Mosses have been around for over 350 million years, and they’re still going strong today. And while moss looks lovely carpeting cool woodland glades, it’s less welcome in our lawns.
Lawn moss can form dense mats, outcompeting grass for water and nutrients and making the lawn uneven and spongy to walk on. These primitive plants thrive in damp shady conditions and can quickly spread in struggling lawns.
How to get rid of moss in lawns
Moss in lawns is a sign that there is an underlying problem with the lawn. This can be caused by any of several factors, including:
- Poor drainage
- Lack of fertiliser
- Grass cut too short
- Heavy foot traffic
Feathery, fern-like mosses are most common in poorly drained areas. Acidic soils tend to encourage mat-forming mosses.
Ridding lawns of moss requires a two-pronged attack – firstly, to remove the moss and secondly, to stop it coming back.
Physically removing moss is done by scarifying, i.e. raking over the lawn to remove moss and thatch (dead grass). For small gardens this can be done by hand with a spring tine rake. For large areas, it’s easier to use a mechanical scarifier.
If the moss problem is mild, it may be possible to get on top of it by simply scarifying and then improving the overall health of the lawn by regular lawncare to stop the moss coming back. However, getting rid of moss in lawns where there is a serious problem needs a combination of moss killer, scarifying and lawncare.
Chemical moss killers containing ferrous sulphate (also called sulphate of iron) are the most effective method of eradicating moss in lawns. Some chemical moss killers also include a fertiliser, which is useful for lawns where the grass has lost its vigour. Chemical moss killers are typically applied in autumn or spring when the weather is cool and wet, so that lawn seed sown afterwards to cover bare areas is most likely to germinate.
For gardeners who prefer not to use synthetic chemicals, organic moss killers are also available. These don’t contain ferrous sulphate, using bacteria instead to break down the moss. An advantage of organic moss killers is that since the bacteria effectively ‘digest’ the moss in situ, it doesn’t go black and needs no raking out. Organic moss killers need a temperature above 15ºC (59ºF) to work and can be applied from late spring to autumn.
Tips on using moss killer
- Moss killer can be applied either by hand or by using a manual spreader that can be pushed over the lawn. Chemical moss killers affect soil acidity levels, so it’s important to apply moss killer evenly across the whole lawn, not just in problem areas, otherwise the lawn may grow back patchy and discoloured.
- Always read the manufacturer’s instructions before applying moss killer, and use only at the concentrations specified, as applying too much moss killer is likely to damage or even kill the grass.
- Moss killer should be applied in fine weather, but again, always check the manufacturer’s instructions, as some products require watering to activate.
Using ferrous sulphate (sulphate of iron) as a moss killer
Ferrous sulphate is often seen advertised as a solution to lawn moss. Most chemical moss killers contain ferrous sulphate, and when contained in a proprietary moss killer and correctly applied, it is effective.
However, it should not be used on its own as a moss killer, firstly because it is not approved as a pesticide, and secondly because used in the wrong quantities it is likely to do more harm than good, killing off grass as well as moss.
How to apply chemical moss killer
The best time to apply a chemical moss killer is autumn or spring, when the weather is cool, and damp and any bare patches left after moss has been removed can be re-seeded.
- If the moss is very thick, scarify first to thin it out before applying moss killer.
- Apply moss killer according to the manufacturer’s instructions.
- Once the moss turns black (this usually takes two to three weeks) use a spring tine rake or mechanical scarifier to rake it out of the lawn.
The raked-out moss can be composted, but it is slow to break down, so should be added to your compost heap gradually.
Moss in a lawn indicates that there is an underlying problem with the lawn, and unless this is fixed, the moss will return. The best way to discourage moss from coming back is to get the grass growing vigorously.
How to reinvigorate your lawn
- Aerate the lawn in autumn by spiking holes in the soil at regular intervals. For small gardens, you can do this using a garden fork, pushing it in as far as possible and then removing it. For large areas, it’s easier to use a mechanical aerator.
- Re-seed sparse or bare patches of lawn. Shady areas of your lawn are always going to be more prone to moss, so for these areas, use grass seed mixes especially designed for shade.
- After aerating and re-seeding the lawn, brush in a lawn top dressing. You can buy pre-prepared top dressing from garden centres or make up your own mix using three parts loam, six parts sharp sand and one part multipurpose compost. Spread it evenly over the lawn, using a firm garden brush to work it in.
- When mowing, take care not to cut the grass too short, as this will stress the grass, reducing its vigour and encouraging moss.
Moss in lawns doesn’t need to be a problem. With a little care and attention, you can turn a mossy lawn into beautiful green turf to be proud of.