How to Level a Bumpy Lawn: Thin Layers Win

The short answer: thin layers, or lift and fill

Measure the dip first. A hollow of about 10mm or less can be levelled by top dressing: a sand-and-soil mix brushed in at no more than about 3mm per go, in spring or autumn, while the grass is growing.³⁵ A deeper hollow needs the turf lifted, topsoil added underneath, the soil firmed and the turf put back.¹ If the whole lawn is extremely lumpy, starting again may be the best option.⁵

Most failed levelling jobs come from one mistake: tipping a thick layer of soil onto grass. The grass can't push through it, so it dies and you get a bare patch on top of a bump. The rest of this page is how to avoid that.

Measure the dip before you buy anything

Lay a straight board across the hollow and measure from the underside of the board to the bottom of the dip. The UK Lawn Care Association uses exactly this test and says that at 10mm or less, top dressing is the answer.⁵

The sources don't agree on the cut-off. Love The Garden (Miracle-Gro) says dips up to 2 to 3cm can be filled with top dressing and treats anything deeper as a job for lawn soil.⁶ Between 10mm and 30mm you're in a grey area. You can top dress over several passes, which is slow but gentle, or lift and fill, which is quicker but cuts the turf. Pick on patience, not on a rule.

Small dips: top dress in 3mm layers

How deep per go

Rolawn, the turf grower, caps a spring or autumn dressing at 3 litres per square metre, which is about 3mm deep. In summer the cap halves to 1.5 litres, about 1.5mm.³ The finish test is simple: once you've brushed it in, the grass should be clearly visible with no obvious clumps of dressing on top.³

Suppliers and the RHS quote weights instead. The RHS rate is 2 to 3kg per square metre, about a shovelful at a time.² A UK supplier of ready-mixed 70:30 dressing gives 2kg per square metre for a light dressing, 4kg for medium and 6kg for heavy.⁸ Gardeners' World allows up to 6kg for a heavy dressing but says to start small, because it is easier to add more than to take it off.⁷

To compare the two, we use the density our lawn top dressing calculator uses, about 1.5kg per litre. That makes Rolawn's 3mm cap roughly 4.5kg per square metre, and a 6kg dressing roughly 4mm. Our calculator labels 6kg per square metre “Heavy / levelling”, but that is above the 3mm limit for a single pass. Don’t spread it in one go. Keep each pass at or under 3mm, and split the heavy rate over more than one pass.

What to mix

The standard UK lawn dressing is 70% sports sand to 30% screened topsoil, sold in 25kg bags and bulk bags.⁸ The RHS recipe for a home-made mix, measured with a bucket, is 3 parts sandy loam, 6 parts sharp sand and 1 part well-rotted compost or soil improver.² The RHS says sharp sand for this job is washed, gritty horticultural sand and not builders' sharp sand.² Gardeners' World prints the sand and soil quantities the other way round,⁷ so if you mix your own, the RHS version is the one this page follows. If you only want to buy one thing, buy the ready-mixed 70:30.

Plain sand on its own is a poor choice. Love The Garden recommends a lawn dressing that mixes sand and topsoil with some organic material, because it adds nutrients and helps the roots.⁶

Worked example: five square metres of 10mm dips

Say your dips add up to 5 square metres and each is 10mm deep. This is GardenCalc's own sum:

• Volume: 5 m² × 0.01m = 0.05 m³, which is 50 litres.
• Weight at 1.5kg per litre: 50 × 1.5 = 75kg, so three 25kg bags.
• Cost: three bags at £5.45 including VAT (Amenity Choice, checked 8 October 2026, delivery extra) is £16.35.
• Passes: 3mm at a time means three passes of 3mm and one of 1mm. That is four passes. Each 3mm pass over 5 m² takes 15 litres (about 22kg, roughly one bag), and the final 1mm pass takes 5 litres (about 7.5kg). That is 50 litres in all.

If you're dressing the whole lawn as well, Rolawn sells a 500-litre bulk bag for £145.82 including VAT (a sale price against £174.99, checked 8 October 2026). It covers up to 167 m² at 3 litres per square metre.⁴ Use the top dressing calculator for your own area.

How to apply it

1. Mow short, without scalping, and let the grass dry.⁷
2. Scarify out thatch and aerate if the ground is compacted. The RHS treats top dressing as the step straight after aerating.²
3. Spread the dressing in small heaps, then work it into the hollows with a rake held upside down or a stiff brush.³
4. Check the finish. If a lot is left sitting on the grass, apply less next time. If it all disappears at once, apply a little more.²
5. Water it in, and don't mow straight away. Gardeners' World says to leave it at least a week, ideally two.³⁷

Bigger hollows: lift the turf, pack the soil, relay it

The RHS method for bumps and hollows is an H-shaped cut through the turf with a flat-bladed spade. You peel the two flaps back, fork over the base, and add topsoil to a hollow or remove soil from a bump. Then you firm the soil level, replace the flaps, check the level and adjust if needed.¹ Love The Garden uses a cross-shaped cut instead, 4 to 5cm deep, and forks the exposed soil to about 5cm before filling. It says to tread the new soil down so it won't sink further.⁶

Finish by pressing the turf edges down with the back of a rake, brushing a sandy lawn dressing into the cut lines, and watering thoroughly.¹ Water the lawn a couple of days beforehand so the soil is moist and the flaps peel back without crumbling.⁶

Worked example: one 40mm hollow

A hollow 1.5m long and 1m wide, 40mm deep. Again, our own sum:

• Topsoil to add: 1.5 × 1 × 0.04 = 0.06 m³, or 60 litres.
• Weight: our topsoil calculator uses about 1.2kg per litre, so 60 litres is about 72kg.
• Buy a little extra. The soil settles and you'll want to check the level before the flaps go back.

For the sums on larger areas, see our guide to how much topsoil a lawn needs.

Bumps are the same job in reverse

Cut and peel the turf back, dig out the high spot until the soil is level with the lawn around it, rake smooth, tread it down and fold the flaps back.⁶ Put the spare soil to use filling a hollow somewhere else.

When to level a lawn: spring or autumn, never in drought

The sources agree on the condition and disagree a little on the season. The RHS puts spring and autumn top of the list for repairs, because damp, cool weather helps a lawn recover.¹ It does its own top dressing in September and October.² Gardeners' World prefers early to mid-autumn, with late spring as the other option.⁷ Love The Garden prefers spring, after the last frosts, once growth has restarted.⁶

All of them want the grass growing. Rolawn says to top dress only while the grass is actively growing, and not in drought or frost.³⁴ If you're unsure whether your lawn is awake, our grass growth temperature guide covers the soil temperatures that matter. In practice that means: spring once you're mowing regularly, early autumn, and only a light 1.5mm dressing in summer, and never in a dry spell.³ Winter is out.

Seed the filled patches

Where you lifted turf and the join looks thin, or where a dip has been filled with bare soil, sow seed. The UK Lawn Care Association suggests 30g per square metre on filled holes and about 25g per square metre over the rest of the lawn so the repairs blend in.⁵ The RHS says to follow the packet, usually 15 to 25g per square metre.¹ Our grass seed calculator works out the weight for your area.

Cover the seed with only a light sprinkling of soil or compost to hide it from birds.¹ We cover the topsoil question properly in our guide on whether to mix grass seed with topsoil. Keep the new grass watered until it is established. The UKLCA says that can take 4 to 16 weeks depending on season and weather, and not to mow until the new grass is 7 to 8cm tall.⁵

When to give up and start again

Patching has limits. The UKLCA says that when a lawn is extremely lumpy, the better route may be to take the grass off and relay it from seed or turf. It is hard work, but you can fix drainage and poor soil and clear buried debris in the same go.⁵ The RHS says much the same for a lawn in a really poor state.¹

Start again if:

• The lumps are all over the lawn, not in a few spots.
• It's a new-build garden. The UKLCA says these often show buried debris or thin soil once the ground settles, and recommends digging up, preparing the ground and relaying.⁵
• Hollows keep coming back after you fill them. Something underneath is moving, such as rubble or a failing drain. Love The Garden says to get an expert in if low spots sit around drainage pipes.⁶
• The garden slopes. The UKLCA says re-contouring or retaining walls need expert knowledge.⁵

Common mistakes

• One thick layer. Rolawn says the dressing should never be so deep that it smothers the grass.³ Go back next season instead.
• Working in drought, frost or winter. Rolawn says to apply dressing only while the grass is actively growing, and not in drought.³
• Mowing too soon. Rolawn warns that mowing straight after dressing can remove it and wear the mower.³
• Skipping the cause. The RHS says to find and fix what caused the damage, otherwise the lawn goes the same way again.¹ Moles, frost heave, worm casts, heavy foot traffic on wet ground and broken drains all make lumps.⁶
• Not firming the soil in a lifted hollow. It will sink again.⁶

Do the sums

This guide gives you the method. The calculators give you the quantities. Use the lawn top dressing calculator to turn your area into bags of dressing, and the grass seed calculator for the seed on your filled patches.

Frequently asked questions

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Sources and checking notes

Guidance and figures were checked against the sources below on 8 October 2026. Prices are what each supplier listed on that date and will change. Where sources disagree (the depth at which top dressing stops being enough, spring versus autumn, the order of sand and soil in a home-made mix) the page says so. The worked examples are GardenCalc's own sums, not figures from a source.

1. Royal Horticultural Society, Repairing lawns: reseeding and returfing.
2. Royal Horticultural Society, Lawn care in autumn.
3. Rolawn, How to apply top dressing.
4. Rolawn, Lawn Topdressing bulk bag, price and coverage checked 8 October 2026.
5. UK Lawn Care Association, How to level a lumpy lawn.
6. Love The Garden (Miracle-Gro), How to level a lawn.
7. BBC Gardeners' World Magazine, Complete guide to top dressing a lawn.
8. Amenity Choice, 70/30 Fine Turf Lawn Top Dressing 25kg, price checked 8 October 2026.