Professor Buczacki is a horticultural expert, writer and former chair of Gardeners' Question Time
Is manure better than garden compost for the allotment?
Stefan says: This is something that puzzles many gardeners, both new and experienced, so it may help if first we think about why we need to add bulky organic matter – of whatever kind – to the soil.
The first reason is that organic matter will improve soil structure through increasing its water retentiveness, by opening up the compacted nature of a clay and by helping to bind together sand particles and so enhance crumb formation. Overall, there is little to choose between garden compost and well-rotted farmyard manure in this respect, although a few features of each should be borne in mind.
Garden compost must be well made, well decomposed and not contain diseased plant material or abnormally high proportions of any one type of matter, such as lawn mowings. Farmyard manure should also be well decomposed and it’s most important that if the manure is only available fresh, it should only be dug into the soil in the autumn. Otherwise, it will begin to decompose further and the micro-organisms responsible for this decomposition will deplete the soil of nitrogen as they do so. It may also contain herbicide residues.
The second reason why organic matter is beneficial is that it will provide nutrients for your plants. And here again, there is little to choose between the two. Both well-rotted compost and well-rotted manure contain around 0.6% nitrogen and 0.4% each of potash and phosphate, so unless you use unrealistically vast quantities, neither is likely on its own to provide enough nutrient without the addition of fertiliser.
It’s also important to remember that the addition of any organic matter to the soil is not a once and for all exercise. Once incorporated, it will continue its decomposition and must, therefore, be replenished annually.
And finally, a reminder that it’s now becoming rather late just to layer organic matter on the surface in advance of this season’s planting. There is insufficient time for the worms to drag it down in to the soil so you’ll have to do that yourself and thoroughly fork it in.
