Natural - occurring in nature.
Nematodes - microscopic, elongated, cylindrical, parasitic worms that live in water and soil.
Node - the location on a stem where buds form.
Nodules - swellings on the roots of legumes where nitrogen-fixing bacteria live.
Nonselective pesticide - a poison that kills a wide variety of pest species.
Nutrients - substances a plant takes in and uses as food for growth and development.
Nymph - a stage or series of size changes between egg and adult in the life cycle of insects that go through incomplete or simple metamorphosis.
Organic - of plant or animal origin.
Organism - microscopic bacteria, fungi, bacteria, earthworms, and insects
Ovary - the swollen bottom part of the pistil that contains the ovules or immature seeds.
Overwinter - depends on the context, technically "to pass, spend, or survive the winter" but in gardening terms could also mean The process of bringing frost-tender plants through the winter by moving them indoors.
Oxygen, O2, - a colorless, tasteless, odorless gas that is 1/5 of the volume of the atmosphere.
Parasitic - an organism that lives on or in another living organism (the host) and obtains nutrition from the host.
Parthenocarpy - is the natural or artificially induced production of fruit without fertilization of ovules. The fruit is therefore seedless. Stenospermocarpy may also produce apparently seedless fruit, but the seeds are actually aborted while still small. Parthenocarpy (or stenospermocarpy) occasionally occurs as a mutation in nature, but if it affects every flower, then the plant can no longer sexually reproduce but might be able to propagate by vegetative means.
Pathogen - a disease-causing organism.
Pelletized - the coating and forming into pellets of very small seed so they are easier to handle.
Penetration - the point at which a pathogen enters a host.
Perennial ryegrass - a cool-season turfgrass with seeds that germinate quickly. The cultural requirements are similar to those of Kentucky bluegrass; however, it is not quite as hardy or disease resistant as bluegrasses.
Perennials - plants that do not die after flowering, but live from year to year.
Perlite - an amorphous volcanic glass that has a relatively high water content, used as a plant growth medium. When used as an amendment it helps prevent water loss and soil compaction.
Petals - a whorl of structures that surround the inner reproductive organs of a flower. Together they are called the corolla. They often attract insects by color or nectar, facilitating pollination.
pH - The acidity or alkalinity of a material. (see soil pH
Pheromone - a chemical substance that convey information to and produce specific responses in certain animals.
Phloem - the part of the vascular system that moves food through the plant.
Photoperiodism - responses of plants to the relative lengths of light and dark cycles.
Photosynthesis - the production of sugar from carbon dioxide and water in the presence of chlorophyll, activated by light energy and releasing oxygen.
Phototropism - the bending of a plant toward the direction of more intense light.
Pinch - To remove the spent bloom or the growth tip of a plant by pinching it off with the fingers. It encourages rebloom and compact growth, breaking off the terminal growing point of a plant to encourage axillary buds to grow.
Pith - the soft, spongy central cylinder of parenchymatous tissue in the stems of dicotyledonous plants
Pistil - the female part of the flower, consisting of one or more carpels and enclosed ovules.
Pollard - a tree cut back to the trunk to make a dense cluster of branches and foliage.
Pollen - the microspores that carry the male gametophyte of seed plants.
Pollination - the transfer of pollen from the anther to the stigma.
Pollinator - an insect or other vehicle by which pollen is carried from one flower to another. A plant that provides pollen for a self-infertile plant.
Post-emergent herbicide - a pesticide that kills plants after they have grown to seedling stage or beyond.
Potpourri - a mixture of dried flower petals with herbs and spices used for its fragrance.
Potting medium - material used for growing plants in containers. Mixes may include vermiculite, perlite, sand, peat, charcoal, loam and fertilizer.
Pot Up - To transplant a seedling or plant to a pot or similar container.
Powdery mildew - A fungal disease that affects many plants.
Pre-emergent herbicide - a pesticide that kills plants as they germinate.
Primocanes - on raspberries and blackberries, new, first-year canes.
Procumbent - having stems that trail along the surface.
Propagation - to increase the number of plants by sexual or asexual means
Protozoans - organisms made up of a single cell or a group of basically identical cells.
Prune - to cut back parts of plants for better shape, disease control or improved fruiting.
Pupa - a stage in complete metamorphosis when an insect transforms from the larval to adult stage of development.
Raised bed - a gardening area where the soil has been elevated above ground level. This gardening technique is especially used where soil drainage is poor. Beds can be raised in a structure of wood, brick, cement blocks, etc.
Rasping - mouthparts that are rough and used to scrape a surface to feed.
Reel mower - a mower with multiple blades mounted on a cylinder. The blades cut against a bar. It makes precise cuts and is ideal for lower mowing heights. The blades require professional sharpening. These mowers are safer to use than rotary mowers.
Renewal spur - on grapevines, the cane pruned to one or two nodes on the cordon; becomes the fruiting cane the following year.
Renovation - removing an old planting and putting in a new one or removing and replacing only part of a planting. In strawberry culture, this process involves removing the leaves of the plants and cultivating the aisle to reduce the width of the row of plants to no more than 15 inches.
Respiration - the process where food is oxidized (burned) to release energy.
Rhizome - an underground, horizontal stem.
Root - the portion of the plant usually found below ground. They are distinguished from stems by not having nodes.
Root girdling - encircling roots at or below the surface of the ground that tend to strangle the plant.
Root hairs - tubular outgrowths of surface cells of the root.
Root prune - to cut back the roots of a plant to encourage them to develop more fibrous roots or to reduce the mass of roots. Usually done before transplanting established plants or repotting houseplants.
Rooting hormone - a chemical that stimulates the growth of roots.
Rootstock - the root onto which a scion or bud is grafted or budded.
Rotary mower - a mower with a blade that spins in a horizontal plane from a central rod. Its advantages are the ability to cut tall grass, versatility of movement, a less expensive purchase price and blades that can be easily sharpened.
Row cover fabric - a loosely woven translucent fabric used to keep insect pests off crops. It also functions as a cloche.
Saprophyte - an organism that obtains nutrition from dead organic matter.
Scale - Sucking insect pests, scale need to be controlled early. Keep a careful watch on susceptible plants. Other than selecting resistant varieties of new plants, the most effective control is the use of ultrafine horticultural oil, usually requiring at least 3 applications 6-7 days apart until no new scale is detected.
Scarification - the physical or chemical treatment given to some seeds in order to weaken the seed coat sufficiently for germination to occur.
Scion - the upper part of the union of a graft.
Scorch - injury to leaves due to lack of sufficient water, excessive transpiration or injury to the water-conducting system of the plant.
Seed - the organ that forms after fertilization occurs.
Seed leaves - A germinating seed first produces leaves that are atypical to the mature leaves of the species. These leaves help to nourish the plant as it begins its development.
Selective herbicide - a pesticide that kills only one type of plant, for example broadleaf herbicides only kill broadleaf weeds, not turfgrasses.
Self-cleaning - herbaceous plants that drop spent blossoms, thus not requiring deadheading.
Sepals - structures that usually form the outermost whorl of a flower. Together, they are called the calyx.
Sesquioxide - an oxide containing three atoms of oxygen combined with two of the other constituent in the molecule.
Sewage sludge - the solid matter that settles out during the treatment of sewage.
Sexual reproduction - production of new generations involving the exchange of chromosomes from both a male and female parent.
Sharp sand - a coarse sand used in building.
Short-day plant - a plant that requires a night longer than its critical dark period, usually 12 hours or more, to develop flowers.
Side-dress - to apply fertilizer to the side of a row of growing plants or around single plants.
Slice seed - a technique used to sow seed. A machine cuts or slices grooves into the lawn or soil and drops seeds directly into the grooves. It is used to fill in a thinning lawn without disturbing the existing grass excessively.
Soaker hose - a porous tube that allows water to seep from it; used to irrigate plants. It is used to conserve water and to avoid wetting plant foliage.
Softwood cutting - a nonwoody piece of a woody plant that is cut from the stock plant to asexually propagate a new individual plant.
Soil - The top layer of the earth's surface, consisting of rock and mineral particles mixed with organic matter.
Soil conditioner - any material added to soil to improve its structure, texture, tilth or drainage.
Soil ph - The acidity or alkalinity of the soil. The pH affects the plant’s ability to take up essential nutrients. The optimum pH varies from species to species. In general, most plants will grow in a soil pH of 6.5-7.0.
Soilless mix - potting medium that contain a mixture of ingredients from the materials listed for potting medium, but no mineral soil.
Soluble salt - salts from fertilizers and tap water that are dissolved in water.
Solvent - a liquid that can dissolve a substance.
Species - a group of closely related individuals that have the potential to reproduce with each other; a unit of classification.
Specific epithet - the second name of the binomial given to a species; for instance, "rubrum" is the species epithet of Acer rubrum.
Sphagnum moss - Sphagnum is a genus of between 151 and 350 species of mosses commonly called peat moss, due to its prevalence in peat bogs and mires. A distinction is made between sphagnum moss, the live moss growing on top of a peat bog on one hand, and sphagnum peat moss (North American usage) or sphagnum peat (British usage) on the other, the latter being the decaying matter underneath. Sphagnum can hold large quantities of water inside their cells; some species can hold up to 20 times their dry weight in water, which is why peat moss is commonly sold as a soil conditioner and/or used in seed starting mixtures.
Spines - a sharp-pointed woody structure, usually a modified leaf or leaf part.
Spore - a minute reproductive body produced by primitive organisms, such as ferns and fungi.
Sporophyte - the part of a life cycle when the full complement of chromosomes are present.
Spreader-sticker - substances added to pesticides to make them spread over and stick to a surface more readily.
Spur - on grapevines, canes pruned to 1 to 4 nodes.
Square-foot gardening - a system of gardening developed by Mel Bartholomew that uses 4 foot by 4 foot plots subdivided into 1-foot squares for growing a specific number of a particular type of vegetable to maximize space and facilitate ease of maintenance.
Stake - a piece of pointed wood or metal that is driven into the ground to support a plant.
Stamen - the male part of the flower. It consists of the anther and the slender filament that holds it in position.
State specialists - professors at landgrant universities who provide expertise for Extension workers.
Stem - the main trunk of a plant. It develops buds and shoots.
Stem back - To cut back the flowering stem of a plant to the next growth point, either a leaf node or to the crown.
Stigma - the part of the pistil that receives the pollen grains; usually the top of the pistil.
Stock plant - a plant used as a source for cuttings.
Stomata - an opening or pore in leaves that is surrounded by guard cells.
Strain - a subgroup of a species; the descendants of a common ancestor.
Stratification - storing of seeds at low temperatures under moist conditions in order to break dormancy.
Style - the slender part of a pistil between the stigma and the ovary.
Succession planting - planting portions of a crop over a period of time to get a continuous harvest over a long period of time.
Succulent - having tender, new growth or thick, fleshy tissues which store water, such as cactus.
Sucker - a shoot arising from the root or lower part of the stem of a plant.
Sunscald - plant injury caused by exposure to bright sunlight, excessive heat and/or wind.
Susceptible host - an organism that can be infected by a pathogen.
Swale - a low-lying or depressed and often wet stretch of land; also : a shallow depression on a golf fairway or green .
Symbiotic - a relationship in which two or more dissimilar organisms live together in close association.
Symptom - evidence of disease or damage.
Synthetic - substances produced by chemical or biochemical means.
Systemic - a group of pesticides that are absorbed into the tissues of plants, thereby poisoning the organisms that feed on the plant.