HALF-HARDY: Plants that in our climate will live outside only in summer, and are killed by frost.
HARDENING: OFF Gradually accustoming plants raised in warmth to cooler conditions. See frame.
HARDY: A plant that should be capable of thriving outside all the year round.
HAULM: The stem of a plant, usually applied to vegetables, e.g., pea, bean, potato.
HEAD: A cluster of flowers, collection of branches at the top of the trunk of a tree, or the hearted part of a green vegetable, e.g., cabbage.
HEDGE: Shrubby plants grown in a continuous row as a boundary or division.
HEEL: A small side-shoot torn from the parent plant with a piece of bark attached at the base, often used as a cutting.
HEELING IN: The practice of planting bare root stock temporarily if the permanent site is not ready, in order to prevent the roots from drying out.
HERB: This word is now generally taken to mean plants, often aromatic, grown for seasoning food, medicinal purposes, or for the fragrance of their leaves or seeds.
HERBACEOUS: Herbaceous plants are those with soft, not permanently woody, upper growth. An herbaceous border contains a collection of such plants.
HERBICIDE: A chemical which will kill plants, often referred to also as a weedkiller.
HOUSE PLANTS: Are usually of a tender nature and have been grown for indoor decoration.
HUMIDITY: Moisture in the atmosphere.
HUMUS: Organic matter in soil.
HYBRID: A cross between two species of plant. Hybridization is the deliberate crossing of parent plants, and is usually performed by plant breeders to produce a new variety.