How Do I Prepare Ground for Laying Lawn or Turf?

A beautiful lawn starts well below the surface. Whether you're laying instant turf or sowing seed, the effort you put into ground preparation will determine how well your lawn establishes, how drought-tolerant it becomes, and how much maintenance it needs down the track. Here's how to do it right, New Zealand conditions and all.

Step 1: Clear the Area Thoroughly

Before anything else, remove all existing vegetation, rocks, rubble, and debris. This means:

• Killing or removing existing grass and weeds — a non-selective herbicide (such as a glyphosate-based product) applied a couple of weeks before you start will knock back persistent weeds. Always follow label directions and observe withholding periods.
• Removing tree stumps and large roots — these will rot and cause the ground to sink unevenly over time.
• Clearing construction rubble — plaster, concrete chunks, and timber offcuts buried in fill soil are a common issue in newer NZ homes and will create dead patches.

Give the area at least two weeks after herbicide application before cultivating, so you can see if any weeds regrow and treat them again.

Step 2: Test and Improve Your Soil

New Zealand soils vary enormously — from the heavy clays of Auckland and Waikato to the free-draining volcanic soils of the central North Island and the stony soils found in many Canterbury and Otago sections. A basic soil test (available from garden centres or through BRANZ-affiliated labs) will tell you your pH and nutrient levels.

• Ideal lawn pH is generally between 6.0 and 7.0. If your soil is too acidic (common in high-rainfall areas), lime can be worked in to raise the pH.
• Clay soils benefit from the addition of gypsum and quality topsoil or compost to improve drainage and structure.
• Sandy or free-draining soils benefit from organic matter to improve water and nutrient retention.

Aim to have at least 100–150 mm of good quality topsoil across the entire area. If your existing soil is poor, bringing in screened topsoil is well worth the investment.

Step 3: Grade and Level the Ground

Proper grading is critical for both appearance and drainage. A lawn that holds water will develop moss, fungal problems, and bare patches.

• Slope away from the house — the ground should fall away from your foundation at a gentle gradient (generally at least 1:50, or 20 mm per metre) to direct surface water away from the building. This aligns with good practice under the NZ Building Code.
• Fill low spots and cut down high spots, working the soil when it's moist but not waterlogged.
• Use a long straight board or laser level to check for hollows — these will become puddles after rain.
• If you have significant drainage issues, consider installing agricultural drainage pipe (ag pipe) before you finish grading. A landscaper or drainlayer can advise on this.

Step 4: Cultivate the Soil

Once graded, the soil needs to be loosened to allow grass roots to penetrate easily.

• Rotary hoe or cultivate to a depth of around 150–200 mm.
• Break up any large clods and remove stones larger than about 25 mm.
• If adding compost, fertiliser, or lime, incorporate these during cultivation so they're mixed through the root zone rather than just sitting on top.

Step 5: Add Pre-Lawn Fertiliser

A pre-turf or pre-seed fertiliser (sometimes called a starter fertiliser) is high in phosphorus to encourage strong root development. Work it into the top 50–75 mm of soil according to the product's directions. Your local garden centre or Mitre 10 or Bunnings will stock suitable products.

Avoid using high-nitrogen fertilisers at this stage — too much nitrogen before establishment can burn young roots.

Step 6: Firm and Settle the Soil

This step is often skipped but is really important.

• Roll or tamp the soil lightly to firm it and reveal any remaining hollows.
• Water the area and leave it for several days — this will cause the soil to settle naturally and show up any low spots that need topping up.
• Top-dress any hollows with additional screened topsoil and re-level before laying turf or sowing.

The surface should be firm enough that you only sink about 5–10 mm when you walk on it.

Step 7: Lay Turf or Sow Seed

Once your ground is prepared, you're ready to go. A quick comparison:

• Instant turf should be laid immediately on delivery, staggering the joins like brickwork, and watered thoroughly straight away.
• Lawn seed should be raked lightly into the surface, covered with a thin layer of seed-raising mix or fine compost, and kept consistently moist until germinated.

For both methods, autumn and spring are the best times in most NZ regions — soil temperatures are warm enough for germination and establishment, but the heat and dry of summer won't stress new growth.

When to Call a Professional

Ground preparation is largely DIY-friendly, but there are situations where a qualified landscaper or earthworks contractor will save you time, money, and headaches:

• Large or sloping sections requiring significant earthworks or retaining walls (retaining walls over a certain height may require a building consent — check with your local council).
• Poor drainage requiring ag pipe installation — if this connects to a stormwater system, a licensed drainlayer may be required under the Plumbers, Gasfitters and Drainlayers Board rules.
• Sections with contaminated fill or unknown underground services.

You can find qualified local landscapers and earthworks contractors on tradedirectory.co.nz.

Sources & Further Reading

• BRANZ – Building Research Association of NZ
• MBIE Building Performance – NZ Building Code
• Mitre 10 NZ – Garden & Lawn
• Bunnings NZ – Garden
• Plumbers, Gasfitters and Drainlayers Board
• WorkSafe NZ – Safe use of chemicals