Well the wet weather of November carried on through December with 89mm or 3.75 inches . Interestingly this matched last December as well . Outcome of all this wet weather is MOSS and more Moss, although moist conditions are not the only factor responsible for moss, it certainly is the main contributor.
Other factors that add to the problem – Thatch, Shade , Drainage, Air movement, Cut height and Feed.
Moss in most cases is always present on lawns, but in most cases the % cover is so small that you don’t notice it in a healthy lawn , until one of the factors that contribute to its growth is no longer in balance.
Thatch can build up at surface level, and below – it is a mat of dead and decaying root and grass material that can prevent surface water draining through , it provides a perfect medium for moss spores to grow on and prevents air getting to grass roots and air movement around the blades of grass. Healthy soils are less prone to this as fungi and bacteria will feed on this thatch , break it down and convert it to a natural fertiliser that encourages grass to grow strongly. Getting that balance is not easy, but regular scarification to remove this thatch can help.
Shade – provides perfect conditions for Moss , hence as we moved into autumn with shorter days and less light the spores that are present quickly multiply. You will always notice Moss where you have trees that create shade and plants that spread out over the edges of the border on to the lawn. Hedges throw shade and often we find gardens moss free on one side and then as you move towards the hedge it increases. North facing gardens also are a potential moss haven – no direct sun and constant shade.
Drainage is vital to move away excess moisture , again if you have water sitting on the surface the moss quickly grows , aeration will help remove excess water – but to get the real benefit it should be done in conjunction with top dressing in order to get some sandy loam in to the growing area. Clay soils are the worst and you should always ensure remedial work is carried out when conditions are appropriate.
Air movement – hugely important, many small lawns can be surrounded by fences and hedges which provide the structure of the garden. Probably not possible to change the design , but you should be aware that there will be less air movement , and lawns will take longer to dry out.
Cutting height is a major factor in encouraging moss – too often grass is cut too short and the blade scalps the surface, the grass never recovers and the surface is populated by the moss spores. Essential to adjust cutting height through out the year according to the conditions and never cut more than a 1/3 of the grass length at any one time – also need to take in to account the grass variety and type of mower that you are using.
Keeping the soil fed with a balanced nutrient programme around the year ensures that the grass is growing strongly and can smother the moss out. In the South East we are seeing an increase annually in temperatures to the extent that grass will grow all year around – it probably slows down a little in November / early December with the lower light level, but not that you really notice. Feeding is a mixture of providing the essential elements that grass needs to grow , but also feeding the soil, if we can encourage an environment for soil fungi and bacteria to flourish the soil will support the grass and without excessive growth the grass will be strong and less prone to disease