In my previous post When to Scarify your lawn, I emphasised how important it is to remove dead grass, thatch and lateral grass growth in your lawn.
Too much thatch and lateral grass means the that the desired grass has to work very hard to push through and reach the air and also absorb sunlight.
Sunlight is essential for photosynthesis to take place and if your grass has to work too hard it will weaken and non desirable grass species, as well as moss, can start to colonise the surface of your lawn.
Good aeration is essential but sometimes you might need some chemical help to assist - a simple treatment is the application of sulphate of iron, to help suppress the moss.
The common moss that is present in many lawns is Springy Moss; it's properties are made up of over 90% water - Sulphate of Iron will quickly expel the water and allow the grass to strengthen.
Even after as little as one hour, moss will start blacken; after two days, the moss content will have reduced and turned dark brown whilst the grass will have turned extremely green.
Always try to apply Sulphate of Iron on a dry still day but with rain imminent - ideally no longer than 12 hours .(this is to avoid scorching) the moisture dissolves the sulphate of iron. Once the moss has died back, you can scarify out the debris - ideally 5-14 days after application.
Sulphate of Iron is often referred to as iron sulpahe - either/or really.
The material is very fine and will easily blow everywhere if applied in windy conditions; be very wary and try only to do this job on a still day - wind-blow materaial will scorch any soft tissue on plants close to the lawn.
Do not rely on the drop spreader's gate calibration and always follow a simple calibration method as I described in the post calibrating a fertiliser spreader.
It is inadvisable to store open bags sulphate of iron through the winter - the dry powdery material absorbs even the lightest of atmospheric moisture and the material can become lumpy and unworkable through a drop spreader - try to buy just enough for your needs, although you can use sulphate of iron throughout the winter provided the grass is not frozen.
If you do find yourself forced to use material that cannot be distributed through a spreader, it is possible to apply sulphate of iron suspended within a water solution. Measure out the required amount of material and water that is needed if you wish to apply as a liquid, add the sulphate of iron to the water and stir until all of the lumps are dissolved - let stand overnight.
The following morning, sieve out the liquid using a funnel and old stocking. You will have noticed that there will be residual powder at the bottom. This can still be used later, now calibrate your sprayer and apply the iron solution to the lawn.