Importing and spreading topsoil (5–10 cm)

Why you need it

Builders often strip the topsoil and sell it, or bury it, leaving dense, lifeless subsoil at the surface. Grass will germinate on subsoil but stays thin and pale, dries out quickly and needs constant feeding. A layer of real topsoil gives roots organic matter, nutrients and structure.

How much

At least 5–10 cm (2–4 in) settled depth; 15 cm (6 in) is better for a lawn that will see dry summers. Order about 20% more than the calculated volume, because it settles. As a guide, 100 m² at 10 cm deep needs 10 m³ of soil, roughly 13 cubic yards for about 1,100 sq ft at 4 in.

What to buy

• Screened (sieved) topsoil, dark and crumbly, free of stones, roots, plastic and weed roots.
• Ask for a soil analysis certificate if the supplier has one; check pH and that it is not mostly sand or clay.
• Avoid soil that smells sour or has been stored in a wet heap for months.

Spreading

Spread it over the loosened subsoil in layers, lightly mixing the first layer into the subsoil so there is no sharp boundary. Then let it settle and level it.