How to use moss killer
Updated: October 2026
The patio still looks green the next morning, and it is tempting to spray again at twice the strength. How to use moss killer, once you have chosen the type, is three clocks: a lawn treatment you water in, a patio liquid you leave through a dry spell, and a brush you finish the same day. This page does not choose the type. That split is on [lawn moss killer or patio cleaner](/hub/weed-control/moss-remover/sub/moss-remover-lawn-or-patio). Prices sit on the [moss remover comparison](/hub/weed-control/moss-remover). The pack rate overrides every figure below. The Products Compared editorial team used HSE guidance, the Westland fact sheet and the amazon.co.uk notes on 19 October 2026, and did not treat a lawn. A qualifying purchase through our links can earn us a commission at no extra cost to you.
The patio still looks green the next morning, and it is tempting to spray again at twice the strength.
The patio still looks green the next morning, and it is tempting to spray again at twice the strength. How to use moss killer, once you have chosen the type, is three clocks: a lawn treatment you water in, a patio liquid you leave through a dry spell, and a brush you finish the same day. This page does not choose the type. That split is on lawn moss killer or patio cleaner. Prices sit on the moss remover comparison. The pack rate overrides every figure below. The Products Compared editorial team used HSE guidance, the Westland fact sheet and the amazon.co.uk notes on 19 October 2026, and did not treat a lawn. A qualifying purchase through our links can earn us a commission at no extra cost to you.
Our top picks
| Badge | Product | Surface | Sequence | Weather | Note | Price | Offer |
|---|---|---|---|---|---|---|---|
| Best overall |  Wet & Forget Wet & Forget 5 L | Hard surface | 1:5, spray, leave, no scrub | No rain for 4–5 hours | 8.8 | about £29.89 | View offer |
| Best value |  HG HG algae and mould remover 1 L | Hard surface | Dilute as the bottle says | About 36 hours claimed | 8.6 | about £8.35 | View offer |
| Alternative |  Westland Westland Moss Master | Lawn | Spread, then water in if dry | March to September, moist soil | 7.4 | about £11.10 | View offer |
On this page
Lawn treatments follow the growing season, not the patio
Use a lawn product only on grass that is growing, on moist soil, and not in drought or frost. That is the HSE pattern for ferrous-sulphate mosskillers in the G212 phrases. It is a pattern, not a dose you copy onto another bottle. In this set the lawn product is Westland Moss Master. The fact sheet says March to September, 100–150 g/m² where moss is the target, and water in within 48 hours if it stays dry. The 3.62 kg box is titled 80 m², which matches the area near a 45 g/m² feed rate, not at 100–150 g/m². Spread the moss rate on the square metres that rate actually covers.
Mow about three days before an iron treatment, and not again for about four days. That is the G212 line. It is not a Moss Master bullet, so the box wins if it disagrees. Keep off the lawn until the granules are watered in, unless your pack says otherwise. Pet wording is on moss killer, pets and runoff.
Iron products blacken moss. G212 treats that as expected, and the usual rake is about two weeks later. Moss Master's bullets claim no raking and no black moss. Some reviewers agree. Others report black spots, scorch, and a lawn that still needed raking. Do not copy Ferromex's millilitres onto this box. Ferromex is not in this set. Its useful lesson is to wash iron off paving, which is why granules stay on the grass.
If the grass scorches, or the moss is untouched at the rate you used, stop and read the pack before a second handful. Doubling the dose is what HSE tells gardeners not to do. A patio liquid will not repair a thin spread of granules.
Spray-and-leave patio cleaners are judged in days
A leave-on cleaner wants a dry surface and a dry spell afterwards, not a jet wash the same hour. Wet & Forget's instructions are 1 part to 5 parts water, then spray and leave. Do not apply if rain is due within 4 to 5 hours. The bullets say no scrubbing or rinsing, and they recommend gloves and eye protection. Reviewers describe rain and time lifting green growth. Heavy black growth takes longer than a light film. Judging the slabs the next morning is how a slow product gets called a failure.
HG is a concentrate. The listing claims a change in about 36 hours and up to 200 m² when diluted. The ratio is not in the scraped specification, so you use the bottle. A weak first mix is a reason to read the label, not to invent a stronger one. Patio Blast is spray-and-leave for paths, drives and decking. One reviewer used 3:1 from a watering can. That is their method, not a printed rate. Resolva's listing states no dilution and no method. If that is your bottle, the label is the only sequence. This page will not print a dose for Resolva or Patio Blast.
Do not rinse a leave-on product into a gully unless the pack says to rinse. That water is how a biocide reaches a pond. If the surface is still green after the label's window, a second application at the same rate is the step reviewers took. A brush is the same-day alternative, not a stronger chemical.
Brushes on block paving are a same-day job
A manual brush is scrape, then sweep, then stop before you empty the joint. On the Mitclear, reviewers use the triangular scraper for tough weeds and the brass wire for moss. On the Sbestily, pulling the head towards you shifts dead growth that has already been sprayed. Work along the joint rather than across the face of the slab, so you are not polishing the stone with wire. The Dustpan brush has a small head, which reviewers found tiring on a large path, so plan the area you can finish rather than attacking the whole drive in one go.
Keep pets away while wires are moving. A Mitclear review describes a bristle in a dog's paw and in a shoe. That is mechanical, and it applies while you brush. The cordless LIGO and the Ark Mat grind soft moss. They do not pull established grass, and they do not vacuum the sand. If the disc stalls, ease off. Pressure-washing the sand out is the mistake. Block paving relies on that sand, and a jet wash that leaves the blocks rocking has traded moss for a loose drive.
The 140 W LIGO weighs 1.5 kg. Reviewers who tried it on block paving called it slow. If the head is not shifting the moss, a manual wire brush in this set is the fallback. None of the mains listings states the plug type, and a UK socket wants a BS 1363 plug on 230 V.
When the result means you should stop
Stop if you are on a roof, even when a listing mentions roofs. Stop if the stone is etching or fizzing. Limestone and some sandstone are the usual victims, and the remedy is to stop, not to add a homemade mix. Stop if the product is for the other surface: Moss Master on slabs, or Wet & Forget and HG used as a lawn feed.
Stop if the patio is wet again because the fall is wrong or a downpipe discharges onto it. More product will not mend the drainage. The same stop applies to a suspected bat roost. If the type itself was the mistake, go back to the buying guide.
Common questions
When should I apply a lawn moss killer in the UK?
Apply while the grass is growing and the soil is moist, outside drought and frost. Westland's fact sheet says March to September for Moss Master. G212's ferrous-sulphate phrases match that season and add a watering-in step if it stays dry for 48 hours. Autumn scarifying, if you do it, is a separate RHS job, often October or early November, and it is not a reason to spread granules on frozen ground.
Why did the grass go black?
Iron mosskillers blacken moss. G212 treats that as expected, and you rake the dead material later. Moss Master's listing claims you will not see black moss. Reviewers are split: some saw no blackening, and one reported black spots and scorch. Blackening of the moss is the iron effect. Yellow, scorched grass is a sign you were heavy-handed or the lawn was already stressed, not a sign to add more.
How do I dilute Wet & Forget?
Mix 1 part Wet & Forget with 5 parts water, spray it on the hard surface, and leave it. Do not scrub it off and do not apply it if rain is forecast within 4 to 5 hours. Wear gloves and eye protection, as the bullets recommend. The 5 L bottle's coverage claim is 100–300 m² after dilution, which is a range, not a guarantee that your patio sits at the top of it.
What if it rains?
On a lawn treatment, rain within 48 hours can replace watering in. A downpour that washes granules onto the paving is the stain risk, so brush or wash iron off the slabs if that happens. On Wet & Forget, rain inside 4 to 5 hours breaks the instruction. Wait for a dry window and apply again at the same rate, not a stronger one. Patio Blast has no rain line in the scrape, so you use whatever the bottle prints.
How do I use a wire brush without emptying the joints?
Scrape and brush along the crack, hard enough to lift moss and soft weeds, and stop while the jointing sand is still there. Sweep the loose moss off the surface. Do not follow the brush with a pressure washer. Reviewers on the Sbestily also retighten sections as they go, because the screw joints loosen. Keep dogs inside until you have picked up loose wires.
Related pages
Sources
Public UK sources and the amazon.co.uk listings compared on this page. Updated October 2026.
- RHS: Moss in lawns (retrieved October 2026)
- RHS: Algae, lichens, liverworts and moss on hard surfaces (retrieved October 2026)
- HSE: Pesticides in the garden and home (retrieved October 2026)
- HSE: G212 ferrous sulphate label phrases (retrieved October 2026)
- HSE: Biocides overview (retrieved October 2026)
- Westland Moss Master fact sheet (retrieved October 2026)
- Wet & Forget UK: mould, lichen and algae remover (retrieved October 2026)
- amazon.co.uk listings, 19 October 2026, twelve ASINs in this set (retrieved October 2026)