Iron blackens moss in days; it does not fix why it was there

Lawn moss killers, compared

Moss in a lawn is a symptom: compaction, shade, poor drainage or grass too weak to compete. Every product on this shelf treats the symptom, and the honest ones say so on the pack. The active substance is almost always iron — iron(II) sulphate — which blackens moss within days and is also a nutrient, which is why half this corpus is sold as a combined fertiliser-and-moss product rather than a treatment alone. The form follows: granules spread dry, or a concentrate diluted and sprayed. The weight and coverage pair works exactly as it does on fertiliser, and the rate is on the pack. Two columns here exist for reasons that are legal rather than agronomic. The waiting time — how long before the lawn may be walked on, mown, or used by pets and children — is published because it is part of the authorised use, and it is the single most practical thing on the label. And the approval: products that make a pesticidal claim are authorised, carry a registration number and are sold under conditions that vary by country. A fertiliser with iron in it and an authorised moss herbicide are not the same category of product even when they look identical on the shelf, and this site reports what each label states without recommending either. The rest is what happens afterwards: dead moss is a black mat that has to be raked or scarified out, and the bare ground it leaves has to be seeded or the moss returns to the same place. We compare weight, coverage, active, form, waiting time and approval.

Every part here, laid out figure by figure

1. 

   LERAVA 2-5

   An iron fertiliser for grass — the only product here with no weight published, and the dearest square metre.

   Weight

   Not published

   Coverage

   20 m². No weight is published, so no application rate can be worked out.

   Active

   Iron sulphate, with potassium and magnesium; no percentages published

   Form

   Granular iron sulphate, evenly spreadable

   Waiting time

   Stated as usable all year round

   Approval

   On lawns, all lawn types

   Amazon reference

   B0D3QRCZ1Y (one reference across 5 Amazon marketplaces)

   EAN

   4260771321995

   • A plainly named active — iron sulphate — which two of the three lawn products here do not give
   • Names potassium and magnesium alongside the iron
   • No weight published, so the application rate cannot be established

   Best for: A small mossy patch, applied carefully and well away from paving

   Check price on Amazon
2. 

   Prinox MX067

   A hard-surface biocide concentrate at 1:20 — NOT for lawns — with a spray bottle and measure included.

   Weight

   1 L of concentrate

   Coverage

   1:20 for light growth, 1:10 for heavy; 1 bottle for up to 125 m²

   Active

   Not named; stated chlorine-free and acid-free

   Form

   Liquid concentrate; a 500 ml mixing bottle with a spray head and a measuring cup are supplied

   Waiting time

   Apply to dry surfaces; leave 3–4 days, then rinse off; long-term effect claimed up to 12 months

   Approval

   Facades, roofs, terraces, paving, wood, concrete, natural stone, plastic, awnings, gravestones, garden furniture — all water-tolerant surfaces. NOT lawns.

   Amazon reference

   B0DVXT698H (one reference across 1 Amazon marketplace)

   EAN

   4260760852240

   • The most dilute concentrate here — 1:20 at the light setting, and the lowest cost per square metre
   • A 500 ml mixing bottle with a spray head and a measuring cup are included
   • Not for lawns — on grass this kills grass

   Best for: A green patio, a north-facing wall or a shaded path — never a lawn

   Check price on Amazon
3. 

   VEXIL V10008

   A hard-surface biocide that publishes how long each organism takes — and its registration number.

   Weight

   1 L of concentrate

   Coverage

   1:10 light — 1 L for 100 m²; 1:5 heavy — 1 L for 50 m²

   Active

   Not named; stated free of acid and chlorine. Registration number BAuA N-114607 published.

   Form

   Liquid concentrate

   Waiting time

   Algae 2–3 days; moss 1–3 weeks; stubborn lichen 3–12 months

   Approval

   Facades, garden furniture, gravestones, ornamental stone, terraces, wood, plastic, concrete, natural stone, glass, ceramic, PVC. NOT lawns.

   Amazon reference

   B0F168P7DV (one reference across 1 Amazon marketplace)

   EAN

   4262440110466

   • Publishes a timescale for each organism separately, which is the honest way to sell this
   • Publishes a biocide registration number and the statutory use warning
   • Not for lawns — on grass this kills grass

   Best for: A green terrace or facade, treated once and left alone for a month

   Check price on Amazon
4. 

   WOLF Garten SW 100

   The only product here that publishes its iron content — 6 % — with 14 % nitrogen, for 100 m².

   Weight

   3.5 kg

   Coverage

   3.5 kg for 100 m² — 35 g/m²

   Active

   14 % nitrogen, 5 % potassium oxide, 6 % iron — the only iron figure on this shelf

   Form

   Granular: 14 % nitrogen, 5 % potassium oxide, 6 % iron

   Waiting time

   February to October; moss cleared in 2–3 weeks; deep green in 7 days

   Approval

   On lawns

   Amazon reference

   B01MYTIO5Q (one reference across 4 Amazon marketplaces)

   EAN

   4008423875560

   • The only published iron content on this shelf, at 6 %
   • A full declaration — nitrogen, potassium and iron, with a matching weight and coverage
   • 6 % iron will stain concrete, stone and paving permanently

   Best for: A mossy lawn in spring, treated well away from every hard surface

   Check price on Amazon
5. 

   Treufix 01

   Five litres of concentrate diluted 1:2 at its weakest and used undiluted at its strongest — for hard surfaces.

   Weight

   5 L of concentrate

   Coverage

   1:2 light, 1:1 medium, undiluted for heavy; 5 L supplied. No area published.

   Active

   Not named. Registration number BAuA N-116020 published, with the statutory use warning.

   Form

   Liquid concentrate

   Waiting time

   Algae 2–3 days; moss 3–6 weeks; lichen 3–12 months. Surface must be dry and stay rain-free 24 h.

   Approval

   Gravestones, roofs, wooden fences, terraces, roof tiles, facades, paving, driveways. NOT lawns.

   Amazon reference

   B0D8BPFTKP (one reference across 1 Amazon marketplace)

   EAN

   4262387270377

   • The only listing here that says to remove heavy moss mechanically first
   • Publishes its registration number, the statutory warning, and separate timings per organism
   • Not for lawns — on grass this kills grass

   Best for: A badly overgrown north-facing terrace or roof, scraped first and then treated

   Check price on Amazon
6. 

   Neudorff 01238

   An organic-mineral feed with extra iron, sold on the argument that a dense lawn needs no scarifying.

   Weight

   10 kg

   Coverage

   10 kg for 200 m²; stated rate 50 to 80 g/m²

   Active

   NPK 8-4.5-13 plus an extra portion of iron; no iron percentage published

   Form

   Organic-mineral granule, NPK 8-4.5-13 with added iron

   Waiting time

   Spring, summer and autumn; mow to 4–5 cm first and apply to a moist lawn

   Approval

   On lawns, including lawns maintained by a robot mower

   Amazon reference

   B01BPLG8YO (one reference across 5 Amazon marketplaces)

   EAN

   4005240012383

   • Publishes a full NPK, which only one other lawn product here does
   • Gives the preparation properly — mow to 4–5 cm, apply to moist grass
   • No iron percentage, and iron stains hard surfaces permanently

   Best for: A lawn being brought back over a season rather than treated once

   Check price on Amazon
7. 

   Compo 26173

   The only plant protection product here — once a year, May to August, above 10 °C, lawn unusable for days.

   Weight

   9 kg

   Coverage

   9 kg for 300 m² — 30 g/m²

   Active

   Not named; described as containing a weedkiller and a moss killer, with all main and trace nutrients

   Form

   Homogeneous fine granule, stated to dissolve quickly

   Waiting time

   At most once a year, May to August, above 10 °C; apply to dew-wet lawn 1–2 days after mowing; do not use the lawn for 2–3 days

   Approval

   On established lawns only — NOT in the year of sowing

   Amazon reference

   DE B00UT2LM2O · ES B00U65S5BU

   EAN

   4008398261733

   • The only product here that treats broadleaved weeds as well as moss
   • Publishes a complete application protocol — timing, temperature, sequence and re-entry
   • A plant protection product, with an annual limit and an exclusion period — unlike everything else here

   Best for: An established lawn with both moss and broadleaved weeds, treated once in summer

   Check price on Amazon