How to Topsoil and Seed a Lawn

What you need

Topsoil, grass seed, a rake, a wheelbarrow, a lawn roller or a flat plank, a hose or sprinkler, and a tape measure. Buy the seed for your conditions — sun or shade, hard-wearing or fine — and read the coverage on the packet before you order, because the rate is what the seed calculator needs.

Step 1 — Measure the lawn and work out the topsoil

Measure the length and width of the area and work out the topsoil volume for the depth you need — about 100 mm (4 in) of topsoil over bare ground is a good starting point. Enter the numbers in the topsoil calculator: it gives you the volume with wastage and the weight, so you can order by the cubic yard or by the tonne, whichever your supplier uses. Topsoil is heavy — a cubic yard weighs over a tonne — so have the delivery put as close to the lawn as possible.

Step 2 — Prepare the ground

Clear weeds, stones and old turf, then dig or fork the ground over and rake it level. Remove any low spots where water would sit, and firm the ground lightly by walking over it on a plank — soft, fluffy ground settles unevenly after the seed is down. If the ground is heavy clay, the topsoil layer matters even more: it is what the roots will actually grow in.

Step 3 — Spread and level the topsoil

Tip the topsoil in barrow-loads and rake it out to an even depth, checking with a straight edge or a taut string line. Roll or tread it firm, then rake the surface lightly so the seed has something to grip. The finished level should sit just below paths and edging, because the grass will grow up from it.

Step 4 — Sow the seed

Work out the seed from the coverage on the packet — the lawn seed calculator does the division for you. Sow half the seed walking in one direction and half at right angles, so the coverage is even, then rake very lightly so the seed is just covered. A new lawn needs the full rate; overseeding an existing lawn needs only half.

Step 5 — Water and wait

Keep the soil damp — light watering once or twice a day, not a flood — until the seed germinates, usually in one to three weeks depending on the weather and the seed. Keep off the lawn until it is established, and make the first cut when the grass is about 75 mm (3 in) tall, taking off only a third of the height. Mowing too short, too soon, is the fastest way to lose a new lawn.

Worked example

A patch 10 ft × 20 ft is 200 ft². At 4 in deep that is 66.67 ft³ (2.47 yd³) of topsoil; with 10% wastage it is 73.33 ft³ (2.72 yd³, or 2.08 m³), weighing 2.70 tonnes at 1,300 kg/m³. For seed, a lawn 50 ft × 20 ft is 1,000 ft²; at 500 ft² per lb that is 2 lb (0.91 kg) for a new lawn, and half that — 1 lb (0.45 kg) — for overseeding. Those are exactly the numbers the topsoil calculator and the lawn seed calculator give you.

Common mistakes

• Seeding unprepared ground. Seed on hard, weedy or uneven ground germinates patchily and the weeds win. Prepare first, seed second.
• Sowing too much or too little seed. Too little leaves bare patches; too much makes seedlings compete and die. Use the packet rate and the calculator.
• Letting it dry out. Seed that dries after germinating dies. Light, regular watering matters more than one heavy soak.

Safety

Topsoil and seed are low-risk materials, but the bags and barrow-loads are heavy — lift with your knees and take loads you can control. If you are digging deep, check for underground cables and pipes first. Keep seed and any fertiliser away from children and pets, and wash your hands after handling soil.

Try these calculators

• Topsoil Calculator — volume and weight for any area and depth.
• Lawn Seed Calculator — seed for a new lawn or overseeding.
• Soil Calculator — soil volume and bags for beds and borders.