H4 - Hardy (average winter)

Plants hardy through an average British winter, making them dependable outdoors in most lowland gardens when properly planted and established.

What it means

H4 plants withstand about -10 to -5 degrees C and are hardy through an average UK winter. Most lowland Britain is broadly around H4, so an H4 plant or hardier is usually safe outdoors in most UK gardens. Milder coasts and cities can suit H3 plants, while colder inland areas, uplands and much of Scotland favour H5 to H6 choices. RHS ratings compare plant hardiness, not geographic zones.

Example plants

Many familiar herbaceous perennials, shrubs and bulbs are H4, including geraniums, astrantias, peonies, lavender, roses, hydrangeas and numerous narcissi. Some evergreen shrubs and ornamental grasses also fit this rating. Exact tolerance is influenced by soil and exposure: a plant hardy in a dry, sheltered border may struggle in a waterlogged, windswept site despite carrying an H4 label.

Protecting these plants

Most established H4 plants need no routine winter protection in lowland gardens. Plant at the correct depth, improve drainage where needed and water newly planted specimens in dry spells until rooted in. Apply a light organic mulch around, not over, crowns in autumn. Protect tender new growth from late frosts, and give recently planted or container-grown specimens extra shelter during their first winter.

RHS hardiness ratings describe a plant's cold tolerance, not a geographic zone. Local conditions vary; the RHS or a local garden centre can advise. Page updated 18 Sep 2026.