growth in a specific manner. (See also Growth regulator.)
Horticultural oil
An oil made from petroleum products, vegetable oil, or fish oil used to control insect pests and diseases. Oils work by smothering insects and their eggs and by protectively coating buds against pathogen entry.
Horticulture
The science of growing fruits, vegetables, flowers, and other ornamental plants.
Humus
The end product of decomposing animal or vegetable matter. (See also Compost.)
Hybrid
The results of a cross between two different species or well-marked varieties within a species. Hybrids grown in a garden situation will not breed true to form from their own seed.
Hydroponics
A method of growing plants without soil. Plants usually are suspended in water or polymers, and plant nutrients are supplied in dilute solutions.
Hypocotyl
The seedling stem that develops below the cotyledons.
Imbibition
The portion of the germination process that involves the absorption of water, causing the seed to swell, and that triggers cell enzyme activity, growth, and the bursting of the seed coat.
Incomplete flower
A type of flower that lacks one or more of the four parts: pistil, stamen, sepals, or petals.
Indeterminate
A plant growth habit in which stems keep growing in length indefinitely. For example, indeterminate tomatoes are tall, late-fruiting, and require staking for improved yield.
Inorganic
Being or composed of matter other than plant or animal.
Insecticidal soap
A specially formulated soap that is only minimally damaging to plants, but kills insects. Usually works by causing an insect's outer shell to crack, resulting in its interior organs drying out.
Integrated pest management
A method of managing pests that combines cultural, biological, mechanical, and chemical controls, while taking into account the impact of control methods on the environment.
Intercalary meristem
Found mostly in monocots, these cells divide and provide the growth of the leaf from the base of the plant.
Internode
The area of the stem that is between the nodes.
Invasive
Growing vigorously and out competing other plants in the same area; difficult to control.
Ion
An electrically charged particle. In soils, an ion refers to an electrically charged element or combination of elements resulting from the breaking up of an electrolyte in solution.
Joint
A node; the place on a stem where a bud, leaf, or branch forms.
Key, dichotomous
A tool for plant or animal classification and identification. Consists of a series of paired statements that move from general to specific descriptions.
Lateral bud
An undeveloped shoot or flower that is found at the node. Also called the axillary bud.
Lateral meristem
Cylinders of actively dividing cells that start just below the apical meristem and are located up and down the plant. Also called the vascular cambium.
Layering
A method of stimulating adventitious roots to form on a stem. There are two primary methods of layering. In ground layering, a low growing branch is bent to the ground and covered by soil. In air layering, moist rooting medium is wrapped around a node on an aboveground stem.
Leaching
Movement of water and soluble nutrients down through the soil profile.
Leader
A developing stem or trunk that is longer and more vigorous than the laterals. (See also Central leader.)
Leaf curl
Rolling and curling of leaves.
Leaflet
A single division of a compound leaf.
Leaf scar
A visible, thickened crescent or line on a stem where a leaf was attached.
Lime
A rock powder consisting primarily of calcium carbonate. Used to raise soil pH (decrease acidity).
Loam
A soil with roughly equal proportions of sand, silt, and clay particles.
Lodge
To fall over, usually due to rain or wind. Corn and tall grasses are examples of plants susceptible to lodging.
Long-day plant
A plant requiring more than 12 hours of continuous daylight to stimulate a change in growth, e.g., a shift from the vegetative to reproductive phase. (See also Short-day plant, Day-neutral plant.)
Macronutrient
Collectively, primary and secondary nutrients.
Microclimate
Climate affected by landscape, structures, or other unique factors in a particular immediate area.
Micronutrient
A nutrient, usually in the parts per million range, used by plants in small amounts, less than 1 part per million (boron, chlorine, copper, iron, manganese, molybdenum, zinc, and nickel).
Monocotyledon
Plants with one seed leaf. Also referred to as monocot.
Monoecious
Plants that have imperfect flowers (male and female) occurring on the same plant (e.g., corn).
Mulch
Any material placed on the soil surface to conserve soil moisture, moderate soil temperature, and/or control weeds. Wood chips, bark chips, and shredded leaves are mulches that eventually add organic matter to the soil; inorganic materials such as rocks are also used.
Mutation
A genetic change within an organism or its parts that changes its characteristics. Also called a bud sport or sport.
Mycorrhizae
Beneficial fungi that infect plant roots and increase their ability to take up nutrients from the soil.
Nematode
Microscopic roundworms that live in soil and living tissue, as well as water, and survive as eggs or cysts.
Nitrate
A plant-available form of nitrogen contained in many fertilizers and generated in the soil by the breakdown of organic matter. Excess nitrate in soil can leach to groundwater. (See also Nitrogen cycle.)
Nitrifier
A microbe that converts ammonium to nitrate.
Nitrogen
A primary plant nutrient, especially important for foliage and stem growth.
Nitrogen cycle
The sequence of biochemical changes undergone by nitrogen as it moves from living organisms, to decomposing organic matter, to inorganic forms, and back to living organisms.
Nitrogen fixation
The conversion of atmospheric nitrogen into plant-available forms by rhizobia bacteria living on the roots of legumes.
Node
The area of the stem that bears a leaf or a branch. The joint of a stem.
Noxious weed
(1) Weeds that have been declared by law to be a species having the potential to cause injury to public health, crops, livestock, land, or other property. (2) A very invasive, difficult to control plant.
N-P-K
Acronym for the three major plant nutrients contained in manure, compost, and fertilizers. N stand for nitrogen, P for phosphorus, and K for potassium.
Nutrient
Any substance, especially in the soil, that is essential for and promotes plant growth. (See also Macronutrient, Micronutrient.)
Nymph
The immature stage of an insect that undergoes simple metamorphosis. Usually similar in form to the adult.
Open-pollinated seed
Seed produced from natural, random pollination so that the resulting plants are varied.
Organic
(1) Relating to, derived from, or involving the use of food produced with the use of feed or fertilizer of plant or animal origin without employment of synthetically formulated fertilizers, growth stimulants, antibiotics, or pesticides. (2) Being or composed of plant or animal matter. (3) A labeling term that refers to an agricultural product produced in accordance with government standards.
Organism
A living being.
Ornamental plant
A plant grown for beautification, screening, accent, specimen, color, or other aesthetic reasons.
Osmosis
Passage of materials through a membrane from an area of high concentration to an area of lower concentration.
Outer seed coat
The protective outer shell for the seed.
Ovary
The part of a flower containing ovules that will develop into seeds upon fertilization. Along with the style and stigma, it makes up the pistil (female sexual organ).
Ovule
Within the ovary, a tissue/structure that will develop into a seed after fertilization.
Parasite
An organism that lives in or on another organism (host) and derives its food from the latter.
Pathogen
Any organism that can cause a disease.
Perennial
A plant that lives more than two years and produces new foliage, flowers, and seeds each growing season.
Perfect flower
A type of flower with both stamens and pistils.
Permeability
The rate at which water moves through a soil.
Petals
Part of a flower, the floral structure inside the sepals, often brightly colored.
Petiole
The stalk of a leaf.
pH
The acidity or alkalinity of a solution on a scale of 0-14, with a value of 7 signifying neutral, values below 7 signifying acidic, and values above 7 signifying alkaline. Relates to the concentrations of hydrogen (H+) ions in the soil. pH values are logarithmic.
Phloem
The principle nutrient-conducting structure of vascular plants.
Phosphorus (P)
A primary plant nutrient, especially important for flower production. In fertilizer, usually expressed as phosphate.
Photoperiod
The amount of time a plant is exposed to light.
Photosynthesis
Formation of carbohydrates from carbon dioxide and a source of hydrogen (as water) in the chlorophyll-containing tissues of plants exposed to light.
Phototropism
The phenomenon of plants growing toward the direction of a light source.
Physiology
The study dealing with the functioning of plants, their mechanisms of response, and their physical and biochemical processes.
Pinch
To remove a growing tip from a stem, thus causing axillary shoots or buds to develop. (See also Deadhead, Shear.)
Pistil
The female component of the flower. It is in the center of the flower and has three parts, the stigma, the style, and the ovary.
Plant disease
Any lasting change in a plant's normal structure or function that deviates from its healthy state.
Pollen
A plant's male sex cells, which are held on the anther for transfer to a stigma by insects, wind, or some other mechanism.
Pollination
The first step in fertilization; the transfer of pollen from anther to a stigma.
Pollinator
An agent such as an insect that transfers pollen from a male anther to a female stigma.
Pome fruit
A fruit having a core, such as an apple, pear, or quince.
Postemergent
A product applied after crops or weeds emerge from the soil.
Potassium (K)
A primary plant nutrient, especially important for developing strong roots and stems. In fertilizers, usually expressed as potash.
Powdery mildew
Fine, white to gray, powdery fungal coating on leaves, stems, and flowers.
Preemergent
A product applied before crops or weeds emerge from the soil.
Primary nutrient
A nutrient required by plants in a relatively large amount (nitrogen, phosphorus, and potassium).
Propagate
To start new plants by seeding, budding, grafting, dividing, etc.
Prune
To remove plant parts to improve a plant's health, appearance, or productivity.
Quarantine
A regulation forbidding sale or shipment of plants or plant parts, usually to prevent disease, insect, nematode, or weed invasion in an area.
Quick-release fertilizer
A fertilizer that contains nutrients in plant-available forms such as ammonium and nitrate. Fertilizer is readily soluble in water.
Radicle
The root portion of an embryo.
Relative humidity
The ratio of water vapor in the air to the amount of water the air could hold at the current temperature and pressure.
Rhizome
A stem that forms the main axis of the plant. Can form at or just below the ground (for example, in bearded iris).
Rhizosphere
The thin layer of soil immediately surrounding plant roots.
Root bound
A condition in which a plant's roots have completely filled its container. Typically, the roots begin to encircle the pot's outer edge. Further growth is prevented until the plant is removed from the container.
Root cap
The cells that protect the root tip as it pushes through the soil. These cells slough off and are replaced by others as roots grow downward.
Root hair
Thin hair-like structure that grows from the epidermis of the region of maturation of the root. This structure absorbs water and nutrients from the soil.
Root meristem
A type of apical meristem located at the tips of roots. Provides for elongation of the roots and produces the cells that will become the epidermis, cortex, xylem, cambium, and phloem of the mature root.
Rotation
The practice of growing different plants in different locations each year to prevent the buildup of soil borne diseases and insect pests.
Sand
The coarsest type of soil particle.
Sanitation
The removal and disposal of infected plant parts; decontamination of tools, equipment, hands, etc.
Scarification
Artificial methods to soften the seed coat including scratching or rupturing the seed coat with sandpaper, nicking it with a knife, or degrading it with concentrated acid.
Secondary nutrient
A nutrient needed by plants in a moderate amount: calcium, magnesium, and sulfur.
Seed
Matured ovule that occurs as, or in, mature fruits.
Seed coat
The outer layer of a seed that provides protection for the enclosed embryo.
Seed dormancy
An adaptive feature of some plants to keep the seeds from germinating until conditions exist that favor seedling survival.
Seed scarification
Involves breaking, scratching, or softening the seed coat so that water can enter and begin the germination process.
Self-pollination
Pollination that can occur when the anther and stigma are in the same flower or if the anther and stigma are in different flowers on the same plant or in different flowers on different plants of the same species, variety, or cultivar.
Sepal
The outer covering of the flower when it is in the bud stage. They are leaflike in structure and usually green; however they can be colored and look like petals, as in tulips. They may fold back as in roses or remain upright as with carnations. Together, all the sepals form the calyx.
Shear
To cut back a plant (as opposed to selective pruning or deadheading). Often used to regenerate plants with many small stems, where deadheading would be too time consuming.
Shoot
One season's branch growth. The bud scale scars (ring of small ridges) on a branch mark the start of a season's growth.
Shoot meristem
The apex of a shoot where cells actively divide to provide more cells that will expand and develop into the tissues and organs of the plant. Also called apical meristem.
Short-day plant
A plant requiring more than 12 hours of continuous darkness to stimulate a change in growth, e.g., a shift from the vegetative to reproductive phase. (See also Long-day plant, Day-neutral plant.)
Shot-hole
Roughly circular holes in leaves resulting from the dropping out of the central dead areas of spots.
Shoulder ring
One of the ridges around the base of a branch where it attaches to a trunk or to another branch.
Side-dress
To apply fertilizer to the soil around a growing plant.
Silt
A type of soil particle that is intermediate in size between sand and clay.
Slow-release fertilizer
A fertilizer material that must be converted into a plant-available form by soil microorganisms.
Soil
A natural, biologically active mixture of weathered rock fragments and organic matter at the earth's surface.
Soil salinity
A measure of the total soluble salts in a soil.
Soil structure
The arrangement of soil particles or their aggregates.
Soil texture
How coarse or fine a soil is. Texture is determined by the proportions of sand, silt, and clay in the soil.
Soluble salt
A mineral (salt) often remaining in soil from irrigation water, fertilizer, compost, or manure applications.
Species
A group of individual plants interbreeding freely and having many (or all) characteristics in common.
Specimen
An individual plant with outstanding characteristics (leaves, flowers, or bark), generally used as a focal point in a landscape.
Spore
(1) The reproductive body of a fungus or other lower plant, containing one or more cells. (2) A bacterial cell modified to survive in an adverse environment. (3) The reproductive unit of ferns.
Stamen
The male, pollen-producing part of a flower consisting of the anther and its supporting filament.
Stem cutting
A section of a stem prepared for vegetative propagation; forms adventitious roots on the stem.
Sterile
(1) Material that is free of disease organisms (pathogens), as in potting medium. (2) A plant that is unable to produce viable seeds.
Stigma
The receptive surface on a pistil that receives pollen.
Stolon
A horizontal stem, either fleshy or semiwoody, that runs along the soil surface.
Stoma, stomata
An opening into a leaf that is formed by specialized epidermal cells on the underside (and sometimes upper sides) of the leaf.
Strain
A variation within a cultivar or variety.
Stratification
Chilling seed under moist conditions. This method mimics the conditions a seed might endure after it falls to the ground in the autumn and goes through a cold winter on the ground.
Style
On a pistil, a tube connecting the stigma and the ovary.
Sunscald
Winter or summer injury to the trunk of a woody plant caused by hot sun and fluctuating temperatures. Typically, sunscalded bark splits and separates from the trunk.
Systemic pesticide
A pesticide that moves throughout a target organism's system to cause its death.
Taproot
A type of root system that grows straight down with few lateral roots.
Taxonomy
Classification or naming of plants or animals.
Tender
Not tolerant of frost and cold temperatures. In horticulture, tender does not mean weak or susceptible to insect pests or diseases.
Tendril
A slender projection used for clinging, usually a modified leaf. Easily seen on vines such as grapes and clematis.
Terminal
The tip (apex), usually of a branch or shoot.
Terminal bud
The bud that is found at the tip of shoots.
Thatch
A brown, fibrous, spongy layer located between the soil and the grass blades.
Thin
(1) To remove an entire shoot or limb where it originates. (2) To selectively remove plants or fruits to allow remaining plants or fruits to develop.
Tolerant
A plant that will produce a normal yield even if infested by a disease or insect pest. (See also Immune, Resistant.)
Top-dressing
The practice of spreading a thin layer (1/4 inch) of soil, compost, humus, or a sand and peat mix over the turf or soil.
Trace element
See micronutrient.
Transpiration
The loss of water through the leaf stomata. The transpired water comes from the photosynthetic process and also from water in the cells.
Tree
A woody plant that typically grows more than 12 feet tall and has only one main stem or trunk.
Tropism
The tendency of a plant part to turn in response to an external stimulus, either by attraction or repulsion, as a leaf turns toward light. (See also Geotropism, Phototropism.)
Trunk
The main stem of a tree. Also called a bole.
Tuber
A below ground stem used for food storage (e. g., potato).
Tuberous root
An underground storage organ made up of root tissue. Sprouts only from the point at which it was attached to the stem of the parent plant. Dahlias are an example.
Tuberous stem
A below ground stem consisting of a swollen hypocotyl, lower epicotyl, and upper primary root (for example, in tuberous begonias).
Turgor
Cellular water pressure; responsible for keeping cells firm.
Twig
A young stem (1-year-old or less) that is in the dormant winter stage (has no leaves).
USDA zones
Areas derived by the USDA that indicate average-low winter temperatures. Used as a plant hardiness indicator. Other plant hardiness zones developed by other entities use different numbering systems.
Variety
In the wild, a plant growing within a species that is different in some particular characteristic from other members of that species. When grown from seed, a variety will maintain all of its particular characteristics. Also called a botanical variety.
Vascular system
The internal structure of the stem that transports water, minerals, and sugars throughout the plant.
Vascular tissue
Water, nutrient, and photosynthate-conducting tissue. (See also Xylem, Phloem.)
Vegetative propagation
The increase of plants by asexual means using vegetative parts. Normally results in a population of identical individuals. Can occur by either natural means (e.g., bulblets, cormels, offsets, plantlets, or runners) or artificial means (e.g., cuttings, division, budding, grafting, or layering).
Virus
An infectious agent composed of DNA or RNA, too small to see with a compound microscope. Multiplies only in living cells.
Weed-and-feed
A combination fertilizer and herbicide sometimes used on lawns.
Wilt
Drooping and drying plant parts due to interference with the plant's ability to take up water and nutrients.
Wilting point
Point at which the water content within plant cells is low enough that cellular turgor is lost and the plant wilts.
Woody perennial
A plant that goes dormant in winter and begins growth in spring from aboveground stems.
Xeric
A plant or landscape that conserves water. Most xeric plants need minimal supplemental water after an establishment period (18 to 24 months after planting) unless there is extreme drought.
Xylem
The principal water conducting tissue of vascular plants.