How and When to Overseed a Lawn in the UK
Last updated: September 2026
Overseeding means sowing grass seed into an existing lawn to thicken it up, fill thin patches and bring in tougher grass varieties. It is far cheaper than returfing and, done at the right time, you'll see a difference within a few weeks.
When to overseed
The best window in the UK is early September to mid-October. The soil is still warm from summer, autumn rain keeps it moist, and weeds are slowing down. March to April is the second-best time, but you'll need to water more if spring turns dry. Avoid midsummer (too dry) and winter (too cold for germination).
How much seed do you need?
For overseeding, around 20g per m² is typical. For patching bare spots, use closer to 50g per m². For a brand new lawn from bare soil, about 35g per m² is usual. Always check the rate on your seed box, as mixes vary. For example, a 50m² lawn overseeded at 20g/m² needs 1kg of seed; add about 10% for spillage and uneven spreading. The Grass Seed & Lawn Feed Calculator works out the amount and the best mix of pack sizes.
Choosing the right seed
Hard-wearing (ryegrass) mixes suit family lawns with kids and pets.
Fine lawn mixes look beautiful but don't cope with heavy use.
Shade mixes contain fescues that tolerate lower light under trees.
Drought-tolerant mixes with tall fescue root deeper and stay greener in dry summers.
Match the seed to how you use the lawn, not just how you want it to look.
Step-by-step
Mow short. Cut the lawn to about 25mm and collect the clippings so light reaches the soil.
Scarify. Rake out thatch and moss with a spring-tine rake or a hired scarifier. Seed needs to land on soil, not a mat of dead grass.
Aerate compacted areas. Push a garden fork in 75–100mm deep at regular spacings, or use a hollow-tine aerator.
Sow. Spread half the seed walking up and down, then the other half walking across, for even coverage. A spreader makes this easier on large lawns.
Top-dress. Brush a thin layer of sieved topsoil or lawn dressing over the seed to protect it and keep it moist.
Water. Keep the surface moist, not soaked, until the seedlings are established. Little and often is better than one heavy soak that washes seed away.
Aftercare
Germination usually takes 7–21 days depending on the temperature. Keep off the lawn as much as possible and hold off mowing until the new grass is about 75mm tall, then take just the top off with sharp blades. Don't use weedkiller or weed-and-feed products for several weeks before or after sowing, as they can stop seed germinating – check the product label for the exact interval.
Feeding after overseeding
A pre-seed or autumn lawn feed helps new roots establish. Most granular lawn feeds are applied at around 35g per m², but always follow the label – too much can scorch young grass.
Frequently asked questions
Can I just throw seed on my lawn?
You can, but much of it will be eaten by birds or fail to root. Scarifying first and top-dressing afterwards makes a big difference to how much seed takes.
How long before I can mow after overseeding?
Usually three to four weeks, once the new grass reaches about 75mm. Use a high setting for the first few cuts.
Why hasn't my grass seed come up?
The most common causes are dry soil, cold weather, seed sitting on thatch rather than soil, or recent weedkiller use.
Is overseeding better than new turf?
For a lawn that is thin but mostly healthy, yes – it's much cheaper. If the lawn is more weeds and moss than grass, starting again with turf is often quicker.