Assessing your soil

There are lots of ways you can go about assessing what type of soil you have:

Take a look around!

The simplest way to assess your soil is to look at what grows well and not so well there. List the plants that really thrive in your garden then look up what growing conditions they prefer. Do they all like acid soil? Do they want wet ground? Then look at the types of plants which aren’t doing as well and see if they dislike the conditions preferred by the more successful plants. This isn’t foolproof since other environmental conditions will also influence plants (eg light levels, shelter, frost pockets), but it will give you a good starting point.

Soil texture tests

There are a couple of easy ways of testing your soil texture which can be easily done at home:

Feeling your soil

Take a sample of your soil (do this from a ‘typical’ area, not somewhere where you’ve added soil improver) and add enough water to enable you to roll it into a ball about the size of a walnut. Squeeze the ball firmly between your forefinger and thumb and shake it. If the ball crumbles then your soil is on the sandy side. If it doesn’t crumble then you need to roll your ball into a sausage shape, then gently bend it round to form a ring. If the sausage cracks as it bends round then you have silty soil, if it stays relatively intact then your soil is likely to be clay. This gives you a basic indication, but there are more thorough feeling tests you can do to get a more specific soil texture.

Settling velocities

Take a typical sample of soil and use a 2mm sieve to remove any particles which are more then 2mm in size. Then put the sieved soil in a jar of water and shake it vigorously. Take a sample of the mixed soil and water and put it aside to dry, then leave the jar to settle. Afer 5 minutes take another sample (the same size as before) of the water (without disturbing the sediment at the bottom of the jar). After 8 hours take a final sample. Once your samples are dried compare their weights – the first sample will contain sand, silt and clay. The second sample will only contain silt and clay (as the sand will have settled). The final sample will only contain clay (because the silt will have also settled). You can then calculate the relative proportions of each particle size in the soil and relate this back to the soil textural triangle to identify your soil type.

Soil pH test

pH testing kits are available from all good garden suppliers and will give you a good indication of your soil pH. When taking a sample of soil to test you may want to consider sampling several different areas of your garden, particularly if you notice different growth patterns in each, or if different areas have been managed differently over time.

pH testing kits all follow the same basic procedure:

  1. Put a small soil sample in a test tube or similar container.
  2. Add barium sulphate (a white powder) which helps to clear the water. The proportion of soil to barium sulphate should differ depending on your soil texture: 3:1 soil:barium sulphate for soils with very little clay in them and 1:3 for soils which have a lot of clay. Use 1:1 for loams.
  3. Add distilled/deionised water and then pH indicator (often a green solution) which will change the colour of the water to show the pH.
  4. Shake the tube to ensure everything is well mixed and then leave it to settle for a minute or so.
  5. When it’s settled you should find the water has changed colour. Match this to the colour chart which you should have in your kit to identify the soil pH.

Soil nutrient levels

These are very difficult to accurately assess without specialised technical equipment. However, there are several things you can do to be able to estimate nutrient levels:

  • Test your soil texture; generally the more clay in the soil the more nutrients are retained.
  • Test your soil pH; if it’s very high or very low you may find some nutrients are being made unavailable as a result.
  • Look at the colour of your soil to assess organic matter levels. Humus in the soil will give it a dark colouring.
  • Check your plants for any disorders which could be related to nutrient deficiencies. Chlorosis is the most likely symptom, but other problems, such as blossom end rot, can also be caused by nutrient deficiencies.

Poor drainage

Poor drainage will be pretty apparent in most cases. You’ll find pools of water collecting on the soil surface, little grooves in the soil surface where water runs off because it can’t drain downwards and plant roots rotting due to waterlogged soil. You may even find that your soil is a blue, mottled colour on the surface and has an unpleasant smell due to the stagnant water in it.

To identify a pan in the soil you will need to dig a test pit. A pan should be obvious as a horizontal line of compacted soil running through the edge of your test pit.