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Salad crops from a cold greenhouse this winter


All over the land as the autumn gives way to winter, load of greenhouses lay empty. For a lucky few, the story is different with their owners able to afford to heat their greenhouses over the winter period with electric or oil fueled heaters.
However with a little planning and ingenuity its possible to produce some free heat in your Greenhouse by using the old Victorian method of hotbeds, slightly altered to suit todays requirements.
Hot beds use the action of bacteria and micro organisms breaking down heavy organic matter such as straw to produce heat as a bi produce of this process. The skill is to start and then to control the heat in the same way you would regulate the heat in a greenhouse in the summer months with watering and opening and closing the vents. First you will need to construct a a raised bed using the side of some old pallets cut in half to form the sides of the beds. The beds can be placed on a soil base or a greenhouse bench within the greenhouse. In some cases, the benches might need additional support to be added to support the weight, this can be achieved by adding a second framework of wood under the existing bench structure.
Next fill up to about a third full of fresh strawy manure, ideally with areas of straw that the animals have used to urinate on. This is because the urine in high in nitrates and this method relys on the bacteria and micro organisms acting or what is in effect feeding on these nitrates. Lightly compact down the straw and apply a nitrate fertilizer, ideally containing ammonium sulphate you will need about a handful per square metre, finish off by watering the straw lightly with a watering can full of water. You will need about a handful per square metre.
Then apply a layer of garden soil about 50mm deep over the strawy manure and lightly compact down. The cover with 30mm of John Inness Number One soil-based compost and again lightly firm down and water. Around the sides of the pallets, push some straw or old newspaper to create insulation finally covering the whole area with plastic to act in the same way as a gardening cloche would outside.
Over a period of several days, you will start to see that the soil warms up. Once this happens, its time to sow your seeds. The seeds can be sown in the normal way as you would in seed drills outside. Start with some asy crops such as salid leaves or raddish to see how you get on and then as you get used to regulating the heat you can try forcing other crops such as rhubarb and other crops
Once you have sown your seeds, the skill to control the temperature in the soil to an even slightly warm temperature by rolling back the plastic covers during the warmer days and opening the glasshouse vents if you find some very warm days and at night closing the vents and on cold nights - insulating the hotbeds with some old carpet or sacking is also a good idea if some of the nights are very frosty.


Some examples of crops you could try


When your crops have finished, you have an ideal supply of organic matter from the beds to add to your summer crops such as runner beans and marrows.