WHAT CAUSES MOSS IN LAWNS
Finding that you have a significant amount of moss in your lawn is perhaps the most common horticultural problem you will come across in a garden. However, while moss is neither a pest nor a disease it is perhaps the least understood of all lawns problems. Why, because simply killing of the moss in your lawn is no solution at all. At least while the moss was alive your lawn ‘looked’ green, but with the moss dead, subsequently turning brown and exposing the soil beneath, your lawn will look worse than ever!
With that in mind, try and resist the lure of row upon row of Moss killers that will be calling out your name as you walk round every supermarket and garden centre. To understand what causes moss in lawns you must look at the bigger picture, and it is all down to the local environment. There are certain conditions that moss requires in order to flourish. Say yes to two or more of these conditions and there is a high probability that there could be a moss problem in your lawn just waiting to be discovered. Put simply, moss is unable to get a decent foot in your lawn if the grass is properly maintained and healthy. Therefore a good lawn care regime is your best defence against a subversive moss attack. As soon as the lawn falls into poor condition moss will be given the advantage and will try and take over.
Under the right situations moss will thrive in your lawn. Moss also has a great capacity for spreading quickly and for good reason too, it can self propagate from smaller pieces of itself as well as being able to produce juvenile plants from spores. However, of all the environmental conditions that favour the growth of moss, a shady lawn has to be one of the best. The reason for this is because - unless you have a specific mix of grass specially cultivated for shady areas - lawn grass does not cope well in shade, nor will it like the damp soil conditions that tend to accompany this. The grass will grow weakly in these low light areas, eventually to become increasingly patchy if left to its own devises. Furthermore, without the warmth of direct sun the soil will find it harder to dry out. The moss will excel in these more favourable conditions and over time will out-compete the grass.
WET SOIL AND POOR DRAINAGE
Lawns that grow on soils that are periodically waterlogged will be at risk from moss for similar reasons to that of lawn grown in shady areas. This can be partly due to compacted soil, or by the lawn being laid onto a heavy/clay soil. The roots of the grass require air pockets in the soil so that the plant cells within the roots have access to oxygen. This oxygen is required for these cells to metabolise - without which the cells, and later the roots themselves, will die. Simply put, the health of your lawn can severely suffer in waterlogged conditions allowing the moss to take a foot hold. In extreme or prolonged conditions the moss will once again out-compete the turf.
NOT ENOUGH WATER!
This may sound at odds with the previous statement but there is some sense to it- even though it may not be immediately obvious. When lawns are left to fend for themselves over hot dry summers, they will tend to thin out and brown off. Unfortunately, these gaps within the turf can be all that is required for dormant mosses and their spores to take off. All you need to do is wait for the autumn rains to arrive for your moss to take a clear advantage over these weakened areas.
THIN, SHALLOW SOILS
If your turf or grass seed was grown on soil that is less than four to five inches deep, it is not considered deep enough to grow and maintain a healthy, vigorous lawn. Of all the environmental conditions that can have a detrimental effect on your lawn, this is probably the one that is the most difficult to deal with. Unless you are prepared to remove your turf and start again (with the addition of a few more inches of topsoil) it is probably going to take a few years to deal with. Why? Because other than periodically brushing thin layers of topsoil on to your existing turf there is not much else you can do. As mentioned before, the better condition your grass is, the better it will be at fending off moss.
Put simply, lawn grass does not care for acidic soil whereas moss will happily to its hearts content. In order to be sure that soil acidity is a factor you will need to carry out a soil test to assess the acidity of the soil. If your soil is indeed acidic then it is likely in need of adjustment. In order to rebalance the soil, lime can be applied in the autumn.
CUTTING YOUR LAWN TOO SHORT
This is quite possibly one of most common reasons as to why moss is allowed to gain an advantage in lawns. Cutting your lawn as short as possible, may well make your grass look amazing but over time the constant removal of healthy growth will tire the grass and leave it in a weakened condition. As I am sure you know by now, a weakened lawn will allow moss to take advantage and establish itself.