problems with moss killer on grass

Problems with Moss Killer on Grass

Common problems when putting moss killer on the lawn. Some moss killers can be very aggressive to the grass yet others like washing up liquid shouldn't be used.

I've Blackened the Grass with Moss Killer!

Ferrous or iron sulphate (or sulfate) 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 strong, therefore check your calculations and information
  • If applied by 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 in which case you could have applied evenly and correctly but still get blackened grass.

Good moisture levels or dampness are essential for grass safety and aids the moss killer to work.

How long does Moss Killer take to Work?

Dry moss killers containing iron such as Lawnsmiths Winter Green or Lawn Sand can take several days to work. Gentle moisture from dew or a light shower or just good soil moisture enable the moss killer to work very effectively.

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

Moss-Off is a none iron based treatment and takes 7-10 days to work but is one of the few moss killers to have a residual affect. 

Can I Use Moss Killer after Over Seeding?

Often after scarifying and over seeding in autumn the moss starts making a come back so may need some intervention. 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 quite aggressive.

If possible wait until the new grass is a couple of 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 a good dose of ferrous into the lawn and moss without damage to the grass. After the grass is 4 months old you can start using 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.

Lawn Sand Moss Treatment

Very common on golf courses and sports turf and in the hands of a skilled professional with the correct tools and equipment does a great job. We do not recommend this for the typical homeowner though. 

The Moss in my Lawn didn’t Die!

It sometimes happens so:

  • Check your concentrations and remeasure the area
  • Did it rain soon after 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!

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 best keep off the lawn for a day or two.

Will Rain Affect Moss Killer?

There is good rain and bad rain!

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

Does Washing up Liquid Kill Moss?

Simple answer is yes. However, modern anionic detergents will disrupt chemical activity in the soil, kill friendly bug life and worms and cause your grass some serious problems. 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