Agriculture Reference
In-Depth Information
manure, make sure that it is from an organic source because the risk of accidentally
contaminating your tunnel soil with pesticide residues (as many growers did
during the aminopyralid debacle of 2008) is not worth taking.
Compost
Compost is generally a better option than manure and is the principal means of
feeding the polytunnel soil, although not the only means. Always use the best
organic compost that you can get hold of. Ideally that means making your own
(and we include some topics in the Resources section to help you do just that), but
if not, you will need to buy quite a lot of it: 70 litres for each square metre of bed.
Home-made compost ideally begins as alternate layers of 'browns' (drier, high-
carbon material) and 'greens' (wetter, high-nitrogen material) placed in a large
heap. Never add meat, fish, grain products or cooked vegetables, or you are likely
to find rodents setting up camp nearby. The composting process can be of two
types, 'cold' or 'hot', depending on how the pile is treated after first being made.
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A cool pile
Cool composts are simply left alone for several months to a year, and after an
initial burst of heat it is the activity of worms and low-temperature fungi and
bacteria that creates the compost. It can take ages, which is why these piles
are often made and then left over winter. Eventually, nice-looking compost is
the result, but it may still contain seeds, bacteria and fungi from whatever
was used to make it. If you have used manure to make your cold compost, the
lack of high temperatures makes it just as unsuitable as manure itself for use
around plants that are to be eaten raw (see left).
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A hot pile
Hot compost piles are turned every few days, ensuring that the contents
become mixed and aerated. A hot pile makes compost much more quickly
than a cool one: all the material in it can be converted within as little as two
weeks, generating heat along the way. Because of the insulating nature of a
big pile of compost and its cover (very important, or heavy rainfall can cool
everything again), heat builds up as the bacteria break down the vegetable
matter. Eventually the whole thing reaches a high enough temperature to kill
seeds and disease organisms throughout the entire pile.
If you do have to buy commercial compost, buy an all-purpose or potting compost
rather than a 'soil improving' or mulching compost, because these latter types
can contain a lot of woody material, which can cause a population explosion of
woodlice in your polytunnel.
