Moss is not really the problem, it is a sign of one. It moves in where grass struggles and fills the gaps the grass leaves behind. The UK’s mild, damp autumns and winters suit it perfectly, which is why so many lawns are half moss by March.
Why is there so much moss in your lawn?
Moss wins wherever grass is weak. The usual reasons:
- Shade from trees, hedges, fences or the house.
- Wet or compacted soil, especially on clay that stays soggy all winter.
- Low fertility, so the grass thins out.
- Mowing too short, which scalps the grass and lets light onto bare soil.
- Acidic soil, common on sandy and upland soils.
Is sulphate of iron legal as a moss killer?
Only in an approved product. Sulphate of iron sold as a lawn tonic or greener is a fertiliser, and it is not approved as a moss killer. To control moss, buy a lawn moss killer approved for amateur use. Most are iron sulphate based, and the label carries a MAPP number and the rate to use.
That is why What a Green Lawn leaves plain iron sulphate out of the product amounts on a UK phone. The card still works out feed, lime and the other products from your mapped lawn:
An approved moss killer, or a feed, weed and moss killer, has its own rate, so follow its label. The card itself says the amounts are estimates and to check local regulations.
When is the best time to kill moss?
March to April and September to October. The moss is green and growing, the soil is moist, and the grass grows fast enough to fill the gaps. Autumn is often better, because you can scarify and overseed straight after. Avoid drought, summer heat and frost.
How do you apply moss killer?
Pick a calm day when the soil is moist and no heavy rain is forecast. Spread evenly with a spreader or sprayer, in two passes at right angles, and follow the label on watering in and on keeping children and pets off. Keep it off paving and patios, because the rust stains are close to permanent. The moss turns black within about two weeks.
What do you do once the moss is dead?
Scarify or rake out the black moss. On a mossy lawn that can mean several bin bags. Then overseed the bare patches before moss or weeds fill them. See when to scarify your lawn and when to overseed your lawn for timing.
How do you stop moss coming back?
- Raise the mower height, see what height to cut grass.
- Cut back overhanging trees and hedges, or sow a shade-tolerant mix with fine fescue.
- Spike or hollow tine compacted, wet areas in autumn.
- Feed the lawn so it stays thick.
- Test the soil pH and lime only if the test shows acidic soil.
Log each treatment in What a Green Lawn with the product and amount, so next spring you know what you used and when.