How to prepare soil before laying a new lawn

Here's the thing nobody tells you when you buy a pallet of turf: the grass is the easy bit. The lawn that's still green and thick in three years' time was won or lost in the week before a single roll went down. Skip the soil prep and you'll be chasing weeds, bumps and dry patches forever. Do it properly and you'll have the kind of lawn the neighbours quietly resent. This guide walks you through every step, in order, with the real numbers you need — depths, pH ranges, timings — so you can get it right the first time.

The key insight: You can lay perfect turf on bad soil and get a bad lawn. You cannot lay turf on great soil and get a bad lawn. The soil is the lawn.

Start by clearing what's already there

Before you can build something good, you have to remove what's in the way. That means old grass, weeds, and anything that isn't soil.

Strip the old grass and surface weeds

If you've got an existing scruffy lawn or a weed-choked patch, you have two honest options:

• Skim it off — Hire a turf cutter (a half-day rental is cheap) and slice the top 30–40 mm clean off. This is fast, removes the thatch and most surface weed, and gives you a clean canvas.
• Spray it off — For larger or rougher areas, a glyphosate-based weedkiller knocks everything down. Wait until it's actively growing, spray on a still, dry day, and give it the full label interval to work.

Kill the perennial weeds first — this is non-negotiable

Annual weeds are a nuisance. Perennial weeds — couch, bindweed, dock, dandelion, oxalis — are the ones that come back through your brand-new lawn and ruin it. They regrow from a single scrap of root left in the soil.

• Spray, wait, repeat. Hit them with a systemic (glyphosate) weedkiller, wait the full 2–4 weeks for it to travel down into the roots, then check for regrowth and spray any survivors again.
• Never rotary hoe living perennial weeds. Chopping the roots just multiplies them — every fragment becomes a new plant. Kill them dead before you cultivate, not after.

Yes, this adds a few weeks to your timeline. It's the cheapest insurance you'll ever buy.

Cultivate, then clear the debris

With the weeds dead, it's time to open up the soil so roots can get down into it.

Cultivate or rotary hoe to a proper depth

Compacted soil is a wall that roots can't penetrate. Loosen it.

• Dig or rotary hoe to 100–150 mm. A rotary hoe (rotavator) makes short work of anything bigger than a courtyard. For small areas, a fork and some honest sweat will do.
• Don't work soil when it's wet. Cultivating wet clay turns it into compacted clods that set like concrete. Wait for it to be moist but crumbly.
• Break up any hard pan. If you hit a compacted layer a spade's depth down, break through it — otherwise water will pool there and your turf will rot or dry out above it.

Remove rocks, roots and debris

Now rake the loosened surface and pull out everything that isn't soil — stones bigger than about 25 mm, old roots, builder's rubble, bits of brick. Rocks left near the surface dry out the grass above them and ping your mower blades later. Be thorough; this is tedious but it matters.

Build the soil up

Loosened native soil is rarely good enough on its own. This is where you turn dirt into a growing medium.

Add topsoil and organic matter

You want a workable, fertile layer for roots to live in.

• Aim for at least 100 mm of good topsoil across the whole area. If your native soil is thin, poor or pure clay, import quality screened topsoil to make up the difference.
• Mix in organic matter — well-rotted compost, aged manure or a soil conditioner — at roughly 20–30% by volume. This feeds soil life, holds moisture in sandy soils, and opens up heavy clay.
• Blend it in, don't layer it. A clean band of compost under a band of topsoil creates a barrier roots won't cross. Fork it through so it's mixed evenly.

Test and adjust your pH

Grass takes up nutrients best within a fairly narrow pH band. Too acidic or too alkaline and your fertiliser is half wasted no matter how much you throw down.

A cheap soil pH kit from the garden centre tells you what you're working with in ten minutes. Here's what to aim for:

• Lime raises pH (makes acidic soil sweeter). Work it in during cultivation, not on top at the end.
• Sulphur lowers pH (for chalky, alkaline soils) but acts slowly — allow several weeks.
• Retest after adjusting. pH changes gradually, so don't assume one application has done the job.

Level, grade and create the final tilth

Everything so far has been about what's under the surface. Now you make the surface itself.

Level and grade for drainage

• Grade a gentle fall away from the house — about a 1–2% slope (1–2 cm drop per metre) is enough to move water away from buildings and stop puddles, without looking like a hillside.
• Fill the hollows, knock down the humps. Rake until the surface flows smoothly. Bumps and dips you ignore now become scalped patches and soggy spots forever — a roller can't fix what a rake should have.

Firm it, then rake to a fine tilth

This is the make-or-break final step, and it's the one most people rush.

• Firm the soil by treading. Shuffle across the whole area on your heels in overlapping rows, then again at right angles. This removes hidden air pockets that would settle into dips after the first rain.
• Rake to a fine, crumbly tilth. The finished surface should be even and break down to roughly pea-sized crumbs — fine enough for turf roots to knit straight into.
• Firm and rake more than once. A couple of cycles of tread-then-rake gives you a genuinely settled, true surface.

Lay down a pre-turf starter fertiliser

Just before the turf goes down, apply a starter fertiliser — one that's higher in phosphorus (the middle number on the bag) to drive fast root establishment. Rake it lightly into the top few centimetres so the new roots meet food the moment they reach down. Then you're ready to lay.

A simple prep timeline

Frequently asked questions

How long does soil prep actually take?

Plan for 3–4 weeks of elapsed time, even though the hands-on work might only be a few days. Most of that is waiting for weedkiller to fully kill perennial roots — and that wait is the whole point.

Do I really need to import topsoil?

Only if your existing soil is thin, heavily compacted, full of builder's rubble, or pure clay. If you already have a decent depth of workable soil, you may just need to add organic matter and improve what's there.

Can I skip killing the weeds and just dig them out?

For perennials like couch and bindweed, no. Their roots run deep and break easily, and every fragment you leave behind regrows. Spraying and waiting is far more reliable than digging.

What pH should I aim for if I'm not sure of my grass type?

Target 6.0 to 6.5. That sweet spot suits nearly every lawn grass and keeps nutrients available, so you can't go far wrong while you decide on a variety.

Should I roll the soil before laying turf?

A light roll or thorough treading helps settle the surface, but don't compact it hard — roots need air and space. Firm enough to remove air pockets, loose enough to rake to a crumb. That balance is the goal.

How Lawnova builds your prep plan for you

Soil prep has a lot of moving parts — and the right depths, pH targets and timings depend on your grass type, your climate and your soil. Lawnova takes the guesswork out: tell us about your patch and we'll generate a step-by-step prep schedule tailored to your region and conditions, with reminders so you spray, cultivate and lay at exactly the right moment.

Get your free Lawnova plan

Get the soil right, and the lawn looks after itself. We'll help you nail it.