Earth matters: Anna Pavord's mulching masterclass

You can shower it in fertiliser and TLC, but a plant is nothing without decent soil

New gardeners are usually told that, before they start flailing around outside with spades and wheelbarrows, they must draw a plan of what they intend to do. This is what we expect of professional garden designers, but it is not necessarily the best way forward for amateurs. Paper designs tend to get over-complicated. The obvious is avoided at all costs. Nor can paper contain all the information you need to make the right decisions and which you get as you prowl over your patch. You take in the slight rises and falls in the ground and the consequences that these will have on your hopes and ambitions. You are aware of things beyond your boundary that you would rather not see and which a well-placed plum tree may be able to conceal. You sense where the sun falls and which patches are permanently in shade. You feel the wind and begin to understand the problems that this might cause with a too-hastily-erected wigwam of peas. Think simple is the best advice. And think big, however small your plot.

More important for anyone taking on a new garden or allotment is learning to understand your soil. Vegetable heaven is a soil that is well-drained, fertile, open, and neither too acid nor too alkaline. If you have an old garden, somebody else might have already converted the underlying sand or clay into a workable tilth. If not, grit your teeth and prepare to mulch, mulch, mulch.

Soil is a mixture of bits of rock, water and organic matter such as rotted leaves. Sandy soils (ideal for carrots, which swell easily in this open, free-draining medium) are made from relatively large bits of rock; clay soils (good for brassicas, which prefer a solid soil) from small particles. One is called light, the other heavy. Adding bulky manures to soil is the only way to improve soil structure. The extra organic matter (humus) closes up the big spaces in sandy soils, making them capable of holding more water. In clay soils, humus adds extra air spaces between the too-closely-packed particles and improves drainage.

What you grow and how you grow it is to some extent determined by type of soil. The five main kinds each display characteristics that make them reasonably easy to recognise:

CHALK A pale, shallow, stony topsoil indicates chalk. It is free-draining and moderately fertile.

CLAY Clay is heavy, slow-draining and often quite sticky. It can be hard to work but is full of nutrients.

PEAT Rich in organic matter, peat looks very dark and crumbly. It retains moisture well and makes an acid soil.

SANDY SOIL Light, gritty and free-draining, sandy soil is easy to work, but it needs lots of humus to make it fertile.

SILT Silt is fertile and retains moisture well but is easily compacted. It has rather a silky feel if you squeeze it.

No amount of chemical fertiliser will change the structure of your soil. Plant roots need passages along which they can run and from which they can then absorb the nutrients necessary for healthy growth. Humus helps to create these vital passages. In town gardens it may be difficult to acquire bulky manures, the best source of humus, but make a resolution to haul in a sack of some nourishing mulch once a week until the whole plot has been covered. It will pay enormous dividends in improved growth. If you have space, make your own compost. It should have the colour and texture of rich fruit cake.

The minerals that plants need for healthy growth are generally lumped together under the heading "trace elements" and include boron, copper, iron, manganese and zinc. In fertile soils they are present naturally, but lack of them shows up in plant deficiency diseases. Organic animal manures are rich in trace elements and if you use these regularly, you are unlikely to have problems. Magnesium deficiency (which makes leaves turn brown and wither) is more prevalent on acid soils than on alkaline ones. Chlorosis is more likely on limey soils: leaves that should be bright, pulsating green turn a pallid, sickly yellow. It is caused by the fact that the plant cannot absorb the minerals it needs from the soil because they are locked up by too much lime. You can correct the imbalance by watering with a solution of chelated iron (sequestrene).

Acid or alkaline

Acid and alkaline are terms that apply to the pH (the potential of hydrogen) in the soil. The scale runs from 1 to 14 with neutral around 7. Most vegetables and fruit do best in this middle range. Asparagus is not happy on very acid soils, whereas blueberries demand it. Generally, though, fertility and drainage have a greater effect on growth than the pH level. There are simple kits available with which you can gauge the pH level of your soil, but remember to take readings from more than one part of your garden.

You can tinker with acid soils by adding extra lime if you want to make them more amenable to the growing of vegetables. It is far more difficult to convert an alkaline soil to a comfortable home for lime-hating plants. Raspberries, for instance, always look happier in slightly acid soils than they do in heavy, clay ground.

Cultivation methods

Only masochists make digging loom large in the gardening calendar. You dig to get air into compacted soil, to bury weeds or other organic material and to give robins a decent breakfast. But digging no longer has the heroic status it once had. On light soils, forking over will often be enough. Mushroom compost or any other weed-free compost that you can spread thickly on top of the ground will eventually be pulled down by worms. That is a lot less trouble than doing it yourself.

If you garden on light, sandy soil, it may not be necessary to dig the earth at all. Weedkill it thoroughly, mulch it heavily and plant direct into the ground. The main problem here is hanging on to water and nutrients. By leaving the soil firm over winter, you will be helping it to hold as much water as possible. On light, well-drained, fertile soil, you can make a fruit and vegetable garden without ever having to dig at all. But to maintain fertility you have to mulch heavily.

The no-dig method works well in areas where you have permanent crops such as fruit bushes or asparagus. You can use it on ground where you grow transplanted crops such as tomatoes, courgettes and leeks, and also for second early and maincrop potatoes, both of which can be put in now. For seedbeds, you need a fine tilth and a mulch in these circumstances is a hindrance. Here, a rake is the best tool, to bash down clods of earth, to smooth over the surface and (using the back of the rake) to make shallow drills for kohlrabi, carrots, salsify and other vegetables to grow from seed this month.

See Anna Pavord's book, 'Growing Food' (Frances Lincoln, £7.99), a revised and updated edition of 'The New Kitchen Garden'

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