Know Your Soil Type and Organically Improve It

Improving Your Garden Soil

Recognising your soil type and improving it organically

We rarely have the opportunity to choose our site or the soil for our garden, and have to make do the best we can. Most gardens are on old sites and may be exhausted and pest ridden. Those in towns are likely to be polluted and out of balance, especially if many chemicals have been used. New sites and country gardens may have been treated better, or worse if they were recently formed. Sites run derelict and full of rampant weeds will probably have better soil.

improving garden soils Generally, most soils will produce flowers, shrubs or tree fruit without much improvement, but need to be better for vegetables and soft fruit. Problem soils tend to be local problems and it is always a good idea to see how neighbours cope. Almost all soils can be improved, but it may even be an easier option to put on extra topsoil if the existing soil is very poor. Most types of soil need basically the same treatment to improve them: the addition of copious quantities of organic material. Anything else is of little consequence by comparison.

Soils can be divided into types in many ways, but what concerns the gardener most is their effects on plant growth and ease of labour. There is no need to know their exact composition, but how they behave.


Loamy Soil

Loamy soils are produced when old meadow or grass sward is dug up, or where other soils have been heavily enriched with organic material. This is the best type of soil for most plants. The best loams have a rich, brown, sugary texture, made mostly of earthworm droppings, which encourages plants grown in them to produce masses of fine root hairs that pull up granular soil particles with every root. You can make your own loam-like soil for your most favoured plants by stacking and rotting down turves of grass.


Heavy Clay Soil

Heavy clay soils are hard to dig, stick to every tool and boot, drain poorly and pool with water in heavy rain. However, they are the richest soils, rarely suffer mineral deficiency and resist drought well, though eventually set like concrete. Clay soils must never be compacted while wet, so do not stand on them. They need copious amounts of coarse organic material, sharp sand or grit, and they benefit from liming and fixed bed gardening. Heavy soils encourage slugs, but also produce the best cauliflowers and roses.


Sandy Soil

Sandy soils are a joy to dig, wash easily off tools and shoes, and never pool with water even in downpours. They need much more organic material, rock dust (especially ground rock potash) and organic fertilisers than other soils because their wonderful aeration burns off humus quickly. They warm up quickly in spring for early crops, but dry out badly. If not too stony, they will produce super carrots.


Silty Soil

Silty soils are more like sandy soils than clays, because they do not retain water and are fairly easy to work. Often built up on old river beds, they benefit from ground rock dusts. They are good for most crops if well fed, but tend to splash and cap badly in the wet.


Lime-Rich / Thin Chalky Soil

Lime-rich or worse, thin, chalky soils cause chlorosis (yellowing leaves with green veins) in lime-hating plants by locking up iron and other nutrients. Slightly lime-rich soils suit most plants though, especially brassicas, if they are also rich and moist. Good for many trees, figs and grapes, these soils need feeding and mulching. Thin ones over chalk or limestone are then hot and hungry, so raised beds will significantly improve them.


Stony Soil

Stony soils tend to be freer draining, though not always. The stones are of little consequence to most plants, but frustrate cultivation, especially hoeing. These soils are better with permanent plantings and mulches rather than for growing annuals and vegetables, though these can thrive on cleaned beds. ‘Hoeing mulches’ of sharp sand make hoeing and sowing much easier.


Peaty Soil

Peaty soils are not always advantageous. Though very high in organic material they can be short of nutrients, dry out easily and are not stable enough for large trees. They will grow good salads and soft fruits, though, and will be naturally suited to lime-haters such as rhododendrons. With the addition of lime, many other plants can be grown, and weeds thrive.


Wet Soil

Wet soils tend to be sour or acid, they may need to be limed and drained, especially if low lying, but be cautious not to overdo it. Water gives life and it is only water-logging that is a problem. Adding copious amounts of organic material improves the drainage and water dispersion.


Having your garden soil analysed for nutrient content is unnecessary. It is supposedly accurate, but you’d be better off simply applying a bag of seaweed meal. It is difficult to get accurate readings from the patchy soils in gardens, containing all sorts of detritus from dead cats to car batteries, so it is best not to worry about this sort of fine tuning. Aim to incorporate some broad-spectrum organic fertilisers and as much organic material as possible, and most soils will be productive.

The only thing worth checking if you’re doubtful is the pH – the acidity or alkalinity (lime content) of the soil. Don’t bother with cheap meters – they are invariably inaccurate. Instead, use a simple chemical test kit with an accurate colour chart. These are inexpensive and available in most garden shops. The basic pH may vary between ground level and deeper if the soil layers have built up a rich surface mould, so take several samples from a typical worked soil. The pH may change as the soil is enriched particularly as more organic material is added, so most soils tend to become more acid. For this reason, liming the soil every few years will be of benefit especially for vegetables and grassed areas. Lime can be plain chalk, or better still Dolomitic lime which contains more magnesium and other nutrients. Best of all, though, is calcified seaweed which contains all the trace elements too. Never apply lime at the same time as manures or compost. Apply it before rain on top of the soil or grass and rake, brush or allow to leach in during late autumn or winter.

Although most soils can be improved and thereby made acceptable to a wider range of plants, there is a difference between improvement and change. Various materials are sold as soil improvers and some flocculating agents based on lime or gypsum, do help lighten textures when applied to clay soils. But for most soils, applying generous amounts of well-rotted organic matter will give the greatest benefit. All soil types contain the same materials; stones, silts, sands, clays and organic material – it is their proportions that change. What affects plants most is not the nutrient levels of a soil, but the physical texture, the aeration and moisture retention.

All these are improved by adding more organic material, especially when combined with a mulch. Introducing organic material adds to the nutrient level directly and increases another component of healthy soil, its micro-life. This then attacks not only the fresh resource but also the soil’s mineral content.

This almost limitless resource is then made available to the plants. There is sufficient in the soil of almost every element to last for millennia of heavy cropping if the micro-life has other materials to enable it to break the particles down. Most of all, they need water.

Air is the next most important component of garden soil. Almost all micro-life and plant roots need oxygen and give off carbon dioxide. Much of the latter is reabsorbed by the soil, but fresh air has to replace the former. The size and shape of organic particles in various stages of decomposition keep soils open and allows aeration. This is greatly augmented by earthworm burrows which descend for several yards. So it is the earthworms that are most effective at bringing the greatest depth of soil into use – gardeners cannot dig this deep. The soil composition also varies with depth and only the top few inches throb with life. A foot deep is subsoil containing almost nothing but worms and plant roots. Initially, digging may be necessary but it does disrupt the soil layers. You should never mix the sterile subsoil with the fertile topsoil. The most active and productive part is those top few inches, and these are optimised with several more inches of an organic mulch keeping them warm, well fed and moist.


06. January 2011 by admin
Categories: Garden Management, Soil Improvement | Tags: , | Comments Off on Know Your Soil Type and Organically Improve It


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