Damping down Wetting greenhouse floors and staging with water to increase humidity, particularly in very hot weather.

Dead-heading The removal of spent flowers or flowerheads.

Deciduous Of plants that shed leaves at the end of the growing season and renew them at the beginning of the next: semi-deciduous plants lose only some of their leaves at the end of the growing season.

Degradable pot A pot made from degradable material such as compressed peat or paper.

Dehiscence Term used of fruits (usually capsules) and anthers to describe the process of opening at maturity to release their contents.

Dehiscent Of a fruit, usually a capsule, or an anther that splits along definite lines to release seeds or pollen.

Determinate 1) Used of inflorescences where the central or terminal flower opens first so that the main axis cannot extend further; 2) Used of bushy or dwarf tomatoes.

Dibber Sometimes known as a dibble, a tool used for making holes in soil or potting compost into which seedlings or cuttings are inserted.

Dicotyledon A flowering plant that usually has two cotyledons or seed leaves in the seed; it is also characterised by the (usually) net-veined leaves, the petals and sepals in multiples of two, four, or five, and by the presence of a cambium.

Dieback The death of tips of shoots as a result of damage or disease.

Dioecious Bearing male and female reproductive organs on separate plants.

Diploid Having two basic sets of chromosomes.

Disbudding The removal of surplus buds to promote the production of high-quality flowers or fruits.

Distal end (of cuttings) The end that was originally farthest from the crown of the parent plant.

Division A method of increasing plants by dividing them into pieces, each with a root system and one or more shoots (or dormant buds).

Dormancy The state of temporary cessation of growth and slowing down of other activities in whole plants, usually during the winter; seed dormancy: non-germination of seed when placed in conditions suitable for germination due to physical, chemical, or other factors inherent in the seed; double (seed) dormancy: non-germination of seeds due to two dormancy factors in the seed.

Double digging A cultivation technique in which the soil is worked to a depth of two spits. Also known as “trench digging” or “bastard trenching”.

Drainage The passage of excess water through soil; the term is also applied to systems of drainage used to remove excess water.

Drill A narrow, straight furrow in the soil in which seeds are sown or seedlings planted.