Advice on Garden Soils - Clay | Sandy | Loam |  


Garden soils can be silt, sandy or clay based. (There are other types of garden soil as well, but these are a good starting point)

The great 'diarist' - John Evelyn - wrote in 1675...That in his opinion, there were no less than 179,001,060 different types of earth........! Time is short, so forgive me if I only mention a few!

Garden Soil Types

 are normally referred to as being one of three basic 'soil structure' groups; Sandy soil, Clay soil and Loam.. This is just the start, but it is a good starting point, for each of these groups tell us much about the garden soil, and what - if anything - needs to be done to improve it.

The one thing above all I have personally found, is that encouraging a good earthworm population in your soil will improve all your other efforts hugely. 

A Simple Soil Test

The easiest way to find which structure group your garden soil is in, is by testing it in an old coffee jar - take the label off as you will need to see through it. (I'm sure that there are many other jars suited to this job; I happen to drink a lot of coffee!)

This is a great way to get the kids involved - they can even do it for you!

This is What You Do! Let's assume that you garden soil looks the same in all parts of the garden, and the soil seems to be roughly the same sort of texture to the full depth of a garden spade. 

Take a couple of typical (!) spoonfuls; break it up as much as you can, then place it in the jar - just under half a jar full is ideal. Fill the jar with water to within a cm of the top and give it a really good shake (Make sure that the lid is on!) Keep shaking until all of the soil has 'dissolved' and you just have a murky-looking liquid. Leave the jar somewhere to let the contents settle; this will take a few hours.

What Soil Have You Got?

  You should now have several layers of 'soil' types in your jar. At the bottom will be the stone/sand layer, then a 'silt/clay layer, followed by an organic layer. Right at the top the will be a settling of clay. (The cloudy water is in fact a solution of clay particles.) From largest to smallest, the particles are... stones, sand, silt, clay. The one we have missed (organic) can come in all sizes! From the finest humus particles, right up to dead things!

The stone, sand, silt and clay elements are all mineral (in-organic). The organic content is made up of the 'remnants' of things that once lived. If it lived (Animal or Vegetable), and it is now dead, then for the purpose of this article, it is now the 'organic' content of your soil. (There are -should be - living things in your soil. These are not part of your soil's organic matter! Another section for this).

The mineral bits that you can actually see individually, are sand particles. You will need a microscope to see the individual particles of silt, and the smaller individual clay particles can only be seen with an electron microscope! Whatever your soil group, it will have all three mineral particle sizes in it. The ratio of these particles, determines your soil group.

Your Soil Type Is.....

a clay - or silt - soil if you have more of those particles in it than sandy particles. If you rub it between finger and thumb when wet, a 'silt soil' will have a light smooth feel, but won't shine. The finer 'clay soil' will shine and feel sticky. If the soil feels rough to varying degrees, then you have a sand soil. Maybe a coarse sand with larger, rougher particles or a smooth sand, with smaller, softer particles.

If your 'test' reveals more or less equal portions of sand, silt and clay, then you are blessed with the ultimate (generally speaking) A 'loam soil'.

The organic content of the soil is also very important. You can also change the organic content of the soil quite easily. You cannot change the soil structure group very easily. If is is 'clay' it will remain clay - unless you take some very, very drastic measures.

You can improve a clay soil: You can improve a sandy soil: But it will still remain clay or sandy!

Heavy Clay soil profile image
Heavy Clay Soil in Dry Weather

Silt/Clay Soils....

are possibly the most difficult to improve, but do have a real advantage over sandy soils - so don't start feeling sorry for yourself just yet.

They are sticky when wet, and form hard lumps, which are impossible to break down when dry. In hot weather they form large, deep, cracks.  These cracks can rupture roots, and cause moisture loss - which makes the problem even worse. Regular hoeing helps to fill the cracks and forms a surface mulch, which will help retain the soil moisture.

Without doubt, all clay soils can be improved quite substantially, with the addition of organic matter, by way of strawy stable manure, or a good grade of peat. Composted bark - not bark chippings - is also good. A few years of such applications can provide you with a workable soil. Clay still - but workable.

If your clay soil is seriously waterlogged, then you will need to think (do something) about land drainage. Plants will not grow in waterlogged conditions 

Now for the advantage. Clay soils are usually rich in plant nutrients. They also retain much of the fertilizers that you apply. This is because the soil moisture - which holds the nutrients to a degree - does not soak away, taking the nutrients with it. It may evaporate, but the nutrients stay put!

Sandy Soils are usually warmer than clay soils. This makes them better for the earlier crops of vegetables - but not so good for the moisture-loving fruit crops. They do not hold soil moisture. The soil moisture usually drains away; taking much of the nutrient away with it. These soils need fertilizing often - but sparingly. The only way to improve the basic moisture-loss problem, is to incorporate substantial amounts of organic material (which holds moisture). 

Fertilizers and organic material should be incorporated in just the top few inches of these soils. The nutrients then take longer to leach away. Organic fertilizers are probably best in such soil; they don't wander off with the first rainfall!

Sandy soils are usually acid (see below) and require frequent - but small - applications of garden lime.

Loam Soils have all the advantages of both the above soils, with none of the disadvantages. Simple as that!

Most plants grow well in them, they are easy to 'work' in most weather conditions, and they hold soil moisture and therefore the nutrients quite well. As with both the above soil types, Added organic matter can only improve it more!

Organic matter

has to be present in the soil for plants to grow. That's why desserts are simply 'desserts' - not sandy soils!

A soil rich in organic matter (Humus) will both hold moisture, and allow surplus moisture to drain away! How? Organic matter acts as a sponge in collecting and holding onto soil moisture, but it also helps the soil to form a good 'crumb structure'. That is to say, that it assists the individual soil particles to group together into larger groupings - or crumbs. This then allows the soil to become more workable or friable; instead of being one solid mass. 

A friable soil has an open structure, which allows air into the small spaces between the individual crumbs. Roots need oxygen. It also allows soil moisture to percolate into these spaces. Soil moisture holds nutrients. It also allows the roots to 'travel' and seek out this air and ready supply of nutrient.

Organic matter/humus also breaks down (rots away) and releases nitrogen into the soil, which is absolutely vital to plant growth.  The ultimate in recycling! You put all of your dead plant/vegetable matter into the soil; it breaks down into Nitrogen which is the main ingredient needed for new  plant growth.

Make sure that any organic matter you add to the soil is already on the way to rotting! All plant and vegetable waste should be 'composted' first, before being added to the soil. Peat, composted bark, rotted stable manure and the like are all ready to use.


 Hopefully, you should now know whether you have a sandy, loam or clay soil. You should also be aware of any organic content in your soil. All of this will have shown up in our simple 'coffee-jar' test.

Now you will need to know if your soil is acid or alkaline (or neutral). An Acid Soil does not have much - if any - lime in the soil. An Alkaline Soil does have lime in it - to varying degrees. A Neutral Soil; well, it has lime in it, but not enough to class it as an alkaline soil. 

You can get a cheap basic testing kit at most garden centres to tell if your soil is acid or alkaline - and to what degree. (You can also do a basic test by drying a teaspoonful of soil, and then sprinkle some vinegar on it. If it bubbles, it will probably have lime in it. If is doesn't it will probably be acid or neutral!)

Most plant need lime in the soil to live and thrive. Rhododendrons, Camellias, Ericas and a few others do not. In fact the presence of lime in the soil will make them quite ill - probably terminal!

Lime encourages soil life, for the bacteria that sorts out your organic matter into Nitrogen, are quite lethargic in acid soils.  

Lime improves the 'tilth' (crumb structure' of heavy soils such as clay soils.  A really sticky clay soil can be put right quite dramatically with a dressing of lime. The lime coaxes the individual clay particles to form 'groupings, allowing moisture to drain, and plant roots the freedom to roam.

Lime can act as a deterrent for some pests - slugs and leather-jackets are not keen on lime. It will also act as a preventative for club-root in brassicas.

Lime in the soil is good for earthworms. Most soils will benefit with a high earthworm population. As well as helping to break down raw organic matter, they make a network of drainage channels in the soil - great for heavy clay soils.

Always use 'garden' lime - Always read the instructions.

Garden Lime - NPK Explained


By David Hughes -