Moss on lawns

Most gardeners have trouble at some stage with moss on lawns. This is unsightly and is often a result of poor growing conditions. By improving the health of the lawn, moss can be kept at bay.

Moss in a lawn. Image: John Trentholm/RHS

Quick facts

Common name Moss
Botanical name Various
Areas affected Lawns and artificial turf
Main causes Damp conditions, poor drainage and low grass vigour
Timing Treat in autumn or spring

What is the problem?

Moss can be a temporary problem following drought or waterlogging, or more persistent, suggesting a problem with underlying conditions. On new lawns this may be due to poor site preparation. On established lawns poor vigour, acidic soil conditions, a lack of feed, insufficient aeration, poor drainage, shade, close mowing and over-use are likely to blame.

Killing and removing the moss is just the start. To remain moss-free, the vigour of the grass must be improved and any other contributory factors addressed. Good autumn lawn maintenance is essential to maintaining lawn health.

If, despite remedial action, moss remains a problem, such as under trees or in a poorly-drained site, consider alternatives to grass. Bear in mind that artificial turf may also suffer from problems with moss and other green growths.

Appearance

There are several types of moss that grow on lawns. These are usually coarse, loose, green or yellowish-green tufts between the grass, but can form densely matted tufts or, in the case of Polystichum, appear like small forests of miniature Christmas trees.

Moss gives the turf an uneven colour and surface. Loose mosses make the lawn feel spongy to walk on.

Cause

Poor growing conditions favour the growth of moss in lawns. These might include:

  • Sparse grass cover
  • Worn areas of turf, especially along walkways and where children play
  • Shady areas, especially beneath trees
  • Compacted soil
  • Wet weather and waterlogged conditions
  • Drought-stressed grass
  • Mowing too close
  • Impoverished lawns or infertile soil
  • Poorly prepared or poorly maintained lawns
  • Acidic soil conditions

Control

Non-chemical control

Scarification: Remove loose moss in autumn, by scarification (vigorous raking). On small lawns this can be done by hand, raking out the moss with a spring-tine rake, but on larger lawns mechanical scarifiers can be hired.

MO Bacter: A non-chemical product called MO Bacter Organic Lawn Fertiliser claims good control of moss, as well as feeding the lawn. The added benefit is that the dead moss should break down in situ, negating the need for scarifying.

Chemical control

For moss control use a proprietary product (e.g. Vitax Green Up Mossfree), such as those based on ferrous sulphate (sulphate of iron) in spring or early autumn. When the moss blackens after two or three weeks use a spring-tine rake to remove it. The dead moss can be added to the compost heap. Although slow to rot in bulk, moss can be composted if well mixed with plenty (four times the volume of the moss) of other ingredients. Moss can be stored and added gradually as other ingredients become available. As moss is very widespread any spores that survive the composting process won’t add significantly to the risk of moss forming in the garden. Best practice is to avoid consigning moss to the green waste collection, and disposal by composting, or in extreme cases stacking or burial is recommended.

Mosskillers combined with a fertiliser (nitrogen, phosphorus or potassium, indicated by the abbreviations NPK) (e.g. Scotts Lawn Builder Lawn Food Plus Moss Control, Vitax Green Up Lawn Sand Moss Control or William Sinclair J. Arthur Bower's Autumn Lawn Food & Mosskiller) are beneficial where grass vigour is low.

Apply mosskillers either by hand or with a push-along spreader. Be careful not to apply lawn sand (ferrous sulphate mixed with a carrier) at too high a rate as this can blacken and kill the grass as well as the moss. Apply lawn mosskillers in fine weather. Some require watering after 48 hours if there has been no rain. Check pack for details.

Control with a mosskiller will only be temporary unless the conditions which allowed the moss to become established are improved.

New lawns: Good preparation should ensure moss control is rarely required on a new lawn. However, if the need does arise, double check the manufacturer's recommendations on the pack before applying. Many products should not be applied within the first six months or after a certain number of cuts.

Artificial lawns: Brinton's Patio Magic (containing benzalkonium chloride) will control moss on artificial turf. Keep artificial turf in good condition by regular brushing. Ensure water is not allowed to pool on the surface.

Note on ferrous sulphate: Although ferrous sulphate is widely offered as a fertiliser and soil acidifying agent, unless it is contained within a proprietary lawn mosskiller it is not approved for use as a pesticide and cannot be legally used to control moss. In addition, if it were to be applied as a mosskiller on lawns there is a high risk that it will blacken and potentially kill the grass - a problem seldom encountered with proprietary lawn mosskillers, especially those in pelleted forms, making them easy to apply evenly and accurately.

Download

Weedkillers for gardeners (Adobe Acrobat pdf document outlining weedkillers available to gardeners - see sections 1d and 2a for lawn mosskillers)

Links

Chemicals: using safely and effectively

Moss removal programme

This is an example of a programme you could follow to get rid of moss, and prevent it coming back.

Autumn treatment:

  • Early Autumn: Apply autumn fertiliser and mosskiller
  • When moss has browned or blackened, scarify the lawn. Aerate with a garden fork or hollow tiner if necessary. Brush in a light lawn top-dressing of three parts loam, six parts sharp sand and one part peat substitute by volume
  • If grass is sparse, lightly over-seed before applying the top-dressing, at a rate of 17-34g per sq m (½-1oz per sq yd) with new lawn seed

Spring treatment:

  • Mid- to late March: Apply spring fertiliser and mosskiller during fine weather
  • Early April: Lightly rake out dead moss
  • Lightly over-seed sparsely grassed areas and lightly top-dress as above if necessary

Moss prevention

To prevent moss returning, encourage vigorous grass growth by feeding and regular lawn maintenance, paying particular attention to the following:

  • When seeding or laying a lawn in a shaded area, use a grass seed mix or turf specified for shady areas.  Reducing shade will also help
  • For compacted areas use a garden fork to spike the lawn, or a mechanical slitter on large lawns. This will aerate the turf
  • On heavy soils use a manual or mechanical  hollow-tiner in autumn to take out small plugs of soil every three or four years, and then brush in a mixture of three parts sandy loam, six parts sharp sand and one part peat substitute by volume
  • Avoid mowing grass too short
  • On very acid soils an application of garden lime at not more than 50g per sq m (1½oz per sq yd), will slightly reduce acidity and discourage moss

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  • anonymous avatar

    By anonymous on 13/07/2014

    Thank you for the post, hope this will help me out. Where I live, we had a much harder winter than usual and in early January, unusually we had some snow. Not just a sprinkling of the stuff but we had 8 inches over one night. Some of you around the world would say 8 inches of snow is nothing but we just can not cope with it here. There was massive disruption to everything, but the kids loved it, as of course the schools were closed for several days. I believe that this snow has caused there to be more moss in the lawn than ever before. It created the ideal conditions for moss to thrive with damp soil being the main factor. Of course the snow wasn't the only thing to contribute to the moss problem as it didn't stop raining from early November until early March with that bit of snow in the middle. http://www.gardeningnorthside.com.au/

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  • anonymous avatar

    By anonymous on 13/07/2014

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