Key takeaways
- Lawn sand is iron sulphate (kills moss), sulphate of ammonia (greens grass) and sand (spreads it evenly)
- Moss turns black within a few days and is ready to rake out after about two weeks
- Use the rate on the pack and weigh it out; too much scorches the grass
- Apply in April to May or September, on a dry, mild day with moist soil underneath
- Water in after a couple of days if it hasn't rained
- Keep it off paving, pots and clothes, as it leaves rusty stains
Lawn sand is a dry lawn treatment that kills moss and feeds the grass in one go. Despite the name, the sand only carries the active ingredients. The real work is done by iron sulphate, which blackens moss, and sulphate of ammonia, which greens up the grass.
This guide explains what lawn sand is, when to use it and how to spread it without scorching your lawn. For the bigger picture on why moss keeps coming back, see our guide to getting rid of moss in your lawn.
What is lawn sand made of?
Lawn sand is three things mixed together:
Weigh out enough for one square metre first. It shows you how thin the layer should be.
- Iron sulphate (also called ferrous sulphate) kills moss and turns it black.
- Sulphate of ammonia is a quick nitrogen feed that greens the grass.
- Fine sand dilutes both, so they spread thinly and evenly.
Without the sand you’d drop concentrated chemical in clumps and burn the grass. Products vary in strength, so always read your own pack. Buy a product that’s sold and labelled as a lawn moss killer, rather than mixing your own.
How does lawn sand work?
Each ingredient tackles a different problem, which is why lawn sand is such a popular spring job.
The iron kills the moss. It dries and blackens the moss within a few days. Dead moss can then be raked out.
The nitrogen feeds the grass. It pushes fresh leaf growth and deepens the colour within a week or two. That matters, because dead moss leaves gaps. Well-fed grass spreads into them before weeds or more moss can.
The iron scorches soft weeds too. Weeds with soft leaves, such as daisies, clover, pearlwort and speedwell, brown off and shrink. Lawn sand rarely kills them at the root, so they can recover. For a proper clear-out, see our guide to common lawn weeds.
This is what you’re after. The moss has turned black within days while the grass around it stays green.
When should you apply lawn sand?
Apply lawn sand in April to May or in September, on a dry, settled day. In both windows the grass is growing well enough to fill the gaps the moss leaves.
A dry, mild April day with damp soil underneath is ideal. A spreader gives a far more even layer than scattering by hand.
The weather on the day matters as much as the month. Look for:
- A dry day, with no heavy rain forecast for a couple of days.
- Moist soil underneath, ideally a day or two after light rain, so the grass isn’t stressed.
- Mild weather. Hot, sunny spells raise the risk of scorching.
- No frost forecast.
Mow two or three days before, not on the day itself. Box off the clippings so the granules land on the moss, not on a layer of cut grass.
How to apply lawn sand step by step
Even spreading at the right rate is everything. Get it right and you get black moss and green grass. Get it wrong and you get a striped, scorched lawn.
- Weigh out the dose. Check the rate on the pack, usually given in grams per square metre. Weigh out enough for one square metre so you can see how it looks.
- Spread it evenly. Use a wheeled spreader on bigger lawns. On small lawns, split the dose in half. Walk one half up and down, then the other half across at right angles. Spread by gloved hand only on tiny patches.
- Leave it a couple of days. The iron needs time on the moss to work. Keep children and pets off the lawn.
- Water it in. If no rain has fallen after a couple of days, water the lawn well. This washes the product off the grass blades and helps stop scorching.
- Rake out the dead moss. After about two weeks, the moss is black and brittle. Rake it out with a spring-tine rake or a scarifier.
- Overseed bare patches. Fill any gaps with grass seed so moss and weeds don’t move back in.
This pairs well with a session to scarify and aerate your lawn, which also helps with the compaction that moss loves.
About two weeks on, the dead moss lifts out in dark clumps. It’s hard work, but it leaves room for the grass to fill in.
Lawn sand vs other moss killers
Lawn sand isn’t the only option. Here’s how it compares with what you’ll find at the garden centre.
| Product | Kills moss | Feeds grass | Kills weeds at the root | How it goes on |
|---|---|---|---|---|
| Lawn sand | Yes | Yes | No, scorches only | Dry, by spreader or hand |
| Liquid moss killer | Yes | Usually no | No | Diluted in a can or sprayer |
| Feed, weed and moss killer | Yes | Yes | Yes | Dry granules by spreader |
| Lawn feed alone | No | Yes | No | Dry granules or liquid |
Liquid moss killers are quicker to apply over big areas but don’t feed the grass. Combined feed, weed and moss killers add a selective weedkiller, so they’re handy if your lawn has weeds as well as moss.
If you’d rather go gently, you can feed your lawn well and rake moss out by hand. It’s more work on a very mossy lawn, but there’s no scorch risk. Whatever you choose, follow the label.
Is lawn sand safe for pets, children and paving?
Lawn sand is safe enough used as the label says, but it needs a little care.
Stray granules left on paving turn into rusty spots once they get wet. Sweep them off before it rains.
Keep pets and children off until it’s been watered in and the grass has dried. Store the bag sealed, dry and out of reach.
Watch your paving. Iron sulphate leaves rusty brown stains on patios, paths, pots and decking. These are hard to remove. Sweep stray granules off hard surfaces straight away, before they get wet. Wear old clothes and shoes, and rinse the spreader after use.
Don’t overdo it. Too much lawn sand burns the grass as well as the moss. If you’ve already overdone it, our guide on too much iron sulphate on a lawn explains how to help it recover.
Why does moss come back after lawn sand?
Because lawn sand kills the moss but doesn’t fix the reasons it grew. Moss thrives in shade, damp, compacted soil and thin grass.
Thick, well-fed grass with plenty of light leaves moss nowhere to settle. Keep pets off until any treatment has been watered in.
To stop it returning:
- Aerate compacted areas in autumn so water drains away.
- Top-dress the lawn with a sandy mix after scarifying, to improve the surface.
- Mow a little higher, especially in shade. Very short grass lets moss in.
- Cut back overhanging branches to let in more light.
- Feed in spring so the grass stays thick.
Common lawn sand mistakes
Guessing the dose. Scattering by eye leaves dark, scorched stripes. Weigh it out.
Applying before heavy rain. The rain washes the iron off before it works.
Spreading in a heatwave or drought. Stressed grass scorches easily. Wait for mild, moist weather.
Treating the wrong problem. Fungi and mushrooms in the lawn aren’t moss and won’t respond to lawn sand.
Expecting one go to fix moss forever. Lawn sand is a seasonal knock-back. Pair it with the aeration, feeding and light that keep moss away.
Frequently asked questions
What is lawn sand made of?
Iron sulphate, sulphate of ammonia and fine sand. The iron sulphate kills moss and turns it black. The sulphate of ammonia is a quick nitrogen feed that greens the grass. The sand spreads both thinly and evenly, so you don’t get scorched patches.
Does lawn sand kill moss?
Yes, it usually turns moss black within a few days. It doesn’t fix the reasons moss grew, though, so it often returns unless you deal with shade, compaction or poor drainage. Rake out the dead moss after about two weeks, then overseed any bare patches.
When should you apply lawn sand?
Apply it in April to May or in September, on a dry, settled day. The grass needs to be growing so it can fill the gaps. Avoid frost, drought and hot, sunny spells, which all raise the risk of scorching the grass.
How much lawn sand do I use per square metre?
Use the rate printed on the pack. Rates vary between products, so don’t assume one brand matches another. Too much scorches the grass as well as the moss. Weigh out the amount for one square metre and use a spreader for even coverage.
Will lawn sand kill weeds as well as moss?
It scorches some weeds but rarely kills them outright. Soft-leaved weeds such as daisies, clover and pearlwort are checked, which gives the grass a head start. Deep-rooted weeds like dandelions usually regrow. Dig those out, or use a selective lawn weedkiller as the label directs.
Do you need to water in lawn sand?
Yes, if it hasn’t rained within a couple of days. The wait gives the iron time to work on the moss. Watering then washes it off the grass blades and into the soil, which helps stop scorching. Always follow the timing on the pack.
Does lawn sand stain paving and clothing?
Yes, it can leave rusty brown stains that are hard to shift. Keep it off patios, paths, pots and decking. Sweep stray granules off hard surfaces before they get wet. Wear old clothes and shoes, and wash the spreader straight after use.
Once the moss is out, our lawn care calendar shows what to do next month by month, or browse more lawn care guides.
Our team produces practical UK gardening guidance from source research, contributor records and established horticultural practice. Editorial standards are overseen by Matt W.
