Geraniums, commonly known as hardy geraniums or cranesbills, are perennial plants native to temperate regions. They thrive in well-drained soil and prefer full sun to partial shade. However, their ability to survive winter outdoors depends heavily on the specific species and the climatic conditions of the region. While some geraniums are frost-tolerant, others, like the popular Pelargoniums (often mistakenly called geraniums), are tender and cannot withstand freezing temperatures.
The United States Department of Agriculture (USDA) Hardiness Zones provide a guideline for determining which plants can survive winter in specific regions. True hardy geraniums (genus Geranium) can typically survive in zones 3–9, depending on the species. For example, Geranium macrorrhizum is hardy in zones 3–8, while Geranium sanguineum thrives in zones 3–9. In contrast, Pelargoniums are only hardy in zones 9–11 and must be brought indoors or treated as annuals in colder zones.
True hardy geraniums have evolved several adaptations to survive winter. Their root systems are robust and can endure freezing temperatures, while the foliage often dies back in winter and regrows in spring. Some species, like Geranium cantabrigiense, form dense mats that protect the crown from frost. Additionally, these plants enter dormancy during winter, reducing metabolic activity to conserve energy until warmer temperatures return.
Even hardy geraniums face challenges in winter, particularly in zones at the lower end of their hardiness range. Prolonged exposure to sub-zero temperatures without snow cover (which acts as insulation) can damage roots. Wet, poorly drained soil can lead to root rot, as geraniums dislike standing water. In zones with harsh winters, mulching around the base of the plant can help protect the roots from freeze-thaw cycles.
To improve survival rates, prepare geraniums for winter by cutting back dead foliage in late fall to prevent disease. Apply a 2–3 inch layer of mulch (such as straw or shredded leaves) to insulate the soil. In containers, move hardy geraniums to a sheltered location or bury the pots in the ground to prevent root damage. For Pelargoniums, dig them up before the first frost, trim them back, and overwinter them indoors in a cool, bright spot.
In zones 3–5, even hardy geraniums may require extra protection, such as burlap wraps or frost blankets. In zones 6–8, they generally survive with minimal care, provided the soil drains well. In zones 9–11, Pelargoniums can remain outdoors year-round, though they may need protection during rare cold snaps. Always check the specific hardiness of your geranium variety and adjust care accordingly.
After winter, inspect geraniums for signs of damage, such as blackened stems or mushy roots. Healthy plants will show new growth at the base in early spring. If damage occurs, prune affected areas and ensure proper drainage to encourage recovery. In severe cases, replanting or replacing the plant may be necessary.
