Moss in your lawn is generally a result of poor growing conditions such as low fertility, compaction, over-acidity, poor drainage and / or excessive shade.
Listed below are a number of causes and solutions to some common problems.
Circa Week 20: use a moss control based on ferrous sulphate (sulphate of iron).
This product is often a constituent part of a spring lawn feed often referred to as Weed and Feed or Spring lawn feed with added moss killer.
If you are planning to feed your lawn, consider using products such as these, and follow the application method written on the packaging.
Otherwise use the specific moss killer as per the manufacturers instructions.
Once treated, the moss dies and blackens.
The blackened moss can be allowed to decompose naturally, but it's better to rake it out and remove it.
Treated areas should be scarified two weeks after application of moss control.
This can be done by manually which extremely hard work, or can be done mechanically.
Manual Control : use a multi-tined rake to scrape the moss off the lawn surface.
Where large areas require treatment it is advisable to hire a machine suited to the purpose.
Providing the debris removed hasn’t been treated with a weed/moss killer it can be composted in thin layers onto the compost heap.
On completion you may find areas of the lawn devoid of grass so sow a suitable grass seed to rectify the situation.
In the remaining areas feed your lawn with a proprietary lawn feed suited to the season it is applied.
For the remainder of the season do not mow the grass too short.
Leaving longer strong growing grass, creates less space for moss to become established.
Other methods of Moss Control
Moss can thrive on poor soil as it needs less nutrients than grass.
To remedy this, apply a lawn or general fertiliser in the spring or summer. (See note above)
Do not apply a high nitrogen fertiliser in late autumn, as this will encourage lush grass growth that may be vulnerable to frost and diseases.
Symptoms are that after heavy rain a poorly drained lawn will remain wet for quite some time,thus providing ideal conditions for moss to thrive in.
Moss needs constant high levels of dampness to reproduce and thrive, whereas lawn grasses wont tolerate such conditions.
The type of soil can also be a major factor e.g. heavy clay.
Similarly, surface compaction brought about by children playing on it can also be a factor.
Drainage can be improved by using a hollow-tined aerator which is pushed into the lawn at closely spaced intervals, resulting in cores of compacted soil being withdrawn.
Prior to using the aerator remove the thatch of dead grass and moss with a lawn rake.
Once the holes have been formed fill these with sharp sand or grit to produce drainage channels.
Repeat this procedure every spring until conditions improve.
This task is best not done in summer when the underlying soil can be rock hard.
Soil too acid:
Some kinds of moss prefer an acid soil, as do some of the finer lawn grasses.
Check the soil pH, and apply either ground chalk, ground limestone or an alkaline fertiliser such as Nitro-chalk.
Do not overdo it or you may encourage weeds and grass diseases.
Compacted or badly aerated soil:
Grass takes in air, water and nutrients through its roots, so to remain healthy it needs a good soil structure, whereas moss roots are merely for anchorage, meaning it can tolerate compacted soil.
To alleviate this problem, spike the lawn to increase aeration then top-dress the lawn with a mixture of sand, peat and loam to improve the surface structure.
Grass kept too long:
Lawns made of coarser grasses are cut to 25mm (1”) or more provide ideal conditions for trailing types of moss.
To alleviate the problem, reduce the cutting height of your mower, and mow more frequently.
Finer lawn grasses are more suited to close mowing.
Grass kept too short;
Finer lawn grasses are usually cut very short and this encourages cushion-forming mosses.
Close mowing causes scalping which damages the grass, which in turn allows moss to spread.
Use a cutting height of 13 to 20mm (½"- ¾") for finer grasses.
Too much shade:
Mosses need less light than grasses and the damp conditions associated with shade also suits them.
Prune overhanging trees and shrubs and reduce the height of tall hedges.
Too many weeds or pests:
Weeds compete with grass, pest damage the roots, so anything that weakens the grass will give moss a chance to spread.
Use lawn sand or a lawn weed killer to keep weeds at bay or a soil insecticide for pests.
Do not walk on lawns when they are frozen.