Soil types and methods of improvement

Do you know what type of soil is in your garden ? If not then you should as it is useful to know when formulating a plan for improvement or choosing suitable plants. No soil is perfect and everyone likes to have a moan about theirs from time to time. We have come across all types of soil in the area we serve and it is not guaranteed that you will have exactly the same soil as your neighbour. 

Mineral soil consists of sand, silt and clay particles along with small quantities of organic matter, water and gases. They are often described using terms such as sandy, clayey, chalky, loamy etc. There are ways of determining what type of soil your garden is made up of the easiest being by feel and with experience this method can be extremely accurate.

A sample of soil about the size of a golf ball is moistened and worked between the fingers to remove stones and break up any lumps.The resultant ball of soil can now be assessed with regard to it's texture and classified as one of the following
  • sand - has little tendency to bind together even when wet and cannot be rolled into a worm
  • loamy sand - can be rolled into a worm but it easily falls apart
  • loam - can be moulded into a ball and has no feel of grittiness, silkiness or stickiness
  • sandy loam - as loam but the ball of soil is readily deformed and gritty
  • silty loam - as  sandy loam but is silky to the feel instead of gritty
  • clay loam - binds together strongly, does not readily deform and is polished when rubbed 
  • clay - binds together very strongly, is very difficult to deform and rubbing produces a marked polish
  • silty clay - as clay but also silky
  • sandy clay - as clay but also gritty
This list is rather long and detailed for use in the garden so we will restrict the possible outcomes to sand, clay and loam. Pure silt and peat soils are extremely rare in garden settings so are not mentioned here. Chalky and other lime rich soils can be either clay or sand based and so deserve a special mention later in this article.

Sandy soils

Often referred to as light soil, sandy soil is easily worked, drains quickly after rainfall and warms up quickly in the spring. However it is not all good news for gardeners with sandy soil as they don't hold on to nutrients or water very well which can lead to dry plots which are low in fertility. Sandy soil is surprisingly easy to compact because the particles readily pack together, especially when organic matter levels are low. They are usually very acidic leading to certain nutrients becoming unavailable to plants. This means plants have to be chosen very carefully to suit.

To improve sandy soil we must help it to retain moisture and nutrients. To do this involves the working in of large quantities of organic matter in the form of compost, manure and leafmould. Not only will this retain moisture and nutrients in the soil but it will improve the soil structure, help avoid compaction and aid your plants in fighting off diseases. Mulching is also beneficial as it stops the sun drying out the soil and prevents heavy rain from causing  surface capping.

Clay soils

Often described as heavy, clay soil is difficult to cultivate as it is sticky when wet and rock hard when dry. They tend to be slow draining, prone to waterlogging and slow to warm up in spring which can delay cultivation in the spring. There is an optimum time to cultivate clay soil which is when it is not too wet and not too dry, only experience will tell you when this is. It is advisable to keep traffic to a minimum when clay soil is wet because in this state it is very easily compacted.

Clay soils does however have it's advantages. They usually contain a rich supply of food for plants as the clay particles have the ability to hold on to nutrients until they are released for use  by roots. They hold on to water much better than sandy soils and therefore require less irrigation in the summer months.

To improve clay soils we must make them easier to work, quicker to warm in spring,  improve drainage and help them resist compaction. As with sandy soils, the best way to do this is to add large quantities of organic matter. Organic matter helps the clay to breakdown into small crumbs which are much easier to cultivate than a large sticky lump. This has the added benefits of making water and nutrients more available to plant roots, making the soil warmer and less prone to compaction. Adding lime to a clay soil can also make clay easier to work but this should only be done if your soil is acid.

Loam soils

Loam is probably the perfect soil to have in your garden but it is not very widespread. It is a mixture of clay, sand and silt particles which avoids the extreme disadvantages of clay or sandy soils. They are fertile, well drained, easily worked and quick to warm in spring.

Loam soils do however benefit greatly by the addition of organic matter to help replenish used nutrients, improve soil structure and reduce compaction.

Chalky and other lime rich soils

These soils may be light or heavy, are mainly derived from calcium carbonate and are therefore alkaline in nature. You can do a quick test to check for calcium carbonate in your soil by putting it in a jar of vinegar. If it froths then free calcium carbonate is present and you have an alkaline soil. Many chalky or limestone rich soils are shallow, free draining and medium to low fertility. Added organic matter can decompose very quickly making it difficult to maintain fertility levels unless it is added on a regular basis. Soil structure is usually good so surface capping and slumping does not readily occur and compaction is less of a problem than on other soils. This means that these soils can be cultivated and travelled on for most of the year.

To improve these soils we must maintain adequate fertility levels by the regular addition of organic matter. If the soil is thin and stony then it is worthwhile to remove the larger stones and add more topsoil which is of good quality and from a local source. Do not be tempted to dig these soils to deeply as subsoil and bedrock can easily dilute the topsoil and make it less fertile. The subsoil is a lighter colour than the topsoil so it is easy to see when you are going too deep and you can adjust the cultivation depth accordingly.

There is a large area of alkaline soil over limestone in the Tadcaster and Sherburn in Elmet region and so is very familiar to us at Eco Garden Maintenance. The soil is not too shallow though and in most places you can cultivate to a spades depth without bringing any subsoil or bedrock to the top. In most gardens it is  a lovely dark colour with numerous stones visible and of medium fertility. Usually the soil in this area is a pleasure to work with being neither too clayey or sandy, but it still benefits hugely from the regular addition of organic matter. Ericaceous plants cannot be grown successfully in these soils so it is best to plant them in pots rather than having to look at sickly yellow leaves and poor plant growth.

As we can see there are many types of soil,  all of which have to be managed slightly differently. Despite this the one common way to improve them all (except peat based soils) is by the addition and working in of large quantities of bulky organic matter. It really is wonderful stuff as it can remedy all sorts of problems, resulting in beautiful healthy gardens which are a pleasure to behold.