How to assess the soil beneath your lawn

Imagine a typical spring scenario: your new lawn comes up beautifully, everything is a fresh green and you water diligently. Then heavier rain arrives and persistent puddles appear on the lawn. Or a few hot days strike and the grass starts to weaken before your eyes. We reach for fertiliser, add more water and sow more seed.

Yet the problem often lies below the surface. Beneath ten centimetres of neatly spread soil, a layer compacted by construction machinery may still remain. No mower will remove it, and even the best fertiliser will not force a path through it for the roots.

Surprisingly, the most expensive soil beneath a lawn is often not the costly load delivered by a lorry. It is the soil we forget to check before sowing. We cannot choose the right preparation until we know what type of soil we have in the garden.

Is it mainly sandy, clay or loamy? Its type gives us clues about how it handles water and air; what helps one soil may be unnecessary in another. By also checking how water moves through it, we can choose suitable preparation for the grass roots.

Only then does it make sense to think about grass seed. Understanding this sequence can also save you unnecessary spending on work your garden does not need. Take a spade and a little water, and let us get our hands dirty — a simple feel test will give us the first clue.

Choose at least three different places in the area of your future lawn. Add more if the garden is large or visibly varied. Remember to test places where water collects and strips that excavators have driven over.

Take a little soil from roughly 10 centimetres deep at each location (keep the samples separate). Remove stones and small roots. Then moisten a handful of soil gradually and rub it in your hand. It should feel evenly moist. Water should not run out when you squeeze it in your palm.

Now try rolling the soil into a ball and then into a roll about as thick as an ordinary pencil. Watch what happens. Does the soil feel gritty? Does it stick? And what happens when you try to bend the roll?

• Heavy clay soil: If the material is sticky, mouldable and smooth rather than gritty, and you can bend the roll without it cracking, you have clay in your hand. This is the type of soil that readily sticks to your soles after rain, but hardens and cracks in summer. Its fine particles give clay an enormous surface area, and it holds water and nutrients very well — an advantage. Trouble starts when it becomes compacted. It loses its large pores, water stands in it, and some of the water is held so tightly by the clay that plants cannot draw it out. Wet soil therefore does not necessarily mean well-watered roots. Always check clay for compaction and drainage. The aim is to create conditions through which both water and air can pass. The conditions for amending clay soil are explained in the overview of model mixes.
• Medium loamy soil: The ball holds its shape, but the roll is harder to form and cracks when you try to bend it. The soil crumbles, feels a little gritty and a little sticky, but none of these qualities is extreme. You are fortunate: this is an ideal compromise. The mix of different particles retains water while letting the excess pass through. The rule for loamy soil is simple: preserve what works. Correct only specific shortcomings. If water infiltrates, do not buy unnecessary mountains of sand. But take care: even excellent loam can be ruined by driving machinery over it when wet. When to preserve loamy soil and when to amend it is explained in the overview of model mixes.
• Light sandy soil: You can clearly feel sharp grains between your fingers. The ball falls apart, and you cannot form a roll at all. Digging with a spade is easy, but after a warm day the soil is bone dry. Sand has very large pores. Air and water pass through it immediately, but dissolved nutrients are also carried away with the water. What we struggle to create in clay, sand has in abundance. Your task here is to help the soil retain water and nutrients. Definitely do not add more sand. How to help poor sandy soil is explained in the overview of model mixes.

This home test will point you in the right direction. If you are unsure, or are planning a major and expensive replacement of soil materials, arrange a laboratory particle-size analysis. It makes sense to do this before buying, so that you do not purchase something that will not help.