I have covered some raised beds with polythene, to heat up the soil for sowing and planting. Would it be advisable to make holes in the polythene with a fork to allow rain in to the soil or should I leave it without holes. Advice please.
Brenjon
Holes in polythene
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Kleftiwallah
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Leave it un-holed. If a large puddle forms on top, it will help hold the plastic down when the wind blows. I think black or clear plastic, they both work equally well. Cheers, Tony.
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Geoff
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Somebody once offered to experiment with a soil thermometer to find out if clear or black polythene warmed it up most but I don't think they ever reported back the results, so anyone with a thermometer volunteering? I agree, no holes.
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Geoff
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An entry in Q&A in the recent Gardener's World Magazine:
Q : Is clear or black polythene best for warming soil?
A : Sparsholt College in Hampshire recently did trials and found that clear polythene warmed the soil more than 2ºC higher than anything else, including black polythene, fleece and carpet.
Q : Is clear or black polythene best for warming soil?
A : Sparsholt College in Hampshire recently did trials and found that clear polythene warmed the soil more than 2ºC higher than anything else, including black polythene, fleece and carpet.
The only snag using only clear polythene is that the light allows the annual weeds and some of the perennial weeds to germinate.
I have experimented in the past using clear until the weeds have germinated and then covered with heavy duty black Polythene to kill the weeds off.
I have also covered with black h/d Polythene form the Autumn and removed for a short time in early Spring until germination of weeds begins then covered again. This method actually although more faffing about is the best. I think it is because you actually get the natural rainfall which assists germination and the weeds growing.
And certainly no holes.
JB.
I have experimented in the past using clear until the weeds have germinated and then covered with heavy duty black Polythene to kill the weeds off.
I have also covered with black h/d Polythene form the Autumn and removed for a short time in early Spring until germination of weeds begins then covered again. This method actually although more faffing about is the best. I think it is because you actually get the natural rainfall which assists germination and the weeds growing.
And certainly no holes.
JB.
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Kleftiwallah
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I think I'll settle for 2 degrees under and fewer weeds. 
Cheers, Tony.
Cheers, Tony.Hi Tony,
The one thing that you have forgotten is that the weed seed is still there and will germinate once the black polythene is removed. If you uncover for a couple of weeks now the germination of the annual weeds will commence irrespective if they show or not and by then replacing the black polythene the first flush of annual weeds will not materialize.
The trouble with clear polythene is that things like Speedwell will very easily flower and seed before you want to use the bed thus adding to the problem.
JB
The one thing that you have forgotten is that the weed seed is still there and will germinate once the black polythene is removed. If you uncover for a couple of weeks now the germination of the annual weeds will commence irrespective if they show or not and by then replacing the black polythene the first flush of annual weeds will not materialize.
The trouble with clear polythene is that things like Speedwell will very easily flower and seed before you want to use the bed thus adding to the problem.
JB