Snow falls fast. A bitterly chill wind whips up. Icy rain lashes down diagonally. I am thankfully huddled indoors in the warm. Trees and plants cannot up their roots and move indoors in freezing temperatures. How do they survive the worst that winter can throw at them?
Plants don’t hang around. Deciduous trees drop their leaves in the autumn. Annuals complete their life cycle and set seed before winter descends. Perennials disappear below ground and go dormant for the winter period. Bulbs wait for spring underground. Slowing down and seeking shelter underground makes sense. Soil temperatures stay warm and do not drop as low as air temperatures.
Aquatic plants can find themselves under a layer of ice. The water temperature is colder at the surface than in the depths. Generally, the water retains its liquid state below the surface and ensures survival.
Snow as Insulation
Snow can provide an insulation blanket for the plants it covers. Every gardener knows that grass does not need cutting in winter. It slows its growth as many other plants to conserve energy, relaunching with renewed vigour in the spring.
Tough Leaves and Needles
Evergreens rely on tough, waxy leaves. Conifer needles are well-adapted to harsh conditions with a reduced surface area. Their design prevents too much snow and ice settling. Little photosynthesis takes place in winter, but the retention of needles helps them to conserve energy and water. Conifers have an advantage over deciduous trees. They do not need to regrow all their leaves in the spring.
Trees stand tall in the freezing air and do not have the option of hiding below ground. Thick bark provides some protection. A gradual drop in temperature allows the tree to prepare. When the temperature drops below 0ºC, the water inside plants can freeze. Water expands as it freezes. Sharp ice crystals rupture and kill plant cells. Trees protect themselves by drawing water out of their cells into the spaces between cells. The remaining liquid inside the cells gets thicker with sugary sap and resists freezing.
Killer Late Frosts
Sudden, unexpected drops in temperature carry greater risks to trees and plants. A late frost can damage plants just as they emerge with vulnerable, spring leaves.
This winter has recorded the UK’s coldest temperature since 1995 and coldest February temperature since the 1950s. We have become accustomed to warmer winter temperatures in the South West under climate change. Plants continue into late winter and re-emerge early. Gardeners are increasingly filling their gardens with tropical and less frost-resistant plants. It seems inevitable that some plants will not survive this winter, although the RHS reassures us not to assume that a plant will not ultimately re-emerge from underground.
As we shelter indoors against the bitter cold, the winter resilience of trees and plants seems all the more admirable. The bonus of a harsh winter is that they may not have to cope with so many pests and diseases in 2021.
References and Further Reading
- Andrews, C. J. (1996): How do plants survive ice? Annals of Botany 78: 529–536, 1996.
- Botts, Beth (2014): How trees, plants protect themselves from winter’s freezing temperatures. Chicago Tribune. 14 December 2014.
- Let’s Talk Science (2020): How Do Trees Survive in Winter? 16 March 2020
- MinuteEarth (2014): How do Trees Survive Winter? YouTube. 27 January 2014
- LifeNoggin (2016): Why Doesn’t Winter Kill All The Fish and Plants? YouTube. 12 December 2016
- RHS (2021): Frost damage. RHS Gardening.
- SciShow (2020): 3 Extreme Ways Trees Survive the Winter. YouTube. 5 March 2020
- Stout, Richard (2010): How Plants Survive the Cold (Or Not). How Plants Work. Plant Guy. 7 January 2010.
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