Growing vegetables under cloches

We don’t use cloches much at the allotment, for two reasons:

1. We start almost everything off in the greenhouse, and only move it outside when the weather is clement
2. We have a nine raised beds – six of them for rotated crops (the others hold early strawberries, late strawberries and asparagus) so we can cover them with fleece if we want to start crops off under cover.

However, we are wondering about whether to put cloches over our earliest potatoes – my parents, down in Torquay have already got their first earlies in the ground under cover, and they were harvesting a month before we were.

At this time of year, lots of gardeners are covering their soil with cloches to warm it up – I’ve never been entirely convinced by this process for two reasons – first I don’t quite see how the soil is warmed (okay, covering it can remove the chill of frost but it can’t actually make it any warmer than the ambient air temperature unless you use black plastic to conduct heat) by covering it, and second, covering soil ignores the action of convection: soil isn’t just made warmer or colder by the sun or frost but also by the movement of water through the soil which freeze in cold temperature and then melts in warmer ones. So if all the soil around the cloche freezes, then surely when it melts again, the meltwater will penetrate quite a way into the soil that hasn’t frozen at all, and drop its temperature?

On the other hand, the value of cloches in protecting tender plants, whether those overwintering or new seedlings, is undoubted – and that’s where we cover our raised beds with one of three media: glass, horticultural fleece or mesh, depending on the plants in question.

I now have ten beef tomato seedlings, so I shall be offering at least seven of them at seedling swaps, and I’ve just covered one of our empty raised beds with fleece and sown the first row of salad seedlings.

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Posted by The Allotment Blogger on Monday, February 15, 2010

11 Comments:

Anonymous Damo said...

I keep meaning to make some cloches and see if they make any difference but haven't got round to it yet. Our local society had a veg expert in who said you should cover as much of your plot with black plastic as possible a few weeks before sowing to warm the soil up. Haven't tried myself yet though, it's on my 'nice to have' as opposed to 'must do' list. Best of luck.

February 15, 2010 at 11:42 AM  
Blogger Paula said...

I think it's possible that enough of the soil does stay warmer under the covers. If you think of the way that clouds hold warmth in at night (the temps surely drop when it's clear at night), a covering on the beds may do the same thing for the first half-inch or so of soil, or maybe deeper. Folks are growing stuff under cover through the winter in places like Maine and Wisconsin, so it must work.

February 15, 2010 at 9:00 PM  
Anonymous allotments4you said...

everyone really seems to be getting on with planting their seedlings and I haven't even thought about it yet...none of my packets say stuff should go in just yet so I don't think I'm behind but I am feeling very lazy whilst I read through everyone else s progress!!

February 16, 2010 at 12:18 AM  
Blogger spodge said...

Hi , Why don't you buy a soil thermometer,and test the difference if any?

February 16, 2010 at 4:12 AM  
Blogger Jo said...

I'm considering planting some of my early potatoes in containers, starting them off in the greenhouse, to get a few extra early ones. The rest will go in the allotment once it warms up.

February 16, 2010 at 9:20 AM  
Blogger The Allotment Blogger said...

Spodge - that's a very good idea!

Damo and Paula - I'm not saying it doesn't make a difference, just that I'm not sure that it makes enough of a difference to be worth the effort - I am trying to find a good peer reviewed horticultural study to find out the truth.

Tanya - well, we're between three and six weeks behind where we were last year, according to my planting diary, so I feel quite slovenly.

Jo - hmmm .... I wonder if I can stick a couple of our first earlies in a greenhouse pot? It's a very good idea but I don't know if there's room. I shall go and check!

February 18, 2010 at 4:11 AM  
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July 31, 2010 at 7:45 PM  
Anonymous Growing Vegetables said...

Last year ie 2010 I tried an experiment on my plot where I covered half of the row where I was going to sow my carrots and parsnips with cloches two weeks before I was due to sow them, and left the other half open to the weather. Once I had sown the seeds I left teh cloches off.

The results, both the carrots and the parsnips in the soil warmed up first germinated sooner and at a higher percentage of germination.

I will be doing the same again this year to check the results.

January 1, 2011 at 3:34 AM  
Anonymous Matt Houldsworth said...

I have always put out the cloches on my allotment in mid to late January to warm up the soil. I am not sure if it really makes a difference, but at this time of year there is little else to do so getting the job of cleaning the cloches and making sure they are in good repair is one thing I can be doing.

You mentioned that you don't use cloches as you have raised beds, I use one of my bigger cloches on a raised bed, it is great for covering early carrots and salad crops.

January 13, 2012 at 2:02 AM  
Blogger The Allotment Blogger said...

Growing Vegetables - that makes sense, and we do find that the raised beds have a similar effect as they act as a wind break and we work the soil in each bed in relation to the crop that will get planted so parsnips get sand etc which makes the soil friable (and warmer where one adds compost or manure) - it would be good to hear the results of this year's test too.

January 17, 2012 at 4:29 AM  
Blogger The Allotment Blogger said...

Matt, you have a point (and an extremely large cloche!) but we find there's plenty to do in the greenhouse and with overwintered crops, to be honest.

January 17, 2012 at 4:31 AM  

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