- A lumpy lawn gets worse with every mow, as bumps and hollows make the mower scalp the grass and leave bare patches.
- Cutting an H through the turf lets you peel it back, take soil out of a bump or add soil to a hollow, firm the ground and lay the turf back down.
- Do the job in a mild spell when the soil is not waterlogged and the weather is not snowy or frosty, or leave it until spring.
Why a Lumpy Lawn Gets Worse Every Time You Mow It
Walk across a lawn that has been mown for years and your feet find what your eyes miss: a hump here, a dip there, a soft spot where the ground has sunk. The mower finds them too. The RHS lists an uneven surface of bumps and hollows among the causes of scalping, where the mower cuts so low that it leaves bare patches.
The fix needs a flat-bladed spade, a garden fork and a rake. Cut an H-shaped incision through the uneven patch, peel back the two flaps of turf, remove soil from a hump or add topsoil to a hollow, firm the soil down level, lay the flaps back and brush a sandy dressing into the cuts. The grass is never thrown away, so the lawn keeps its own turf, and its own colour, across the repair.
The RHS puts lawn repair in spring and autumn, when the weather is damp and cool and the lawn is most likely to recover well. Its January jobs list repeats the same H-cut as winter maintenance, and its November list allows turf to be laid in mild spells. So a mild day now is a good day for this job, and a smooth first cut in spring is the payoff.
Left alone, the problem feeds itself. Bare patches left by scalping give weeds a place to settle, and repairing them helps stop weeds colonising bare areas. A depression that fills with water when it rains is a drainage issue, and divots and other depressions make mowing a pain and create tripping hazards.
Why Lawns Go Lumpy in the First Place
Knowing the cause tells you where to look and whether the repair will last.
Settling is the first cause to suspect on a lawn laid from turf. Gardeners’ World says turf should always be laid on soil that has been levelled and firmed beforehand. If that step is skipped, the soil develops depressions as it settles, and the lawn looks unsightly.
Wear is the next cause. Frosty or soggy winters take their toll on a lawn, especially one that is walked on a lot. Ants add humps from below: years of nest building push fine soil to the surface, and the ground ends up uneven. Worm casts add small mounds. They are a sign of healthy soil, and if you don’t like them you can brush them off with a hard broom once they dry out.
How to Level a Bump or a Hollow With an H-Cut
Pick a mild day when the soil is not waterlogged and the weather is not very wet, snowy or frosty. Those are the limits for laying turf in November, and they fit here, as you are lifting and relaying turf.
**Cut and peel.** Mark the lumpy patch. Cut through it with an H-shaped incision, using a flat-bladed spade, and peel back the turf as two flaps. The RHS gives no depth for the H-cut, but its patch repair lifts turf to a depth of about 5cm (2in), which is a sensible guide for how thick to slice.
**Change the level.** Fork over the base so the soil is loose and you can see what you are dealing with. On a bump, remove the excess soil. On a hollow, add new topsoil to raise the level. A wheelbarrow helps: soil taken off one hump can go straight onto a hollow elsewhere.
**Firm it down.** Firm the soil by walking up and down on it, taking small, heavy steps, and fill any freshly created dips with topsoil before compressing again with your feet. That is Gardeners’ World’s method for new turf, and it works the same way here. Firming is the step people skip. Loose soil settles, so a repair that is not firmed sinks back into a hollow. Fresh fill settles too, which is why you should overfill slightly.
**Lay the flaps back and check.** Replace the two flaps and check the lawn is level. If it is not, lift a flap and add or remove soil, then firm and check again.
**Close the cuts.** Compress the turf edges with the back of a rake, then brush a sandy lawn top-dressing into the crevices where the turf was cut. The recipe, if you want to mix your own, is three parts sandy loam, six parts sharp sand and one part peat-free multi-purpose compost. You can buy it ready made in garden centres. The dressing fills the gaps left by the spade, so the flaps sit snug against the lawn around them. If you like the result, you can top dress the lawn in early autumn across the whole surface to keep it smooth.
**Water thoroughly.** Newly laid pieces of turf dry out easily until they are well rooted, so water regularly if rain does not do it for you. The joints in new turf dry out faster than the rest of the roll, and your H-cut lines are joints, so give them the same care.
One more benefit: repaired patches can come out a different colour to the rest of the lawn, and turf taken from elsewhere on the lawn is less likely to show the difference. An H-cut reuses the turf already in place, so the colour should match.
How to Fill a Dip That Is Too Shallow or Too Deep for the Usual Cut
Shallow and deep hollows need different handling.
For a small, shallow dip, use a slow fill. Wait until the turf has started to grow, then fill the depression with sieved topsoil, letting the grass grow through the soil before adding more, until the lawn is level. The slow pace is the point: the grass grows up through each layer before the next goes on. This method needs growing weather, so wait until the grass is growing.
For a deeper dip, do not tip soil in and hope. If the depressions are more than two or three inches (5 to 7.5cm) deep, Family Handyman warns, dirt dumped directly into them will probably wash away. Instead, cut the turf around the hole with a spade, remove it, fill the hole with a soil and compost mixture and replace the turf. The roots then stabilise the fill and hold it in place. For larger patches, Gardeners’ World says to pull back the turf over the depression, add topsoil until the level is right, firm, replace the turf and water thoroughly.
Wet down the first load of fill to compact it, then add a second. A lawn roller will also compact it. Overfill slightly, then draw a straight 2×4 on its edge across the dip to make a flat surface and move the excess out of the way.
If water still pools in the hollow once it is level, the cause is drainage and the repair is sound. Look at why water pools on your lawn before you blame the repair. Look out for waterlogging as the weather gets wetter, spike the lawn with a garden fork or mechanical aerator, then brush a mix of sharp sand and loam into the holes.
What to Do About Ant Heaps and Wet Weather
Ant heaps need a different first move. Disperse them by brushing the excavated soil on a dry day before the lawn is mown, otherwise the mower smears the soil on the lawn surface. Brush first and mow second. If you want the full method for the heaps themselves, see how to level ant hills without killing the grass.
If the surface is uneven from years of ant activity, peel back the turf in the raised areas, remove the excess soil and relay the turf. That is easier in winter, when ants are less active.
Wet weather sets the calendar. If the soil is waterlogged, frozen or under snow, leave the spade in the shed and wait for a mild spell or for spring. The cold has a second cost: walking on a frosty lawn damages the blades of grass, which go brittle in the cold, and can leave brown footprints that take a few weeks to disappear. A fresh repair is the last place you want those footprints.
How to Stop the Bumps Coming Back (and When to Call Someone)
Find the cause, then take it away. Once a lawn is repaired, it is worth finding and remedying the cause of the damage so the lawn stays in good shape.
If you cross the lawn in wet weather, lay stepping stones. Set them level with the soil surface so they do not interfere with mowing. Stay off frosty grass, for the reason above, and keep up the routine of lawn maintenance in spring and autumn. Mow in mild weather only when needed: grass keeps growing above 7°C (45°F), and the advice is to raise the cutting height to about 5mm (¼in) higher than in summer. Brush ant heaps before every mow, and brush worm casts off once they dry.
Settling is the other cause, and time fixes it: recheck a repaired spot after the first heavy rain and top up if it has dropped. Top it up while the dip is small and the soil underneath is still firm.
Some jobs belong to a professional. If the lawn is in a really poor state, you might need to re-lay or re-seed it entirely instead of patching it up. If the ground slopes down to the house, re-grading can stop basement flooding and prevent the foundation from settling, Family Handyman says. That is whole-yard regrading and far beyond a spade and a fork. For a handful of bumps and dips, a spade, a fork and a mild day will do.
