Problems with Moss Killer on Grass

I've Blackened the Grass with Moss Killer!

Ferrous or iron sulphate (or sulphate) will blacken and kill moss. It will also blacken the grass for the following reasons:

• Lawn sand is the easiest way to blacken the grass if not distributed evenly.
• If applied as a liquid, the concentration you made up is too intense; therefore, check your calculations and information.
• If applied by a spreader as a combined moss killer and fertiliser, you either applied too much by miscalculating the amount required or by uneven spreading.
• The weather is too dry for the treatment, so you could have applied it evenly and correctly but still get blackened grass.

Good moisture levels or dampness are essential for grass safety and aid the moss killer in working.

How long does Moss Killer take to Work?

Dry moss killers containing iron, such as Lawnsmith Winter Green High Iron Lawn Fertiliser or Lawn Sand, can take several days to work. Gentle moisture from dew, a light shower, or good soil moisture enables the moss killer to work effectively.

Iron sulphate, typically applied as a spray, works within hours and is the cheapest method of moss control in grass.

Moss-Off is a non-iron-based treatment that works in 7-10 days. However, it is one of the few moss killers with a residual effect. 

Can I Use Moss Killer after Over Seeding?

The moss often returns after scarifying and overseeding in autumn, so some intervention may be needed. You can use Moss-Off, though the best time is straight after scarifying and before the seed goes down. The situation is a little more complicated with ferrous sulphate, as it can be pretty aggressive.

If possible, wait until the new grass is a few months old. Then spray with Green-up Ferrous Sulphate at half rate, leave it a couple of days, and if the young grass looks fine, go and re-apply. This way, you get ferrous matter into the lawn and moss without damaging the grass. After the grass is 4 months old, you can use your ferrous sulphate at 4g/m2 in cool, damp conditions. After 6 months, the grass is hardened off and safe for full-rate moss killing; for more information on which lawn moss killer to use and when read our lawn advice.

Lawn Sand Moss Treatment

It is very common on golf courses and sports turf, and it does a great job in the hands of a skilled professional with the correct tools and equipment. However, we do not recommend this for the typical homeowner. 

The Moss in my Lawn Didn’t Die!

It sometimes happens so:

• Check your concentrations and remeasure the area
• Did it rain soon after the application?
• Did you make up a mixture and leave it a day or so before application? Always mix and apply on the same day.

I’ve stained my patio with moss killer!

It's a very common problem, so always read the product label! Once stained, it will not wash off!

Any iron-based moss killer will stain hands, equipment, and hard surfaces, so wash or brush off immediately after application. It will also stain feet and paws if still active, so keeping it off the lawn for a day or two is best.

Will Rain Affect Moss Killer?

There is good rain and bad rain!

• Good rain occurs before the moss killer is applied to the lawn or is a drizzle within 24-48 hours of application.
• Bad rain is too much rain within 24-48 hours of applying moss killer to the grass, which dilutes your work. Do not reapply until you assess the situation several days later. 

Does Washing up Liquid Kill Moss?

The simple answer is yes. However, modern anionic detergents disrupt chemical activity in the soil, kill friendly bug life and worms, and cause serious problems for your grass. So, do not use household detergents on soil or plants, and do not use moss killer to clean your dishes! 

Is there a completely safe Moss Killer?

Yes, Moss-Off.

What is the Best Way to Treat Moss in my Lawn?

Start with our Moss Advice pages.