Moss in lawns is generally a result of poor drainage, too much shade or acidic soil – often all three. While there are chemicals for moss control, without remedying the cause, the moss will simply return. Aeration will improve drainage and lime will reduce acidity. Alternatively, the moss can be left alone. Aerifying machines can be rented.
Some lawns develop thatch – a layer of old roots and stems – and if this layer becomes too thick the lawn will thin out. Soil that is compacted, low in organic matter or microorganisms is more susceptible. Thatch can be removed with a thatching rake or power thatcher. Power dethatching machines can be rented. Aeration will also help. The lawn will then need to be overseeded and top-dressed.