Organic gardening: Take care of topsoil
Daily Telegraph Organic Gardening Homepage
Your topsoil will thank you if you encourage it with a decent mulch, writes Tom Petherick
Despite an impossibly wet summer with all its attendant problems of fungal diseases and waterlogging, the recent good weather has at least rewarded us with a brief Indian Summer.
There was no rain on my garden for the first three weeks of September and, despite heavy morning dews that don't add much in the way of moisture, the soil surface is already drying out.
In any garden those few inches of humus-rich topsoil are precious indeed, so means must be made to protect them. The best way to do this is by the use of a mulch.
When soil dries out to the point that it crumbles and forms dust that blows away when handled or worked, this amounts to erosion - something we cannot afford, as good topsoil takes years to build. It must be maintained and a covering of mulch can do this.
Building a fertile soil in the garden should be one of the prime aims for the organic gardener, but there are only a few ways that soil builds naturally without human effort.
One is under permanent grass pasture, another is under still water where silt gathers and a third is on the forest floor.
In the woods a combination of leaf litter and the bodies of animals, insects and all the other matter that inhabits the topmost layer of the forest floor makes and protects soil. Applying a mulch to the surface of the ground mimics this.
As well as preventing soil from drying out and eroding, mulching will also add nutrients, especially if the chosen material is home-made compost or well-rotted organic matter in the form of stable or farmyard manure.
All sorts of materials act well as mulches: mown grass (if you don't mind the rapid change of colour from green to brown), straw (but not hay because of the seed content) and any bagged (but expensive) organic compost from a nursery or garden centre.
All will act as slow-release fertilisers, ultimately rotting down and being consumed by the soil. Just remember to apply a mulch when the soil is damp, otherwise moisture will struggle to get through the mulch to the soil beneath.
There are also living mulches in the form of green manures. Whereas bulky organic matter is suitable for most garden situations, be they beds, borders, shrubs or trees, a green manure comes into its own on larger patches of bare soil awaiting next year's sowing and planting.
The vegetable garden is the obvious place, because green manure needs to be dug in the following spring after it has been cut or mown off. It is not too late to lay some down over the next couple of weeks while soil temperatures are still high.
Simply broadcast the seed on the surface, rake it over lightly and give it a water. If you can cover the patch with a layer of horticultural fleece to keep the birds off and create warmer conditions for germination, so much the better.
My own choice for green manure is red clover because as a legume it fixes nitrogen. A covering of clover over winter will protect and stabilise the soil from heavy rain and will only be killed off by the harshest and most persistent frosts. It will come into flower by Easter and provide good early bee and insect forage before being cut and turned into the soil.
As well as sowing it on to bare ground, I grow it as an under-storey beneath my winter brassicas - particularly the tall ones such as purple sprouting broccoli. In addition to providing nitrogen for the brassicas, and protecting and feeding the soil, the clash of the clover's red flowers with the yellow of the going-to-seed broccoli is too good a sight to miss in spring.
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