HABIT: The shape or form of a plant, growing vertical, laterally, or rounded. It is important to know the habit of a plant so one can expect certain growth patterns. HABITAT: The kind of environment inhabited by a particular species. HALF HARDY: An indoor plant which requires a minimum temperature of 50�-55�F for healthy growth. Compare hardy and tender. HALOPHYTE: Those plants that will tolerate salt in the soil. Mostly coastal plants in the dunes, or marshes. HARDENING OFF: The process of gradually acclimatizing greenhouse or indoor grown plants to outdoor growing conditions. Usually used when talking about transplanting of greenhouse plants or seedlings. HARDINESS: the ability to withstand harsh environmental conditions. HARDINESS ZONE: U.S. Department of Agriculture classifications according to annual minimum temperatures and/or lengths of growing seasons. Also referred to as USDA zone. HARDPAN: hard, compacted, often clayey layer of soil through which roots cannot grow. HARDY: A plant which can withstand prolonged exposure to temperatures at or below 45�F. Compare half hardy and tender. HEADING BACK: Cutting an older branch or stem back to a stub or twig. HARDSCAPE: Includes any garden feature that is not a plant. Like birdbaths, deck, fences, trellises, benches, and patios. HAY: Stems of grass. Most popular feed for horses and cattle. HEART ROT: most commonly heard of in reference to trees. The center merely has rotted out. Can also happen in root vegetables HEAVING: the partial lifting of a plant out of the soil as a result of alternating freezing and thawing of the soil. HEDGE: Suitable trees, shrubs, or bushes planted relatively close together so that the branches will intertwine to provide a barrier fence for a windbreaker or privacy. Hedges can be any height or width depending on the plant material used. Generally they are long lived species. HEDGE ROW: Just as it reads - a row of plant material (shrubs and trees) that are suitable for hedges. HEEL: A strip of bark and wood remaining at the base of a side shoot cutting pulled off a main shoot. Some cuttings root more readily if a heel is attached. HEEL CUTTING: A short, side branch taken as a cutting with a small piece of the main stem. HEELING IN: covering the roots of dormant plants with soil or mulch for short periods. HEIRLOOM PLANT: Plants that have been grown for 50 years or more. HERB: A plant grown for flavoring, scented foliage or medicinal purposes. HERBARIUM: A collection of dried specimens and a research center. HERBICIDE: An agent that stops plant growth or kills a plant. HIGH SHADE: Always a difficult gauge but generally it is the shade beneath trees that have been "limbed up" or pruned to get some light in. HERBACEOUS: Describes a plant with soft rather than woody tissues. HILL: A cluster of plants or roots with a pile of soil around it. HILL UP: It sounds like an old fashion term but means to pull the soil around the stem of a plant for support. HONEYDEW: sugary substance secreted by aphids and other juice-sucking, plant-feeding insects. HORTICULTURE: The art and science of gardening. Commercial horticulture would include fruit, flower and small scale vegetable growing including the nursery industry. Agriculture covers broad acre farming of plants. HORTICULTURAL OIL: This includes both a dormant oil and a summer oil - used to smother eggs and developing insects on trees and ornamentals. The heavier oils are used in the late winter or very early spring, making sure the temperatures are over 40?F but, before the plant leafs out. The lighter summer oil can be used anytime the temperature is below 85?F. HORTUS : Plant dictionary by Liberty Hyde Bailey. Plants that were and are cultivated in the U.S. and Canada. HOST: Any plant material that will support a parasite. HOT CAP: Cones that are used a lot in cooler zones to protect newly planted seedlings from cold weather and birds. Usually made of plastic or a very heavy translucent waxed paper. HOT HOUSE: Another term for a greenhouse. HOUSE PLANTS: Plants that are grown and raised indoors in containers. HUMIDIFIER: A piece of equipment used to raise the humidity of the air in a room. HUMUS: The brown or black organic part of the soil resulting from the partial decay of leaves and other matter. It is the stable form of organic matter that remains after most of plant or animal residues have decomposed. HYBRID: A first generation cross between two genetically diverse parents. HYDROPONICS: The science of growing plants in mineral solutions or liquid, instead of in soil. HYGROMETER: An instrument used to measure the relative humidity of the air.