H7 - Very hardy

The toughest plants, able to endure exceptionally severe cold and suited to demanding British gardens, particularly where winters are intensely frosty or exposed.

What it means

H7 is the hardiest RHS rating, for plants able to withstand temperatures below -20 degrees C. Such plants are appropriate for the coldest inland, upland and northern British situations, including severe Scottish gardens, and are extremely dependable for frost tolerance in lower-risk areas. Hardiness does not guarantee success against every challenge: winter wet, poor drainage, wind, shade and salt can still matter. This measures plant tolerance, not geography.

Example plants

H7 plants commonly include exceptionally tough alpines, saxifrages, sedums, sempervivums, some dwarf conifers, hardy willows and mountain-origin perennials. Certain hardy bulbs and rock-garden plants also qualify. Their exact performance depends on origin and cultivation: a high-mountain alpine may tolerate deep frost but resent damp lowland winter soil, while a hardy tree may need space to develop properly.

Protecting these plants

Routine frost protection is rarely necessary for established H7 plants. Instead, provide the conditions their type needs, especially sharp drainage for alpines and rock-garden plants. Use gravel or grit around vulnerable crowns, keep winter-wet containers sheltered, and anchor young trees in exposed sites. Newly planted specimens still benefit from mulching and wind protection until their roots have spread into surrounding soil.

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.