Ferrous Sulphate As Moss Killer for Lawns

To use Ferrous Sulphate as a moss killer, the chemical is usually mixed with water to form a solution.  To begin with use a ratio of  approximately 10 gms Ferrous Sulphate/1 litre water but if this does not produce the desired effect, a ratio of 50 gms Ferrous Sulphate/1 litre water can be used.  The solution can be sprayed or watered on the area of grass to be treated although it is advisable to test a small area first.

You can purchase Ferrous Sulphate as Moss Killer from a number of suppliers on Amazon.

An application rate guideline is approximately 5 square metres for every litre of chemical solution mixture.  Be careful to avoid spraying the solution onto other garden plants and paths.  After a couple of days the moss will start to turn black and this should be raked out.  DO NOT PUT TREATED DEAD MOSS RAKINGS IN THE COMPOST BIN.


Depending on the level of moss present, the solution can be used as an inhibitor by spraying during the period of growth from late Autumn to early Spring.  This will effectively kill the upper layer of moss but if the moss  is very deep, the spray will not penetrate the lower layer.  By treating the upper layer of lawn with Ferrous Sulphate moss killer every four to eight weeks during the Winter months, this will help to slow down the growth of lower level moss but may not completely get rid of it.

If moss remains in the lower level of lawn, it is best to rake out the moss in early Spring.  Although this can be a time consuming process, it is advisable where moss infestation is deep.  Once the lower level of moss is raked out, you can treat the lawn with a solution of Ferrous Sulphate which could achieve a 90% success rate in moss eradication.

Ferrous Sulphate has a chemical formula of FeSO4 and is sometimes known as Iron Sulphate, Iron Sulfate, Ferrous Sulfate, Green Vitriol or Copperas.

Always read the Material Safety Data Sheet (MSDS) provided by your Ferrous Sulphate supplier before commencing work.  Wear suitable Personal Protective Equipment (PPE) and keep out of reach of children and animals.

Purchase ferrous sulphate to kill your moss. There’s an extensive supply at Amazon.

Rich Hudson
I'm Managing Director of a leading UK chemical supplier. My company supplies most of the chemicals I blog about, you can buy them online at Chemicals.co.uk. I also keep a personal blog at RichHudson.co.uk.
Rich Hudson
Rich Hudson
Rich Hudson

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  1. V.Tunkel says:

    I want to use ferrous sulphate on small succulents (sempervivums, etc) growing in pots which over the winter have become smothered by moss growing between them. I intend to kill the moss growth first so that I can then remove it without uprooting the succulents.

    Is this a sensible suggestion? Will the succulents be harmed or retarded?

    • The Chemical Blog says:

      The impact of the iron salts contained in Ferrous Sulphate will vary depending how absorbent the roots and leaves of the succulent are. FeSO4 doesn’t kill grass but we would still recommend testing on a small area first – this also applies to succulents – our best advice would be to take a succulent that you wouldn’t be too upset about losing and use it as a test specimen.

      We hope this helps, thank you for your question.

  2. noelmc cormack says:

    what would be the best way to get rid of moss in a 3 acre paddock. Hope you can help thanks noel

    • Hi Noel,

      Thanks for your comment. For a 3 acre paddock, you will need about 2.4 litres of the solution. This will require 24 gms of Ferrous Sulphate.
      We advise that you test a small area first, and don’t let any animals graze on the treated area for 4 weeks.
      If the moss is thick, use the Ferrous Sulphate solution every 1-2 months during winter, and rake it out in early spring.

      Hope this helps. Get in touch if you have any questions.

  3. Andy Holmes says:

    Do you mean 24 g on a 3 acre paddock? In your helpful intro, you seem to be saying that application should be 2-10 g per square metre. Since there are about 4,000 sq m in an acre, I suspect you mean 2.4 kg, which will need 50-250 litres of water.

  4. Allan Spalding says:

    When using Ferrous Sulphate on the lawn to kill off moss, how do you keep cats and hedgehogs of your lawn for a week.

    • Hi Allan
      Thanks for your question
      I know this article states that you should keep pets away from the lawn for a week, but there have since been some conflicting opinions on this.
      Ferrous sulphate could be unlikely to harm cats. Quite often, cats use their sense of smell and don’t go near a treated lawn anyway. If they do, it’s unlikely that harm will come to the cat but it may decrease the effectiveness of the moss killer.
      Read the directions from your particular supplier, as each solution could have different precautions. If you still need to keep cats and hedgehogs away, you would have to purchase a product that does this.
      Hope this helps.

  5. Tony Palmer says:

    can you sulphate of iron on tarmacadam

    • Hi Tony,
      Thanks for your question.
      Yes, ferrous sulphate should sufficiently kill the moss growing through your tarmac. It will stiffen up, and you can then sweep it up. Begin with a small amount of iron sulphate and build it up slowly if it’s not doing the job.
      Hope this helps,
      The Chemical Blog

  6. DO NOT put sulphate of iron on tarmac. Unless you really really really want unsightly brown stains.

  7. Can you please tell me if this product is harmful to dogs and how long you must keep them of the lawn of treated areas?

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