When is the best time to overseed a lawn in the UK?
The best time to overseed a UK lawn is early September, when the soil is still warm from summer (typically 12 to 16 degrees Celsius in Cambridge) and increasing autumn rainfall provides natural irrigation. Grass seed germinates fastest at soil temperatures above 10 degrees Celsius, and September in the UK reliably delivers this. The second-best window is mid-April to early May, though spring overseeding requires more watering if the weather turns dry. Avoid overseeding in summer (risk of drought stress on new seedlings) and winter (soil too cold for germination). ELawnCare schedules most overseeding jobs for the first two weeks of September, and our germination success rate at that timing is 95% or higher.
How to overseed a lawn step by step
Start by mowing the existing lawn short, to about 20 to 25 millimetres, and collecting all clippings. Scarify or vigorously rake the surface to remove thatch and create grooves where the seed can make contact with soil. Spread grass seed evenly at 25 to 35 grams per square metre using a seed spreader or by hand. Lightly rake the seed into the surface, then firm it by treading or using a roller. Apply a starter fertiliser high in phosphorus to encourage root development. Water the area immediately and keep it moist (not waterlogged) for the first two to three weeks. Avoid mowing until the new grass reaches 50 millimetres, then cut at the highest mower setting for the first two cuts.
What grass seed to use for overseeding UK lawns
For overseeding an existing UK lawn, choose a seed mix that matches or complements what is already growing. A utility lawn mix containing perennial ryegrass and red fescue works for most situations. If the lawn is in partial shade, choose a shade-tolerant mix with a higher proportion of strong creeping red fescue. For heavy-wear areas (children's play areas, dog runs), pick a mix with a high ryegrass content for durability. Avoid cheap seed mixes that contain annual meadow grass (poa annua), which grows fast but dies off in winter, leaving bare patches. Look for seed certified under the British Seed Houses or Germinal scheme for consistent quality and reliable germination rates.