The Different Characteristics of Garden Soils
Garden Soil Characteristics
Here I examine the different soils that we are likely to come across and how their performance is influenced by their ingredients.
Soil can be broadly divided into heavy (clay), medium (loam) and light (sand and peat). This is a simplification but it is perfectly adequate for our purposes. Let’s start by looking at heavy soils, as it is these that many of us garden on and with which the most problems seem to be associated.
Heavy soils (clay and silt) are characterised by their small particle size (fine texture). This results in them frequently being poorly drained, and all that that implies by way of the ground becoming waterlogged more easily. Along with this is the likelihood that thewill get compacted easier and more often. Whilst this clearly affects the drainage, an even worse result is the difficulty with which roots can penetrate it. If a plant has to struggle to push out sufficient roots to sustain it, growth is unlikely to be good.
Heavy soils are slow to warm up in the spring, mainly because of their normally high water content. This is not always important but it is worth remembering if early crops are wanted. In a dry summer they have the tiresome habit of becoming rock hard the moment they dry out and, frequently, huge cracks appear that you could disappear down. Either that or if they have been well tilled, they simply turn into a mass of indestructible lumps.
From this, you could be forgiven for imagining that heavy soils have a formidable list of vices but few, if any, virtues. In fact, this is far from the truth. Probably the least obvious benefit of heavy land is that, being firm and comparatively unyielding, plants can get a very good foothold in it. Once, that is, they get themselves established. Likewise, most plants will grow much better in heavy soils because they have a far greater reserve of plant nutrients and moisture in them.
Taking these two things alone, once a plant, particularly a tree or shrub, establishes itself in clay, it is likely to grow far better than its companion growing in sandy soil. The water retention properties of heavy soils can also be to our advantage. They hold a lot more water in the winter but this also means that they hold a good supply in the summer. They are, therefore, the last to dry out when there has been little or no rain.
At the opposite end of the soil scale are sandy soils. These are far less common than clay and, apart from little local pockets, they are found mainly in areas such as parts of Surrey, Bedfordshire, Cheshire, Lancashire and west Norfolk. In fact, they coincide with the market gardening regions of the country and it gives us an excellent indication as to their suitability for gardening; on the whole, they are first rate.
These soils are coarse and open textured and, as such, are very quick to dry out; rain that falls on them quickly drains away. Unfortunately, this also means that the water carries a lot of plant nutrients with it, so sandy soils are often starved, from the plant’s point of view.
This quick-drying characteristic means that sandy soils have the advantage of warming up early in the year and are excellent for the production of early crops. They are also very easy to cultivate. Any plants that resent too much water are likely to thrive on sand, because of its drip-dry nature.
Another big virtue is the readiness with which roots are formed, and with which plants grow in it; hence its popularity with market gardeners. In a nutshell, once a plant is put into a sandy soil, it is up to the gardener how well it does; nature has done all it can. One thing to note is that, whereas clay soils can be either acidic or alkaline, sandy soils are always acidic.
Soils with a medium texture, not surprisingly tend to have diluted versions of the advantages and disadvantages of clay and sand. They are as near perfect as one could wish for. They can be cultivated quite easily, plants grow well in them, they have a reasonable reserve of nutrients, they hold water well but have good drainage; in fact, they are everything that most gardeners would like.
Gardeners who are not blessed with this Utopian soil, and that covers nearly all of us, should never despair though; with time and effort, even the most unpromising soil can be turned into a first rate one that will do everything that is asked of it. The whole art of improving a soil to this extent is to do the right thing at the right time and always to be patient.
Although clay, sand and loam include the majority of soils in this country, there are several others that are found in certain areas. The most common of these is probably the thin soil that overlies chalk. This can be found in Wiltshire around the Salisbury Plain, through to the Chilterns and Hertfordshire and just into Cambridgeshire. There, the band of chalk disappears underground, to reappear as red chalk in a small area around Hunstanton on The Wash in Norfolk.
Other well-known chalky areas are the North and South Downs of England. The soil above chalk is frequently thin and may, despite common sense telling you the opposite, be acidic. This acidity, though, is only in new gardens where the soil has not been disturbed. Under these conditions, there is usually a band of very organic and acidic soil at the surface. Once cultivations start and the soil is mixed up, the chalk imparts its alkalinity to this top soil. The texture of these chalky soils can vary greatly but is normally on the heavy side.
One of the advantages of this soil is that, due to the porous nature of chalk, it usually has good reserves of water. The chalk acts as a sponge and can hold a remarkable amount. At the same time, this porosity means that chalky soils are usually well drained. They may be wet clay on top but, underneath, there is very little chance of waterlogging.
Chalk is a fairly soft rock and, if solid chalk is near the surface, difficulties can be experienced in getting trees and shrubs established. The problem stems from the impenetrability of the chalk until fissures have been created in it for the roots to travel along. If your garden is overlying chalk and you want to plant trees and shrubs, it is necessary to break up the chalk to a depth of at least 60cm (2ft) with a pick or crowbar to give the roots a reasonable start in life. Once they have a bit of strength, they can usually manage for themselves. This problem is highlighted in beech woods on downland where nearly every gale has its victims. You can quite easily see the enormous platforms of roots with hardly any penetration into the chalk. Although we won’t have quite such a severe problem with, the chalk must still be broken up to allow the roots to tap the reserves of moisture it holds.
Chemically close to chalk are the limestone soils of Derbyshire, the eastern half of Yorkshire and parts of Somerset. These have just the same characteristics as chalky soils except that they are usually much lighter in texture because the limestone breaks down into an almost sandy material.
Chalk and limestone soils are really quite common and newcomers certainly shouldn’t be frightened of them. Much less common are peaty and fenland soils. These are normally found in flat, low-lying districts such as south-east Yorkshire, the Somerset levels and the Fens of Lincolnshire. However, they also occur in most mountainous areas, such as along the Pennines, in Derbyshire, Cumbria and many places in Scotland.
These highly organic soils are often very fertile and physically perfect for growing plants in, but they require careful handling if you are not used to them because they have very little reserve of nutrients and the highcontent is soon broken down once cultivations start. The peaty soils in the north are very acidic but the Somerset ones are less so because of the proximity of limestone (for instance around Cheddar) to the surface. They are the sort of soils that can often be improved by importing a heavier grade from outside the district.