Garden guide
How to Overseed a Lawn (and How Much Seed You Need)
The short version
Overseeding means sowing fresh seed into an existing lawn to thicken it up. Mow short, rake or scarify to expose soil, sow at 15–25g per m², firm the seed in, and keep it moist for three weeks. That's the whole job.
When to do it
Mid-April to May or September — warm, moist soil with rain on the way. September is best: the soil is at its warmest, weed seeds are few, and autumn dew does half your watering. Avoid drought, frost and heatwaves.
Step by step
Mow the lawn short (2–3cm) and rake out moss and thatch so seed reaches soil. Sow half the seed walking up and down, half side to side, for even cover. Rake lightly, then firm by treading or with the back of a rake — seed needs soil contact, not burial.
Aftercare that makes or breaks it
Water lightly every day it doesn't rain — a drying seedbed kills germinating seed. First mow when the new grass reaches 5–7cm, on a high setting with sharp blades. Hold off weedkiller for at least six months on new seedlings.
How much seed to order
Overseeding needs 15–25g per m² — about half the new-lawn rate. A 40m² lawn takes roughly 1kg. Our grass seed calculator converts your area to kilograms and finds the best-value box or bag.