What is Ferrous Sulphate?

What is Ferrous Sulphate?

Ferrous or iron sulfate (also spelled sulphate) is a constituent of garden and lawn moss killers and some fertilisers. It is exactly the same chemical compound 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 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 and give directions for its use to achieve moss control. 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

This is either straight ferrous sulphate or perhaps with a little fertiliser added. Just basic ingredients and nothing unique or particularly scientific.

Lawn Sand

This is another method of applying ferrous sulphate to kill moss. This is just ferrous sulphate, with a dash of nitrogen fertiliser all mixed with sand to facilitate easy spreading.

If you have ever used Lawn Sand you may have experienced severe lawn damage as well. Unless kept dry, applied in the right conditions, evenly and at the correct dosage you can defoliate your lawn in days! I rarely use Lawn Sand because of this so unless you have the experience and confidence I suggest you give Lawn Sand a miss.

Ferrous or Iron Sulphate as Fertiliser

Ferrous sulphate as a fertiliser is 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 cheaper but the benefit of being able to sell or market it as a moss killer is lost.

Granular Fertiliser

There are excellent winter fertilisers available that have very high iron content which cause blackening such a Lawnsmith® WINTER GREEN. These pass nicely through any fertiliser spreader and therefore pose no spreading problems. This is a slightly more costly iron option but the time saved, together with the fertiliser content easily make up for it.

If you like things as ‘hassle free’ as possible then this is the method for you: just follow the application details on the product. Rates at the upper end of the application rate scale will cause blackening.

Soluble Iron

You can also buy soluble iron or ferrous sulphate ‘as is’ and apply through a watering can with a weed & feed sprinkle bar or by knapsack sprayer. It is easy to get concentrations right, simple to apply, value for money and beneficial for the grass. Low concentrations give the lawn a superb green-up whilst higher concentrations ‘harden’ the turf against disease. Rates at the upper end of the scale will cause blackening. This is how most sports and commercial users apply ferrous sulphate whether as a fertiliser or moss killer. See the next page for more detail.

Ferrous Sulphate is not Lawn Food

Though ferrous sulphate can be classed as a fertiliser it is not lawn food. It is purely iron and sulphate in chemical form and is perhaps the equivalent of a vitamin to you or me. There is no nitrogen in it so will not make your grass grow. This means you will still need to feed your lawn as normal which can be done without a gap between the two products if you wish.