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Lawns in damp or poorly drained conditions can suffer from unsightly problems such as cyanobacteria (an algae-like growth), dog lichen and liverworts. Cyanobacteria in particular can make the lawn very slippery.
Dog lichen, Peltigera canina, on a lawn. Image: RHS
Algae-like growths, lichens and liverworts are often found growing in damp or shady places in the garden. Although harmless in other areas of the garden, even lending a mature look to the landscape, they can be problematic on lawns. As well as affecting the appearance of the lawn, they block light from reaching the grass and can make the surface slippery.
Algae-like growths: Dark green or blackish jelly-like growths that often appear in damper, cooler weather over the surface of the lawn, making it slippery are caused by a cyanobacteria called Nostoc. These are sometimes referred to as gelatinous algae or blue-green algae but are technically classified under bacteria, not algae.
Lichens: In turf the most common lichen is Peltigera spp. (dog lichen); it is brown or grey and formed of flat structures that grow horizontally in the turf.
Liverworts: Liverworts on lawns usually have a green, flattened body and no leaves. A common example is Marchantia, which is often topped with umbrella-like sexual organs.
Slime moulds: Wet weather in autumn or spring can also lead to the growth of slime moulds. These growths, which may be white, yellowish or orange, produce small grey fruiting bodies that subsequently release masses of purplish-brown spores. The growths are purely superficial and do not harm the grass but they are unsightly.
Cyanobacteria, dog lichens and liverworts are found on lawns where poor drainage and shady conditions cause a damp surface. Compacted soil is especially prone to developing algae, particularly around the drip line of trees or shrubs.
In very wet weather algae may appear on only slightly compacted lawns and is also frequently found on turf beneath trees.
Correcting the underlying conditions should clear up gelatinous algae and moss growth. Try the following:
There are few chemical controls available to gardeners, but if lawn mosskillers that contain ferrous sulphate (e.g. Vitax Green Up Lawn Sand or Maxicrop Moss Killer and Lawn Tonic) are used on the lawn to control moss, incidental control of algae-like growths, lichens and liverwort should also result. Note: Brinton Patio Magic (containing benzalkonium chloride) will control algae-like and other growths on artificial play surfaces.
Inclusion of a weedkiller product does not indicate a recommendation or endorsement by the RHS. It is a list of products currently available to the home gardener.
Weedkillers for gardeners (Adobe Acrobat pdf document outlining weedkillers available to gardeners; see sections 2a and 2c)
Algae on leaves
Algae, lichens, liverworts and moss
Algae, lichens, liverworts and moss on hard surfaces
Algae, lichens and moss on trees and shrubs
Algae, liverworts and moss on borders and containers
Moss on lawns
Slime mould on lawns
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The Royal Horticultural Society is the UK’s leading gardening charity. We aim to enrich everyone’s life through plants, and make the UK a greener and more beautiful place.