Overseeding a Lawn in the UK: Steps, Timing and Seed Choice
How to overseed a thin or patchy UK lawn, including the best time of year, how much seed to use, choosing a mix and aftercare to get it growing.
Overseeding means sowing new grass seed into an existing lawn to thicken it and fill gaps. It is one of the most cost-effective ways to revive a tired lawn, and it works best when you give the seed what it needs: contact with soil, moisture and time.
When to overseed
The best window in the UK is early autumn, from late August to early October. The soil is warm, rainfall is more reliable and weeds are less competitive. Spring, from mid-March to May, is the second-best time, though dry weather and weed growth can be challenges.
Avoid midsummer, when seedlings dry out, and deep winter, when the ground is cold and germination is slow.
Choose the right seed
Match the mix to how you use the lawn:
- General-purpose or family mix: a hard-wearing blend with perennial ryegrass for play and traffic.
- Shade mix: includes shade-tolerant fescues; useful under trees or beside walls.
- Fine or ornamental mix: slower, finer grasses suited to well-kept lawns.
- Patch repair mix: often combined with seed and fertiliser for small areas.
Look at the mix on the packet, rather than relying on the name. Cheaper mixes sometimes contain fast-growing grasses that do not stand up well to wear.
How much seed
As a guide, overseeding a thin lawn takes around 15 to 25 grams per square metre, while sowing a bare patch takes around 35 to 50 grams. Follow the manufacturer's recommendation on the pack, and err on the side of even coverage rather than heavy piles.
Step by step
- Mow the lawn short, to around 2.5 to 3cm, and remove clippings.
- Scarify or rake vigorously to remove thatch and moss and expose bare soil. See scarifying a lawn.
- Aerate compacted areas; see aerating a lawn.
- Spread seed by hand or with a hand-held spreader, in two directions for even cover.
- Top dress lightly with sieved soil or lawn dressing, just enough to cover the seed.
- Firm the surface by walking over it gently or using a roller.
- Water lightly and keep the surface moist, not flooded, until the seedlings emerge.
Aftercare
- Watering: little and often in dry weather for the first few weeks.
- Keep off: avoid heavy use for four to six weeks.
- First mow: wait until the new grass is around 6 to 8cm tall, then cut with sharp blades on a high setting.
- Feeding: apply a starter or autumn feed, and avoid high-nitrogen spring feeds in autumn.
- Weeds: do not use weedkiller on new grass until it has been mown several times, and always check the label.
Protecting seed from birds
Birds love grass seed. Light netting, fleece or a scattering of dark thread can deter them, or you can use a seed that comes pre-coated. Watering also helps, as the seed becomes less attractive once it begins to sprout.
Common problems
- Patchy germination. Often caused by uneven coverage or seed drying out.
- Moss returning. If moss is the underlying cause, treat the reasons such as shade and drainage; see getting rid of moss in the lawn.
- Weeds taking over. Weed growth can outrun slow grass seedlings if the lawn is not mown and fed properly.
- Poor results in shade. Even shade mixes need some light. In dense shade, consider groundcover instead.
When to re-turf instead
If more than around half the lawn is bare or full of weeds, starting again with turf may be quicker and more reliable; see laying turf step by step.
Paying for help
A gardener can scarify, aerate, overseed and feed in a single visit, which saves hiring equipment. On Compito you can search by postcode, compare ID-verified local providers, and send a request describing your lawn. See how it works.
Worked example: a thinning family lawn
A 40m2 lawn is thin and weedy after a dry summer. In mid September the owner mows short, scarifies, aerates the worn path to the washing line, spreads seed at roughly 20 grams per square metre in two directions, tops with a thin layer of lawn dressing and waters lightly each morning for three weeks. Seed costs perhaps £15 to £30 for a lawn this size, depending on the mix. By late October the new blades are visible, and a high first cut follows. The owner keeps the children off for a month and feeds in spring.
Overseeding calendar
| Time | Task |
|---|---|
| Late August | Order seed, check forecasts |
| September | Prepare and sow |
| September to October | Water, protect from birds |
| October to November | First cuts, high setting |
| March to April | Feed and continue care |
Weeds and overseeding
Seed will not outcompete a heavy weed cover. Deal with broadleaf weeds in advance, following the label and waiting the recommended period before sowing. Many weedkillers prevent seed from establishing, so read the instructions on both products.
Special cases
- Dog lawns. Choose hard-wearing mixes and overseed worn areas regularly.
- Heavy clay. Combine with aeration and top dressing.
- Newly laid turf. Usually does not need overseeding in its first year.
- Shade. Raise the mower height and choose shade mixes; see planting for shade.
Why germination fails
Seed that dries out on the surface, seed eaten by birds, sowing in cold weather and poor soil contact are the usual culprits. Fixing these usually matters more than buying an expensive mix.
Frequently asked questions
Can I just throw seed onto the lawn?
You can, but germination will be poor. Seed needs contact with soil, so some preparation such as raking, scarifying or lightly forking is worth the effort.
How long does grass seed take to germinate?
In warm, moist conditions, typically one to three weeks, with ryegrass faster and fescue slower. Cooler weather extends this.
Will overseeding fix a mossy lawn?
Only if you deal with the cause of the moss first. Seed will struggle in the same conditions that allowed moss to develop.