After clearing the site, rotavate, plough, or dig over the whole area, removing any large stones that are brought to the surface, and then rake the ground to produce a fine tilth. This will improve the soil structure and make subsequent levelling easier. However, do bear in mind that ploughing or rotavating heavy, clay soils may create a compacted layer below the soil surface which could impede drainage. This may need to be broken up using a sub-soiling machine or by double digging.

Topsoil

The ideal topsoil for a lawn is a well-drained, sandy loam at least 20 cm (8 in) and preferably 30 cm (12 in) deep, overlying a free-draining and well-structured subsoil. In these conditions the grass can become deep-rooted and receive ample nutrients and water from the soil. If the topsoil is very shallow or poor, you may need to add new top-soil; this may be bought or moved from other parts of the garden.

Soil pH

Most grasses grow well at pH levels of 5.5-7; fine fescues and bents grow best at pH 5.5-6.5, whilst perennial ryegrass, the meadow grasses, and many warm-season grasses grow better at pH 6-7.

If the soil is very acidic (below pH 5), rotavate or dig lime into the soil, then leave the site for about a week before applying fertilizer. Although lime may be added once the lawn is established, large quantities may encourage certain diseases; therefore, use only a small amount and repeat the following year if necessary.

Drainage

If the soil has a naturally high sand content, and is too free-draining, incorporate some well-rotted, organic matter to help retain nutrients and water. However, you should avoid using too much, as organic matter quickly rots down, resulting in soil sinkage and an uneven surface.

If the soil does not drain freely and the lawn is likely to be heavily used, then you will probably need to improve the drainage. This may be achieved by adding approximately two parts of sand to every one part of heavy, clay soil by double digging. However, a cheaper and less arduous method of improving the drainage would be to install a drainage system during the site preparation stage. This will avoid continual and expensive attempts to resolve the problem after the lawn has been established.

The most successful type of drain for lawns is made up of a row of pipes laid in a trench, which is backfilled with gravel. The ideal distance between drains and the depth of the drain will depend on the amount of rainfall and the type of soil. For most loamy soils receiving moderate rainfall, one drain every 5-8 m (15-25 ft) is sufficient, whereas heavier, clay soils or sites in areas with a high rainfall will need drains laid at closer intervals.