Moss in lawns
Green carpets of moss that replace grass in thin, shady, compacted or poorly drained lawns, a sign of poor growing conditions rather than a disease.
Also known as: Lawn moss
Symptoms and identification
Patches of soft, dense, green or yellow-green moss spread through the lawn and crowd out grass. The lawn is thin, spongy or boggy, and moss is most common in shade, on damp soil and in winter.
Causes
Moss grows where grass struggles: shade, compacted or waterlogged soil, acidic or infertile soil, mowing too short, and thick thatch. Killing the moss without fixing the cause means it returns.
Organic treatment
Rake or scarify out the moss in spring or autumn, aerate, top-dress with sandy loam and overseed with a shade-tolerant grass mix. In deep shade, replace lawn with shade-tolerant ground cover.
Prevention
Raise the mowing height, feed the lawn regularly, aerate compacted soil, improve drainage and light by cutting back overhanging branches, and apply lime only if a soil test shows acidity.
Chemical treatment (use with care)
Lawn moss killers containing iron sulphate can blacken moss before raking it out. Use as the label directs and fix the underlying cause as well.