Winter Desiccation
Winter desiccation is a common winter injury caused by water shortage, not by the cold itself. It occurs when plants lose water through evaporation from their leaves or needles while the ground is frozen and the roots cannot take up any moisture. Evergreen plants that stay active and continue to transpire through the cold season are particularly at risk.
Causes
Winter desiccation results from several unfavourable conditions occurring at once:
- Frozen soil prevents the roots from taking up water.
- Dry, cold air and winter sun increase evaporation.
- Wind intensifies the loss of moisture from the leaves.
Long frosty spells combined with strong sunshine are typical triggers, especially in late winter or early spring.
At-risk plants
Evergreen shrubs, perennials and herbs are particularly vulnerable, for example:
- Box (Buxus sempervirens)
- Cherry laurel (Prunus laurocerasus)
- Rhododendron
- Yew (Taxus baccata)
- Bamboo and other evergreen grasses
- Rosemary (Rosmarinus officinalis) and other Mediterranean herbs such as lavender or thyme
Freshly planted young plants can also be affected, as their root system has not yet grown deep enough to draw water from lower soil layers.
Symptoms
Typical signs are brown, curled or shrivelled leaves and needles, especially on the sun-facing side. Plant tissue dies off due to the water shortage. The damage often only becomes visible in spring, when affected shoots fail to sprout again.
Prevention and measures
With the right preparation, winter desiccation can be prevented effectively:
- Plant evergreens in sheltered, semi-shaded spots.
- Water thoroughly before the onset of winter, especially newly planted specimens.
- Cover the root area with mulch, leaves or brushwood to stabilise soil temperature.
- Shield plants from winter sun and wind with fleece, hessian sacking or fir branches.
- Water sparingly on frost-free days even in winter, especially for potted plants and rosemary beds.
Summary
Winter desiccation is not cold damage but winter drought. With thoughtful planting, winter protection and occasional watering on mild days, sensitive species such as Rosemary or box can be brought safely through the winter.