Reading the Damage Winter Has Done

After a wet winter, most lawns tell you exactly what has gone wrong. You will see standing water in the lowest corners, patches of moss spreading like a green rash, and a surface that squelches underfoot long after the rain has stopped. Ruts left by boots or a wheelbarrow are a sure sign of compaction, and where the grass has died out completely you may find algae, liverwort or creeping buttercup moving in.

The underlying problem is almost always the same. When soil is walked on while saturated, the pore spaces between particles collapse and the air is squeezed out. Roots suffocate, the soil structure seals over, and water can no longer drain away. That is why the moss and the weeds appear — they are symptoms, not the cause. Address the compaction first and the rest becomes far easier.

Wait Until the Soil is Workable

Nothing you do to a waterlogged lawn will help if the ground is still wet. Working it now will smear the structure further and leave you with a surface like a cobbled yard by June. The old test is still the best: take a handful of soil from a spade's depth, squeeze it, and open your hand. If it holds a ball or ribbons between your fingers, it is too wet. If it crumbles apart, you can begin.

You also want the worst of the frosts behind you. Grass seed needs soil temperatures of roughly 8–10°C to germinate reliably, which in most of the UK means from mid-April onwards. In the south-west and on light soils you might start sooner; on heavy clay in the north, be patient until early May. Never aerate or seed onto frozen or frosted ground — you will simply crack the surface and bury the seed where it cannot grow.

Aerating Compacted Ground

Aeration is the single most valuable job you can do this spring. For heavy clay, hollow tining is worth the effort or the hire fee: it removes small plugs of soil and creates proper channels for air and water. On lighter or sandy soils, solid tining with a spiking fork is usually enough.

• Hollow tining: work across the lawn in one direction, then at right angles, at roughly 10–15 cm spacing.
• Garden fork method: push the tines in to about 10–15 cm, rock gently back and forth, and withdraw. Do not lever the fork, or you will tear the turf.
• Brush in afterwards: sweep a sandy loam or sharp sand into the holes to keep them open. This is the step most people skip, and it makes the biggest difference on clay.

If the lawn is still holding water, leave it. Aerating saturated ground does more harm than good.

Filling Hollows and Levelling

Winter often leaves dips and hollows where the soil has settled or been washed about. These collect water and scalded grass, so they are worth correcting now. Use a loam-based topsoil that matches your existing soil as closely as possible — a sandy topsoil on clay will create a sump, and a heavy one on sand will cap the surface.

For clay soils, a mix of roughly three parts topsoil to one part sharp sand or horticultural grit helps drainage. Add it in thin layers of no more than 1–2 cm, firm gently with the back of a rake or a board, and let it settle before adding more. Finish slightly proud of the surrounding level, because it will drop. Take care never to bury the crowns of existing grass, or you will kill the very turf you are trying to save. For deeper hollows, lift the turf, adjust the soil beneath, and lay it back — slower, but far more reliable.

Overseeding Thin and Bare Patches

Once the surface is level and the soil has warmed, tackle the thin areas. Rake the patch firmly to expose bare soil and remove dead thatch and moss. Choose a seed mix to suit the spot: ryegrass-based blends for family lawns and heavy wear, finer fescue and bent mixes for a smarter finish, and shade-tolerant mixes for north-facing or tree-shaded borders.

Sow at around 15–25 g per square metre, mixing the seed with dry sand or soil so you can see where you have been. Rake it in lightly, then firm the surface with the flat of a board or by treading in small steps. Keep the patches moist for the first three weeks — little and often is better than a soaking. Ryegrass usually shows in 7–14 days; finer grasses can take three weeks or more. If birds are a nuisance, a light covering of fleece or netting saves a great deal of seed.

Aftercare, Feeding and Wildlife

New grass needs time. Keep off the repaired areas until the seedlings are around 5 cm tall, and mow for the first time with the blades set high, removing no more than a third of the leaf. Feed lightly in late spring once growth is underway, and avoid quick-release nitrogen on dry ground.

Resist the urge to declare war on moss straight away. Moss thrives where drainage is poor, shade is heavy and pH is low, so a simple soil test is worth doing. Worms, blackbirds and starlings are your allies here — they break down thatch and hunt leatherjackets and chafer grubs. Leave a strip of clover and selfheal to flower between mowings if you can; the bees will thank you, and your lawn will be the better for it.