How to apply a lawn wetting agent

Some lawns stay brown in patches however much you water them. Water beads on the surface, runs off into the gutter, or wets the top few millimetres and stops. The soil underneath stays dry, and the grass above it suffers.

Often the cause is water-repellent soil, also called hydrophobic or non-wetting soil. A wetting agent helps water soak in again. This guide covers how to tell whether you need one, how to choose between liquid and granular products, how to apply them evenly, and how to check they’ve worked.

Why soil repels water

Water-repellent soils result from waxy organic compounds coating soil particles. The coating comes from breaking-down plant material and soil organisms. Once the soil dries, the coating pushes water away instead of letting it soak in.

Sandy soils with little clay are the most prone, because sand grains have less surface area to cover and are easily coated. Water Corporation notes that Western Australia’s sands are often water-repellent, and a Perth council brochure on fertilising describes non-wettable sand as very common. But it isn’t only a Perth problem. Any lawn on sandy soil, or with a lot of thatch and organic matter near the surface, can develop dry patches once it dries out.

A wetting agent is a surfactant: it reduces the surface tension of water and helps it spread across the coated particles and soak in.

Check before you buy

Dry patches have several causes, and a wetting agent only fixes one of them. Spend ten minutes checking.

1. The water drop test. Find a dry patch and pour a little water onto the soil surface, or drip it from a cup. If it beads or sits on top for a while before soaking in, the soil is water-repellent. Do the same on a healthy area to compare.
2. The screwdriver test. A few hours after watering, push a screwdriver into the dry patch and a healthy area. If it slides easily into the healthy area but stops in the patch, water isn’t getting in.
3. The catch-cup test. Put a few straight-sided containers in the dry patch and the area around it, and run your sprinklers. If the patch collects much less water, the problem is coverage, not the soil. Fix the sprinklers first.
4. The tug test. Pull on the grass at the edge of the patch. If it lifts easily with few roots, look for lawn grubs, which cause similar brown patches.

If the water drop test shows beading and the sprinklers cover the patch well, a wetting agent is likely to help.

Choosing a wetting agent

Lawn wetting agents come in a few forms.

• Liquid concentrates are diluted and applied with a hose-end sprayer or a pump sprayer. They’re quick to apply and easy to spread evenly over a large lawn.
• Hose-on ready-to-use packs come with their own hose attachment and pre-set dilution.
• Granular products are spread with a broadcast or drop spreader, like fertiliser, then watered in.
• Combined products contain a wetting agent with fertiliser or other ingredients. They’re convenient, but the timing has to suit both parts, so check the label.

Products also differ in how they work and how long they last. Laboratory research on golf-green sands has found that different wetting agents behave differently, and that some may even add to water repellency if used repeatedly. That’s a good reason to use a wetting agent when your lawn needs it, at the label rate, rather than by habit.

Make sure the product is made for lawns. Wetting agents for potting mix and garden beds may have different directions.

When to apply

• Before the soil dries out. Re-wetting soil that’s already bone dry takes far longer. In much of Australia, that means late spring, before the summer heat.
• When dry patches first appear. Treat them early, before the grass thins.
• As the label directs through the warm months. Many products need re-applying during a long, dry season. The label says how often.
• When you can water it in. Check your local water rules, and choose a day when you’re allowed to water.

There’s little point applying a wetting agent in a wet winter, when the soil is already moist and the coatings are less of a problem.

Before you apply

• Read the whole label, including the rate, how to dilute it, whether to apply to moist or dry soil, and how much to water it in.
• Measure your lawn, or just the area you’re treating, with the Lawn Area Calculator.
• Work out how much you need with the Product Application Calculator, using the label rate.
• Mow first, so the product reaches the soil rather than sitting on long leaves.
• Spike or core compacted areas. Opening the surface with a garden fork or a core aerator helps the wetting agent and water get in, especially on stubborn patches.
• Check the forecast. Light rain can help water it in; heavy rain can wash it off a slope before it soaks in.

Applying a liquid with a hose-end sprayer

1. Fill the bottle with the amount of product the label gives for your area, and dilute it if the label says to. Many hose-on packs are already set up.
2. Set the dial, if your sprayer has one, as the label or the sprayer’s instructions direct.
3. Start at the far end of the lawn and walk backwards, so you don’t walk through what you’ve applied.
4. Walk at a steady pace in parallel strips with a slight overlap, sweeping the spray evenly.
5. Finish the bottle over the area you planned. If you run out early or have some left, adjust your pace next time.
6. Water in as the label directs.

The hose-end sprayer guide covers how to check your pace against the label’s coverage.

Applying a liquid with a pump sprayer

A pump sprayer gives you more control over exactly how much goes where, which is useful for treating patches.

1. Calibrate the sprayer with clean water so you know your output for a given area. See the sprayer calibration guide.
2. Mix the label rate for the area you’re treating, in the water volume your calibration shows you need.
3. Spray evenly, in strips with a slight overlap, keeping the nozzle at a constant height.
4. Water in as the label directs.

Applying granules with a spreader

1. Calibrate your spreader for this product. Granular wetting agents may flow differently from fertiliser. See the broadcast spreader guide.
2. Fill the spreader on a tarp or hard surface.
3. Do the edges first, then walk parallel passes so the throw patterns meet.
4. Close the gate when you stop or turn.
5. Sweep granules off paths and driveways back onto the lawn.
6. Water in as the label directs.

Watering in

Most lawn wetting agents need watering in to move them off the leaves and into the soil, where they work. Follow the label: some say to water in straight away, and some give a minimum amount of water.

• Water evenly. If your sprinklers miss part of the lawn, the wetting agent won’t be watered in there either.
• Split the watering on slopes and clay, into two or three shorter cycles, so it soaks in rather than running off.
• Don’t flood it. Water that runs off carries the product with it.

Treating stubborn patches

Some patches stay dry even after a wetting agent. For these:

1. Spike the patch with a garden fork every few centimetres, or core it.
2. Apply the wetting agent at the label rate, over the patch and a little beyond its edge.
3. Hand-water slowly with a trigger nozzle on a gentle setting, letting each round soak in before the next.
4. Check with a screwdriver a few hours later to see how deep the water went.
5. Repeat the watering over the next few days if needed, within your local water rules.

A patch on a slope, under a tree, or next to a hot wall or path may also need extra water or a change to the sprinklers.

Has it worked?

Give it time. Some products start working soon after watering in; others take longer. Then check:

• The water drop test. Water should now soak in instead of beading.
• The screwdriver test. It should push in more easily, to a similar depth as in the healthy lawn.
• The lawn. Grass in the patch should start to recover within a few weeks of warm weather and regular watering.

If nothing changes, look again at the cause. Uneven sprinklers, lawn grubs, compacted soil, shade or tree roots competing for water can all cause dry patches that a wetting agent won’t fix.

Safety

Wetting agents are generally less hazardous than herbicides or insecticides, but read the label all the same.

• Wear the protective equipment it lists, often gloves and eye protection when handling the concentrate.
• Keep it out of drains and waterways. Don’t apply it to paths and driveways, and sweep up any granules that land there.
• Keep children and pets off the lawn for as long as the label says.
• Store it in its original container, out of reach of children and pets.

What you may see, and what to do

Common mistakes

• Waiting until mid-summer, when the soil is already bone dry and very hard to re-wet.
• Not watering in, so the product sits on the leaves.
• Applying more than the label rate to fix a bad patch.
• Treating every dry patch as hydrophobic soil without checking the sprinklers or looking for grubs.
• Applying unevenly, which leaves untreated strips that stay dry.

Log it

Log each application in your Lawn Journal, with the product, the area and the date, and add a note when you check the results. Over a summer or two, you’ll see which parts of your lawn need treating and when to get in first.