Glossary for Gardeners – D

Glossary for Gardeners

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damping-off
A disease caused by many different organisms. In the most conspicuous cases, a seedling’s stem collapses at or near the soil surface, and the seedling topples. Another type rots seedlings before they emerge from the soil or causes seeds to decay before germinating.
day-neutral plant
A species capable of flowering without regard to day length. See short-day plant, long-day plant.

deadhead
To remove individual, spent flowers from a plant for the purpose of preventing senescence (going dormant) and prolonging blooming. For effective results, the ovary behind the flower must be removed as well.
deciduous
A plant that sheds all of its leaves annually.
decomposition
The breakdown of organic materials by microorganisms.
defoliation
The unnatural loss of a plant’s leaves, generally to the detriment of its health. Can be caused by high winds, excessive heat, drought, frost, chemicals, insects, or disease.
dehorning
A drastic method of pruning a neglected tree or shrub. Entails the removal of large branches, especially high in the crown, a few at a time over several seasons.
dermaptera
An insect family made up of species having chewing mouthparts and a pair of large, forceps-like appendages near the tail. Wingless or with one or two pairs of inconspicuous wings. Earwigs are an example.
desiccation
Drying out of tissue.
determinate
A plant growth habit in which the stems stop growing at a certain height and produce a flower cluster at the tip. Determinate tomatoes, for example, are short, early-fruiting, have concentrated fruit set, and do not require staking. See indeterminate.
dethatch
To remove thatch (a tightly intermingled layer of stems, leaves, and roots, living and dead, that forms between the soil surface and green vegetation of grass).
diageotropic
Horizontal growth of a plant part.
diatomaceous earth
The fossilized remains of diatoms (a type of tiny algae).
dicot
A plant having two cotyledons (seed leaves).
dicotyledon
See dicot.
dieback
Progressive death of shoots, branches, or roots, generally starting at the tips.
differentiation
A change in composition, structure, or function of cells and tissues during growth.
dioecious
A plant species having male and female flowers on separate plants. An example is holly. See monoecious.
disbud
The selective removal of some flower buds so the remaining buds receive more of the plant’s energy and produce larger, showier flowers. Roses, chrysanthemums, and camellias often are disbudded.
disc flower
A small, tubular flower in the center of a composite head.
division
The breaking or cutting apart of a plant’s crown for the purpose of producing additional plants, all genetically identical to the parent plant.
DNA
Deoxyribonucleic acid. The substance that the genes which carry genetic information is made of.
dominate species
The most abundant species in a plant community.
dormancy
The annual period when a plant’s growth processes greatly slow down.
dormant bud
A bud formed during a growing season that remains at rest during the following winter or dry season. If it does not expand during the following growing season, it is termed a latent bud.
dormant oil
A horticultural oil applied during the dormant season to control insect pests and diseases.
double, semidouble
A flower with more than the normal number of petals, sepals, bracts, or florets. May be designated botanically by the terms flore pleno, plena, or pleniflora.
double worked
Grafted twice, i.e., grafted to an intermediate stock.
drainage
The ability of soil to transmit water through the surface and subsoil.
drip tip
A pointed leaf tip helping to drain water from the leaf surface.
drip zone
The area from the trunk of a tree or shrub to the edge of its canopy. Most, but not all, of a plant’s feeder roots are located within this area.
dripline
An imaginary line on the ground directly beneath the outermost tips of a plant’s foliage. Rain tends to drip from leaves onto this line.
drupe fruit
See stone fruit.
dwarfed
Restricted plant size without loss of health and vigor.