Why Topsoil Matters for Turf
Turf is essentially a thin layer of grass with a few centimetres of root zone attached. When you lay it, the roots need to grow down into whatever is underneath. If that's compacted clay, builder's rubble, or thin, poor-quality soil, the turf will survive for a few weeks on stored energy and watering, then slowly decline.
Good-quality topsoil gives turf what it needs: a loose, nutrient-rich growing medium that holds moisture but drains freely. The initial investment in a proper topsoil base pays for itself within the first season — you'll get quicker establishment, fewer bare patches, and a lawn that handles drought and heavy use far better.
What Grade of Topsoil?
For turf, you want screened topsoil with a sandy loam texture. This means:
- Free of stones over 10-20mm
- Good crumb structure — not dusty, not sticky
- Drains well but retains moisture
- pH between 5.5 and 7.5 (most UK topsoil falls in this range)
If ordering by BS3882 classification, a general-purpose grade is ideal for turf. Premium grade works too but costs more and the additional organic content isn't necessary for lawn use.
Avoid economy or unscreened topsoil for turf laying. Stones and clods create an uneven surface that shows through the turf, and lumpy soil doesn't make good contact with the turf roots.
How Deep Should the Topsoil Be?
The minimum is 100mm (4 inches) of topsoil below the turf. For a lawn that performs well long-term, 150mm (6 inches) is better. If you're on heavy clay or compacted subsoil, the extra depth gives roots somewhere to go during dry spells when the clay shrinks and hardens.
Check our topsoil depth guide for more detail on this.
Remember: the finished level needs to account for the turf thickness (typically 15-25mm) plus the topsoil. If your target finished level is flush with an adjacent path, the topsoil surface needs to be 15-25mm below path level.
Step-by-Step Preparation
1. Clear and Grade the Subsoil
Remove all debris, old turf, weeds, and stones from the area. If the subsoil is compacted (common in new-build gardens), break it up with a fork or rotavator to a depth of 75-100mm. This prevents a hard pan forming between subsoil and topsoil.
Grade the subsoil roughly to your desired contour. It doesn't need to be perfectly level — that's what the topsoil layer is for — but significant high and low spots should be addressed now.
2. Spread the Topsoil
Tip or barrow your screened topsoil across the area and rake it roughly level. Use a quantity calculator to work out how much you need — for 50m² at 150mm depth, that's 7.5 cubic metres (roughly 13 bulk bags).
Spread in layers if the total depth is over 100mm, lightly firming each layer before adding the next. This prevents excessive settlement later.
3. Level the Surface
This is the most important step and worth spending time on. Use a long straight-edge (a 2m length of timber) and a spirit level to create a smooth, even surface. The topsoil should have a very slight fall away from the house (1:80 is enough) to help surface water drain.
Fill any hollows, scrape down any high spots, and check levels from multiple directions. Walk over the area — any soft spots that sink underfoot need more soil and re-levelling.
4. Firm the Surface
Walk over the entire area with short, overlapping steps to consolidate the soil evenly. Alternatively, use a light garden roller (not a heavy construction roller — you want firm, not compacted).
After firming, check levels again and re-rake any areas that have become uneven.
5. Final Rake
Rake the surface to create a fine tilth — the top 10-20mm should be loose and crumbly for the turf roots to penetrate. Remove any stones that have come to the surface.
The finished surface should be like a well-prepared seed bed: firm underneath, loose on top, and level enough that a golf ball would roll smoothly across it.
6. Pre-Turf Fertiliser (Optional but Recommended)
Apply a pre-turf or starter fertiliser at the recommended rate and lightly rake it in. This gives the turf an immediate nutrient source as roots establish. Any general-purpose lawn fertiliser will do — look for one with a balanced NPK ratio.
Laying the Turf
Turf should be laid within 24 hours of delivery — it deteriorates quickly in the roll, especially in warm weather. If you can't lay it the same day, unroll and lay it flat in a shaded area and water it.
Key Points
- Start along a straight edge (path, patio, or a taut string line)
- Butt joints tightly together — no gaps, no overlaps
- Stagger joints like brickwork — don't align them
- Stand on boards placed on already-laid turf to distribute your weight — never stand directly on the prepared topsoil
- Use a sharp knife to cut turf around edges, beds, and obstacles
- Don't use small offcuts at edges — they dry out and die. Keep full-width pieces at all edges and use offcuts in the middle
After Laying
Water thoroughly immediately after laying — the topsoil beneath should be wet to at least 50mm depth. Continue watering daily for 2-3 weeks (twice daily in hot weather). Reduce to every 2-3 days once you can't easily lift a corner of turf — that means roots have established.
Don't mow until the turf has rooted (typically 2-3 weeks). Test by gently tugging a corner — if it lifts easily, it hasn't rooted yet. First mow should be on a high setting, removing no more than a third of the grass height.
Common Mistakes
- Skimping on topsoil depth. 50mm of topsoil over clay gives you a lawn that looks great for 6 weeks and struggles for years
- Not levelling properly. Every bump and hollow in the topsoil shows through the turf. Time spent levelling is never wasted
- Laying turf on dry topsoil. If the topsoil is dust-dry, water it the day before laying. Turf placed on dry soil loses moisture from the underside and can die from the roots up
- Not ordering enough. Turf is sold by the square metre. Order 5% more than the measured area to account for cutting waste around curves and edges