How to level a bumpy lawn

A bumpy lawn is more than a looks problem. The mower scalps the high spots and misses the low ones. Water collects in the hollows. People trip, and children’s games end in sprained ankles. Over time, the scalped bumps thin out and the soggy hollows grow weeds.

The good news is that most lawns can be levelled without starting again. The method depends on how deep the hollows are and what’s causing them. This guide covers finding the cause, measuring the problem, and fixing it with topdressing, lifting turf, or both.

Why lawns go bumpy

Find the cause before you fix the surface, or the problem will come back.

• Settling soil over trenches for pipes, cables or irrigation that weren’t firmed properly when they were filled.
• A leaking pipe washing soil away underneath, which keeps a hollow sinking.
• Rotting tree stumps and roots, which leave hollows as they break down.
• Tree roots growing near the surface, which lift the lawn into ridges.
• Dogs digging, and the holes being filled loosely.
• Uneven preparation when the lawn was first laid.
• Wear and compaction along paths and in play areas, which press the surface down.
• Thatch, which builds up unevenly and makes a lawn feel lumpy and spongy. The renovation guide covers this.

If a hollow sits over a pipe or keeps sinking, check for a leak before filling it. If a ridge follows a tree root, don’t cut the root to level the lawn: it can harm or destabilise the tree.

How uneven is it?

1. Mow the lawn at your normal height, so you can see the surface.
2. Lay a long straight board across the lawn, or stretch a string line tight between two pegs just above the grass.
3. Measure the gaps under the board or string in a few places with a ruler.
4. Mark the high and low spots with flags or a dot of paint.
5. Look after rain or watering. Puddles show you the low spots clearly.

Sort what you find into three groups:

When to level

Level while the lawn is actively growing, so it grows up through topdressing and roots back in quickly after you lift and re-lay it. Clemson University Extension recommends renovating warm-season lawns in late spring to early summer, and topdressing during the active growing season. Avoid levelling going into the cooler months, during a heatwave, or under tight water restrictions.

Choosing material

Clemson University Extension advises using sand to topdress only where your native soil is sandy, and otherwise using a material that matches your existing soil. Very different materials in layers can hold or shed water differently, and can cause problems with drainage and rooting.

• Ask your landscape supplier about products made for lawn topdressing.
• Avoid material with weed seeds, stones, clods or building rubble.
• Order with the Topdressing Calculator. Sand weighs roughly 1.3 to 1.5 tonnes per cubic metre, depending on grade and moisture, so ask your supplier for their product’s density.

Fixing shallow hollows with topdressing

Topdressing is for hollows and unevenness that you can fill in thin layers. Clemson University Extension recommends no more than about half an inch, roughly 13 mm, at a time.

1. Mow the lawn a little lower than usual, without taking off more than a third of the leaf.
2. Core aerate first if the soil is compacted. The holes help the topdressing bind with the soil underneath.
3. Tip small piles of material into the hollows from a wheelbarrow or bucket.
4. Spread it with a levelling rake, pushing and pulling in different directions so the material settles into the low spots and is scraped off the high ones.
5. Brush it in with a stiff broom so it sifts down between the leaves.
6. Check the leaves still show. Grass buried completely can’t get light.
7. Water it in gently, to settle the material and wash it off the leaves.
8. Repeat once the grass has grown through, usually after a few weeks in the growing season, until the hollow is level.

Filling a deep hollow in one go seems quicker, but it smothers the grass and leaves a bare patch that takes longer to fix.

Fixing deep hollows by lifting the turf

When a hollow is too deep to fill in a few thin layers, lift the turf and fill underneath it.

1. Cut the turf across the middle of the hollow with a flat spade or sharp knife, and then across again to make a cross, or cut an H shape.
2. Peel back the flaps carefully, keeping as much soil on the roots as you can.
3. Fix the cause, such as a leaking pipe or rotting root, if you can.
4. Add soil that matches your existing soil, a little at a time, firming each layer with your foot or the back of the spade.
5. Check the level with the board or string line. Allow for the thickness of the turf you’ll lay back.
6. Water the soil to settle it, and top up if it sinks.
7. Lay the turf back, pressing it down firmly so it makes good contact with the soil.
8. Topdress the cuts lightly and water well. Keep it moist, like new turf, until it roots.

Fixing bumps and ridges

Bumps are fixed the same way in reverse.

1. Cut and peel back the turf over the bump.
2. Remove soil until the surface is level with the lawn around it, checking with the board.
3. Firm the soil, lay the turf back, press it down and water it in.

A heavy roller can press down small lumps, but it also compacts the soil, and compaction is one of the things that makes lawns thin and hard for water to get into. Lifting and re-laying is usually the better fix.

Levelling a whole lawn

If the whole lawn is uneven:

• Start with coring while the lawn is growing strongly.
• Topdress the whole lawn in thin layers, concentrating on the low spots, over several applications through the growing season.
• Lift and re-lay the worst hollows and bumps.
• Consider starting again if the lawn is very uneven, badly drained or full of weeds. The laying new turf and starting from seed guide covers preparing a level base.

Aftercare

• Water lifted and re-laid areas like new turf until they root, then return to your normal watering.
• Keep traffic off topdressed and re-laid areas while the grass grows through.
• Mow once the grass has grown above your mowing height, on a higher setting to start with, so the mower doesn’t scalp the patches before they settle.
• Check after rain. A spot that sinks again needs more soil underneath, or there’s a cause you haven’t found yet.
• Feed at the label rate while the lawn is growing, to help it spread over topdressed areas.

Edges, paths and sprinkler heads

Levelling often shows up problems where the lawn meets hard surfaces.

• Keep the lawn just below paths and edging, so the mower can run along the edge without scalping.
• Raise sunken sprinkler heads so they sit level with the new surface. A head left below the topdressing will spray into the soil.
• Don’t build up soil against the house or over the damp-proof course when you level near walls.

Low spots that hold water

A hollow that holds water after rain may be more than a levelling job.

• Check whether water is flowing onto the lawn from a downpipe, path or neighbour’s yard.
• Check the soil isn’t compacted clay that water can’t soak into.
• Make sure the ground slopes away from the house.
• For persistent drainage problems, get advice from a landscaper or plumber before filling the hollow.

Before you dig

Most levelling only disturbs the top few centimetres, but pipes, irrigation lines and cables can be shallow. Mark sprinkler heads and irrigation lines before you start. If you need to dig deeper, contact Before You Dig Australia, a free service that tells you where underground services are.

A worked example

A back lawn has three problems: a long hollow about 10 mm deep where an old trench settled, a deep hollow about 40 mm deep where a stump rotted, and a ridge along a path.

• The shallow trench hollow: topdress in late spring, about 5 mm at a time, twice, a few weeks apart.
• The stump hollow: too deep to topdress. Lift the turf in an H shape, dig out the rotted wood, fill with soil in firmed layers, and re-lay.
• The ridge: lift the turf, take out the excess soil, and re-lay.

The numbers are only an example. Measure your own lawn and fill in thin layers.

Common mistakes

• Filling a hollow in one thick layer, burying the grass.
• Using material that doesn’t match the soil, which can cause layering and drainage problems.
• Levelling a hollow over a leaking pipe without fixing the leak.
• Rolling the lawn to flatten bumps.
• Levelling in autumn or winter, when the grass grows too slowly to recover.
• Cutting tree roots to level the lawn.

Log it

Record your levelling in your Lawn Journal: where, how deep, what you used and the date. Add a photo before and after. If a spot keeps sinking, your journal will show it, which is often the first clue to a leak or settling problem underneath.