"Andy" wrote in message
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I am working on raising the organic content, and put clear
plastic over it for two weeks at the beginning of April to
heat it up a little.

Andy.


Indeed. Up until a while ago, the recommendation was to use an opaque
black plastic mulch as this was supposed to work better. And it seems
most commercial growers and amateurs followed this advice. This was
presumably based on "common sense". The idea being, that all the heat
under a clear mulch would be lost again overnight.

And so nobody anywhere in the world it seems, ever thought of
doing a simple experiment (cost £ 10 max ? ) to find out which
worked better. As it now seems that a clear mulch in fact works
much the better of the two.

A black mulch, itself absorbs the heat which is then transferred to
the soil underneath - but only where the mulch and the soil are
in close contact. A clear mulch allows most of the UV and other
waves straight through, which then warm the soil directly. A film of
condensation then builds up inside the clear plastic mulch which
then acts as a barrier to heat loss overnight. There isn't however
sufficient air trapped under a clear mulch to form an insulating
barrier on its own, a miniature greenhouse effect duck .

The only real disadvantage of clear mulch is supposed to be the
possibility of weed growth underneath. As this combination of warmth
and moisture at some stage of each 24 hour cycle on the top surface
of the soil will create ideal conditions for weed germination.

However, this has the actual advantage that any troublesome weeds
which are present, should show themselves before planting. And
so can be removed at that stage before there are any crops
to disturb. This is a point which seems to have been lost
on the developers of intermediate "wonder" mulches which are
claimed to combine the light transmission characteristics of clear
mulches and the weed suppression (i.e germination delay)
characteristics of black mulches.


michael adams

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