Growing vegetable crops with heat
Many gardeners live in temperate climates where temperatures fall below freezing in winter and where frost can be expected on perhaps 200 days out of the year. In this sort of climate, the best chances for raising out-of-season vegetables go to those lucky gardeners who can supply heat, either by heating a greenhouse, by using heated propagators, or by heating frames either with-warming cables or by placing the frames on hot-beds.
With the help of supplied warmth, crops can be raised by several different methods. They can be sown in a heated propagator throughout late autumn and winter, and then brought on under frames or cloches or in a cold house. Crops can be sown in a hot bed or in warmed soil in a frame in winter and cropped there, or sown in autumn or early winter in a heated greenhouse, and cropped there. Alternatively, crops can be lifted and forced in heat, either in a heated greenhouse or in a warm frame.
There are heated propagators of all sizes, to supply as much or as little heat as required. There is even a single-tray kind which can be used to bring on five or six different vegetables. The trick is to be sure that you have a large enough area under your unheated frames or cloches to take the young plants at the wider spacing they need while they are being hardened off, or as they mature, if being cropped there. If the weather is very bad, you may have to keep the plants indoors for the time being, and then you will need more space for suitable containers, although not heat. Vegetables which can be grown by this method are, , , , radish and tomato.
Vegetables in frames
Frames can be fitted with soil-warming cables, or with cables around the sides which will warm the air. Such frames will remain permanently in position, and need to be within reach of an electricity supply. Alternatively, light wooden frames can be placed on top of specially prepared hot beds, sited in a position in the garden where as much sun as possible is available, and where there is the most protection from wind or frost. The crops, for instance, French beans beetroot, marrow, carrots and turnip, can be sown thinly, or station-sown direct into heated soil and left to mature there.
Raising greenhouse crops
The heated greenhouse, in which crops can be sown and matured, allows for very luxurious cropping, so long as you can supply, a good deal of heat. For example, ifare to crop in winter, the night temperature should not fall below 16°C (60°F). Tomatoes can also be cropped from late winter onwards, in the same amount of heat. French beans, , lettuce and , however, need only gentle heat, 10-13°C (50-60°F) during the day and a little less at night. Asparagus, and can all be forced in a matter of a few weeks with heat; you can enjoy crops in succession throughout the winter.
Of course, supplying extra heat at the coldest time of the year does make many vegetables an expensive luxury. However, those crops which need only gentle heat and those which can be forced in whatever time you like, depending on how much heat you supply, can be had at little extra cost, since there is no need to heat the whole greenhouse. Your greenhouse can be partitioned and lined with plastic sheeting—the type which consists of a double sheet with air bubbles between the layers is particularly effective. Decide in advance how much of the greenhouse you can afford to heat, and make the partitions as small or as large as necessary.
The use of artificial light to prolong the day length and increase the intensity of light will make the production of winter crops easier still. For instance, you can use ordinary electric light bulbs which supply some heat as well, or you can try the effect of fluorescent strip lights. The mercury vapour lamps which produce a greenish-blue light in the ultra violet wavelength are particularly suitable for growing plants. Advice on the most suitable kinds of lamp for particular crops and the cost of running them can be found at the Electricity Board.