If you grow vegetables, you already know some of the crucial requirements: a fertile soil and adequate water for starters. You also know that, in a temperate climate like Britain, warmth is vital; nothing will grow outdoors in winter. You probably worry less about light, and usually of course you don’t need to because light tends to vary in tandem with temperature. Normally if there’s enough light, it’s warm enough, too.
A gardener’s guide to growing vegetables in winter
Usually, but not always. By the end of April, the length of the day is the same as in early August, but in the vegetable garden the two seasons couldn’t look more different. August (most of the time) looks and feels like summer, with crops of all sorts growing away like mad. The end of April can also feel like summer, at least on a good day, but the vegetable plot is a study in brown, with bare ground and most new-season crops little more than seedlings. The problem is that until some time in April, depending on where you live, the soil and air are both too cold for seeds to germinate or for plants to grow. There may be 15 hours of daylight every day by the end of next month, but most of it is wasted.
There are, of course, ways to try to get ahead of the game. You can grow crops in a greenhouse, or on a windowsill and plant them out later, but the scale is limited. Yet there is a potential source of free heat in the garden; any heap of decaying organic matter, as long as it’s large enough, will get hot and stay that way for weeks or even months. You may well have wondered vaguely if all that heat could be used to grow early crops, but have been unsure how to make that work in practice.
Don’t worry – the “hot bed” technique is ancient. It last flourished in the era of the Victorian kitchen garden but more recently, someone else has endured the years of trial and error needed to devise a practical system. His name is Jack First and the fruits of his experience are explained in a little book called Hot Beds (Green Books, £9.95). Essentially, the technique requires a bed of decomposing material, with a frame around it to contain the growing medium, and a transparent glass or polythene “light” on top to keep the heat in. You could buy all the kit, but the book provides instructions for making your own. Using the methods described, the author routinely harvests radishes, rocket and salad leaves in early March. He then picks lettuce and turnips in late March, while carrots, beetroot and even potatoes arrive in April and May. And all that in Keighley in West Yorkshire – which is not the warmest or sunniest place in the world.
How to grow potatoes in pots for early spuds
Books such as this sometimes strike me as not particularly realistic, unless you’re prepared to live what amounts to one long episode of The Good Life. But First has realised that although many of us may strive for perfection, few of us will achieve it. So, for example, although the basis of his traditional method is stable manure, he has plenty of suggestions for those of us who can’t get hold of the genuine article. The method will work with leaves, paper, cardboard, wood shavings, sawdust, straw and even old cotton and wool clothes – anything, in fact, that could go on the compost heap. Some of these materials are low in nitrogen, but we all produce more than a litre of the remedy for that every day.
How to make your own compost
Similarly, the details of frame ventilation sound at first so complicated that it’s hard to see how they could be achieved by anyone with a normal working life, but it turns out that such attention to detail isn’t strictly necessary. Six hot beds that First set up at schools around Keighley all managed to produce decent early crops, despite a lack of expert attention, staff illness, school holidays and even vandalism. Hot beds are quite forgiving.
Just one final point. It’s obviously a bad idea for crops to squash up against the lights as they grow taller, so to avoid this First recommends gradually jacking up the frames with bits of wood. But an alternative solution is to replace the lights with plastic cloches. If you visit the National Trust’s Acorn Bank garden near Penrith you can see this system in operation for yourself.