Overseeding means adding grass seed to an existing lawn. It can help thicken areas where useful grass remains but the lawn has become thin or worn. For a small bare patch, you can work locally; where little good grass remains across the whole area, a more substantial renovation may be appropriate.
Choose a period when the soil is warm enough for growth, moisture can be maintained and the young grass has time to establish. In the UK, spring and early autumn often offer suitable conditions, although local weather and the seed mixture matter more than a fixed calendar date.
Check why the lawn is thin
Look at the pattern before reaching for the seed. A worn route to a gate suggests repeated traffic. Thin grass beneath a tree may be competing for light and moisture. A lawn that stays soft and wet after rain needs a different investigation from one that dries out quickly.
Seed can fill gaps, but the new grass faces the same conditions as the old lawn. Reduce traffic, improve light where practical and address compaction or drainage where these are contributing to the problem.
Choose a seed mixture
Match the mixture to the lawn's use and growing conditions. Our grass seed guide explains the choices. A hard-wearing mixture is a practical starting point for a busy family lawn; a shady area calls for a mixture intended for the amount of light available. Check the packet for the overseeding rate and aftercare instructions.
Measure the area you intend to treat. Multiply its square metres by the packet's grams-per-square-metre rate, then divide by 1,000 to calculate kilograms. See our seed quantity guide for an example.
Prepare the lawn
Mow the existing grass before sowing so it doesn't overshadow the seed. Remove loose clippings and debris. Rake the surface to expose some soil between the grass plants; the aim is to give the seed contact with soil, not to pull out healthy grass unnecessarily.
A lawn with substantial thatch or moss may need more preparation. The RHS autumn lawn guide explains scarification and aeration. The amount of scarification depends on the condition of the lawn and its ability to recover. If the ground is compacted, consider whether aeration is needed; avoid working on saturated soil.
Bare patches may need the surface lightly loosened and levelled before sowing. Firm loose soil gently so it doesn't settle unevenly later.
Sow evenly
Weigh out the quantity recommended for the measured area. Apply it evenly by hand or with a suitable spreader. Dividing the seed into two batches and covering the area in different directions can make an even distribution easier.
Lightly rake the exposed areas so that seed makes contact with the soil, without burying it deeply. Follow the mixture's own instructions. A light watering with a fine spray can settle the surface without washing the seed into piles.
Keep the seedbed moist
Newly sown seed needs consistent moisture, but the surface should not be left waterlogged. Check it regularly and water gently when rainfall is insufficient, following local water restrictions. Sunny, windy conditions can dry a surface faster than cool, damp weather.
Keep people and pets off the seeded areas while the young plants establish. Germination varies with the grass species, soil temperature and moisture, so avoid judging a mixture by a single expected day.
The first cut
Wait until the new grass is established enough to mow and the ground is firm enough to walk on without damage. Follow the seed supplier's guidance for height and timing. Use a sharp mower blade and take only a small amount off on the first cut. Our first-cut guide explains what to check. If the young grass pulls out or the soil is soft, give it more time.
Continue to reduce traffic while the new grass strengthens. A thin lawn can take time to fill in, and larger bare areas may need further attention once you can see what has established.