How to Kill and Prevent Lawn Moss
Follow our detailed checklist and learn how to both remove and prevent lawn moss
Grow a Healthy Green Lawn by Removing and Preventing Lawn Moss
A checklist by the team at DIY gardening
Moss is an unsightly green and uneven mass that plagues many lawns in the UK.
The flowerless plant forms thick chunks that contain millions of spores which allow the plant to spread quickly in shaded and damp areas of the garden.
Moss is opportunistic and will thrive on compacted soil, boggy lawns and in areas that receive very little direct sunlight.
Lawn moss may also appear if the soil has unusually low levels of nutrients as this prevents the grass from thriving, leading to bare patches of soil.
The team here at DIY Gardening have created a helpful guide for anyone that wants to rid their garden of lawn moss and grow a lush green lawn.
Step 1) Check For Drainage Issues (a quick case study)
Take a look at the photo below:
We checked the soil nutrients and there were no issues, the pH levels and amounts of Potassium, Phosphorous and Nitrogen were all within norms.
The ground was neither compacted nor suffering from excessive foot traffic, neither was the grass cut too short. Yet, 90% of this “lawn” is in fact, moss.
On closer inspection, one can see that the four sides of this lawn area are elevated. Rainwater, especially during the winter, flows and collects in this area where it pools.
While this isn’t obvious in the summer, come winter the entire area is damp and boggy. The lowest point of the lawn holds around an inch of surface water for several days after heavy rainfall. This makes the area a perfect breeding ground for mosses, especially in the rainy season.
No amount of chemicals, sunlight, grass seed or added nutrients will prevent this moss from returning, the issue here is drainage or to be more precise; lack of drainage.
Should the owner of this garden wish to grow a lush, green healthy and moss-free lawn, they would need to install French drains to divert the rainwater away before it reaches the lowest point of the lawn.
The lawn should then be topped with at least six inches of topsoil to elevate the lowest part of the lawn which, given the size of the garden, should then be sown from seed.
The first item on our checklist is drainage; a percolation test can be performed but may not be necessary in the winter if the ground is waterlogged after rainfall.
The solution to drainage issues may simply be aeration of the soil or a more drastic approach may be required, such as installing drainage channels or elevating the lawn in specific sections. The FlowerPotMan website has published a guide to diagnosing and fixing garden drainage issues. Go check it out, it’s a great read.
Step 2) Increase Sunlight Into The Garden
Common lawn grasses require a minimum of between 4 and 6 hours a day of sunlight. Any less than this and the grass will thin out and mosses and weeds will start to take over.
When designing a garden, attention should be made to areas that receive very little sunlight. Instead of sowing seed or laying turf, consider creating a flower border, a patio, path, decking or other area made from materials that don’t require sunlight to thrive.
The next step is to maximise the amount of light coming into the garden, do consider both indirect and direct sunlight.
This can often be achieved by:
- Installing shorter fence panels at the boundary
- Using trellis instead of solid fence panels
- Aggressively cutting back and topping shrubs
- Reducing the height and spread of any trees nearby
- Relocating sheds if possible
Moss will thrive in shaded areas where grass doesn’t grow well and one of the most important steps is to maximise the amount of light coming into the garden.
You cannot compensate for lack of light by using more grass seed or over-fertilizing the lawn.
Grass requires light for photosynthesis, without it the grass thins out and moss takes over.
Increase the amount of light reaching the lawn and moss growth will be stunted while grass should thrive.
Step 3) Conduct a Soil Nutrient and PH Test
Like any plant that grows in the garden, grass requires nutrients and will thrive if sown in soil with the correct PH level.
Too much or too little of the key nutrients and the grass may struggle to grow, leading to bare patches where moss will take over.
A test can be performed to determine the levels of the key nutrients currently in the soil; Potassium, Phosphorous and Nitrogen. The test should also reveal the PH level, or acidity of the soil.
Based upon the results, you can then add manure, topsoil, sand and fertilisers until your soil contains the optimal levels of the key nutrients and is within the normal PH range.
Taking this step improves the quality of the grass and helps to stop lawn moss from forming and spreading.
DIY soil test kits are available to buy online, or you can send a sample to the Royal Horticultural Society, who, for a fee, will send you the results and details about how to improve the quality of the soil.
Step 4) Kill and Remove Any Existing Lawn Moss
There are two ways to kill and remove lawn moss:
Option 1 – The Traditional Method
The traditional method of lawn moss eradication involves treating the entire lawn with iron sulphate and waiting for the lawn moss to die and turn black.
The dead matter can then be pulled out, either manually with a rake or with an electric scarifier.
Following this, the lawn should be overseeded with new grass seed and topped with nutrient-rich soil that should be brushed in.
Option 1 is a popular method that works well in small gardens. For larger areas, the method requires a lot of hard work and option 2 may be preferable.
The best time to start option 1 is either in the spring or autumn when the new grass is actively growing.
Option 2 – The Organic “No Rake” Method
Option 2 is to use an organic moss killer that also contains a bacteria that consumes the dead moss, dead grass and decayed thatch that collects at the base of the lawn.
This product is known as a “no rake” moss killer.
BO Bacter is our preferred product.
Simply dilute the granules with water and apply to the lawn moss or sprinkle the product over the lawn and water in with a hose.
As the moss is killed off and consumed by the bacteria, the existing grass should spread into the area.
For areas heavily infested with lawn moss, treat with BO Bacter and then sprinkle grass seed and topsoil over the area.
You may need to apply multiple doses of BO Bacter and overseed several times a year as the No Rake method takes time. While this process is time-consuming it’s not particularly labour intensive.
The best time to start option 2 is also in the spring or autumn when the grass is actively growing.
Whether you choose option 1 or 2, you may need to add some topsoil and the type required will depend on the results of a soil test.
For most lawns, a mixture of loam, sharp sand and peat (or peat alternative) will create a nutrient-rich and well-aerated soil, perfect for germinating and feeding grass seed.
Iron Sulphate For Moss
Iron Sulphate is a powder which, if diluted with water, creates a powerful lawn moss killer. Expect the moss to turn brown or black and then die off quickly after contact with Iron Sulphate. Grass will absorb iron and will turn a lush green.
Perfect for lawns but you’ll need to rake out the dead moss after using this.
Organic Moss Treatment
Evergreen is our favourite lawn moss killer as it ticks so many boxes for us. It’s organic, pet safe, won’t stain patios, contains high levels of potassium and includes bacteria that breaks down moss and excess dead thatch in your lawn bed.
We think this is by far the best moss killer and fertiliser for grass lawns.
Designed specifically for removing moss and thatch from lawns, the hooks on this roller grip the moss and tear it from the lawn. The grass is left untouched and is free to grow into the space created. This is the best moss rake we’ve tested
You’ll also need to purchase the pole/handle for this roller head.
Step 5) Choose Shade Tolerant Grass Seed
Create a lush, thick, grassy lawn that covers the soil and moss will struggle to form.
Not all grass seeds are the same though,
Shade-tolerant grass seeds have been specifically cultivated so they thrive in areas with limited sunlight.
Unfortunately, there is a catch.
Grass that copes well in shaded gardens usually struggles to withstand even normal levels of foot traffic, let alone excessive damage from pets, children and daily use.
Some shade-tolerant grasses are also sensitive to dry or waterlogged gardens or soil with poor aeration.
Finding the best seed mixture of grass seeds for your garden will depend on many factors including:
- How much or how little light reaches the ground.
- The nutrient content of the soil.
- Whether the ground is dry or damp.
- How much foot traffic the lawn is likely to receive.
DIY Gardening Recommends:
We’ve found the best seeds for most shaded lawns to be a mixture of:
Red Fescue – A fine-leaved ornamental grass that is well-known for its ability to thrive in shaded areas.
Creeping Red Fescue – Also known as Strong Fescue, this grass spreads horizontally via rhizomes. While it doesn’t thrive in cold weather conditions and may provide only sparse coverage in winter, expect good wide and thick coverage in the summer, even in shaded areas.
Bentgrass – Expect good thick lawn coverage, even in cooler climates and in shaded gardens but only where there’s good drainage and soil aeration.
Perennial Ryegrass – A great companion or “filler” grass that fills in gaps and sparse areas often created by shade-tolerant grasses.
As you can see, one type of grass seed is almost never enough to provide good, thick coverage for shaded gardens in all conditions.
Some type of grass thrive in shade but die back from waterlogging, excess wear and tear or when exposed to dry conditions.
The team here at DIY Gardening recommends a mixture of at least four different shade-tolerant grass seeds so your lawn has the best chance of thriving, regardless of the conditions.
Start With Graminex
A good product to start with is Graminex Shade Grass Seed.
- Perennial Ryegrass seed – 20%
- Chewings Red Fescue – 30%
- Slender Creeping Red Fescue – 10%
- Rubra – 20%
- Sheep’s Fescue – 10%
- Kentucky Bluegrass – 10%
With six different kinds of grass included, your lawn should thrive regardless of the conditions (wet, dry, shaded, excess wear/tear, poor soil nutrients etc).
Step 6) Apply Fertiliser and Moss Control
Fertiliser helps the grass to grow so it covers the soil and prevents moss from gaining a foothold.
Moss treatment chemicals such as Iron Sulphate kill off any existing moss, giving the grass the freedom to grow and thrive.
A combination of these two lawn treatments should be applied twice a year; in the spring and the autumn when the grass is growing.
The team here at DIY Gardening has found fertilisers high in Potassium work well on lawns in shaded gardens while BO Bactor or Iron Sulphate is best for moss control.
Going beyond a basic twice-yearly moss control and fertiliser, you can also apply organic seaweed extract every two to three weeks during the growing season.
Step 7) Increase the Grass Cutting Height
Many gardeners have an obsession with cutting their lawn as short as possible. While a golf “putting green” type lawn may look neat, this approach to lawn cutting can cause problems in shaded areas of the garden.
If you cut the lawn too short you can expect:
- Reduced photosynthesis as there’s not enough blade to absorb sufficient light.
- Roots won’t penetrate deep in the soil leading to less nutrient uptake and horizontal spread.
- More sunlight reaches the soil, drying it out in the summer, this leads to a less healthy lawn.
- More space for weeds to germinate and thrive.
In addition, many gardeners who experience issues caused by cutting the grass too short will try to compensate by using more fertilisers. This can reduce the grass root depth as the grass has no need to spread deeper to search for nutrients. Excessive amounts of fertilisers can also scorch the grass.
The end result is a reduction in grass spread, density, root growth and an increase in the size of bare patches which in turn leads to more lawn moss.
Suggested Cutting Height
While many varieties of grass can be cut short, often down to 2.5cm, lawns grown in shade should be allowed to grow taller.
For shaded lawns, we suggest cutting the lawn regularly so it stays no lower than 7.5cm in the Spring and Autumn and up to 10cm in the summer.
If you’re struggling to grow grass in shade and lawn moss is taking hold, try letting your grass grow longer. Experiment with different cutting heights and find a grass length that looks great whilst also providing enough coverage to suppress moss and weed growth.
Don’t Forget The One-Third Rule
The “One Third” rule states that you should never cut more than one-third of the grass blade off in one go.
This is a general rule that applies to any type of grass in any lawn in any location.
For example, if your grass is 9cm long, the rules states you shouldn’t cut it below 6cm in one go.
Aggressive grass cutting removes the most important part of the grass blade. The tips of grass blades are the most active in photosynthesis and also give your lawn its green colour.
Break the one-third rule and you’ll cause excessive lawn stress, this leads to poor lawn top growth, reduced root development, loss of colour and less resistance to disease and moss.
Step 8) Minimise Foot Traffic
Compacted soil is a perfect breeding ground for moss and algae.
You’ve probably seen this yourself; areas where there’s heavy foot traffic often become sparse with little grass growth; moss and algae soon take over.
Common areas are:
- Near washing lines.
- Close to gates and doors.
- Along walking routes to garages, sheds and other buildings in the garden.
There are plenty of grasses that are designed for hard-wearing lawns. For shaded gardens that experience a lot of foot traffic, consider a redesign of the layout so high traffic lawn areas are replaced with stepping stones, paths, patios or other types of flooring that reduces the amount of foot traffic directly on the lawn.
Soil Home Testing
This home soil testing kit contains over 350 tests, so you can quickly get actionable results for Nitrogen, Potassium and Phosphorous as well as the soil’s PH level. No waiting for external sample analysis, get the results at home in a matter of minutes.
This type of testing is the key to growing the perfect lawn, plants and/or vegetables.
Shade Tolerant Seeds
Graminex shade-tolerant grass seeds contain a mixture of six different grass species. This pack is created specifically for shaded garden areas and the broad mix of grass seeds creates the perfect balance for optimal growth, colour and hardiness.
With Graminex, there is no need to buy different seed packs to guarantee germination.
Lawn Aeration Shoes
These spiked shoes are perfect for increasing soil aeration. This product will increase water and nutrient penetration into the soil which can help to stimulate root growth and depth. Better aeration can also reduce the chances of moss taking hold.
Made in the UK, these spikes are conical in shape, this creates a larger hole for better aeration.
Iron Lawn Sulphate
Iron Sulphate is the most popular lawn moss treatment product. Apply twice a year and you’ll be able to control lawn moss so your grass has a chance to grow and thrive. For long term success, make sure you follow the other steps we’ve suggested
Be careful to not to spill Iron Sulphate on patios, it leaves permanent stains.
Organic Lawn Fertiliser
MO Bacter is our favourite lawn fertiliser as it ticks so many boxes for us. It’s organic, pet safe, won’t stain patios, contains high levels of potassium and includes bacteria which breaks down moss and excess dead thatch in your lawn bed.
We think this is by far the best fertiliser available for grass lawns in shaded gardens.
General Lawn Fertiliser
Westland’s Growmore Garden Fertiliser is a general fertiliser comprising 7% Nitrogen, 7% Phosphorous and 7% Potassium. This fertiliser is perfect for preparing the soil near tree and shrub roots where there is competition for both water and nutrients.
Use slow-release granules like this when preparing the soil prior to laying seed or turf.
The lawn Guide Book
Our favourite book: The Lawn Guide by Sharples and Hayman is a great read, learn how to prepare a garden for laying turf or seed. Where this book truly excels is in its lawn maintenance advice and tips which are extremely detailed and second to none.
Want to know how to grown the perfect lawn in any condition? This is the the book for you.
Seaweed Lawn Tonic
Concentrated seaweed extract is an excellent natural and organic pet safe lawn feed. This product encourages root growth, strong plant stems and bright colourful flowering of plants, it can also be used on lawns throughout the growing season.
100% organic and pet safe, this is a realistic alternative to chemical-rich fertilisers.
Lawn Moss FAQs
What Causes Lawn Moss Growth?
Lawn moss is caused by a number of factors. The application of treatment chemicals is only a short term solution that gives you time to make long-term changes to your garden so future moss growth is limited.
Does Weedkiller Also Kill Lawn Moss?
Selective lawn weedkillers are targeted to specific weeds and are not suitable as a general lawn moss and weedkiller. Broad weed and moss treatment chemicals are available but they may also affect the grass and other plants in the garden.
How Often Should a Lawn be Raked or Scarified?
Raking and scarifying a lawn will remove dead moss and thatch, this creates space for the grass to grow and thrive. We recommend raking and scarifying thick, well-established lawns once a year. Lawns in shaded gardens often grow sparser and scarifying should be carried out less frequently.
What's The Best Chemical to Kill Lawn Moss?
Products containing a specific bacteria can be used on lawns with moss. The bacteria consumes the moss while allowing the grass to flourish, this approach is gentle, slow-acting and organic. Iron Sulphate can also be used, although this is a more aggressive approach and excessive use can burn the grass.
Discover More Of Our Lawncare Guides:
All LAWN GUIDES
See all of lawn guides published here at DIY gardening, from how to grow grass in shade to dealing with pet urine damage, wear and tear and moss control. Start Here
Grow Grass in Shade
It can be difficult to grow grass in a shaded garden but with our help and a little effort, you can achieve your goals and grow a healthy lush lawn. Start Here