Lawns: How to keep moss at bay

Martyn Davey, Head of Horticulture and Design, Easton College
Monday, June 4, 2012
2:04 PM

Question: For three years I have neglected our 100m sq of lawn, and moss has really taken over! A selective grass feed and weed killer a year ago was a disaster. If left large black areas where the moss had been killed but devoid of grass. I am now using a small test area (7m sq), where I have forked the ground to improve drainage and raked out a lot of the moss. Is there please a feed, perhaps Tomorite, that will benefit only the grass and not the moss? Or is there a better method which could keep the lawn in use this summer? And can the raked-out moss be composted? (T Waterfield, via email)

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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 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.

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. For moss control use a proprietary product, such as those based on ferrous sulphate (sulphate of iron) in spring or early autumn. The ready-to-use formulations of ferrous sulphate can be used to spot-treat small patches of moss. When the moss blackens after two or three weeks remove with a spring-tine rake.

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. 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, will slightly reduce acidity and discourage moss. When applying fertiliser always use a spreader to help reduce black streaks.