How to use moss killer
Updated: October 2026
You have a pack in the shed and a mossy patch you want gone this weekend. How to use moss killer starts with the label on that pack, not with another brand's calendar. Season, dose, pets and stains differ inside this set, and mixing them puts iron on the patio or a spray down in January. The [Moss killer comparison](/hub/weed-control/moss-killer) is where the twelve listings sit. If you have not decided lawn or paving, use the [lawn or patio](/hub/weed-control/moss-killer/sub/moss-killer-lawn-or-patio) page first. The wrong chemistry does not become safe because you applied it neatly. We did not treat a lawn for this guide. Products Compared editorial team, 16 October 2026. A qualifying purchase can earn a commission at no extra cost to you.
You have a pack in the shed and a mossy patch you want gone this weekend. How to use moss killer starts with the label on that pack, not with another brand's calendar.
You have a pack in the shed and a mossy patch you want gone this weekend. How to use moss killer starts with the label on that pack, not with another brand's calendar. Season, dose, pets and stains differ inside this set, and mixing them puts iron on the patio or a spray down in January. The Moss killer comparison is where the twelve listings sit. If you have not decided lawn or paving, use the lawn or patio page first. The wrong chemistry does not become safe because you applied it neatly. We did not treat a lawn for this guide. Products Compared editorial team, 16 October 2026. A qualifying purchase can earn a commission at no extra cost to you.
Our top picks
| Badge | Product | Season | How to apply | Pets | Note | Price | Offer |
|---|---|---|---|---|---|---|---|
| Best overall |  Miracle-Gro Miracle-Gro Autumn 80 m² | September to November | Spread, then water in | After watering in and dry | 8.8 | about £12.48 | View offer |
| Best value |  GREENFORCE Greenforce 4-in-1 15 kg | Every 4 to 6 weeks | Spread, keep moving | Not stated | 7.8 | about £30.50 | View offer |
| Alternative |  Resolva Resolva Moss Killer RTU 1 L | Not 18 Sep to 1 Apr | Trigger, 10 m² a litre | Not stated | 6.8 | about £4.49 | View offer |
On this page
Read the label before you open it
The Health and Safety Executive expects you to read a garden pesticide label before you buy and again before you use it. Amateur products are for people without training. A professional label is not a stronger weekend version. If all you have is an Amazon bullet, you do not yet have the dose or the surfaces to avoid.
That gap is real on Resolva. The maker says not for lawns, not for concrete or tarmac, and not from 18 September to 1 April. The bullets on the £4.49 litre do not print that closed season. Reviewers cite the winter ban. Rain-fast in one hour is an Amazon bullet. The maker says rain within 12 hours may weaken the result. The label on the bottle wins. The generic 5 litre of 20% ferrous sulphate has no MAPP and no rate in the raw file. Do not invent a home dose. RHS says fertiliser-grade iron should not kill lawn moss unless it is inside an approved proprietary mosskiller.
Season in this set
These windows do not swap. Miracle-Gro Complete 4-in-1 is for established lawns from April to September, once frosts have gone, and it names dandelion, white clover and plantain. Miracle-Gro Autumn is September to November, with iron sulphate named, blackening in seven days and a rake after two weeks. Resolva's maker closes 18 September to 1 April. The 3 litre Resolva that does print a season says late spring to early summer, or late summer to early autumn, when moss is growing. Path and Drive says all year. Green Gone's bullets do not give a month.
BBC Gardeners' World puts chemical moss killers in spring or autumn, bacteria-style products in warmer months, and tells you not to exceed the dose. Moss Master is the bacteria-style claim here, and its bullets do not give a month, so the bottle decides the week. A January spray of Resolva is the mistake reviewers already describe. It is not a loophole because the path looks green.
Spread or dilute, then stop
Granules scorch where a spreader pauses and dumps. Greenforce reviewers say that about the 15 kg bag, and they say the 3 kg powder arrives in chunks that block the spreader. Walk steadily, close the hopper when you stop, and do not go back over a stripe in the same pass. Two half-rates on top of each other are an overdose. The lawn shows pale or black bands a fortnight later.
The Mosskill maker label states 150 ml in 9 litres of water for 10 square metres, up to three applications, and says you do not water that spray in. The Amazon model is 121280 and the label file carries another code, so you measure from the bottle in your hand. Do not copy the liquid rule onto the granule boxes. Those you water in if rain does not. Resolva ready-to-use is 10 square metres a litre. Coat the moss you can see. Do not empty the last of the bottle on the nearest slab, and do not point it at a lawn or at tarmac.
The rake, if your pack blackens moss, comes later. Timing is on the raking page. Do not scarify the same afternoon you spread, and do not copy an eight-week reseeding gap from a different Miracle-Gro code onto your tub.
Pets, children and stains
There is no single pet-safe line. On Miracle-Gro Complete and Autumn, children and pets stay off until the granules are watered in and the area has dried. On Green Gone, they need not be excluded once the hard surface is dry. On the 3 litre Resolva, they return after drying. The £4.49 Resolva, the Greenforce bags and Moss Master do not print a pet line in the spec block. A blank is not permission. The Health and Safety Executive expects an instruction, not a friendly adjective.
Iron stains paving, decking and floors. Brush lawn granules off the patio. Do not hose them into the joint. Marshalls says keep ferrous sulphate off paving. The Mosskill label says wash liquid spills off paving immediately. That is a liquid spill, not a licence to hose granules. Water on granules drives the stain into the stone. The buying guide is where you check you bought the lawn pack for the lawn. A rusty arc on the patio edge is usually the spreader's last half-metre.
When to stop
Stop if the pack is labelled professional and you are not that user. Stop if you cannot keep spray out of a drain or a pond. Stop if the lawn is waterlogged, or you have already treated the same shaded moss twice. Another bag blackens the same moss and leaves the same wet soil. Stop if the trigger has failed or the bottle arrived leaking. Resolva reviews include both, and a dribble is not a measured 10 square metres.
Call someone when the stone could be etched by acid or a pressure washer, when runoff cannot be kept out of water, or when the lawn needs drainage rather than feed. If the grass has gone black in stripes, you have likely overlapped the rate. More iron this week will not green it. Follow the recovery line on your label, not a gap copied from another box.
Common questions
When can I apply moss killer?
Use the window on your listing. Complete 4-in-1 says April to September after frosts. Autumn says September to November. Resolva's maker says not from 18 September to 1 April, which the £4.49 bullets omit and reviewers mention. Path and Drive says all year. If your month is outside the pack you are holding, wait.
Do I water granules in?
Where the granule label says so, yes. Complete and Autumn keep children and pets off until the granules are watered in and dry. Brush granules off paving first. Do not hose them off the stone, because that washes iron into the joint.
Do I water liquid moss killer in?
Not the Mosskill concentrate, if you follow that maker label: no need to water in, and you stay off until dry. The stated mix is 150 ml in 9 litres per 10 square metres. Check the bottle, because the Amazon model and the label file code differ. Do not use that rule on the granule boxes.
When can the dog go back on the grass?
When your label's line is met. On the Miracle-Gro granule boxes here, that is after watering in and drying. On Green Gone, it is once the treated hard surface is dry. Listings with no pet sentence have not given you a time. Keep the dog off until you can point at a line.
What if I spill iron on the patio?
Brush it up. Do not wash lawn granules into the joint. Marshalls says keep ferrous sulphate off paving. A liquid Mosskill spill is what the maker says to wash off immediately. Granules and liquid are not the same spill, and the mark is easier to avoid than to lift.
Can I use Resolva in January?
The maker says no. Resolva moss killer is closed from 18 September to 1 April. The ready-to-use bullets omit that sentence. January is inside the closed period. Path and Drive says all year, but it is a weedkiller for paths, drives, patios and gravel, not a winter licence for the moss killer on a lawn.
How do I avoid stripes?
Keep the spreader moving, and do not open a second pass over a pale strip the same afternoon. Greenforce reviews tie scorch to a dump, and chunks in the 3 kg powder block the mechanism. For a watering can, mark 10 square metre sections before you pour, using the rate on your bottle.
Related pages
Sources
Public UK sources from the research digest. Shelf prices and star lines are the amazon.co.uk figures in the display file. Coverage rates are manufacturer claims, not a trial run for this page.
- RHS: moss in lawns (retrieved 16 October 2026)
- RHS: moss on hard surfaces (retrieved 16 October 2026)
- HSE: garden and home pesticides (retrieved 16 October 2026)
- HSE: COPR and moss claims (retrieved 16 October 2026)
- Westland: Resolva moss killer (retrieved 16 October 2026)
- Westland: Moss Master (retrieved 16 October 2026)
- Miracle-Gro Mosskill label (retrieved 16 October 2026)
- Marshalls: paving aftercare (retrieved 16 October 2026)