Cactus A member of the family Cactaceae, characterised by fleshy, water-storing tissue in the stems and areoles (specialised groups of cells) from which spines, flowers, and shoots develop.

Calcicole Lime-loving; a plant that thrives in alkaline soil.

Calcifuge Lime-hating; a plant that will not grow in alkaline soil.

Callous Protective tissue formed by plants over a wounded surface, particularly in woody plants but also at the base of cuttings.

Calyx (pl. calyces) The collective name for the sepals, the outer whorl of, usually green, segments that enclose the flower in bud.

Cambium A layer of meristematic tissue capable of producing new cells to increase the girth of stems and roots.

Capillary matting Matting made of synthetic fibre that is used to draw water upwards by capillary action to irrigate pot plants on capillary beds or benches.

Capping A crust that forms on the surface of soil damaged by compaction, heavy rain, or watering.

Capsule A dry seed case that dehisces (splits open) when ripe to release its seeds.

Carpel The female part of the flower of flowering plants that contains the ovules: several carpels in a flower are collectively known as the pistil.

Carpet bedding The use of groups of closely planted, low-growing, colourful bedding plants in various patterns or designs.

Catkin A racemose (see Raceme) flower spike, or a spike-like inflorescence, with conspicuous bracts and small often unisexual flowers lacking petals.

Central leader The central, usually upright, stem of a tree.

Certified stock Plant, certified by the UK government as free from certain pests and diseases.

Chilling requirement The requirement of plants for a specific period of dormancy below a particular temperature in order for them to initiate flowering.

Chinese layering An alternative name for air layering.

Chlorophyll The green plant pigment that is mainly responsible for light absorption and hence photosynthesis in plants.

Clamp A method for storing root crops outdoors. The crops are heaped up and protected against frost by layers of straw and soil; a “chimney” hole filled with straw provides ventilation.

Climber A plant that climbs using other plants or objects as support:

• self-climber clinging by means of supporting adventitious aerial roots or adhesive tendril tips;
• tendril climbers by coiling their leaf stalks, leaf tendrils, or modified terminal shoots;
• twining climbers by coiling their stems.
• Scandent, scrambling, and trailing climbers produce long, usually flexuous, stems that grow over or through plants or other supports: they attach themselves only loosely, if at all, to the support.

Cloche A small usually portable, structure made of clear plastic or glass, normally in a metal framework: used to protect early crops on open ground and to warm the soil before planting.

Clone 1) a group of genetically identical plants produced by vegetative propagation or asexual reproduction; 2) an individual plant in such a group.

Cold frame A glazed, box-like, unheated structure, made from brick, wood or glass, with a hinged or removal glass or clear plastic light, used to protect plants from excessive cold.

Collar 1) the part of a plant where the roots meet the stem; also known as the “neck”; 2) the part of a tree where a main branch meets the trunk (or a side branch meets a main branch).

Companion planting Positioning plants together that are reputed to have a beneficial effect on neighbouring plants by discouraging pests and diseases or improving growth.

Compositae The daisy family.

Compost 1) A potting medium comprising a mixture of loam, sand, peat, leaf mould, or other ingredients. 2) an organic material, rich in humus, formed by decomposed plant remains, and other organic matter, used as a soil improver or mulch.

Compound Divided into two or more subsidiary parts, for example a leaf divided into two or more leaflets.

Cone The densely clustered bracts and flowers of conifers and some flowering plants, often developing into a woody, seed-bearing structure as in the familiar pine cone

Conifer Gymnosperms, usually evergreen trees and shrubs that are distinguished from flowering plants (angiosperms) by the naked ovules that are not enclosed in an ovary but are often borne in cones.

Conservatory Another name for a greenhouse, but typically attached to a house. Conservatories today tend to be used as an indoor garden extension to the house, where the sun can be enjoyed all year round.

Contact action The action of pesticide or weedkiller that kills or damages the pest or weed by direct contact.

Coppicing The annual pruning back of trees or shrubs close to ground level to produce vigorous, usually decorative, shoots.

Cordon A trained plant (usually a fruit tree) generally restricted to one main stem by rigorous pruning. A single cordon has one main stem, a double, or “U”, cordon has two, and a multiple cordon, has three or more stems.

Corm A bulb-like, underground, swollen stem or base, often surrounded by a papery tunic. A corm is replaced annually by a new corm that develops from a terminal, or lateral, bud.

Cormel A small corm developing around a mature corm, usually outside the main corm tunic, as in Gladiolus.

Cormlet A small corm arising at the base (and usually within the old tunic) of a mature one.

Corolla The interior whorl of the perianth of the flower, comprising several free or fused petals.

Cotyledon A seed leaf; the first leaf or leaves to emerge from the seed after germination, often markedly different from mature leaves. Flowering plants (angiosperms) are classified into monocotyledons (one) and dicotyledons (two) depending on how many cotyledons are contained in the mature seed. In gymnosperms (conifers) they are often produced in whorls.

Crest A ridged outgrowth, often on perianth segments, as in orchids and some irises.

Cristate An exaggerated crest, commonly seen in fern fronds and the inflorescences of Celosia or the stems of cacti.

Crocks Broken pieces of clay pot. used to cover the drainage holes of pots in order to provide free drainage and air circulation to the root system and to prevent the growing medium from escaping from or blocking the drainage holes.

Crop rotation A system in which vegetable crops are grown on different sections of a plot on a three- or four-year cycle to minimise the build-up of soil-borne pests and diseases in one section.

Cross-fertilisation The fertilisation of the ovules of a flower as a result of cross-pollination.

Cross-pollination The transfer of pollen from the anther of a flower on one plant to the stigma of a flower on another plant: the term is often loosely applied to cross-fertilisation.

Crown 1) The basal part at soil level of a herbaceous plant where roots and stems join and from where new shoots are produced; 2) The upper, branched part of a tree above the bole.

Culm The usually hollow stem of a grass or bamboo.

Cultivar A contraction of “cultivated variety” (abbreviated to “cv”); a group (or one among such a group) of cultivated plants clearly distinguished by one or more characteristics and which retains these characteristics when propagated either asexually or sexually.

Cupped Usually of leaves or flowers, shaped like a cup.

Cutting A portion of a plant (a leaf, shoot, root, or bud) that is cut off to be used for propagation.

• Basal stem cutting: one taken from the base of a (usually herbaceous) plant as it begins to produce growth in spring.
• Greenwood cutting: one taken from the soft tips of young growth after the spring growth flush has slowed down; slightly harder and woodier stems than are used for softwood cuttings.
• Hardwood cutting: one taken from mature wood of both deciduous and evergreen plants at the end of the growing season.
• Heel cutting: one taken with a portion of the bark or mature wood at the base.
• Internodal cutting: one in which the basal cut is made between two nodes or growth buds.
• Leaf cutting: one taken from a detached leaf or part of a leaf.
• Leaf-bud cutting: one consisting of a short section of stem and a single or double pair of buds or leaves.
• Nodal cutting: one trimmed at the base just below a growth bud or node.
• Ripewood cutting: one taken from ripened wood, usually of evergreens, during the growing season.
• Root cutting: one taken from part of a semi-mature or mature root.
• Semi-ripe cutting: one taken from half-ripened wood during the growing season.
• Softwood cutting: one taken from young, immature growth during the growing season.
• Stem cutting: one taken from any portion of a plant stem.
• Stem tip cutting: any cutting taken from the tip of a shoot: sometimes applied to softwood and greenwood cuttings.

Cyme A usually flat-topped, determinate inflorescence in which the central or terminal flower opens first.