How to stop fertiliser and water running off your lawn

December 23, 2024

You spread the fertiliser, it rains that night, and by the morning a good part of what you paid for is in the gutter and on its way to the river. That is runoff, and it is annoying twice over, because the lawn didn't get fed and the creek got fed instead.

The good news is that it is almost always fixable, and it is usually one of two things that people run together as though they were the same problem.

Compaction and water repellency are not the same thing

If water sits on the surface and then runs off, the soil isn't taking it in, and there are two different reasons for that.

Compaction is the soil being squashed tight, usually from foot traffic, a trailer parked on it or years of mowing over the same lines. The pores water needs to travel down are closed up. The fix is aeration, which just means putting holes in it. A garden fork pushed in and rocked back and forth every 15cm or so does the job on a small lawn, and it is a decent afternoon's work rather than a quick one.

Water repellency is different and it is very common in the sandier soils around here. The soil particles get a waxy coating from breaking down organic matter, and water beads on the surface and runs sideways rather than soaking in. Aerating a repellent soil does not fix it. A soil wetter does, and the tell is water sitting in beads on dry soil rather than darkening it.

Worth saying plainly, because two of our other posts had to have it taken out: we don't hire out aerators. A fork is what most backyards need anyway.

Feed it in a way that stays put

Don't fertilise with heavy rain forecast. That is the single easiest way to lose a whole application, and the forecast is free.
Water a granular feed in lightly straight after you spread it, so it dissolves down into the soil instead of sitting on the surface waiting for the next downpour.
Use a slow release feed where you can. It releases over weeks rather than dumping everything available in one go, so there is far less sitting there loose to be washed away.
Follow the rate on the bag. More is not better here. Anything the grass can't take up is just sitting in the soil water, which is exactly what leaves.

Thicker grass holds more than bare ground

The cheapest erosion control you own is the lawn itself. Grass cut too short has a shallower root system and leaves gaps of bare soil between the plants, and bare soil is where runoff starts. Running the mower at the top of the range for your grass rather than the bottom of it, which is nearer 50mm for kikuyu and buffalo and nearer 25mm for couch, shades the soil, slows the water down and gives the roots more to work with.

If you have thin patches, oversowing them is worth doing for the same reason. It is not only about how the lawn looks.

Give the water somewhere to go

If there is one corner where everything collects and then runs out onto the footpath, work with that rather than against it. A shallow dip planted out with something hardy, sometimes called a swale, catches the water and gives it time to soak in instead of sending it straight to the kerb. Edging a slope with shrubs or a groundcover does a similar job and slows everything down on the way past.

Shop related products

Neutrog Upsurge Crumble 20kg. Organic based and slow release, which is the combination that stays put.
Brunnings Green Up Lawn Food 2.5kg. The smaller bag, for a smaller lawn or a patch up.
Brunnings Tough Lawn Seed 1kg. For thickening up the thin bits where the runoff starts.
Brunnings Kikuyu Lawn Seed 1kg. Tough, spreads into gaps on its own, and handles our summers.

The rest is in the Brunnings and Neutrog ranges, and the whole garden centre is here. A 20kg bag is a heavy thing to carry to the car, so local delivery is $5 in Strathalbyn and $10 on the regional run.

Did you know we also stock Cyclone and Gardenmaster garden forks, spades and rakes in the shop, which is what you want for aerating a small lawn. They aren't on the website, so give us a ring on (08) 8536 4333 to check what is on the shelf.