Why Has My Lavender Been Killed by Winter Cold?

Lavender's relationship with cold winters is complicated. English lavender (Lavandula angustifolia) is reasonably cold-hardy when grown in well-drained soil, tolerating temperatures as low as -15°C in dry conditions. French and Spanish lavenders (L. stoechas and L. dentata) are far more frost-sensitive and will not survive sustained cold below about -5°C. However, even normally cold-tolerant varieties can be killed by a combination of factors that individually they might survive: cold temperatures combined with wet, waterlogged soil, or an unusually late hard frost hitting soft new growth in spring.

Why wet soil makes cold so much more damaging

Water-saturated soil conducts cold more efficiently than drained soil, and ice crystals forming within the root system of a plant already weakened by waterlogging are far more destructive than the same frost temperature in dry, aerated soil. This is why the same variety of lavender can survive winter on a sunny, south-facing bank and die in a flat, heavy border just a few metres away. If lavender has been killed in an apparently mild winter, suspect waterlogging as an amplifying factor.

Choosing cold-hardy varieties

For gardens in the UK, northern Europe or cold-winter regions, confine planting to Lavandula angustifolia varieties. Hidcote, Vera, Munstead, Rosea and Imperial Gem are among the most reliably cold-hardy. Avoid L. stoechas varieties (recognisable by their butterfly-like petal bracts) in climates where winter temperatures regularly fall below -5°C; treat them as tender plants that need winter protection or annual replacement.

Confirming whether the plant is actually dead

A lavender that looks dead in early spring may still be alive. Wait until late April or even May before concluding the plant is gone. Scratch the bark of a main stem near the base with your thumbnail — if you find green tissue beneath, the plant is alive and may recover with pruning. Cut back to the highest point of green growth on each stem. If all wood is brown and dry throughout, the plant has not survived.

Winter protection for marginal varieties

Container-grown French and Spanish lavenders can be moved into an unheated greenhouse or cold frame for winter. Garden-grown specimens in borderline climates can be given a mulch of gravel or bark around the base to insulate the root zone, or loosely wrapped with horticultural fleece during the coldest spells. Remove the fleece promptly in mild periods to prevent humidity building up around the foliage.