how long does it take for moss killer to work

How Long does it take for Moss Killer to Work?

Some moss killers work very quickly but more important than how quickly is how well do they work and how easy to apply. Here is the low down.

Green-up Ferrous Sulphate – Easy to apply – Works Very Quickly

Ferrous or Iron Sulphate has to be the number one moss killer for price, ease of use, flexibility and effectiveness. Mixed with water and sprayed on the lawn on the same day it will kill moss on contact in hours. To get the most out of it, the moss should be damp to enable deeper penetration but don’t expect it to go more than a couple of centimetres into the moss. It is therefore, a fantastic product for moss suppression in late autumn, winter and early spring or after you’ve raked a lot of the moss out and want to kill what is left.

Lawn Sand – Quite Tricky to Apply – Works Very Quickly

Lawn sand is a mixture of sand and ferrous sulphate above. It generally won’t go through a spreader unless it is very dry so has to be spread manually. If the spreading isn’t even, and the grass isn’t dry the lawn sand will clump and quickly kill the grass. This is hard work and for experts only.

Winter Green High Iron Fertiliser – Easy and Quick to Apply – Works in a Couple of Days

Once again it is ferrous sulphate as above but with a balanced winter fertiliser. Goes through a spreader and applied during a mild spell in winter, it will green the grass beautifully as well. Burns into the moss deeper than sprayed ferrous sulphate so ideal for a mid-winter application. Use in conjunction with Green-up Ferrous Sulphate for complete moss control during the cooler months and when removing moss in spring.

Combined Moss Killer or 4in1 - Needs Watering in - Works in a Couple of Days

Be careful with these as they can be quite aggressive and always need watering in. If you’re going to use them, try and stick to those with just two ingredients such as the Evergreen Mosskill. They are easier to apply and less likely to damage the lawn. It works over a day or two but does need watering in. For use spring to autumn, not winter.

Moss-Off – Easy to Apply – Takes 7-10 days to Work

Comes as a liquid to mix with water and is easy to apply with a sprayer or watering can. This is an entirely different product to those above and is ideal for two reasons:

  • It has a residual effect so perfect for applying after removing moss and re-seeding to prevent further moss growth in spring
  • It is pet safe and won’t stain like ferrous sulphate products

Moss Eaters - Easy to Apply - Takes a Long Time to Work

These are DIY products that kill and decomposes the moss so should in theory not require moss to be raked out and sold as 'no rake' products. They are easy to apply but are not recommended for the winter months or used by Green Keepers so you have to question 'why not'?

These products have a very high potassium content which does the work however, we feel this is too much of an imbalance of nutrients for the lawn particularly if used regularly. Not too dissimilar from you or I taking high doses of a vitamin; there are potential negative side effects. 

Perhaps the biggest downside to these products is the time it takes them to work. This can easily be many weeks so if you have a fair bit of moss and you're waiting to over seed the lawn you may well miss the perfect opportunity and end up trying to seed in a dry period!