Lawn Care Experts

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Moss Killer & Ferrous Sulphate Buying Guide

Ferrous or iron sulphate is the moss killing component of garden and lawn moss killers and also a constituent of some fertilisers. It is exactly the same material regardless of how it is sold or used. They may vary slightly in concentration and be mixed with other compounds but apart from that they are the same.

Ferrous or Iron Sulphate Sold as Moss Killer

If ferrous sulphate is to be sold as a moss killer then the law requires that it is covered by pesticide legislation plus extra health and safety measures just as any pesticide should be. This adds to the cost!

This enables the manufacturer to advertise the product as a 'moss killer'. The concentrations are high enough to kill moss and low enough to cause the grass little or no damage. You will find these commonly sold as 'Moss Killer' or 'Lawn Sand'

Ferrous or Iron Sulphate Sold as Fertiliser

Ferrous sulphate sold as a fertiliser is exactly the same stuff but sold for different purposes - usually for greening grass and hardening against frost and disease. The concentration to achieve this is usually lower than if used as a moss killer but pretty much every knowledgeable gardener and green keeper knows that it will do the same job as a moss killer at its higher permitted application rates.

Because it is not sold as a moss killer it is not required to be certified as a pesticide. This means it is much much cheaper but the benefit of being able to sell or market it as a 'moss killer' is lost.

Buy Moss Killer & Ferrous Sulphate

When can I apply to moss in the lawn?

  • Anytime after mowing
  • At least 3 days but preferably 5-7 days before next cut
  • Avoid strong sun, frost and freezing
  • Give a 7 day gap if using weed killer (before or after)
  • If raking or scarifying you can use before and/or after - 4 weeks minimum between applications
  • If seeding apply one to two days before seed

DO NOT spray on grass less than 6 months old at full strength. A half rate or lower is safe.

Can I mix ferrous sulphate with other products?

Ferrous Sulphate can be mixed in the same container as our soluble fertiliser. You can also apply ferrous sulphate at the same time as applying granular fertiliser.

Do not mix weed killer with moss killer or ferrous sulphate. If you need to kill moss AND weeds do it about a week apart.

When seeding, you can spray ferrous sulphate on the lawn 1- 2 days before spreading grass seed.

Are these products safe for children, dogs and cats?

If you wish to feed and kill moss at the same time then Winter Green Fertiliser allows the lawn to be used after application though it can stain feet up to 72 hours after application.

If our Soluble Fertiliser or Green-up Ferrous Sulphate is used then the lawn is safe once dry. This would take just a few hours in the warmer months. Ferrous sulphate may stain feet within the first 24 hours of application.

Unlike grass ‘weed and feed’ products, Lawnsmith® Granular Fertilisers do not contain pesticides or weed killers. Though the bag of bulk material should be stored safely away from children and pets, the lawn is safe for use by children, wildlife, dogs and cats immediately after application.

For weed killer we suggest you use one of our liquid products as the manufacturer’s recommendations are that once dry they are safe.

Lawn products where pets graze or forage (rabbits, hens, ducks etc)

There is minimal risk if applying fertiliser in a mini granule form (all Lawnsmith® Granular Fertilisers) and therefore most pets can be allowed on the lawn immediately after application. However, those that forage down at soil level e.g. ducks and hens (and possibly rabbits and guinea pigs) are perhaps better kept off until the fertiliser has dissolved into the soil completely. This can be speeded by watering in.

If you wish to feed and kill moss at the same time then Winter Green Fertiliser is as above but can stain feet up to 72 hours after application.

With weed killer we refer you to the manufacturer’s recommendations, which may be similar to our recommendations for applying Soluble Fertiliser or Green-up Ferrous Sulphate. That is to allow 3 mowings before allowing grazing/foraging pets on the lawn. Ferrous sulphate may stain feet within the first 24 hours of application.

Finally, pets do have some peculiar idiosyncrasies so if you feel your pet is likely to consume or is sensitive to these products then keep pets off or don’t use the product.

How often can I use Ferrous Sulphate products

Green-up Ferrous Sulphate

This can be used as a greening agent throughout the year at a low rate of 0.5 to 1 gram per square metre. You can apply every 4 to 6 weeks as many times as you like.

If you are using it as a turf hardener to improve disease resistance at 2 grams per metre then you are only likely to do this once or twice a year in mid and late autumn

The main use is as a moss treatment at 4 to 5 grams per metre. This can be done every 4 to 6 weeks from late autumn to spring. We suggest no more than 3 applications at this rate in any one year.

Winter Green Fertiliser

This also contains ferrous sulphate and has the same blackening effect on moss. Because it also contains other nutrients we recommend no more than 2 applications in winter or early spring spaced 10 or more weeks apart.


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