Years ago, professional gardeners used lawn sand to control weed growth and kill moss as part of routine lawn care and maintenance.

These days, modern weed killers and moss killers designed specifically for use on lawns have become popular, resulting in traditional lawn sand being considered obsolete.  

Some people have never even heard of it.

In this guide, I’ll explain what lawn sand is as well as when and how to use it.

What is Lawn Sand?

You can still buy lawn sand at most garden centres.

It’s a gardening product commonly used to control moss growth in turf, although it can also kill broadleaf weeds and will give your lawn a boost of green colour. It can also change the pH level of your soil, making it more acidic which is perfect if you have ornamental or fine grasses in your lawn.

Lawn Sand’s 3 Main Ingredients

Lawn sand contains 3 ingredients:

  • Iron Sulphate
  • Ammonium Sulphate
  • Sand

Iron Sulphate

Also known as Ferrous Sulphate, this is the ingredient responsible for killing moss.

The most common way to use iron sulphate to kill moss is to dissolve it in water and spray it across your lawn.

Other iron sulphate benefits include:

  • It strengthens grass turf and makes it more resistant to lawn disease
  • Reduces earthworm activity and the formation of worm casts
  • Blackens and kills broadleaf weeds
  • It gives your lawn a deep green colour

Ammonium Sulphate

This ingredient contains nitrogen which promotes fast grass growth. This is the ideal lawn fertiliser to use in the spring when the soil is still cold. Other types of nitrogen fertiliser will not work until the soil has warmed up in the summer.

Sand

The sand content is used to distribute the product easily either by hand or machine spreader.

How Lawn Sand Works

Lawn sand is designed to be selective in which plants it kills.

The difference in shape between grass and weeds allow it to kill only broadleaf weeds and moss without affecting grass.

When applied to a lawn it settles on moss and broadleaf weeds, ‘burning’ them and turning them black.

Because blades of grass stand vertically, lawn sand can’t settle on them. It falls into the turf instead where it will fertilise the soil.

What’s the Difference Between Lawn Sand and Regular Liquid Moss Killer?

Lawn sand and regular liquid moss killer are the same product. They’re both made from iron sulphate.

The only differences are;

  1. The way they are mixed and applied. Lawn sand is iron sulphate mixed with sand for easy spreading. Liquid moss killer is iron sulphate mixed with water.
  2. The inclusion of a nitrogen based fertiliser. Lawn sand often contains ammonium sulphate that encourages grass growth. Liquid moss killer doesn’t.

Which Should You Use?

It depends on personal preference.

This is my approach;

If I’m repairing a lawn, I’ll use a liquid moss killer because the nitrogen fertiliser isn’t yet required.

If a lawn has come through winter with little moss, I’ll apply lawn sand instead of a liquid moss killer. This will kill the small amount of moss that’s present and also give the grass a shot of fertiliser as spring arrives.

Spring Lawn
Lawn sand is best applied in spring

When to Apply Lawn Sand

When considering applying lawn sand it’s important to also know when to apply it to achieve the best results.

The Best Time of Year

The best time of year to apply lawn sand is in the spring.

Somewhere between the end of March and the middle of April is best but this does depend on the weather. Early signs of grass growth as the weather starts to warm up is the best time to apply it.

If necessary, you can also apply it in the summer.

Avoid applying it too early. The ferrous sulphate will kill the upper layers of moss, but it’ll be too cold for the ammonium sulphate to work and fertilise the grass.

Also avoid applying it in drought conditions as the iron and nitrogen content can scorch and kill grass.

In Between Cuts

It’s also best to apply it in between cuts.

It is generally recommended you don’t apply lawn sand for 3 days after or before the next time you cut the grass.

Its best to cut the grass, wait for 3 days and apply it on the 4th day and then wait at least another 3 days before mowing the lawn again.

Cutting the grass before applying ensures that maximum contact is made between the moss and the moss killing ingredients.

When Weather Conditions Allow

Iron sulphate can stain pathways, drives and clothing; basically, most things it comes into contact with.

It’s very important that you apply lawn sand when conditions allow you to do it safely.

Wait for a dry, calm day with no wind to blow it into and over areas it can damage.

Feeding & Seeding
Lawn sand can be applied with a spreader

How to Apply Lawn Sand

There are two ways to do it;

  • By hand
  • With a spreader

Always make sure you follow the application rates suggested by the manufacturer. Make sure you spread it as evenly as you can without any overlap and without any missed areas.

Calculating How Much Lawn Sand You Need

Measure your lawn to get the total area in square metres.

For example, my front lawn is 5m x 5m.

5 × 5 = 25, or 25 meters squared.

Multiply that by the application rate set by the manufacturer.

I’ll use Westland’s Lawn Sand as an example.

They say you should apply their product at a rate of 80 grams per square meter.

80 grams x 25 meters = 2,000 grams.

That’s how much lawn sand you need to measure out for a single application.

Spreading by Hand

Split your lawn sand into two equal parts and work in different directions for each batch.

As an example, you might take the first batch and spread from north to south or from left to right.

You could then spread the second batch in the opposite direction, from south to north or from right to left.

This will ensure a more even distribution.

Using a Spreader

Split your lawn sand into two batches.

Add the first batch to the spreader and set it to medium (halfway open). Then push your spreader up and down the length of your lawn as if you’re mowing the grass.

Add the second batch to the spreader and then go across your lawn at a 90-degree angle to your first pass.

You will have to cover your lawn twice, but this method will prevent over-application and running out of lawn sand before you’ve finished.

What to Do After Applying Lawn Sand

Your lawn needs to be watered within 48 hours of applying lawn sand for it to work. If rain is due, wait until it rains as this will be sufficient.

If no rain is forecast, you’ll need to water your lawn yourself. Make sure to do so thoroughly.

Be sure to keep your children and pets off the grass until it’s been watered.

Final Verdict

Applying lawn sand is considered old practice in the UK.

It is now much more common to apply iron sulphate in liquid form than it is to apply a dry mix.

They’re essentially just two ways of doing the same job. Personal preference is the only difference.