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.

Labels: allotment-cloches, allotment-vegetables

Allotment Tasks – Warming the Soil

Of the not-very-many things to be done on an allotment in January, warming the soil is perhaps one of the most important and most neglected. And we’re just starting to think about warming ours, having finally dug enough of it to actually think we might get some crops in!

The point about warming the soil is that it helps germination by two means: it absorbs the warmth of the sun in the day, and slows down the loss of that heat at night, which can protect from frosts. If you have hardy crops like carrot, they will germinate in the soil at around 8 degrees Celsius but tender crops like French beans won’t germinate until soil temperature is 12 degrees Celsius – and remember that air temperature tends to be at least a degree above soil temperature and may be as much as three degrees higher than clay soils. Dry soils warm faster because water holds the cold, so having raised beds with good drainage can improve germination if you have a heavy soil

There are two ways to really warm your soil: the first is adding compost or manure which both breaks up heavy soils, giving them less water trapping, and tends to change the albedo (surface colour to us simple folk) making it darker and therefore more inclined to take in, rather than reflect back, the sun’s rays.

The second thing, of course, is to cover the soil with glass, plastic or cloches. Clear plastic is reckoned to be the best option, and this kind of cloche can be lifted easily to hoe out the weed seedlings, which will germinate very fast, and that’s always great news because once those seeds have germinated and you’ve chopped the seedlings in two, they can’t come back to strangle your plant seeds when you do put them in the ground. So quite obviously, the ideal situation is to put down your cloches a couple of weeks before you plan to sow seed, and get ruthless with the weedlings when they appear.

So why, I wonder, don’t we have any cloches … possibly because we are ill-organised and spend too much time chatting. Oh dear, oh dear, I can see allotment-holder-failure on the horizon!

Labels: allotment-cloches, allotment-seedlings, allotment-soil