There are many reasons why moss will begin to grow. Generally speaking moss likes to grow in areas where there is very little competition for nutrients and where conditions typically do not favour other plants. It is typically the opposite conditions that grass requires to grow.
One of the biggest causes of moss growth is because the grass coverage of your lawn is too thin. More simply put - there isn’t enough grass. This can be caused by general poor maintenance or by scalping the lawn when cutting.
By having large spaces between the grass blades, it provides the ideal location for moss to grow. One common technique to deter moss from growing in the first instance is a technique called over-seeding. By laying grass seed on top of mature grass and letting it grow, it creates a thicker lawn, and reduces the space between the grass blades, therefore preventing moss from growing. Not only does it help prevent moss, it creates a better looking lawn too.
Patches of grass in the shade are more susceptible to a moss invasion also, as grass is unable to absorb sunlight and photosynthesis energy. This in turn weakens the grass providing an opportunity for moss to grow. If you are planning on over-seeding shaded patches of grass look for some shade resistant grass seed, as this type of grass will grow better and reduce the likelihood of moss growing.
The lack of water available in the lawn for the grass to use, especially in the summer months is another issue. A lack of water weakens the grass providing moss with a window of opportunity to grow.
To limit the chances of this, try and water the grass regularly. Water thoroughly and deeply. This will encourage the grass to root deeply, allowing them to find water more easily during periods when water may be in short supply.
Another common cause is the lack of aeration of compacted soil. Heavily compacted soil makes it difficult for grass to grow, which in turn makes the grass coverage poor. Compacted soil is likely to occur in areas of the garden that get a lot of use for example paths, walkways and around children’s play equipment. When the soil is compacted, it prevents air, water and other nutrients from reaching the grass roots which is required for healthy grass growth.
Aeration is one of the most underused lawn maintenance techniques, and can single handily provide more benefit to your grass than most other lawn maintenance techniques. To aerate your lawn you can simply plunge a garden fork about 2 inches into the ground creating small holes. Do this around the garden until the whole garden is covered.