Moss in lawns

Moss is one of the most common and frustrating lawn care problems and can invade almost any type of lawn, especially during the cold winter months.

However it is more common in neglected lawns, where the grass has been allowed to become thin and weak due to poor lawn maintenance. Mosses have no root structure and are flowerless plants that rely on sufficient moisture being available to reproduce and spread.

It is most troublesome on lawns during the winter months and into spring time. This is because grass does not grow and light is lacking during the cold, dark winter months. Therefore with no competition from the grass, moss takes the opportunity invade any weak areas on the lawn.

However by promoting a healthy lawn with good management practices you can help prevent the conditions that encourage moss to invade.

Causes of moss

The conditions that moss favours are as follows:

  • Poor surface drainage – This encourages fern and tufted type mosses.
  • Lack of fertility or nutrients – Any lawn low in essential nutrients will be thin and weak and open to invasion.
  • Acid soil conditions – Soils with a low pH encourage moss.
  • Shaded lawns – Lawns which lack light tend to have poor grass coverage which leaves them open to invasion.
  • Mowing lawns too close – Mowing too closely weakens the sward resulting in thin grass coverage inviting moss into the lawn.
  • Drought – Lack of irrigation during drought conditions causes to grass coverage to suffer and moss can invade.
  • Compacted soils – These soils are likely to be lacking in grass coverage giving it the opportunity to invade.

Prevention & control of moss

Dead moss in the lawn

The above image shows a close up of the lawn following moss treatment. Note that the moss has turned black and died and it now ready to be removed with a lawn rake or scarifier.

To prevent the invasion of moss you will need to address the problems and conditions that favour it as outlined above. Addressing the following will help improve the quality of the lawn surface and help reduce the problems:

  • Improve the drainage – This will remove surface water keeping the surface drier.
  • Aeration – This reduces compaction and keeps the soil in good condition.
  • Correct fertiliser program – This promotes a healthy thick sward leaving the moss with little opportunity to invade.
  • Reduce the shade – Lets more light onto the lawn, again discouraging moss which favours shaded areas with very little light.
  • Raise the height of cut on the mower – Raising the height of the mower reduces the stress on the grass and encourages a healthier sward.
  • Irrigation – During dry periods water the lawn to maintain grass coverage and health.

In a nutshell all of the above will help maintain a healthy grass sward which is the best way of preventing moss becoming a problem on your lawn.

If for whatever reason it does become a problem there a couple of ways to control it, these are as follows.

  • There are numerous products on the market available for the control of moss. Most of these control products contain sulphate of iron.
  • The use of a product called lawn sand is the traditional way of controlling moss in lawns. Lawn sand contains three ingredients sulphate of ammonia, sulphate of iron and sand (sand is used as a carrier). The sulphate of iron kills the moss and this ingredient can also be applied on its own. The sulphate of ammonia is a nitrogen based fertiliser which will help with recovery by encouraging growth. The ideal time for an application of lawn sand is in the spring time when the grass is starting to show signs of growth after the winter months.
  • Other products available in both liquid and granular formulations are also available for the control of moss. Most of these products will contain sulphate of iron plus some nitrogen to aid recovery. There are many of these products available on the market, found in most good garden centers. It is important to follow the manufactures recommendations when applying any product used for moss control.
  • Please visit our Lawn sand or Sulphate of Iron pages for more info on moss control.
  • The other control method is to use a chemical moss killer containing the ingredient DICHLOROPHEN. This product gives a longer lasting kill than lawn sand and is usually applied through a sprayer in liquid form. However this product may not be available much longer.

Lawn sand and sulphate of iron are applied with a spreader, these products are very light and powdery so it is best to avoid windy conditions. Both lawn sand and sulphate of iron (if applied in powder form) will need watering in after application.

Sulphate of iron can also be mixed with hot water into a solution and sprayed onto the lawn via a sprayer. It is important to mix it thoroughly to prevent the sprayer becoming blocked.

Timing of moss control

The ideal time for any moss control is early spring when the grass is showing signs of growth after the winter months. The grass needs to be growing to help any bare areas recover after the moss has been killed and removed. If this is done to early you may end up with bare areas on your lawn and the moss may invade your lawn again before the grass starts to grow.

Removal and aftercare

Scarifying to remove moss

A powered lawn scarifier like the machine in the above image is ideal for removing moss from the lawn. These machines are designed for removing vast quantities of moss on larger areas of turf. For smaller lawns a spring tine hand rake may be used to remove the moss, but they can be hard work on a large lawn.

About 10 – 14 days after the moss treatment was applied, the moss should have been killed and is now ready to be raked out of the lawn. There are two options for this task, either a powered lawn rake or scarifier or a hand rake. Which one you choose will depend on the size of the area and the quantity of to be removed.

Once the moss has been removed it can be cleared away and you are ready for the next task. You can now go ahead and over seed and top dress the bare areas (if necessary) from where the moss was removed, this will help speed up recovery and thicken up the grass. Applying a nitrogen based fertiliser afterwards will also help with recovery, however many types of moss killer products now contain a fertiliser for this purpose.

To prevent any future problems keep your lawn in a healthy condition by correcting the causes of moss as outlined above because it will return again if the conditions are favourable. Light applications of sulphate of iron every 4 – 6 weeks throughout the winter months (October – February) before moss becomes a problem will help prevent any moss invasion.

John Storm

Oliver Thompson
Lawn Care Expert

About Oliver: Oliver Thompson, a seasoned lawn care expert from the Cotswolds with over two decades of experience, invites all enthusiasts to join him in exploring the world of lawns, sharing knowledge, and fostering a vibrant community of lawn enthusiasts. More info

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