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Halophytes are plants adapted to saline habitats, able to grow where high salt concentrations would inhibit growth in most other plants. Typical habitats include coastal areas, salt marshes, tidal zones and, more generally, soils with elevated salt content.

‘Hardening off’ is the process of gradually getting young plants used to outdoor conditions. Plants that start their life in protected spaces (indoors or in a greenhouse) are sensitive to temperature differences, wind and direct sunlight. Hardening off allows them to develop more stable cell structures and resilient leaves.

Hardiness describes how well a plant can survive frosts and wintry weather without suffering damage. It’s dependent on genetic factors, origin, location and weather patterns – and it’s a key factor in choosing plants for your garden.

The hardiness zones are a guide to help gardeners tell which plants can survive winter outdoors in a specific area. They are based on average minimum temperatures observed in that area over many years, which are classified as USDA zones.

Heavy feeders are plants that draw a lot of nitrogen from the soil and therefore need plenty of fertiliser. Examples include brassicas, leeks, potatoes, tomatoes and maize. Crop rotation puts this knowledge to use, alternating heavy and light feeders so the soil has a chance to recover and build up its nutrient reserves again.

Hedgehogs (Erinaceidae) form a family of mammals, whose best-known representatives are the species found in Europe, the West European hedgehog (Erinaceus europaeus) and the Southern white-breasted hedgehog (Erinaceus concolor). Most people probably have an immediate picture in mind of these spiny, endearing and gentle creatures, which curl up into a ball when startled or frightened and simply sleep through the winter.

Herbaceous perennials are plants that live for more than two years, sending up new growth from the ground each year. In autumn or winter their top growth often dies back completely. But the roots remain in the soil and produce new shoots in the following spring.

The term horticulture is fairly broad and can refer to both commercial and purely ornamental purposes.

A hothouse, also called a greenhouse, is a glass structure used for growing plants.

Humus refers to all the dead organic matter in the soil that has already been broken down by soil organisms. It is dark in colour, crumbly, and considered the heart of fertile garden soil. Humus stores nutrients, improves soil structure and promotes soil life.