Best Way to Increase Organic Matter in Garden Soil

All soils benefit from organic matter, the only exception being peaty soils, which are rare in the UK. Well-rotted organic matter is a catch-all phrase for a number of materials of plant or animal origin that have been composted down to make a bulky soil improver. It improves the structure of soils that are waterlogged, compacted or too free-draining and feeds a hidden army of soil creatures and organisms that all contribute to the general health and fertility of the soil.

Unlike fertilisers, organic matter is added by the fork or barrow-load rather than being sprinkled on. As it is used up by the soil creatures, regular applications are needed.

Organic Matter Best Way to Increase Organic Matter in Garden Soil

Garden compost

Recycle as much organic matter as you can from your own garden and kitchen by turning it into garden compost. The most efficient way to do this is to collect all the material together in a bin and provide the right conditions for it to rot down.

Fill the bin with a mixture of woody material and green material. You can add a handful of nitrogen fertiliser or a shovel full of garden compost or garden soil to get the process going but do not bother with special compost activators.

Keep the contents damp but not sodden. A square of old carpet or sacking on the top will hold in moisture and warmth. A waterproof cover to keep heavy rain off is essential.

To encourage quick composting, turn the pile once every six weeks. After six months to a year, the compost will be dark and crumbly and ready to use.


Rather than putting piles of autumn leaves in the compost bin, stack them in their own wire enclosure to rot down into leafmould. They do not need warmth or a cover as the leaves are broken down by fungi rather than bacteria (as is the case with compost). Just water the leaves now and again, and in a couple of years the leaves will have rotted down. To speed things up, shred the leaves by running a mower over them before storing them.

Other sources

Most gardeners need more organic matter than they can make in their own gardens. Commercial products usually sold as soil improvers in 80-litre bags are ready processed and adequate for improving the soil of a small border or raised bed. For a larger area, you need a loose load of manure or spent mushroom compost.

Different manures

Well-rotted manure can be used straight away, but if it is fresh you will need to compost it. Make a heap and water it if it is dry. Cover it with a sheet of plastic secured at the edges; this will prevent nutrients being washed out. In about six months it will be ready for use.

Most manure these days contains a lot of wood shavings instead of straw. It needs to be stacked well before use so that the breaking-down process is completed before the manure is added to the soil, otherwise the wood can rob the soil of nitrogen.

Farmyard manure – Horse or cow manure is preferable. Poultry manure is best regarded as a fertiliser.

Spent mushroom compost – This is a mixture of horse manure, peat and lime, which is used to grow mushrooms commercially. After harvesting, it is sold off. It is an ideal soil improver because it is not as acid as other manures. Stack it under cover to allow chemical sterilants to break down.

Municipal compost – Composted green waste is available in some areas. It contains a high proportion of shredded wood – use as a surface mulch.

Garden Soil Best Way to Increase Organic Matter in Garden Soil

Compost bins

Ready-made bins – The best types are large plastic cylinders or cones with a lid. Make the compost in batches, then lift the bin off, leaving a composted heap that can be covered until it is used. Then start filling the bin again.

D-i-y bins – The ideal size for an effective compost bin is about 1 cubic metre. If you have room, make two side by side so you can turn compost from one bin to another (to get air into the mixture)

Site the bin in a shaded area out of view but with access for a wheelbarrow. It should be on free-draining earth (not on concrete or paving) so that worms and insects can migrate in and help aerate the compost. If the soil is wet, put down a layer of twigs first. Leave gaps at the bottom of the sides for ventilation.

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