Using Iron Sulphate on MOSS on Grass and Lawns

Using Iron Sulphate on MOSS on Grass and Lawns

Iron Sulphate for Lawns - How To Use Ferrous Sulphate on Grass

Using Iron Sulphate on MOSS on Grass and Lawns


Iron sulphate is an iron rich fertiliser or lawn tonic for grass.  It is used to give grass an iron tonic to encourage stronger and healthier growth and give grass a lush dark green colour. It is also used to control moss, harden turf, and discourage worm casts. We take a look below at all aspects of iron sulphate and how to use it to best effect, how to mix it correctly and how to avoid pitfalls and mistakes.  



What is Ferrous Sulphate?


Ferrous sulphate is a soluble iron fertiliser. It is known by a variety of names such as Iron sulphate, Ferrous Sulfate, Iron sulfate, Sulphate heptahydrate, Sulphate of iron, and in times long past, as Copperas and Green vitriol.  It is the main active ingredient in many recognised brand name fertilisers, typically 1Kg of these fertilisers will contain just 16% iron sulphate.

Ferrous sulphate soluble fertiliser has almost as many uses as it has names.  Iron is most often used as a green-up tonic for grass.  Lawns love iron and an application of ferrous sulphate has a superb green-up effect on grass, giving it a lovely, lush, dark green colour.  It also encourages strong and healthy growth in grass, helping to create beautiful and healthy lawns.


Iron sulphate is also used for turf hardening, this in turn helps to make the lawn more resistant to disease. The harder turf from using sulphate helps protect against fungal disease of the lawn.  It also makes your soil a much less attractive home for worms, in turn preventing worm casts.  With less worms and other soil-living pests who do not like the iron environment, your lawn is thereby less likely to have birds picking at the grass and digging holes in your lawn. 


Iron will also reduce the alkalinity of soil which is a boost for Ericaceous (lime hating) plants such as azaleas, camellias, magnolias, conifers, and blueberry.  Iron sulphate is often added as a feed to these lime hating plants to 


Whilst grass, and some plants, absolutely love iron, moss hates it. Moss just cannot survive in a soil environment applied with iron sulphate.  Moss will turn black within hours of an application of ferrous sulphate.  Ferrous sulphate is the best moss killer on the market.  In Ireland it has been used for decades by Green keepers on golf courses to kill and control moss.  It would be used several times a year to produce lush dark coloured grass on putting greens totally free from moss. The secret of iron sulphate for killing moss is now out and it is used widely by both professional and domestic users across the whole of the UK.

Ferrous sulphate is a chemical which is often known as Iron sulphate heptahydrate with an iron (Fe) content of 20%. It comes in two forms, a crystalline format and a fine powdered form.  Both forms are the same product though the crystal version contains an extra molecule of water whilst the fine powder has been dried and crushed from the crystal removing the excess water. In our opinion the damp crystal version loses power quicker. The efficacy of iron sulphate is reduced when it becomes damp. Of course when diluted the fine powdered form will go further per gram than the crystal form because a portion of the crystal is just excess water.  Therefore buying dry fine powdered iron sulphate in a re-sealable container will give better coverage and allow for safe storage in optimum conditions to make it last much longer.



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Using Iron Sulphate as a Lawn Tonic to Green Up Grass



If your grass lacks colour, is a pale green, or indeed is even turning brown or yellow, then using using iron sulphate as a fertiliser or tonic is just what you need to improve the colour and encourage strong healthy grass growth.  Using ferrous sulphate as a lawn tonic is a simple process.  What may be more complicated would be explaining to your jealous neighbours how you have such lovely, lush, thick and healthy growth of dark green grass.  

It should be noted that applying iron sulphate in hot and dry conditions is not recommended. If applied in these conditions the sulphate can scorch the grass.  If applying in these conditions then always water well right after the application of the sulphate mixture.  Applying at a rate of 3 or more grams per square metre will blacken and kill any moss in the lawn. This black, dead moss will obviously have an impact on the lush green colour you are trying to achieve. The dead moss will then need to be scarified to improve the appearance of the grass. Applying at a rate of more than 5 grams per square metre will very likely cause scorching of the grass.  While this is something to be avoided accidents do happen. Do not worry about this unduly. Scorched grass from sulphate application will often recover within 2-3 weeks with a regular watering, leaving you with the lovely green grass you envisaged.

1KG of iron sulphate will cover quite a lot of lawn area.  Often it only takes 1 or 2 grams per square metre to green up grass to give it a healthy dark green colour.  To cover an area of 50 square metres you would need to use 1 or 2 grams per square metre. It is often best to do a small test area first, perhaps a couple of metres at a rate of 1 gram per metre to see the results. If the results are suitable then you can proceed to cover the lawn at a rate of 1 gram per metre. If you don’t think it has produced the desired results then up the rate to 2 grams per square metre. So 100 grams would cover 50 square metres.  Mixing is easy, just dissolve sulphate in water, preferably lukewarm water to help it dissolve, and then spray onto the lawn using either a sprayer or a watering can.  You can also apply iron sulphate dry. Read on below for more detailed instructions on spreading dry and mixing for application by sprayer.





Iron Sulphate as a Turf Hardener to Improve Disease Resistance


Using iron sulphate on a lawn will not just improve the colour and the healthy growth of grass, it will also harden the turf and make the lawn more resistant to disease such as fungal attacks. For turf hardening with sulphate it is recommended to mix the sulphate in lukewarm water and apply at a rate of 3 grams per square metre. For a 50 square metre lawn you would simply need to mix 150 grams of the sulphate and spray evenly across the lawn area.  Again, you can apply sulphate with a watering can, a sprayer or apply dry by hand or with spreader.  Please read on below for mixing and application instructions for each method and warnings for drawbacks when applying.





Using Iron Sulphate as a Moss Killer

Iron sulphate is an excellent fertiliser or lawn tonic used for greening up grass though it is also a fact that using at a rate of between 3 grams and 5 grams per square metre will have an adverse effect on any moss in your lawn. Moss simply cannot survive with iron, the iron sulphate will dry up and burn the moss without having any negative effect on the grass, well, other than greening up the grass, which I suppose would be a negative if you prefer pale coloured grass. Iron Sulphate Is An Excellent Moss Killer. It should be mentioned that if you use at a rate of more than 5 grams per square metre then you are also at risk of scorching the grass. However if this occurs then the grass will usually recover with several good waterings

To use safely to kill or control moss in your lawn iron sulphate should be used at a rate of 4 or 5 grams per square metre. Simply dilute the sulphate powder down in lukewarm water which makes it easier to dissolve the powder.  Then spray over the area of your lawn using either a watering can or a sprayer at a rate of approximately 4 or 5 grams per square metre.  For the best and safest application it should be applied at this rate with one litre of water per square metre.  So if you wanted to cover a 20 metre square area of lawn you would need 80-100 grams of sulphate and 20 litres of water.  If you use a 10 litre watering can then you need 40-50 grams of iron sulphate powder with 10 litres of water and apply over 10 square metres. Then repeat and cover the next 10 square metres.  After this application moss should quickly turn black and die, usually within about 2 hours, though sometimes it may take several days. 
When applying with a sprayer you will get better coverage with, for example, a 5 litre tank than just covering 5 square metres so check below for more information on how to calculate the mix and apply best with a sprayer.

Iron sulphate has been used on golf courses for decades by green keepers to control moss.  It has been their secret weapon to produce moss free greens, with a lovely lush dark green coloured grass, which golfers will know is a perfect putting surface allowing the ball to roll smoothly.  All that remains really is the hours of practice to get the darn ball into the hole.




Iron Sulphate for Ericaceous Plants


Ericaceous plants are plants that don’t like growing in soils that contain lime. These plants include azaleas, rhododendrons, camellias, magnolias, conifers, and blueberry. They do not grow well in soils that have a high pH level, also known as an alkaline soil. If you grow these plants in an alkaline soil they may well develop yellow leaves, a condition often known as lime-induced chlorosis or iron chlorosis, and it is caused by a lack of chlorophyll. This in turn is due to several factors such as poor drainage, damaged roots and compacted roots, but more often due to high alkalinity of the soil and lack of nutrients in the soil.  Lack of iron is one of the most common defects of a soil that is high in alkalinity. The high alkaline soil prevents plants from absorbing nutrients which are essential and thus you end up with chlorosis.  

Iron sulphate can help plants that do not like high in lime or alkaline soil. It will help increase soil acidity levels and will enrich the soil and aid plants in the absorption of nutrients from the soil. To apply iron sulphate for ericaceous plants you should add the powder to the soil around the plants at a rate of between 15 grams and 30 grams per square metre, being careful not to allow the sulphate to touch the plant stems or leaves, and then fork the sulphate into the soil. You should apply this to the soil every 4-6 weeks to maintain the correct soil pH level for the plants.  Sulphate can be applied from March to September for ericaceous plants.  The soil should then be well watered after application.  In very dry or hot conditions it is best to water the soil before and after application of sulphate. You can also mix the sulphate in 1 or 2 litres of water and carefully apply to the soil around the plants, again being careful to avoid spraying onto stems or leaves directly. Water again after applying for best and safest results.





Iron Sulphate with Children and Pets

A very common question is about the use of iron sulphate with kids and pets on the grass. It is highly recommended that both children and pets are kept off treated areas for 3-4 days after application of iron sulphate.  Iron sulphate can be toxic if ingested in large amounts.  It therefore can be dangerous to pets who would eat grass. Not so dangerous to children then unless they also eat the grass. Iron sulphate is also classed as an irritant so there is a small chance it might irritate pet paws or kids if they are on the grass.  In our opinion both of these warnings are just a little bit on the safe side. There is more likely to be a greater risk of kids and pets getting onto the treated areas and then carrying sulphate onto paving or other hard surfaces where the sulphate will cause a rust coloured stain that is difficult to remove.

For children there is a small risk of irritation and an even smaller risk of ingesting sulphate. This should definitely be guarded against as a precaution and if possible do keep kids off treated areas for 4 days. Having said that, if the sulphate is applied and well watered into the ground after application the risks are greatly reduced.  There is no reason to panic or regard sulphate as a very dangerous substance. It is just advised to be careful about letting kids onto the grass, if you can prevent them doing so after applying sulphate then this is the safest approach. Even while sulphate is regarded as an irritant, I personally often apply it by hand and it does not cause me the slightest problem. This might not be the case for everyone however.

For pets there is a danger that it can irritate their paws. And for pets that eat at the grass it can be dangerous with a risk of ingesting a toxic amount of sulphate.  This is the same product which goes in iron sulphate tablets for low iron, but too much of it is toxic to both humans and animals. It is recommended to keep pets off treated areas for 4 days and ensure the treated area is well watered.



Iron Sulphate Warnings


Using iron sulphate at a rate of more than 2 grams per square metre can cause moss to turn an unsightly black colour. If you have moss in your lawn and are applying sulphate to give the grass a green up tonic then the black moss will have a detrimental effect on the colour you are trying to achieve. For a good lawn green up use iron sulphate at a maximum rate of 2 grams per square metre.

Using sulphate at a rate of more than 5 grams per square metre can scorch the grass.  If this occurs then the grass will usually recover if the lawn is watered well for the next 1-2 weeks. 

If you use sulphate to kill moss then this will leave patches in your lawn if the moss is widespread. You will have to reseed the lawn to fix the patches.

Iron sulphate should not be applied in hot, dry conditions. Lower doses applied in these conditions can scorch or burn the grass.  If applying in these conditions then always water the treated area with plenty of water. Iron sulphate is best applied in wet conditions which helps to water it into the soil.

Iron is an irritant and it can cause irritation through contact with both humans and pets. We have used it many times ourselves by handling it and never been irritated, though it can cause black stains under the fingernails.  Just because we have never suffered irritation does not mean this is the case for everyone.  It is recommended to wear latex, rubber, or nitrile gloves when using sulphate. If sulphate gets into your eyes then you should wash them out well with water.

Iron sulphate should not be swallowed as too much of it is toxic to both humans and animals. Do not eat sulphate and be careful when spreading that it does not blow back on you.  If concerned you should wear a mask. Do not allow kids or pets onto treated areas if they are likely to swallow sulphate.

Iron can stain hard surfaces.  Always be very careful about your patio areas, paving, fencing, stonework, etc. Iron sulphate will cause rust coloured stains on hard surfaces.  Do not let children or pets onto treated areas as they can carry sulphate onto hard surfaces and cause stains.

When using a watering can or sprayer it is possible that you will have drips after applying sulphate. These drips can drop onto your paving or patios as you carry the can or sprayer back to your shed or garage. If these drips fall on hard surfaces they will cause stains.  It is best practice to have a bin liner or something handy to put the watering can or sprayer inside to take it back to your house or garage etc. to prevent drips falling on surfaces you do not want stained.

In short, when using iron sulphate, we recommend that you wear gloves when mixing and applying, keep children and pets off treated areas for at least 4 days, use care to ensure only grass and lawn areas are sprayed, and always water treated areas well to ensure sulphate does not damage grass.




Iron Sulphate Mixing Instructions for Using Watering Can, Sprayer and Applying Dry


When mixing iron sulphate for use it is always best to dissolve in lukewarm water to aid mixing and avoid clumps forming. You can apply sulphate dry as a powder by hand. Obviously this makes it very difficult to calculate the exact mix you are applying. You do not want to apply more than 2 grams per square metre for lawn green up and no more than 5 grams per square metre for moss control. A slightly heaped teaspoon is approximately 5 grams, just like a spoonful of sugar. So you really want to be applying a half teaspoon for greening and full teaspoon for moss over one square metre. As you can see this is not an easy method for applying sulphate.  Quite often people will use this method when there is thick moss and little grass and spread sulphate on patches of heavy moss for simplicity.

For using iron sulphate with a watering can it is simple mathematics and easy to mix. Use 2 grams per square metre for grass greening applied with one litre of water.  So for 20 square metres you will need 40 grams of sulphate in 20 litres of water.  Usually this will be a standard 9 litre watering can, so you will need 9 litres of lukewarm water and 18 grams of sulphate for greening grass. Then apply this over 9 square metres, then repeat over the next 9 square metres with identical mix of 9 litres water and 18 grams of sulphate. Then mix another 4 grams sulphate in 2 litres of water to finish off the last 2 metre area.

For moss control you can simply double the sulphate in the previous mix. Use 36 grams of sulphate in 9 litres of water and apply over 9 square metres, and repeat this until you have covered the entire area of the lawn.

Once you have covered the entire area with your mix in the watering can it does no harm at all to apply another covering of just water to help wash the sulphate into the soil.  

If you want to apply iron sulphate dry using a spreader this again is difficult to calculate as spreaders can all operate at different rates. Trial areas may be the best way to calculate the amount of sulphate that is spread over an area by weighing the amount put into the spreader and then weighing what remains in the spreader after covering a couple of metres. You still do not want to apply more than 5 grams per square metre as this may scorch the grass.  If this does happen watering the grass well for next week or so will enable it to recover completely, indeed, it will turn a lovely dark green colour once recovered.

 Applying iron sulphate with a sprayer is a different proposition. You will need to use a little bit of maths to calculate using with this method. First of all you will need to know whether you want to use for green up of the grass or for moss control. This will mean 2 grams per metre for greening and 4 grams per metre for moss control.

Secondly, you will then have to calculate the area you want to treat. Because you get a better coverage using a sprayer than you do with a watering can you will want to calculate the area to be treated. Then you should calculate how much area you cover with your sprayer.

If you use a 5 litre sprayer, for example, and spray just water onto your lawn, how far does it cover?  Supposing you do this with just water and it covers 60 square metres, then you want to apply this with 2 grams or 4 grams per metre according to your purpose of greening grass or killing moss. So you will have 60 x 2 grams for grass greening in 5 litres of water in the sprayer. Yes, simple as that. 120 grams of sulphate in the 5 litre sprayer and apply over 60 square metres. If it is for killing moss then obviously you want 60 x 4 grams in the 5 litres of water.  It is important that you spray with water first to see how far you cover if you do not already know this information.  Perhaps your sprayer of 5 litres covers 100 square metres, then you want 100 x 2 grams or 100 x 4 grams according to purpose. 

After you have applied by this sprayer method it is advised that you apply a final covering of just water to ensure that it is well watered into the soil.  You can also apply a covering of water before and after to make it a safer and more efficient application.




Cleaning Iron Sulphate Stains From Hard Surfaces


What do you do if you have had an accident and ended up with iron sulphate stains on your patio, paving, fences, etc?  Iron sulphate will stain hard surfaces and the rust coloured stains can be very difficult to remove so you should always apply carefully and prevent kids and animals from walking on the treated areas as they can carry the sulphate onto other surfaces.

If you have got sulphate stains then the first option to try is lemon juice or white vinegar. Before you start you should be aware that if these methods work you may end up with part of your surface then showing up as cleaner than the rest.

To try to remove sulphate stains cover the stained area with lemon juice or white vinegar and leave for a while. Normally 15 minutes should be enough. I have left it on overnight, then covered with another dose of juice the next and then got to work on it.

So cover with lemon juice or vinegar and leave for at least 15 minutes and then scrub with a hard or metal scrubbing brush in circular motions.  Then wash off with water. Usually this should remove the stains. As I mentioned, the drawback is you might have very clean patches to the rest of the surface.  So perhaps you will have to clean the whole area using the same method. You should be careful when applying lemon or vinegar to the area as it can damage nearby grass and plants if it gets on to them.

If this method does not succeed then you can try other chemical methods. You can use Trisodium Phosphate available from variety of places including  To use this chemical to clean iron stains wear gloves before mixing and applying as it can cause irritation to skin and eyes and can be toxic if inhaled or swallowed. Please always handle trisodium with care.  Mix 2 litres of hot water with 100ML of trisodium phosphate and dissolve completely.  Pour the solution onto the stains and leave for 30 minutes to allow the mix to penetrate the stains.  Then scrub in circular motions with a wire brush to remove the rust stains. Use a firm pressure to get at the stains. Then rinse the area with clean water and check the stains, if they have not been removed repeat the process. 



If iron sulphate is what you need for your lawn, for greening grass, or for killing moss, then you can order ferrous sulfate online now for quick and free delivery within the UK.




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Great article on lawn care. Thankyou. I have a knapsack sprayer (Berthoud Vermorel 1800).

Would you be able to advise on what would be the best spray nozzle pattern to use for moss killing. Also some lawncare advisors say to scarifying pre and post application of iron sulphate abd others say only post application. What would you advise?

Many thanks.

For effectively killing moss with a knapsack sprayer like the Berthoud Vermorel 1800, you should use a flat fan nozzle. This type of nozzle pattern is best suited for uniform coverage on flat areas and helps to ensure that the product is evenly distributed across the area. Flat fan nozzles are excellent for achieving thorough coverage, which is crucial for the effective treatment of moss.

Hi, I have been reading your info on treating moss in lawns with iron sulphate. I think it is confusing to those of us who want to water it on with a watering can as it is much better to state the dilution rate at the beginning . I think I have worked out that the dilution rate is 2g or 5g per litre, I don't think it is helpful to mix that up with 2 or 5g per sq metre as you don't then know in what volume of water. The dilution rate gives you more latitude as to how far you spread it even if 5g per sq metre is the ideal rate for moss killing.

Personally I have found that watering it on is by far the best method as it is then spread the most evenly and being in water the effect on the moss is instantaneous so you can easily see what has been treated. The only drawback is that it is a bit laborious if you have a large area of grass.

We have a scarifyer and I would normally use it when the moss looks dead but because the grass has been growing so fast this year with all the rain there hasn't been a suitable time to do it, however the grass has grown over the blackened moss and looks healthy so I am hoping I can get away with not scarifying that area. I still have a large and much mossier area to treat and hopefully will get to scarify that to improve the grass.

Hopefully my experience this year will be helpful feedback for you? Iron sulphate is a miracle (in moderation perhaps) and not a nasty modern chemical that has unknown bad effects.