How frosts can affect plants


Picture: DENISE BRADLEY - Credit: Copyright: Archant 2016

January 2017 seems (for a change!) to be following what we would expect at this time of year in terms of temperatures, which have so far led to a significant number of frosts. So how does frost affect plants?

Basically in two ways; first, by freezing and disrupting the cells in the plant tissue, and second by freezing the soil, which can interfere with the water supply going to the plant roots. Frost is probably one of the most damaging and problematical aspects of gardening weather. Repeated thawing and freezing, rapid thawing and wind can all exacerbate frost damage and loss, particularly to tender plants.

Unsurprisingly in terms of nature, plants themselves have adapted, and survive frosts by the use of various mechanisms:

The bark of the stem can insulate the living water-conductive tissues in the same way that water pipes are lagged to prevent water freezing within cells.

Sugars and amino acids contained in some plants effectively act as anti-freeze lowering the freezing point of cell contents – shortening autumn days induce this, the process also producing the wonderful autumn colours I have referred to in a previous column.

Some plants even have the ability to allow their cell contents to ‘superfreeze’. In such cases the cell contents remain liquid even though below freezing point. To do this plants have to experience several days of cold weather before the freeze which explains why even hardy plants can be damaged by a sudden sharp autumn frost.

Not all plants have these abilities however, so what can we do to help protect our plants?

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Choose plants that are reliably hardy and check they are suited to the growing conditions in your garden, taking into account things such as frost pockets, wind exposure, and aspect. Where possible the more tender plants should be grown in a warmer sunnier position, ideally against a south facing wall. Where practical, particularly tender plants should be lifted and transferred to the greenhouse.

Protect plants by covering with a double layer of horticultural fleece or other suitable protection when frost is forecast, including container plants which should also be moved to the more protected parts of the garden.

It may also be helpful to delay pruning of previous seasons growth on the more tender plants in order to provide additional frost protection

Mulching of individual plants or even entire beds with a thick layer of organic matter will prevent the ground becoming frozen.

Whilst some frost damage will be irrepairable, don’t be too hasty to dig up and dispose of the plants. Many plants can rejuvenate from dormant buds beneath soil level. If you can resist the temptation, delay removal for as long as possible – you may be surprised at your plants resilience!