Using iron sulphate to control moss

My neighbours and Brenda - especially Brenda - ridicule me when they see me ‘faffing about’ with the lawn. Some men are obsessive about their lawns and I am one of them! Not in the usual way, with ride-on-mowers and rye-grass stripes, my own ambition is to create a fine fescue-grass turf. Whatever kind of lawn you have, iron sulphate will both improve it and control moss.

Including generous donations to friends and family, 25kg lasts me nearly two years.

The curriculum-vitae of this fine, white, faintly green, powder is most impressive. Not only with regular use, will it ensure a moss-free sward, it’s adherents make the following claims.

• It’s a fertilizer that provides the essential trace element, iron. When I waxed lyrical about this, a clever student once remarked “but what about the sulphur?”. He had a good point, one of the effects of clean-air legislation has been that our soils no longer receive the essential nutrient sulphur from air pollution.
• It promotes a beautiful green grass - much more subtle than the dark green promoted by nitrogen fertilizer.
• Sulphate fertilizers acidify the soil and thereby encourage fine leaved grasses.
• It discourages turf disease and from my own experience, I think this may be true
• It is said to discourage worms but the evidence of my own pictures might cast doubt about this. I am happy to have some worms in my lawn for drainage and aeration and many species of worms only cast  below the surface. Any chemical that acidifies the soil will discourage worms.
• It might scorch broad-leaved turf weeds. I do not regard this as significant and indeed it is an effect I try to avoid when iron sulphate drifts onto my borders.
• It reduces frequency of mowing but not very much and it’s rather a frivolous claim. It does slightly check grass growth for a couple of weeks after application. I used to tell myself that the time I spent spreading iron sulphate was more than repaid by the time saved in mowing.

Peculiar legislation

A curious consequence  of our pesticide legislation is a result of the fact that pesticides need to be expensively registered. Iron sulphate as a moss-killer is classed as a pesticide. Iron sulphate as a fertilizer can be sold anywhere without restriction. You can use  iron sulphate on your lawn as a fertilizer, but not in theory as a moss-killer! Is that daft or is it daft?

This suits vendors absolutely fine. They can display their expensive registered moss killers (whose active ingredient is iron) and do not tell you that the cheap iron sulphate fertilizer on the next shelf is much cheaper and often superior.

Application 

For a small lawn it is convenient to dissolve it in water and apply with a watering can. In the past I would stir about a kilogram of iron sulphate in an old dustbin to make my own ‘witches brew’. 

An early lesson I learnt when I started to have my own clients was that it is not a good idea to use a knapsack sprayer. It very quickly ‘clogs its innards’.

Some gardeners spread iron sulphate in lawn sand. The purpose of the sand is to aid even spread. Some gardeners mistake the purpose of lawn sand. It is not to improve the physical condition of the soil. The quantity of sand applied when spreading moss-killer is far too small to have any appreciable effect on soil texture.

Poetry in motion

Now that I have 800 square meters of lawn all the above methods are far too slow. I now just fling it! In fact I love the way the fine powder just drifts across the lawn when on a still day I spread it. I have become quite skillful and as you will see from the pictures, I really enjoy myself! I use my lawn to integrate all my garden features and the lawn has a highly irregular shape. Despite this it takes only  half an hour to do the job. If you intend to use my drifting technique ensure that the iron sulphate you buy is powder-dry in a well sealed bag!

Accuracy and rate of application

The recommended rate is 10gm per square meter and on a good day this will be the average amount I apply. I deliberately fail to apply the iron sulphate evenly, I follow the moss! Parts of the lawn get less, some get more. When I repeat the job three months later, it all gets evened up!

When and how often

I fell in love with iron sulphate forty years ago when I read an article in a professional turf magazine written by an Irish green-keeper. He used it six times a year - but then it rains lot in Ireland and moss grows well! I apply it three or four times a year- when the whim takes me! It can be applied any time of year - but note the proviso below.

Worts and all, things that can go wrong

• It does what it says on the tin, it kills moss and the moss goes black. (Although as stated above, it actually says nothing on the tin). Brenda’s sister was delighted with this sudden effect. Elaine, my bridge partner almost refused to play with me again but we are still together after thirty years and she has a beautiful lawn now. If your lawn is really mossy, first apply it when the grass is growing vigorously so it will cover the dead moss. If you are energetic you can rake-out dead moss. I never do!
• If you apply it, mix it or spill it on stone surfaces it will give  a rusty stain.
• If you have delicate hands wear gloves, especially so, if there is moisture around.
• It has a faint seaweed smell which I rather like
• In theory if it drifts on wet leaves of plants it will scorch them. I never find this a problem in practice and indeed in winter deliberately drift it onto my borders. Many of the plants enjoy iron sulphate too!

Is it a grenade?