Wrap up warm, folks; it appears that we’re experiencing a mini ‘Beast from the East’. According to the Met Office (and I’m sure they know), this happens when Scandinavia experiences a period of high pressure, combined with easterly winds from the continent. When these conditions combine in winter, cold air is drawn into the UK from the Eurasian landmass, resulting in a harsh cold snap similar to that experienced in February 2018.
Wise beings that they are, perennial plants (that is, plants those whose lifecycle last for two or more years) enter a period of dormancy during the winter. Dormancy is a state of temporary inactivity, or minimal activity, generally as a response to adverse growing conditions. Plants are not dead during this time, but instead adopt strategies to conserve energy, such as dropping their leaves, or die-back of above-ground foliage.
As temperatures drop and days shorten, plants accumulate starches, sugars and amino acids within their cells. The increased concentration of these chemical compounds enables the liquid within plant cell membranes to thicken and becomes more gel-like. This slows down all the normal metabolic processes within the plant, thereby conserving energy, and also acts as a kind of antifreeze by lowering the freezing point of the plant’s tissues. Much below zero though, and the formation of ice crystals within most plant cells will rupture and damage the plant’s tissues, due to the expansion of water on freezing.
A rise in spring temperatures can encourage perennials to break their dormancy and put on tender new growth. If this is followed up with a sudden frost, the new growth is particularly susceptible to frost damage. This can have a devastating effect on fruit harvests if a frost occurs after fruit trees have formed flower buds, especially when those buds are in the later stages of development.
Hard, prolonged or sudden frosts can cause the foliage of even evergreen plants to die and turn brown. In these cases, don’t be tempted to cut back the dead or discoloured growth too soon, as it can offer a bit of protection to the rest of the plant. Wait until the frost season has passed and the plant has come back into new growth, before trimming off any unsightly frost damage and applying a liquid feed.
It’s not all gloom and doom though. Frosts can have some beneficial effects in the garden. For heavy clay soils, freeze-thaw action of water within the soil plays a crucial role in breaking up larger clods of earth, that might otherwise be impenetrable to plant roots. Hard frosts can also disrupt the lifecycles of some common garden pests.
Parsnips, beetroots and other bulky root crops that are left in the ground until after a freeze tend to have a sweeter taste, due to the increased concentration of sugars within their tissues. Brassicas such as cabbages and Brussels sprouts harvested after a frosty period will also have a sweeter flavour, for the same reason.
Fruit trees require a certain amount of chilling time during their dormant season, in order to provide a healthy harvest, the following year. This is generally the time during which the air temperature is between zero and six degrees centigrade, so still above freezing. This is also the time to be pruning your fruit trees, but more on that another time. For now, I’d still just recommend sitting in front of the fire with a cuppa!