Frosty welcome

The general public, even gardeners, might run for cover and warmth when there's a danger of frost, but anyone with an allotment should welcome frost like a best friend. Why?

Firstly, a severe frost can clear out pests and diseases lingering from the previous summer. The breeding cycles of some pests are disrupted and unwelcome spores may be killed. It'll also kill annual weeds, so the ones left are the real pests that need some attention.

Secondly, frost helps improve soil. Moisture in the earth expands and separates soil particles, making it more friable. Experienced growers will roughly dig over their allotment in early autumn, leaving the earth in large clumps to enable the frost to penetrate more deeply. It only takes a few frosts to leave the soil, even containing heavy clay, crumbly and easy to cultivate.

Finally, some vegetables benefit from a period of frost...

  • Although some varieties of garlic can be planted in spring, the majority are for autumn planting, so a period of frost will initiate flowering
  • Brassicas such as Brussels sprouts, cabbage, broccoli, turnips and kale develop an improved flavour from cold weather
  • Frost helps turn the starches in parsnips into sugar to give the desired sweet taste

Frost typically develops overnight when skies are clear and there's a lack of wind. What little heat remains in the earth radiates upwards into the upper layers of the atmosphere. Frost can also develop in exactly the opposite conditions, where there's a cloud cover and gusty winds, though this also depends on a cold front approaching and is much rarer.

The lie of the land also has an effect. Cool air can settle at the bottom of slopes with frost pockets forming in valleys where the cool air is trapped. Obviously, the higher the altitude, the greater the risk of frost. Even within an allotment plot there'll be temperature differences, different for north and south facing slopes or walls as well as low lying spots or areas protected by trees. Thus, covering tender plants affords them some protection.

So regard winter's frosts as a gift, as a helping hand.

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