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When to Cloche? New Information on Cloches

Cloches have been used by gardeners for many years to protect their crops from cold weather. Of  course, they’re not complete protection. On average they only keep the plants a few degrees warmer than outside, but that’s actually quite significant.

Cloching can be the equivalent of planting out two weeks or more before nature alone would allow.

Now conventional wisdom, which I’ve always followed and passed on, is that you need to cloche a week or two before you plant out to warm the soil. However, it seems this might need to be revised. They say:

PoshCloche, who manufacture garden cloches for the UK vegetable growers market, have today released data on a series of soil temperature tests undertaken in December 2009. The tests, carried out at a depth of 5cm, revealed that the soil warmed by 1.5 ºC in the first 5 hours of the trial, challenging previously held views that cloches needed to be sited for several weeks to make any impact on soil temperature.

They’ve got various graphs on their site here that show both the outdoor and under cloche temperature over time, including a trial undertaken in December this year. When I’ve planted sweetcorn out, I’ve set out the cloches a week before and then had to take them all up again, plant out and then re-set all the cloches. Having seen this, I’ll be doing a lot less work – setting up the cloches as I plant.

PoshCloche also say

“As soil temperature is such a critical factor affecting seed germination, I was extremely pleased with the extent to which our cloches can advance the soil warming process and in so doing, support vegetable gardeners with earlier planning and sowing of their gardens and allotments”

I have to agree and commend them for an interesting piece of research that should save gardeners a lot of time. Their website is here: PoshCloche

Sweetcorn Under Cloche in Early May

Sweetcorn Under Cloche in Early May

Posted in Allotment Garden Diary
8 comments on “When to Cloche? New Information on Cloches
  1. stuart says:

    hi john.Interesting read. Wondered where you got those cloches i see covering the sweetcorn?

    Cheers, Stuart

  2. John says:

    I think they were off ebay – had them a few years now. They only get used for a couple of months each year so hoping for a few more years life from them yet.

  3. Mike Palmer says:

    The surface layers heat up and cool down quickly with the weather/sun/cloud which is what their 5cm deep measurements are measuring.

    A more meaningful measurement would be at 10cm depth. Once warmed at this depth it only cools slowly and the bottom heat encourages development of root systems.

    We have all sown seed on a nice Spring day only to find that the seed starts but then sits vunerable to pests until proper warm weather arrives.

    Maybe the true value of pre-sowing cloching is the warming of the lower levels.

  4. Brian King says:

    “challenging previously held views that cloches needed to be sited for several weeks to make ANY IMPACT on soil temperature”.

    Having some impact has no great relevance. What is important is achieving the necessary temperature that you need, e.g. to allow germination.

    The often quoted two weeks is just meant to be a rough rule of thumb.

  5. John says:

    Most gardening is rule of thumb. Seeds germinate usually near the surface so that’s the temperature that matters when sowing. Once the seeds have established and the roots go down further, the weather will have warmed (hopefully) and the soil will have warmed to a greater depth.

    I suspect a lot of the benefit of cloches is in reducing wind chill anyway. Not to forget keeping the birds from pulling onion sets up and nibbling seedlings..

    If only they kept the slugs out!

  6. Mr Tunstall says:

    We have pheasants and pigeons roaming on our site as well as a few stray chickens. Cloches do help protect seedlings from the wind too. Try sheets of polythene scrounged off wrapped pallets, its free. Better still make cold frames out of old window frames. Bought cloches are way too expensive.

  7. malcolm cragg says:

    Hi,posh cloches basic madel costs £10 for 20″,thats far too much money.As Mr tunstall says try an alternative like corrugated plastic roof sheets about£7 for 10’or all greenhouse glass and ducktape,we are make and menders ain,t we.

  8. Ali Ridgwell says:

    Interesting reading. Sounds to me if we sow direct into the ground cloche as you go, but if you’re transplanting cloche before hand to warm deeper. Useful infi. Thanks.

    For buying cloches try looking in 99p and £1 shops. They are quite thin and need careful handling, but they do the job and ours are on their third year. They are also not very long, but this suits us fine as we’re in a confined space.

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