Plants need the cold by Sarah J. Dodd

This winter has been exceptionally cold in Cumbria, with long stretches of time where even the daytime temperature has not climbed above freezing and the night temperatures have plummeted well below. Any gardener or nature watcher can see the effects of cold weather on plants – when the temperature hovers around freezing, leaves droop. This is partly due to the effect of ice crystals forming within the cells and damaging them. In addition, the tiny pores on the leaves - which allow water vapour to pass in and out - lock open in cold weather. This means that the plant loses too much water and the leaves wilt, as if there was a summer drought.



On the other hand, many plants benefit from cold weather. Native bulbs such as wild snowdrops and daffodils need a lengthy period of low temperatures in order to flourish.


Most plants are highly sensitive to ‘thermal time’, which means that in order to flower, a bulb needs to experience a fixed amount of low temperatures. When this chill requirement (the vernalisation period) is achieved, the plant then produces a hormone to trigger flower production. From then on, the plant needs warmer spring temperatures for shoots to grow and blossoms to flourish.

The longer the cold period, the better the resulting display of flowers is likely to be. The plant has had a lengthy period of dormancy (resting), so its growth is more vigorous. Severe frosts and snow also kill off harmful fungi and bacteria, so the plant remains healthier.

So while we shiver through the next month, we can look forward to a spectacular display of native flowers carpeting our woodlands when the weather warms up.