When Overseeding Makes Sense
Overseeding means sowing grass seed directly into an existing lawn to thicken it up. It's the right choice when:
- Your lawn is thin but not dead — there's still grass there, just not enough of it
- You have scattered bare patches smaller than about 30cm across (bigger patches are better fixed with turf pieces)
- The lawn has thinned after scarifying or moss removal
- You want to introduce a different grass variety (for example, adding shade-tolerant seed to an area under trees)
- You want to maintain a thick sward as part of annual maintenance
It's not the right choice when the existing lawn is mostly bare, full of perennial weeds, or the soil underneath is terrible. In those cases, removing the old lawn and starting fresh with new turf or a complete reseed is more effective.
When to Overseed
Best: September
September is the sweet spot in the UK. The soil is still warm from summer (grass seed needs soil temperatures above about 8–10°C to germinate), the air is cooler so evaporation is lower, and autumn rain usually provides free irrigation. Germination is fast and reliable.
Second Best: April–May
Spring overseeding works well too. The soil is warming up and daylight hours are increasing, driving growth. The risk is a dry May — you'll need to water more than you would in autumn.
Avoid: June–August and November–February
Summer is too hot and dry — seedlings struggle with heat stress and drought. Winter soil is too cold for germination, and seed will just sit there (or rot) until spring.
Step-by-Step Overseeding
Step 1: Mow Short
Cut the lawn to about 20–25mm — shorter than you'd normally mow. This lets light reach the soil surface, which is essential for seed germination. Don't scalp it completely, but get it low.
Step 2: Scarify
Run a scarifier (or a spring-tine rake on small lawns) across the lawn to remove thatch — that layer of dead grass and moss between the green growth and the soil. Thatch stops seed making contact with soil, which is where it needs to be.
Scarify in two directions (at 90 degrees) for the best results. The lawn will look rough afterwards — that's fine.
For more on scarifying, particularly for moss removal, see our moss guide.
Step 3: Aerate (Optional but Recommended)
If the soil is compacted, aerate with hollow tines after scarifying. This improves drainage and creates small channels that catch seed and hold it in contact with the soil.
Step 4: Sow the Seed
Broadcast the seed evenly over the lawn. For overseeding, use about 25–35g per square metre (check the product instructions — rates vary). This is less than the rate for sowing a new lawn because there's already grass there.
For even distribution: apply half the seed walking in one direction, then the other half walking at 90 degrees. A handheld spreader makes this easier on larger lawns.
Step 5: Top-Dress
Spread a thin layer (5–10mm) of top-dressing over the seeded area. A mix of fine loam, sharp sand, and compost works well. This covers the seed, holds moisture around it, and improves the soil surface.
Work the top-dressing into the grass with the back of a rake or a stiff broom.
Step 6: Water
Water the overseeded area with a fine rose or sprinkler. Keep the surface consistently moist — not waterlogged, just damp — for 2–3 weeks. In dry weather, this means watering lightly once or twice a day.
One missed watering at the wrong time can kill a whole batch of germinating seedlings. This is the stage where overseeding most commonly fails.
Choosing the Right Seed
Match the new seed to the grass already in your lawn. If you're not sure what you have, a general-purpose mix containing ryegrass and fescue is a safe bet.
- Hardwearing/family lawn: choose a seed mix with a high percentage of perennial ryegrass. It germinates quickly (7–10 days), establishes fast, and handles foot traffic
- Fine/ornamental lawn: choose a fine fescue mix (Chewings fescue, slender creeping red fescue). Finer texture, lower growth, but slower to establish and less tolerant of wear
- Shaded areas: use a shade-tolerant mix. These typically contain rough-stalked meadow grass and fine fescues. See our shade guide for more on grass and shade
- High-traffic areas: pure ryegrass or a sports mix. Nothing handles wear like ryegrass
Aftercare
- Don't mow until the new seedlings reach about 50mm. When you do mow, set the blade high and just take the tips off
- Don't apply weedkiller for at least 8 weeks after overseeding — it will kill the young grass plants
- Apply a light feed 4–6 weeks after germination once the new grass is established. If you overseeded in September, an autumn lawn feed (high potassium) is perfect
- Reduce foot traffic on overseeded areas for 4–6 weeks to let the new seedlings root in
Overseeding as Annual Maintenance
The best lawns aren't maintained reactively — they're maintained preventatively. Adding overseeding to your annual autumn routine (mow, scarify, aerate, overseed, top-dress, feed) means the lawn stays thick year-round and bare patches never get a chance to develop.
It's a few hours of work once a year that saves you from major repair jobs later.