habit - a plant's habit is its natural size, shape and form. Terms such as upright, rounded, horizontal, spreading, prostrate and vertical are used for description.
haploid - having a single complete set of chromosomes (n chromosomes)
hand pollination - moving the pollen from one plant to the pistil of another plant . Many types of tools such as paint brushes, cotton swabs, dead bee bodies and others are used to make the transfer.
hardening off - plants that have been grown under ideal conditions in a greenhouse may not be immediately adapted to the more variable conditions outdoors. To help seedlings or plants make this adjustment, a process of "hardening off" may be used. This may involve taking plants out in the spring on a cool morning and bringing them back in if the night is to be frosty. Other ways to harden plants include withholding water and altering the temperature within the greenhouse.
hardiness - a general term for the ability of a plant to withstand environmental stresses. In temperate zones, the main concern is cold temperature hardiness while in other areas, the challenge may be hot, dry summers. The most famous way of designating survivability of plants is the cold hardiness zone map of the USDA. However, other organizations have begun to develop maps based on other criteria such as heat, drought conditions and urban factors.
hardiness zone - this term is most often used when referring to the temperature maps developed by the U.S. Department of Agriculture and, more recently, by Arnold Arboretum. These maps show the United States and Canada divided into zones based on the average low temperature experienced. The zones start with number 1 in the extreme northern areas of the continent and proceed to the south. The lower the number, the colder the climate.
 
hardscape - all the non-living parts of a landscape such as fences, paths, structures, statuary, trellis, arbors, etc.
See softscape.
hardwood cutting - propagation method in which the plant segments for rooting are collected during the dormant season. It usually refers to mature twigs that have been hardened off for winter or wood that is older than one year.
headhouse - a structure attached to greenhouses which is used for propagating, potting, storage, etc.
heading back - there are two basic types of pruning cuts: heading back and thinning cuts. Heading back is the removal of ends of branches to achieve a reduction in plant height or span. The most common form of heading is when plants are trimmed into hedges or into forms such as squares or balls. It is generally give the plant an "unnatural" look.
heal in - this is putting plants into the soil temporarily until they can be transplanted to their permanent location. This  helps to prevent the plant from drying out or may be used if the plant must be moved from its current location but the new site is not yet ready for it.
 
heart shaped - shaped like a valentine heart. It is a leaf having an acute point or apex, and a flat to cordate leaf base.
heavy soil - term for a soil composed predominately of clay particles. These soils are generally poorly drained and lack oxygen spaces needed for plant growth. They are also more prone to compaction.
hedge - a grouping of plants that have dense foliage and are placed close enough so that they grow together forming a solid mass. They may be precisely trimmed and shaped or they may be left "natural" in their growth habit. Although many types of plants may be used for hedges, perhaps the most common species are yews, boxwood and privet.
herbaceous - these plants do not form a woody stem and, in temperate zones, will die back to the ground when exposed to a frost. See Woody
herbicide - a substance that either kills or inhibits the growth of plants. These may be of natural origin or synthetic chemicals. Herbicides may be classified as pre-emergent, post-emergent, selective or non-selective.
 
herbs - plants which do not develop much woody tissue and which usually have rather succulent annual stems. This term also refers to a much smaller group of plants (chives, dill, sage, etc.) grown for culinary, medicinal, functional, or other properties.
hoar frost - a frost that leaves ice crystals on soil and plants owing to condensation of humidity at a decreased temperature.
holdfast - a suction-cup-like organ on some climbing vines, anchoring them to walls and other surfaces.
honeybees - the bees we associate with honey, hives and plant pollination. These insects are not native to North America having been brought here by early European settlers. Native bee species tend to be more solitary insects that do not form large hives and do not produce quantities of honey.
hose-end sprayer - a garden hose attachment used for applying pesticide or fertilizer.
 
horizon (Soil) - typical soils are divided into more or less distinct layers (horizons) moving down toward the center of the earth.
hormone - these are compounds that control general growth and developmental process in the plant. They are sometimes also called growth regulators. The common plant hormones include gibberellins, auxins, ethylene, abscisic acid and cytokinins.
horticulture - a form of intensive agriculture that includes fruits, vegetables, ornamental trees and shrubs, turfgrass, groundcovers, flowers, and floriculture plants. Horticulture is both an art and a science.
hose-in-bose - Describes a flower that has one perfect set of petals within another. It is generally an abnormality, but varieties of plants such as azaleas with attractive hose-in-hose flowers have been bred.
Hosta Journal - the Hosta Journal is the official publication of the The American Hosta Society. This beautiful, full-color magazine type publication is included with membership in AHS. For further information on the Journal or how to join the Society, visit the AHS website above.
humus - highly decomposed, stable organic matter in the soil.
 
hybrid - (v. hybridize) a hybrid plant results from sexual reproduction with two distinct parents. It is the combination of the genetic material of both plants resulting in genotypic variation. Some hybrid plants are sterile and incapable of reproduction. Seed from fertile hybrids may produce plants that vary widely from the parents. Hybrids are often made to produce a plant that has the best qualities of each parent.
hybrid tea rose  
hybridizer - people who actively transfer the pollen from the anther of one plant to the pistil of another or to the same plant. They often have a specific goal in mind when they make the cross such as improved fragrance or different color flowers.
hydrogel - a chemical compound that absorbs many times its weight in water and is used to keep media moist to reduce the number of waterings required. These are often used in potted plants or containers to help minimize irrigation demands.
hygroscopic - when soils get very dry, they get to a point where the only water is that which is held very tightly to the surface of individual particles. This water is so tightly bound that it is not available for use by plant roots. See field capacity.
hypocotyl - the part of the embryo or seedling situated between the cotyledon and the radicle.
 

 

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