What causes moss in lawns

In order to prevent moss from invading lawns or other areas of turf it is important to understand the conditions which favour it. Moss tends to be more of a nuisance during the winter months when grass growth is very slow or has stopped altogether. However there are some other underlying causes on why we seem to suffer from moss year after year. These include:

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  Inadequate drainage – Without doubt, one of the major causes of moss invasion is the retention of water (often for long periods of time) on the surface of the lawn. This is most commonly caused by soil compaction (especially where the lawn has been constructed on a clay soil). Although most types of soil can suffer from compaction, clay soils are more prone to waterlogging than other soil types.

• Excessive shade – A lack of sunlight is a contributory factor to moss invasion. Shade or a lack of light can be caused by buildings, trees, plants and other vegetation in the garden. This is why moss is more prevalent during the winter with its shorter days often lacking in sunlight. Moss thrives in these conditions whereas grass finds it difficult to grow.
• Poor mowing practices – If the lawn is mown too short during the growing season it can place undue stress on the grass leaving it thin and weak. This gives moss and other weeds a great opportunity to invade these weak or bare areas. If the lawn is lacking grass coverage during the winter (when there is little or no growth) then it is very likely moss is going to be a major concern.
• Poor grass coverage – A lawn that lacks grass coverage caused by numerous practices or conditions is almost certainly going to suffer from moss, especially during the cold winter months.
• Soil compaction – Soils that are compacted (lacking in air) are likely to be thin and weak. At best they will only support shallow rooted weed grasses such as annual meadow grass.
• Nutrient deficiency – In order for a lawn to maintain optimum health and good grass coverage, it needs regularly feeding with the correct fertiliser. If there is a nutrient deficiency then growth may be poor and moss will be more of a problem.
• Neglect – Operations such as scarifying, aeration, fertilising etc, should be carried out on a regular basis. Neglecting these essential task will be detrimental to the health of the lawn resulting in weak grass coverrage.
• Excessive thatch layer – Thatch is the accumulation of organic matter in the base of the lawn. When this layer becomes excessive it has a detrimental effect on the health of the lawn. This causes a whole host of problems including the invasion of moss.
• Low pH (Acidic soil) – A soil that has a low pH or is acid is more likely to be affected by moss.

Conclusion – In a nutshell the majority of the reasons listed above will encourage thin and weak growth on the lawn, this of course give moss the ideal opportunity to invade. Therefore it is important to ensure your lawn is kept in optimum condition with a thick coverage of grass. Please visit our moss prevention page for advice and tips on maintaining good lawn health.