Make a hotbed

A century or so ago, a hotbed would have been one of the vital tools in any self-respecting head gardener’s armoury, along with several acres of walled garden, a huge range of glasshouses and dozens of helpers.

You might have to pass on the rest, but a hotbed is entirely do-able even in today’s tiny veg-plot or allotment, and it’s well worth having. It’s a natural form of under-floor heating, traditionally used for producing early crops under glass or out in the open. A hotbed is a great way of making the most of a small veg-growing space. And since it uses materials that you’d otherwise put on your compost heap or simply dig in, it won’t cost you a penny. Here’s what to do.

Find a sunny, sheltered, well-drained corner where the soil has previously been well-prepared, and construct a rectangular frame about four feet long by two feet wide from old planks. Alternatively make a hotbed in a greenhouse border or under a walk-in poly tunnel.

Fill the frame with a mixture of kitchen peelings, cabbage leaves, eggshells, teabags, also any soft annual weeds, old bedding plants, and some fresh lawn mowings if you’re able to cut your grass. If you have a source of fresh manure – horse, ideally, with plenty of straw  – add that, mixing it in with the green waste, otherwise use plain straw, or dead leaves raked up from round the garden. Tread the mixture down firmly, and water so it’s evenly moist, then cap the lot with six inches of good topsoil or used growing-bag compost.

Now you’ll need a soil thermometer (this looks like a long clinical thermometer, from garden centres). Stick it into the centre of the mound and watch the temperature start rising as the contents start to rot; it’s just like a compost heap. After the temperature has peaked it will start to drop slowly, and when it falls to 75F you can start to sow or plant into the soil on top.

By then it’ll be February or early March, so you can use the hotbed to sow or plant early crops such as lettuce, spinach and spring onions. To make the most of the free ‘bottom heat’, cover the hotbed with cloches or sit a cold-frame on top. A Victorian gardener would also have used a set-up like this as a propagator for sowing seeds of veg and annual flowers to provide young plants for transplanting into the garden later. You can still do that nowadays.

But where a hotbed really scores hands-down is for growing frost-tender crops including French and runner beans, courgettes, squashes, outdoor tomatoes and sweet corn, since these are all ‘greedy’ crops that like rich soil and the extra warmth means you can start them several weeks earlier than out in the open – late April instead of mid- to late May. And cover seeds or young plants with cloches or ‘fleece’ till all risk of frost has passed. The natural heat generated underneath will do the rest.

So start now; by using a hotbed you can extend the growing season by a month or more at each end, which means you’ll be harvesting home-grown veggies and salads for far longer than usual. And when your first crop is over and the hotbed has finished rotting down, you’ll still be left with a patch of exceptionally rich soil full of very happy worms that’ll stand you in good stead for future crops. What have you got to lose?