Algae and moss in lawns

A thick, healthy lawn will not allow algae or moss to form because the sward keeps most of the light needed for the algae and moss growth from reaching the soil surface, where these primitive plants live.

If your lawn is thin you might need to solve this problem or replace it with good quality turf. In the event that your lawn does not need to be replaced, then improving the growing conditions will help reduce both algae and moss.


  1. Is your lawn thin?
  2. Is your lawn ‘marshy’?
  3. Do you see a dark green-black slimy layer in your lawn?
  4. Do you see short green fuzzy plants in your lawn?

If you answer yes to the above questions, you have moss or algae growing in your lawn.

Patch of lawn showing signs or moss growth

General Description

Algae – are dark green to almost black primitive plants that form a thin slimy layer on the surface of soil and plant tissues. They grow when your lawn is thin, your soil is wet for most hours of the day and for several days in a row, and if your lawn is shaded. When algae grow, your lawn needs some care. Generally, algae will not kill your turf, but they can cause it to turn yellow or lose its green colour. Often when algae develop in your turf, you can also find them on pavements, walls, and even the trunks of trees. Algae are quite easy to control, both on turf and in your garden.

Moss – is a collection of primitive plants which are green in colour. Generally they are not slimy like the algae but form a short, fuzzy mat in lawns which are thin and sparse. They, like the algae, require damp conditions. Lawns which are thin and wet will allow moss to develop. The same moss that grows on your roofs, walls and fences also grow in thin or poor quality lawns. They have almost no root system, and will often break loose if stepped on.

What to do about algae and moss in your lawn

Listed below are a few suggestions for improving your lawn and reducing algae and moss growth:

  1. Improve the air circulation so it dries faster.
  2. Do not over fertilise your lawn.
  3. If possible, allow more hours of sunlight to reach your lawn (trim back shady trees or prune back overhanging shrubs etc.).
  4. Make sure that your soil drains well and that puddles of water do not form. See Soil compaction & aeration.
  5. Moss can be raked out by scarifying your lawn.
  6. Apply a topdressing to improve drainage and stimulate grass growth.

Using chemicals to control algae and moss

You can use chemicals that will reduce algae growth. There are also chemicals available that will kill moss. We recommend that you obtain advice about chemical and non-chemical grass treatment products directly from the manufacturers.


Algae and moss develop because your lawn is thin and wet. Improving the growing conditions is the best means for reducing these primitive plants.

Further guidance

Further lawn care advice can be found in our Information Centre. You can also sign up for lawn tips to receive regular lawn care advice, news and promotional offers by email which will help you get the best from your lawn.

For more techniques to help you maintain a healthy lawn, explore our other lawn aftercare advice.