winterhart

Winterhart, or winter-hardy, is a horticultural term describing a plant's ability to survive winter temperatures without permanent damage. The designation is climate-dependent and varies with site conditions such as wind exposure, soil moisture, and snow cover. Nurseries and gardeners use it to indicate whether a species or cultivar can reliably survive typical winter conditions in a given region.

Assessments rely on hardiness rating systems. In the United States, USDA hardiness zones express minimum winter temperatures; in the UK and Europe, RHS hardiness ratings and regional guides are common. Labels may specify a zone, a temperature range, or a range of survivable conditions. Even winterhart plants can be damaged in unusually severe winters or prolonged thaw–freeze cycles.

Factors influencing winter survival include temperature extremes, duration of frost, wind desiccation, soil drainage, and moisture availability. Young plants and those with exposed roots are at higher risk. Microclimates, such as south-facing walls or protected courtyards, can improve survival. Proper planting strategy, seasonal care, and mulching help promote winter hardiness.

Common winterhart plants encompass conifers and many perennials such as evergreen shrubs, grasses, and herbaceous perennials like Helleborus, Sedum, and certain Echinacea. When selecting winterhart cultivars, gardeners should consider local climate, typical winter severity, and site conditions, choosing plants rated for the appropriate zone or equivalent.