Black plastic and potatoes

[Ruth M C]

I read last autumn that you can grow potatoes under black plastic and once the shoots lift the plastic a little you cut slits to let them through and subsequently photosynthesise.

So this year as an experiment I am following this method. The black plastic went down over moist soil 2 weeks ago after I prepared the soil with a soaker hose and manure. However I have also read that depriving soil of light quickly reduces its nutrients and fertility. Has anyone found this to be true?

Secondly it has rained quite a bit since and there are puddles on the plastic. To my understanding this means that with no water getting to the soil it may well dry out. Should I put pin holes in the plastic to let the cold water drain in? I shall be adding the slits later anyway so the plastic shouldn't be ruined by this initial action.

And lastly if I do allow drainage of the rainwater into the soil will it lower the temperature of the soil and reduce the effect of the black plastic in warming the soil.

Your advice would be welcome

Kind regards

Ruth

[Aberdeenplotter]

I have also read that depriving soil of light quickly reduces its nutrients and fertility. Has anyone found this to be true?

Secondly it has rained quite a bit since and there are puddles on the plastic. To my understanding this means that with no water getting to the soil it may well dry out. Should I put pin holes in the plastic to let the cold water drain in?

And lastly if I do allow drainage of the rainwater into the soil will it lower the temperature of the soil and reduce the effect of the black plastic in warming the soil.

Hi Ruth,

I cannot see how depriving the soil of light can deplete the soil of nutrients and fertility.

Your soil may well dry out through the natural process of drainage but personally I wouldn't worry too much as you mention you used a soaker hose before covering the area and mositure cannot evaporate because of the cover.

The black polythene will prevent weed germination and for every drainage hole you make in the polythene, you will allow light in and therefore allow some weeds to germinate. For that reason alone, I'd just leave the puddles.

Suppressing weed growth aside, there is no need to have your polythene cover in place for a long period before planting time as it doesn't take long for the soil to heat up once the sun decides to show face.

Finally, rats love areas of ground covered in black polythene and the likes. It's nice and warm and dry in there and if you plant potatoes, there's a ready and available source of food as well.

[Florence Fennel]

I'd thought about this method, but you've just put paid to that AP, I can't abide rats.

[zazen999]

I've done the same albeit with cardboard and they are so easy it's ridiculous. No rats fortunately.

When you come to furtle, you just lift up the cardboard and take the spuds out and leave the plant in place.

It's almost shameful the little amount of work it is!

I'll be doing it again this year.

[Alison]

I've found it much better to use cardboard rather than plastic as this lets the rain water through so there are no watering problems. Rats will only be a problem if you have a rat problem already, it's unlikely to attract more but you may find that slugs like the dark covering.

[Florence Fennel]

Now that's a help you two. I've had some card over a patch of ground for about 3 months (I intended siting another raised bed there). The cardboard is obviously soaked through - can I plant through that rather than lifting it and digging the ground over? I might very well be growing more potatoes than I intended this year if that's the case.

[Alison]

You can defo plant through, just make a small cut in the card (which will be nice and easy if it's wet) and dig a hole for the seed potato. I did this in a totally unworked area of the plot a couple of years ago and just used a bulb planter to dig the hole, chucked a bit of chicken manure in the bottom and filled in. Worked really well and was embarrassingly easy. The ground was really easy to dig afterwards too

[Florence Fennel]

Thanks so much for this Alison, I'll be getting some more seed potatoes now. It sounds too easy - no earthing up! Were slugs a big problem?

[zazen999]

Just pop some organic slug pellets under the card if you can lift it up and then leave them to it.

Embarrassingly easy.

[Florence Fennel]

Thanks Zaz, I'm definitely going to give this a go. I can't do "strenuous" anymore, so this sounds perfick! Sorry to have done a bit of hijacking Ruth, hope your plastic trial works a treat.

[Florence Fennel]

Have just thought - I'd better do a bit of a search on how to grow potatoes now to find out about distance etc., I've only ever done them in planters!

[Alison]

What sort of spuds are they, earlies or main crop?

[Florence Fennel]

I've got a few International Kidney (earlies, I think?), but I'll have to buy more for under the cardboard. What do you recommend Alison? Thanks in advance!

[Lotsaveg]

Have you thought about mixing in or watering in some Mycorrhizal fungi? These are really good at boosting plant and root growth.

[Alison]

If you're going to dig them up as earlies then you can get away with as close as a foot apart in both directions (assuming you're not going to be walking between them) but more is no bad thing.