How do I level a bumpy lawn?

Grass will grow up through a thin layer of dressing but suffocates under a thick one, which is why levelling is a repeated small job rather than a single big one.

What you'll need

• Sharp spade or turfing iron
• Sandy loam top dressing
• Stiff brush or level lute
• Garden fork

Step by step

1. Find out how deep the bumps are.Lay a straight plank or a spirit level across the lawn and measure the gap. Under 25mm is a top dressing job; over that, the turf comes up.
2. Mow short before starting.Slightly shorter than usual so the dressing reaches the soil rather than sitting on leaf.
3. Mix or buy a sandy top dressing.Roughly three parts sharp sand to one part sieved loam or compost for most soils. Pure sand on clay creates a layer that holds water.
4. Apply no more than 10 to 15mm at a time.Tip it onto the hollows and work it in with a stiff brush or the back of a rake until the grass tips are showing through everywhere. Grass buried deeper than that dies.
5. Repeat every few weeks in the growing season.A 40mm hollow takes three or four applications across a spring or an autumn. It is slow and it is the only way that does not kill the grass.
6. Cut and lift the turf for deeper hollows.Cut an H shape or three sides of a square through the turf with a spade, slide the spade underneath to free it, and peel the flaps back.
7. Adjust the soil underneath.Add and firm topsoil in a hollow, or scrape soil out under a hump. Firm it well — soft fill settles and the bump reappears.
8. Lay the turf back and knit the joints.Press it down, brush top dressing into the cut lines and water thoroughly. Keep it damp for a fortnight.
9. Fix the cause if there is one.Bumps over a run of new humps often mean a mole, a buried tree stump rotting away, or a trench that was backfilled loosely. Levelling the surface will not stop those recurring.
10. Overseed thin areas afterwards.Top dressing thins the grass slightly. A light overseed in the same operation fills it back in.

Tips

• Never bury grass more than about 15mm in one go.
• Rolling compacts the high spots and leaves the hollows exactly where they were.
• Autumn is the best season — the grass grows through the dressing and the rain does the watering.

Common mistakes

• Filling a deep hollow in one application — The grass under 50mm of dressing dies, leaving bare soil, and you have converted a bump into a bare patch. Several thin layers keep the lawn alive throughout.
• Hiring a roller — Rolling a lawn compacts it, which encourages moss and worsens drainage, and it does not move soil from a hump into a hollow.

If it doesn't work

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