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Headhouse A work-building in close proximity to or attached to a greenhouse. This facility might be used for purposes such as a workshop, storage area, pesticide room, potting area, or eating area, This building may also be referred to as a service building. (Nelson, 2003)

Herbicide A chemical used for killing weeds. (Nelson, 2003)

Hormone An organic substance produced in one part of the plant and translocated to another part where in small concentrations it regulates growth and development. (Nelson, 2003)

Horticulture The art and science of growing fruits, vegetables, flowers, and woody ornamentals as well as spice , medicinal, and beverage plants. (Nelson, 2003)

Host plant A plant that is invaded by a parasite and from which the parasite obtains its nutrients. (Nelson, 2003)

Humus The relatively stable fraction of the soil organic matter remaining after the major portion of added plant and animal residues have decomposed. (Nelson, 2003)

Hydroponics The culture of plants in root substrate consisting exclusively of water and dissolved nutrients. (Nelson, 2003)

Hypha (plural, hyphae) A single branch of the mycelium that makes up the body of a fungus. (Nelson, 2003)