Soils – An introductory Guide

Ask a gardener about his soil and there will probably be a long moan, too heavy, too light, too chalky, too wet, too dry, too acid or too alkaline. Ask a non-gardener about soil. There will probably be a blank stare and but that’s just dirt, isn’t it?

And yet each generation is the custodian of the soil, arguably the most precious material on earth. One might muse that even water cannot work for the world’s living things without soil. There has been an outcry recently about set aside for farmers but this is close to an ancient rotational custom under another name, the practice that our ancestors found good, that of fallowing ground for a year. Most of the old civilisations had a healthy respect for the soil and looked after it.

The condition of the soil in any one place depends mainly on what is underneath it and on what has been washed down over the centuries from the surrounding hills. The workable depth can range from an inch or two to many feet. But whatever the subsoil only the top layers of any soil are really alive and capable of growing things.

These top layers can be made deeper and more fertile by annually digging or double digging with the incorporation of large quantities of compost or manure in the subsoil. Deep soils are useful for leeks, parsnips, long carrots, especially if wanted for show work, and also for trees, fruit, roses and many large herbaceous plants, but most plants only use the top 150-230mm (6-9 inches) of soil.


This method works the soil to a depth of two spades or spits, without altering the positions of the inert subsoil and the live surface layer. Trenching does the same thing but actually moves 3 spits. It is VERY heavy work and normally only worth doing, if cultivating an entirely new area, when any perennial weeds can be removed at the same time. Both methods are best undertaken in the autumn, leaving the surface as rough as possible to allow birds to find insects and the frost to penetrate and produce a fine soil tilth in the spring.

One other way of deepening the top soil and avoiding digging altogether, is by continually adding compost, well-rotted manure, thin layers of grass cuttings (thick layers tend to heat and get slimy), or other organic materials to the surface and allowing the worms to pull it down. I have been adding all my cast out potting soil to my small garden and have twice had to raise the stone edging to keep the soil off the path. This method of increasing the soil depth by surface mulches – put on top, has the added advantages of keeping weeds down, keeping plant roots cool and moist, and it is the well aerated organic soils which are the best providers in practice of soil nutrients, moisture and oxygen which the roots need and benefit from.

The various soils. The nomenclature of soils can be rather vague but the term a good loam indicates ground that can be easily worked in all weathers, a soil which can hold moisture without being too wet. Gardeners aim for a good

loam but usually have to contend with soil textures with very different problems in order to get a reasonable growing medium from the basic conditions. Fortunately provided there is understanding and good management, most soils can provide good results.

Clay soils are described as heavy soils, and are slow to dry out in the spring and can actually be harmed by being worked when still very wet. During the summer constant hoeing will keep the surface loose and this helps to prevent deep cracks forming. . Clay soils can produce excellent late crops of vegetables when lighter soils are too dry. Rough autumn digging and the incorporation of plenty of organic matter helps considerably. The addition of lime may help. Sandy soils, in direct contrast to clay, dry out very quickly in the spring, but the-good drainage tends to wash out soil nutrients, so sandy soils are often very hungry soils, and require organic matter to hold moisture and heavy feeding, preferably with long term organic fertilisers such as fish, blood and bone. Good early crops can be grown on sandy soils but later in the year concentrated watering and feeding will be necessary. In the flower garden heavy top mulching will be of considerable benefit.

Chalk soils are generally regarded with trepidation as being very limiting and certainly there is a long list of lime hating plants. Chalk and lime are the same chemically. With care even most of these lime hating plants can be grown on chalk. Chalk soils are often shallow and can dry out quickly but deep digging and mulching can make a transformation. Chalky soils are of course very alkaline and the brassica (cabbage) family thrives. Acid loving plants can be grown in containers like pots or gro-bags and should be watered only with rain water. Special acid peat composts can be bought for such containers so individuals can grow their heathers, rhododendrons and azaleas.

Mention has been made of soil nutrients. These are chemicals – everything which is made of matter is composed of chemicals. Anything which is organic has carbon as an integral part of itschemical make up. The chemicals can be as elements – like the carbon in soot or in simple mixtures like the carbon in gunpowder or in compounds like the carbon in wood or flesh or a flower. Plants need to have elements to make up the tissues which make the plant. Some elements are needed in greater quantities than others. Carbon curiously is absorbed from the air – the plants absorb it as carbon dioxide and with the addition of water from the roots create a new series of compounds based upon the sugars. The water contributes two elements hydrogen and oxygen. Water can only be absorbed in any quantity by the root hairs. Oxygen is an ingredient of air where it exists as the pure element in a mixture of gasses – 4/5ths of which is the gas nitrogen. Very few plants can make use of this atmospheric nitrogen – mainly only the plants in the pea family – and most of the plants’ nitrogen is absorbed via the roots where as nitrates in solution it can pass through the cell wall of the root hairs. Plants are made up of cells – these just

about visible when peeling potatoes – the large cells of the potato tuber contain starch and this dries to a white powder on the knife or draining board or wherever a cut potato is left for a short while. What does not show is the cell nucleus – all living cells have a nucleus which controls its operation; it is a programme for responses. This nucleus has many elements in its constituents – nitrogen, phosphorous, potassium, calcium, magnesium, iron, manganese, sulphur and a few others. All these elements – mainly they are minerals, are absorbed by the roots. The quality of the soil reflects the availability of these plant nutrients. Deeper soils will offer more soil for the roots to exploit. Fine soils will enable the roots to ramify finer crevices than cloddy soils. Soils which are around neutral have most of the plant nutrients available whereas very acid soils and very alkaline soils tend not to have all the nutrients ready for the roots to absorb them – even if the element is present it may be insoluble.

There is more of this soil care in this text and in the texts to follow but hopefully this chemical concept is introduced and should not present a threat to any reader.

Most members of the Clematis, Prunus, Forsythia and Hypericum families will do well on chalk, and even some heathers survive but the azaleas and rhododendrons do need the special peat treatment or other lime free growing medium.

Peaty soils are often wet and may waterlog, this would require proper drainage. The ‘peats’ are mostly acid and hungry and would require applications of lime if brassica crops are to be grown. They have the advantage of holding moisture for crops such as peas and lettuce. The plants which are lime haters love peat soils and will grow with enthusiasm and glory.

Nowadays it is possible to test the acid or alkaline quality of the soil, as small kits, known as pH kits are cheap and easy. A good pH value works out at 6.5-7, this means that it is close to neutral and is suitable for almost all plants. A pH lower: than 6 indicates acidity and a probable need for liming. A pH over 7 is for plants with a high lime tolerance.

Town and city soils have been altered considerably over the years but in the country a careful study of the local vegetation will give a good guidance as to what can or cannot be grown. Rhododendrons and heathers = acid soils. Old man’s beard, wild geranium and scabious in the hedgerows and roadsides indicate chalk or limestone soils.

All soils have a few common problems. One of the worst is an infestation of permanent (perennial) weeds such as couch grass, ground elder, creeping buttercup and the two bindweeds, greater and lesser. Most of these can be reduced by careful digging, but even tiny pieces of root left in will grow. Hoeing with these weeds can be disastrous, merely chopping them up and all the bits grow again. If

they cannot be dug out, spot weed killers are quite helpful, but will need several applications. I cleared an asparagus bed of couch grass with a weed killing spot gel. The lesser bindweed with its small twisted roots is probably one of the most difficult to deal with as it is very deep rooted and very prolific. With all weeds constant vigilance is required. The more time that can be given to eradication the more likely will be success. Annual weeds can be kept down by growing ground cover plants and by planting everything slightly closer together than usual.

Another very serious problem is poor winter drainage – if water stands on the surface for weeks at a time it may mean that the land is waterlogged. This effectively kills the roots which are deprived of air – the soil’s spaces contain air unless they are full of water or roots or other organic matter.

The retention of soil and moisture on slopes can be a problem, terraces created by retaining walls of stone or turf run across the slope will help, as will thick planting of ground cover plants. Mounding the earth into raised beds will be of great assistance in drainage and if these beds are not more than .90 metre (3 feet) across, it will make the work of planting, weeding and harvesting fairly easy.

Manures and fertilisers do improve the soil. Farmyard manure and horse manure add some nutrients and much bulky organic matter leading to soil improvement. They should never be applied fresh and if dug in should be used in early autumn so that all is rotted in by spring planting. Poultry manure is very strong and should not be used for several months after collection. It is high in potash which is good for fruit production. Seaweed if available is an excellent ground improver but needs to be left outside for two or three months before using to allow the salt to be washed off.

Green manuring takes time but is good for weed control, retaining the nutrients and aiding soil structure. Mustard is one of the easiest-green manures to grow (though not on acid or waterlogged soils liable to clubroot, which is a disease of brassicas) and mustard has the advantage of driving away wireworms. Mustard can be sown after lifting early potatoes and dug in before the stems get woody.

What plants you grow are largely a matter of your choice but you are stuck with your soil. It is often worth discussing soils with neighbours and garden clubs, as very often what works with one will also work for other local people. Advertisements in local papers can also suggest sources of compost, manures and leaf mould, commodities that will help improve soil structure, but do not buy sight unseen – you

might buy a dose of weed roots and weed seeds from an untidy pile of manure.

Mention has been made of garden compost. What is it? Anything organic that will rot down into a dark odourless material makes compost, it is safe to use in almost any way to improve soils. The improvement is mainly physical helping to keep the soil fine, open and crumbly. There are two basic ways of making compost. The most primitive technique is to use a piece of empty ground, dig a trench one spit deep, fork up the bottom and as household or garden waste appears, lay it in the trench until it reaches about three quarters full and then cover it well with soil. Allow time for it to rot (6-8 months from an October start – 3-4 months from August);, if disturbed too soon, weeds, and sundry potatoes/and tomatoes ,:from the household wastes may start to grow.


However compost is best achieved in covered bins, kept moist, turned and encouraged to heat up. This heat will kill off weed seeds and harmful life. As it cools so the compost is invaded by worms which make the compost even better for plant roots. It is possible to have three bins, one ready for use with well rotted friable material, which is reasonably pleasant to handle; one rotting down and one taking the fresh material. The rotting down is done by bacteria, needing the moisture and the turning for aeration. It will take several months for a real heat up and rot down. There are tumbler bins and additives available to speed up the composting process. The more the compost material is mixed, the better will be the result.

There are few things more pleasing and satisfying than gently digging; it is very therapeutic, and a nicely dug plot conjures marvellous crops and flowers into the mind. Dirt indeed!

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