Winter and early spring are a good time of year for gardeners to enrich their soil with organic matter such as manure and compost. Many of the plants have died back, leaving more room to dig the material into the soil or making it easier to just lay it on top with the “no-dig” technique that helps suppress weed growth too.
Uncultivated soils tend to contain 3 to 6 per cent organic matter, which accumulates from the natural cycle of plants dying and being broken down by microbes. Cultivated soils may be at the lower end of that range, because farmers or gardeners regularly remove plants that have died or been cropped.
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Organic matter improves soil health in several ways. Most obviously, it releases nutrients crucial for plant growth as it is broken down. But it also helps to stop any nutrients from being washed away, because it binds the mineral particles of soil into larger aggregates.
, containing complex networks of air channels, less than the width of a human hair. It is unclear exactly how they form, but they seem to help oxygen circulate to plant roots and microbes, says , who was involved in the study.
Neal and his team took X-rays of a soil particle to create 3D images of the air channels. They made a strangely hypnotic video of a journey zooming through a computer reconstruction of them (see it here: ).
In the same way that it seems to be beneficial to feed your gut bacteria with a diverse diet, it also helps if you feed the microbes in your garden soil with a variety of organic matter, says Neal. “If you’re composting, you’re putting in a broad range of different types of plant material,” he says.
You can judge if soil has enough organic matter by how it looks and feels – the ideal soil is dark in colour and crumbles easily in the hand when dry, according to the UK Royal Horticultural Society. But I generally add more once a year, to be on the safe side.
Depending on how big your garden is, it can be hard to get hold of enough organic matter. In a previous column, I described how you can make your own compost from kitchen and garden waste. This is a good way to reduce the amount of rubbish sent to landfill, but it doesn’t yield large amounts of compost.
You can obviously buy compost or manure from garden centres, although this can be pricey. For my allotment, I order deliveries of horse manure from a local stables or collect it myself for free. It isn’t smelly if it is already well rotted. Shovelling manure onto your soil is heavy work, but it leaves you with the rewarding feeling of having tucked your plants into bed for the winter.
What you need
Manure or compost
A shovel
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