| sand | The coarsest type of soil particle (0.05 to 2.0 mm in diameter). |
| sanitation | The process of removing sources of plant pathogens from a growing area, for example, by cleaning up plant debris and sterilizing tools and growing media. |
| saprophyte | An organism that obtains food from dead organic matter. |
| sapwood | The outer, light-colored, water conducting region of secondary xylem. |
| scab | (1) A crust-like disease lesion. (2) A specific disease that causes scab lesions. |
| scaffold | The principal branches of a tree or shrub arising from the trunk or another main branch to for the plant’s framework. |
| scaffold branch | See scaffold (above). |
| scale | (1) A modified leaf that protects a bud. (2) A type of insect pest. |
| scarification | Nicking, sanding, or otherwise compromising the hard outer coating of a seed to increase its water intake and thus promote germination. Sometimes incorrectly called scarfing. |
| scion | A cutting or bud that is grafted to the stock of another plant. |
| secondary growth | The growth resulting from the activities of lateral meristems (vascular and cork cambium). |
| secondary nutrient | A nutrient needed by plants in a moderate amount: calcium, magnesium, and sulfur. See macronutrient, primary nutrient. |
| secondary phloem | Food-conducting tissue formed by the vascular cambium. |
| secondary xylem | Water-conducting tissue formed by the vascular cambium. |
| seed | A reproductive structure formed from the maturation of an ovule and containing an embryo and stored food. |
| seed coat | A hard outer covering that protects a seed from disease and insects. Also prevents water from entering the seed and initiating germination before the proper time. |
| seed leaf | See cotyledon. |
| seedling | A young plant, shortly after germination. |
| selective pesticide | A pesticide that kills or controls only certain kinds of plants or animals. For example, 2,4-D kills broadleaf lawn weeds but leaves grass largely unharmed. |
| self-fruitful | A plant that bears fruit through self-pollination. |
| self-pollination | The transfer of pollen from the anther to the stigma of the same flower. |
| self-unfruitful | A plant that requires another variety for pollination. See pollinizer. |
| senescense | (1) The aging process. (2) A descriptive term for a plant that is in the process of going dormant for the season, although technically only the parts that are dying (the leaves) are becoming senescent. |
| sepal | An appendage at a flower’s base, typically green or greenish and more or less leafy in appearance. Collectively, the calyx. |
| separation | The process of removing new bulbs or corms from their parent for the purpose of propagation. |
| sessile | Stalkless and attached directly at the base, as in sessile leaves. |
| shade-tolerant | Having the ability to live in low light conditions. |
| 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. |
| short-day plant | A plant requiring more than twelve hours of continuous darkness to stimulate a change in growth, e.g., a shift from the vegetative to reproductive phase. See long-day plant, day-neutral plant. |
| shoulder ring | One of the ridges around the base of a branch where it attaches to a trunk or to another branch, See collar. |
| shrub | A woody plant that grows to a height of three to twelve feet. May have one or several stems with foliage extending nearly to the ground. |
| side-dress | To apply fertilizer to the soil around a growing plant. |
| sieve plate | The perforated end-wall of a sieve tube member. |
| sieve tube | A food conducting cell. |
| sign | Direct evidence of a damaging factor (for example, a pest or pathogen itself, secretions, insect webbing, or chemical residue). |
| signal word | An indication of toxicity on pesticide labels. Pesticides labeled “Caution” are the least toxic, those labeled “Warning” are more toxic, and those labeled “Danger” or “Danger – Poison” are the most toxic. |
| silt | A type of soil particle that is intermediate in size between sand and clay (0.002 to 0.05 mm in diameter). |
| simple fruit | A fruit formed from a single ovary. |
| simple leaf | A leaf in which the blade is not divided into smaller units (leaflets). |
| simple metamorphosis | A type of insect development in which the insect passes through the stages of egg, nymph, and adult. The nymph usually resembles the adult. See complete metamorphosis. |
| slow-release fertilizer | A fertilizer material that must be converted into a plant-available form by soil micro-organisms. |
| soft pinch | To remove only the succulent tip of a shoot, usually with the fingertips. |
| soil | A natural, biologically active mixture of weathered rock fragments and organic material at the earth’s surface. |
| soil salinity | A measure of the total soluble salts in a soil. |
| soil solution | The solution of water and dissolved minerals found in soil pores. |
| soil structure | The arrangement of aggregates (peds) in a soil. |
| soil texture | How coarse or fine a soil is. Texture is determined by the proportions of sand, silt, and clay in the soil. |
| soilless mix | A sterile potting medium consisting of ingredients such as sphagnum peat moss and vermiculite. |
| soluble salts | A mineral residue often remaining in soil from irrigation water, fertilizer, compost, or manure applications. |
| sonic repeller | A sonic wave emitting unit said to disrupt the activities of small mammals. Not proven to be effective. |
| sorus | An area of spore production on the underside of a fern leaf. |
| spandix | A spike of flowers enclosed in a spathe. |
| spathe | A large bract enclosing a spandix. |
| species | The basic unit of plant or animal classification. Plants within a individual species have several characteristics in common. Most importantly, they can cross with one another, but normally not with members of other species. Classification of species is quite fluid, with periodic revision by botanists. |
| specific epithet | The second word in a binomial (scientific) name, following the genus name. For example, in the binomial name Thuja plicata (The tree commonly known as Western Redcedar), “Thuga” is the genus name and “plicata” is the specific epithet. |
| sperm | A male sex cell. |
| spike | An inflorescence in which the flowers are attached to the main stem without stalks. |
| spine | A modified leaf part that is hard and pointed. |
| 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. |
| sport | See mutation. |
| spot treatment | To apply a pesticide to a small section or area of a crop. |
| spur | Commonly seen on fruit trees, spurs are a short, compact twig with little or no internodal development on which flowers and fruit are borne. |
| stamen | The male, pollen-producing part of a flower consisting of the anther and its supporting filament. |
| standard | A plant pruned so that it consists of a single bare, vertical stem, atop which a shaped mass of foliage, usually globular, is maintained. |
| starch | The principal food-storage substance (a carbohydrate) of higher plants. |
| stem | The leaf and flower bearing part of a plant. |
| stem cutting | A section of a stem prepared for vegetative propagation. |
| stem tuber | An enlarged tip of a rhizome containing stored food. |
| 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 part of a female sex organ that receives pollen. Supported by the style, through which it is connected to the ovary. Often sticky when receptive. |
| stinging hair | A multicellular hair containing an irritating fluid. |
| stipules | A pair of appendages found on many leaves where the petiole meets the stem. |
| stock | See rootstock. |
| stolon | A horizontal stem running along, but above, the soil surface and producing roots and leaves where its nodes contact the soil. Strawberries are an example of a plant that produces stolons. Also called a runner. |
| stoma | Tiny openings in a leaf’s epidermis that allow water, oxygen, and carbon dioxide to pass in and out of a plant. (pl. stomata) |
| stomates | See stoma (above). |
| stone cell | A hard, thick-walled plant cell. |
| stone fruit | A fleshy fruit, such as peach, plum, or cherry, usually having a single hard stone that encloses a seed. Also called a drupe. |
| strain | A variation within a cultivar or variety. |
| stratification | The exposure of seeds to moisture or low temperature to overcome dormancy. |
| style | The part of a plant’s female sex organ that supports the stigma and connects it to the ovary. |
| stylet | A nematode’s lance-like or needle-like mouthpart used to puncture and feed from plant cells. |
| suberin | A fatty plant substance present in the walls of cork cells. |
| subspecies | A major division of a species, more general in classification than a cultivar or variety. |
| succession | The progression of a plant community to a stable mixture of plants. |
| succession planting | The practice of planting new crops in areas vacated by harvested crops. |
| sucker | A shoot or stem that originates underground from a plant’s roots or trunk, or from a rootstock below the graft union. See reversion growth. |
| summer oil | A light refined horticultural oil used during the growing season to control insect pests and diseases. |
| 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. |
| surfactant | See additive. |
| sustainable gardening | Gardening practices that allow plants to thrive with minimal inputs of labor, water, fertilizer, and pesticides. |
| symbiotic | Mutually beneficial. |
| symptom | A change in plant growth or appearance in response to living or nonliving damaging factors. |
| systemic pesticide | A pesticide that moves throughout a target organism’s system to cause death. |
