Beating the frost, for free!

It’s April here and the days are growing shorter and cooler. The summer vegetables are dead stalks, having born their fruit. Soon the frosts will hit, so any leafy green vegetables will blacken and die off when the water in their cells expands as it freezes.

I have some mignonette lettuce and some basil plants I want to keep going a little longer. I need to protect them from frost. I made up a little tunnel from some old number 8 fence wire and some clear polythene (from an old mattress bag). That’s not enough protection from a heavy frost but enough to counter a light frost but I have a secret weapon!

My polythene tunnel made from fending wire and an old mattress bag,

My polythene tunnel made from fencing wire and an old mattress bag and held together with PVC packaging tape.

Have you ever noticed how a pile of grass clippings gets warm inside, as it decomposes?

That’s due to all the bacteria consuming the nutrients in the grass clippings, releasing excess energy. I utilise this warmth with my plastic tunnel, to combat the heavy frosts. In past years it’s even beaten the odd snow fall, as long as it doesn’t last too long on the ground afterwards.

This trick only works if the clippings are deep enough, so I remove the soil from between the rows of plants, to form a trench about as deep as the width of my hand. I’m careful not to expose the roots. Into this trench I put fresh grass clippings to form a mound. It’s important not to get the clippings too deep, touching the stems of the plants, I’m protecting. I need the clippings to be at least a total depth of 160mm or as long as my hand. This will generate enough warmth for a few days, up to a week. Finally, I place my tunnel over the clippings and plants.

This does two things:

  1. The decomposing grass clippings generate some heat. It only needs to be a few degrees, just enough to prevent water freezing overnight. The warmer humid air acts as a cold barrier for the plants.
  2. The decomposing clippings release nutrients back into the soil. When I have harvested the plants, I simply turn the lot over with a pitchfork, adding some animal manure and it will turn the worst soil into good soil for the winter garden.
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