Sowing/Growing under plastic

[Colin_M]

I've read many times about people laying black plastic over their soil, to help get it warmed up in the weeks before sowing.

I was wondering how effective clear plastic would be as well. The reason?
- I have a free supply!
- I know black absorbs the sunlight.
I wondered if clear plastic would transmit it through to the soil (dark) which would then still get warm.

Finally I know that potatoes are sometimes sown under plastic, then allowed to grow through when they emerge. Would it be viable for other seeds, where plastic would help keep the top layer of soil from drying out (maybe removing it when sprouts emerge)?

Whatever the scientific reason, I'm interested if people have tried any of the above & their result.

Colin

[Chantal]

I would think clear plastic would warm the soil but surely this would also encourge the weed growth and as such it could be more of a hinderance than a help. I've only ever used black plastic.

[Geoff]

If you dig a patch over then sheet it with clear plastic it warms up and when you see the weeds germinating it is ready to use. If you can lift and keep in place the clear plastic it then becomes a cloche of course.

[Monika]

If you use clear plastic, the weeds will germinate more quickly than in the open, therefore you can hoe them off before you sow the vegetables. It may therefore save you time and effort later on, because germinate they will, in any case.

[Colin_M]

Just to make it clear, I'm talking about using a sheet of clear plastic to help during initial seed germination & sprouting. Unlike the farmers who plant spuds under plastic, then let them grow through, I wasn't planning to do that.

The plan is, when the seeds germinate, I will remove the plastic. It was intended an an accelerator, warming the soil, retaining moisture etc.

It's interesting to hear your comments about weeds. I guess I'll have to take my chances!


Colin

[Johnboy]

Hi Colin,
I only use black H/D polythene but I am coming round to the idea that it may well be worthwhile using black throughout the winter, which prevents weeds germinating, and then a month prior to sowing time replace with clear polythene. Weeds will germinate throughout the winter under clear but if covered with black it will prevent this and then give them a blast of light and then the majority of weeds seeds will germinate all at the same time. I feel that when you have prepared the soil in Autumn you put first the clear and then add the black over the top and simply removing the black to expose to light. I say this because here we get some winds that would make laying polythene difficult at this time of the year. In the past if I had to sow Carrots in the row and Parsnips I have followed the advice given by a contributor a few years ago and use a flame gun over the area prior to sowing. If you have a flame gun you can hoe off those weeds that have germinated and make sure that they perish and also delay at least the germination of those about to germinate.
This is only a thought but I feel that it could work
quite well.
From this year on I will only grow both Carrot and Parsnip in dedicated raised beds along with Early Potatoes and Leeks which should provide enough my needs so the flame gun will not be used by me for those in future.
JB.

[Colin_M]

Thanks JB. I've gone ahead with this on the off chance and will let you know the results


Colin

[dewwex]

i have always read that clear plastic increases soil temperature more. Black plastic heats up more due to its colour, but in fact does not transmit this heat to the ground very well. clear plastic allows the sun through which actually heats the soil up rather than just the plastic. look at it another way, some people in warmer parts actually mulch to keep down soil temperatures during the summer. when we cover our seedlings with newspaper who do the same to some extent.

In reply to John boy.
So you thinking of cover plot throughout winter with black plastic.

just a few thoughts.
1) I plough my plot in late autumn and never have weeds germinating during the winter months.Is it cause you use the clear plastic that you find weeds germinating in the winter?
2)I can understand people using plastic covers over applications of FYM to reduce leaching out of nutrients in the winter, but i don't se much benifit apart from this.
3)surely if you put down clear plastic in say febuary, then net return in soil temperature would be the same as say putting down all through winter?
3)We all trying to warm up our soil, but i wonder are we forgetting the benifits of letting the soil go cold and dorment. Is the cold not a benifit in terms of killing of some types of weeds and harmful plant fungi and diseases? Are the frosts not a benifit to soil structure? Is the covering of soil with plastic long term not having a negative impact on the aeration of the soil.
4)we have probably all been through the pit falls of not having enough aeration in our polytunnels and glasshouses, so i do fear the state of the soil environment under plastic long term. Does your soil not get a dankness texture to it?