Lawns
How to get rid of moss in a lawn, and stop it coming back
Rake or scarify the moss out in early autumn, then fix whatever let it in: shade, compacted or wet soil, acid soil or mowing too short. Moss killer alone only clears it until the same conditions bring it back.
Moss is a symptom, not the problem
Moss spores are everywhere, all the time. What decides whether they take hold is the grass: a thick, vigorous lawn leaves no room, and a thin, struggling one leaves gaps that moss fills faster than grass can. The Royal Horticultural Society lists the conditions that weaken grass and favour moss as shade, drought stress, mowing too low, worn bare areas, compacted or poorly prepared soil, waterlogging in a damp climate, and acid soil.
That is why a lawn treated with moss killer every spring is often just as mossy every autumn. The RHS puts it plainly: control with a moss killer is only temporary unless the conditions that let the moss establish are changed.
Finding the cause in your lawn
Where the moss sits usually says why it is there.
| Where the moss is | Likely cause | What changes it |
|---|---|---|
| Under trees or on the north side of a fence or house | Shade | Lift or thin the tree canopy, or accept moss in that corner |
| Areas where water stands after rain | Waterlogging and slow drainage | Aerate, hollow tine on clay, consider drainage |
| Paths and play areas worn thin | Compaction | Spike or hollow tine, reroute foot traffic |
| Humps and edges cut to the soil | Mowing too low, scalping | Raise the mower, level the bumps |
| Everywhere, in thin, pale grass | Acid or infertile soil | Test the pH, feed, overseed |
A cheap soil test kit settles the acidity question in ten minutes. Shade is the hardest cause to beat: grass needs light, and in deep shade the realistic choices are cutting back the trees, sowing a shade tolerant seed mix, or letting the moss be. The RHS points out that moss in damp, shady places is soft, green and needs no mowing, and that leaving it is a sensible option.
Getting the moss out
Physical removal is the part that actually clears it. On a small lawn a spring tined rake, worked across the lawn in one direction and then at right angles, pulls out a surprising volume. On anything larger a powered scarifier does the same job with blades. The RHS timing is autumn, ideally September to early November, while the grass is still growing strongly enough to fill the gaps before winter.
Scarifying a mossy lawn leaves it looking worse for two or three weeks: thin, scratched and patchy, with barrowloads of debris to clear. That is normal. Overseeding the bare patches straight afterwards, and working a sandy top dressing into them, is what turns the gaps into grass rather than fresh ground for moss.
Moss killers: what they do and when they help
Most moss killers contain iron sulphate, sold as ferrous sulphate or in lawn sand, which blackens the moss within days. Lawn treatment firms commonly apply it a couple of weeks before scarifying, so the machine pulls out dead moss rather than spreading live fragments around the lawn, then rake out the blackened growth after the interval given on the product label.
The RHS takes a different view and advises that synthetic moss killers are not needed, because raking, scarifying and fixing the growing conditions work without them. Either way, the chemical is the smallest part of the job. Iron sulphate also leaves orange stains on stone, concrete and garden timber, so it should be kept well clear of them.
Stopping it returning
The habits that keep moss out are the same ones that make a lawn look good:
- Mow at the right height. The RHS gives 13 to 25mm in summer for an ordinary garden lawn and up to 40mm in spring and autumn, and advises taking off no more than a third of the height in one cut.
- Aerate compacted ground in autumn, with solid tines every two or three years, or hollow tines every three or four on clay.
- Feed in spring and autumn so the grass is thick enough to crowd moss out.
- Clear fallen leaves promptly; a mat of wet leaves is perfect moss habitat.
- Let more light in by lifting low branches or thinning overhanging shrubs.
What professional moss removal costs
Scarifying a lawn of about 100 square metres costs £55 to £95, and a lawn thick with moss that needs two passes and clearing runs £200 to £240. A lawn treatment visit is £30 to £70, with moss and weed control added to a visit for £20 to £50, and a four visit annual programme costs £150 to £400. Hollow tine coring of 200 square metres adds £145 to £190. Check that a quote includes taking the debris away, because a mossy lawn produces a large volume of it.
Common questions
When is the right time to treat moss in a lawn?
Early autumn, from September to early November, when the grass is growing strongly enough to recover after raking or scarifying. Moss killer, if used, goes on a couple of weeks before the moss is raked out.
Why does moss keep coming back?
Because the conditions that let it in are still there: shade, compaction, slow drainage, acid soil or mowing too short. Moss killer clears it for a season; fixing the cause is what stops it returning.
Can moss be raked out in spring?
Yes, on a lightly affected lawn, but the grass then has to recover heading into summer heat and drought. Heavy moss is better left to an autumn scarify.
Is moss bad for a lawn?
It does not kill grass directly, but it fills gaps and spreads where grass is weak. In damp shade where grass struggles, many people simply let the moss stay.