How to apply granular lawn fertiliser

Granular fertiliser is the simplest way to feed a lawn, and the easiest to get wrong. Too much in one spot burns the grass. Uneven spreading leaves green stripes. Granules left on the path wash into the drain with the next rain. The good news is that all of this is avoidable with a little planning, a calibrated spreader and ten minutes with a broom.

This guide covers when to feed, how to work out how much you need, how to spread it evenly, how to water it in, and what to do if something goes wrong.

Does your lawn need feeding?

Before you buy a bag, check that hunger is the problem. A hungry lawn usually turns pale or yellow-green evenly across the whole area, grows slowly in the growing season, and thins out over time.

Patchy yellowing, brown patches or thinning in one part of the lawn usually point to something else: shade, waterlogging, compaction, dry or water-repellent soil, lawn grubs or disease. Fertiliser won’t fix those, and can make some of them worse.

It’s also worth knowing that lawns are commonly over-fertilised. The Fertilise Wise brochure produced for Perth councils makes this point, and notes that any nutrients plants don’t take up can end up in stormwater, groundwater and eventually waterways, where they contribute to algal blooms. A healthy lawn often needs less fertiliser than people think.

Choosing a fertiliser

Every bag shows an analysis, usually as three numbers for nitrogen (N), phosphorus (P) and potassium (K). Nitrogen drives leaf growth and colour, which is why lawn fertilisers are usually high in it. See the NPK answer for more.

• Quick-release fertilisers green the lawn up fast but don’t last long, and are more likely to burn if over-applied.
• Slow or controlled-release fertilisers feed over a longer period. The release rate can be affected by high temperatures and overwatering, so they may run out sooner in a hot, wet summer.
• Organic-based fertilisers, such as those made from manures or blood and bone, release nutrients as they break down. Some contain a lot of phosphorus, so use them in moderation.

If you don’t know what your soil needs, a soil test is the best guide. It shows pH and, with a laboratory test, the main nutrients, so you can avoid adding phosphorus to a soil that already has plenty. See the soil testing guide.

When to fertilise

Feed when the lawn is actively growing, so it can use the nutrients straight away.

• Warm-season grasses (buffalo, kikuyu, couch and zoysia) grow from spring, once they’re growing strongly, through to autumn.
• Cool-season grasses grow most in autumn and spring.
• Avoid dormant lawns. Feeding a lawn that isn’t growing, such as a warm-season lawn in a cool-zone winter, wastes most of the fertiliser.
• Avoid heat-stressed lawns. A lawn struggling in a heatwave is more likely to burn.
• Avoid heavy rain. Feeding just before heavy rain is wasteful and lets nutrients wash away.

Your climate zone’s Lawn Calendar shows when lawns in your area are usually growing.

How much do you need?

1. Measure your lawn. The Lawn Area Calculator helps with odd shapes. Leave out garden beds, paths and the shed.
2. Find the rate on the label. It’s usually given as an amount of product for an area. The rate on the pack is the most you should apply, not a starting point.
3. Work out the total. Enter the label rate and your area in the Product Application Calculator.
4. Weigh it out. Use kitchen or bathroom scales and put the amount you need into a bucket. Don’t pour straight from the bag into the spreader and hope.

Weighing out the total is the best check you have. If you finish the lawn with fertiliser left over, you spread too thinly; if you run out early, you spread too heavily. Either way, you’ll know before you see it in the lawn.

Before you spread

• Read the whole label, including any directions on mowing, watering in and keeping people and pets off.
• Mow a day or two before. Granules reach the soil more easily in shorter grass.
• Check the soil isn’t bone dry. Some labels say to apply to moist soil. If your lawn is very dry, water it a day or two beforehand.
• Check the forecast. Light rain after spreading can help water it in; heavy rain can wash it away.
• Calibrate your spreader for this product. Every product flows differently, and the setting on the bag is only a starting point. The broadcast spreader guide shows how.
• Pick up toys, hoses and dog bowls, and keep children and pets inside while you work.

Spreading it evenly

1. Fill the spreader on a tarp or hard surface, never on the lawn. A spill on the grass will burn it.
2. Do the edges first. Walk around the perimeter of the lawn, using an edge guard or the spreader’s edge setting if it has one, so granules don’t land in garden beds or on paths.
3. Walk parallel passes across the lawn at a steady pace, overlapping so the edges of each throw pattern meet. On a broadcast spreader, that usually means lining your wheel up with the edge of the last pass’s throw.
4. Close the gate whenever you stop or turn. A spreader standing still with the gate open drops a pile of fertiliser in one spot.
5. Keep the same pace. Spreader output depends on walking speed as well as the setting.

Two directions at half the rate

For the most even result, many people set the spreader to deliver half the label rate and cover the lawn twice, the second time at right angles to the first. The total still equals the label rate, and any small gaps or overlaps in one direction are evened out by the other. Weigh out the total, split it in half, and use half for each direction.

Small lawns and tight spaces

A hand-held spreader is better than spreading by hand, which almost always leaves dark green spots and burnt patches. For narrow strips such as a nature strip, a drop spreader keeps granules off the footpath and the road.

Sweep up

Granules that land on paths, driveways and the road will wash into the stormwater drain with the next rain or watering. From there, they go straight to creeks, rivers and the sea.

• Sweep them back onto the lawn straight away.
• Don’t hose them off. That sends them into the drain.
• Check the gutter in front of the house if you’ve fed the nature strip.

The Fertilise Wise brochure lists keeping fertiliser off paths, driveways and roads as one of the main ways homeowners can protect waterways. A study of residential stormwater also found that larger and longer rainfall events carried more nitrogen from inorganic fertilisers into stormwater.

Watering in

Follow the label. Many granular lawn fertilisers need watering in soon after spreading, to wash the granules off the leaves and down into the soil, where the roots can use them.

• Water until it soaks in, not until it runs off. Heavy watering can wash nutrients past the roots.
• Water the whole area evenly. If you use sprinklers, check their coverage first.
• Check your water rules. If you can’t water on the day, choose a day when you can, or when light rain is forecast.

Overwatering after fertilising, or fertilising just before heavy rain, lets nutrients leach below the roots, where the lawn can’t use them.

Keeping people and pets safe

• Follow the label’s directions about keeping people and pets off the lawn. Many products say to wait until the fertiliser has been watered in and the lawn has dried.
• Wear gloves when handling fertiliser, and wash your hands afterwards.
• Store the bag sealed, off the floor and out of reach of children and pets.
• If someone swallows fertiliser, phone the Poisons Information Centre on 13 11 26. For animals, contact your vet.

Weed and feed products

Products that combine fertiliser with a herbicide are pesticides as well as fertilisers. The label must list your grass type and the weeds you want to control, and its directions on rates, timing and watering apply. Take particular care with buffalo, which is sensitive to some herbicides. If you only have a few weeds, feeding the lawn and spot spraying the weeds separately is often the better choice.

Sandy soils, clay soils and shade

• Sandy soils hold few nutrients, so much of a heavy feed can wash straight through. Slow-release fertilisers, and smaller amounts more often within the label’s directions, suit them better. Improving the soil with organic matter helps it hold nutrients.
• Clay soils hold nutrients well but can be compacted, so water and fertiliser may run off. Core aerating before feeding helps.
• Shaded lawns grow more slowly and need less fertiliser than lawns in full sun.

If something goes wrong

If you spill fertiliser on the lawn, scoop up as much as you can, then water the spot deeply to dilute what’s left. See the fertiliser burn answer.

Common mistakes

• Applying more than the label rate, hoping for a greener lawn.
• Filling the spreader on the lawn.
• Feeding a dormant lawn in winter.
• Leaving granules on paths to wash into the drain.
• Fertilising just before heavy rain.
• Not watering in when the label says to.
• Treating every yellow lawn as hungry, without checking for other causes.

Log it

Log each feed in your Lawn Journal, with the product, the amount, the area and the date. Over a season, you’ll see how often your lawn really needs feeding, and you’ll have the dates to hand if the label limits how often you can apply.