Our ‘A’ to ‘Z’ of Gardening Terms

Terms that begin with “P”

PThe chemical symbol for phosphorus. (see below)
palisade mesophyllThe cells just beneath a leaf’s upper epidermis that contain most of the leaf’s chlorophyll and are responsible for most photosynthesis.
palmateA form of espalier training.
palmate venationA leaf whose veins radiate outward from a single point somewhat like the fingers of a hand.
palmately compound leafA leaf in which the leaflets radiate from one point.
panicleA highly branched inflorescence.
parallel venationA vein pattern in which the veins are parallel to each other.
parasiteAny animal or plant that lives in, or on, another animal or plant and withdraws nutrients from its host.
parasitic seed plantA plant that lives parasitically on other seed plants. An example is mistletoe.
parenchymaA thin-walled, undifferentiated cell.
parterreA formal garden in which shrubs, flowers, and paths form a geometric pattern of matched pairs.
parthenocarpicDevelopment of fruit without fertilization.
pathogenAny organism that causes disease. Generally applied to bacteria, viruses, fungi, nematodes, and parasitic plants.
pathologyThe study of diseases.
pectinA substance in cell walls binding cells together.
pedA cluster of individual soil particles.
pedicelThe stem of an individual flower.
peduncleThe main stem supporting a cluster of flowers (as opposed to a pedicel, which is the stem of an individual flower).
pendulousMore or less hanging or declined.
perennialA plant that lives two or more years and produces new foliage, flowers, and seeds each growing season.
perianthCollectively, all external flower parts.
pericarpThe fruit wall, derived from the ovary wall.
pericycleA root tissue giving rise to branch roots.
permeabilityThe rate at which water moves through the soil.
persistent(1) Adhering to a position instead of falling, whether dead or alive, e.g., flowers or leaves. (2) A pesticide that retains its chemical properties in the environment for a long time.
petalsThe usually showy structures around a flower’s reproductive organs.
petiolate leafA leaf in which the blade is attached to a stem by a petiole.
petioleThe stalk of a leaf.
pHA scale measuring the acidity or alkalinity of a sample. What the pH scale actually measures is the hydrogen ion (H+) concentration present. pH values run from 0 (the most acidic value possible) to 14 (the most alkaline value possible). pH values from 0 to 7 indicate acidity, a pH of 7 is considered to be neutral, while pH values from 7 to 14 indicate alkalinity. The scale is logarithmic, thus a difference of 1 pH unit is equal to a 10-fold change in acidity or alkalinity (depending on the direction), a difference of 2 pH units indicates a 100-fold change, and a difference of 3 pH units indicates a 1,000-fold change.
phenological stageCrop development stage.
phenotypeThe physical appearance of an organism.
pheromoneA vapor or liquid emitted by an insect that causes a specific response from a receiving insect. Some pheromones are used to attract a mate. Synthetic pheromones are used as attractants in insect traps.
phloemPhotosynthate-conducting tissue. See xylem.
phosphateThe form of phosphorous listed in most fertilizer analysis (P2O5).
phosphorous (P)A primary plant nutrient, especially important for flower production. In fertilizer, usually expressed as phosphate (P2O5).
photoinduceTo initiate a physiological process as a result of being exposed to a specific photoperiod.
photoperiodThe amount of time a plant is exposed to light.
photosynthateA food product (sugar or starch) created through photosynthesis.
photosynthesisThe process in green plants of using sunlight to convert water and carbon dioxide into sugar.
phototropismA growth response to light. Growth of a plant toward a light source is the most common example.
phytoplasmaA microscopic, bacteria-like organism that lacks a cell wall. Previously called mycoplasma.
phytotoxicToxic to a plant.
picoteeA pattern of flower petal coloration in which the edges of the petal are a contrasting color to the body.
piloseHaving long, soft hairs.
pinchTo remove a growing tip from a stem, thus causing axillary shoots or buds to develop. See deadhead, shear.
pinnately compound leafA leaf in which the leaflets are arranged on both sides of a common axis.
pinnate venationA leaf vein pattern in which the major veins are arranged in rows on each side of the midrib.
pistilThe female sexual organ of a flowering plant, made up of the stigma, style, and ovary.
pitA small opening in a cell wall.
pithA region of parenchyma cells at the center of a stem.
plagiotrophicGrowth of a branch at an angle.
plant growth regulatorSee growth regulator.
plant nutritionA plant’s need for and use of basic chemical elements. See macronutrient, micronutrient.
plasmolysisShrinkage of cytoplasm away from cell walls due to water loss.
pleachTo intertwine branches of a tree, vine, or shrub to form an arbor or hedge.
plenaA term used in botanical names to indicate a double-flowered variety. See double.
plenifloraSee plena (see above).
plenoSee plena (see above).
point sourceA single, identifiable source of pollutants such as a factory or municipal sewage system. See nonpoint source.
pollardA method of tree pruning that involves heading back severely to main branches each year so as to produce a thick, close growth of young branches.
pollenA plant’s male sex cells, which are held on the anther for transfer to a stigma by insects, wind, or some other mechanism.
pollinizerA plant whose pollen sets fruit on another plant. See cross-pollination.
pollinationThe transfer of pollen from a male anther to a female stigma, enabling fruits to set and develop.
pollinatorAn agent, such as an insect, which transfers pollen from a male anther to a female stigma.
polyploidHaving three or more sets of chromosomes per cell.
pome fruitA fruit having a core, such as an apple, pear, or quince.
pomologyThe science of fruits and the art of fruit cultivation, especially fruit trees.
post emergentA product applied after crops or weeds emerge from the soil. See preemergent, preplant (see below).
potashThe form of potassium listed in most fertilizer analysis (K2O).
Potassium (K)A primary plant nutrient, especially important for developing strong roots and stems. In fertilizers, usually expressed as potash. See potash.
predatorAn animal that eats another animal.
preemergentA product applied before crops or weeds emerge from the soil. See post emergent (above), preplant (below).
preharvest intervalThe period of time that must pass from the time a pesticide is applied to a crop until the crop is safe to pick and use.
preplantA product applied before a crop is planted. See post emergent, preemergent (above).
prickleA rigid, straight, or hooked outgrowth of bark or stems. Often called a thorn, but technically different. Roses are examples of plants with prickles. See thorn.
primary growthGrowth arising from cellular activities in apical meristems.
primary nutrientA nutrient required by plants in a relatively large amount (nitrogen, phosphorus, and potassium). See macronutrient.
primocaneFirst-year growth, usually vegetative, on caneberries. Only fall-bearing raspberries produce fruit on primocanes late in summer.
processed fertilizerA fertilizer that is manufactured or is refined from natural ingredients to be more concentrated and more available to plants.
prop rootA supportive root growing from an aboveground stem.
propagateTo start new plants by seeding, budding, grafting, dividing, etc.
protoplasmThe living substance of cells, including cytoplasm and nucleus.
pruneTo remove plant parts to improve a plant’s health, appearance, or productivity.
pseudobulbA thickened, aboveground, modified stem that serves as a storage organ. Found in some orchids.
pubescentHaving short hairs.
pupaThe stage between larva and adult in insects that go through complete metamorphosis.