How deep should topsoil be?

Laying turf: 100mm of good topsoil minimum, 150mm ideal. Lawn from seed: the same, 100mm to 150mm of fine, firmed soil.

Flower borders and shrubs: 300mm to 450mm so roots have room to spread and hold moisture. Vegetable beds: 300mm minimum, and 400mm or more for root veg like carrots, parsnips and beetroot that need deep, stone-free soil.

Raised beds: fill to suit the crop, roughly 200mm for salads and shallow-rooted plants, 400mm plus for deep rooters. Top dressing an existing lawn: only 3mm to 6mm per pass, which is a different job to a full spread.

Grass roots live in the top 100mm of soil. Give them that depth of loose, decent topsoil and they can spread, hold water and feed. Push it to 150mm and the lawn copes far better in a dry spell because there is more soil holding moisture below the surface.

Do not lay turf or sow seed straight onto compacted subsoil, clay or builders' rubble. That layer is dense and drains badly, so roots stall at the join and the lawn goes patchy and yellow. Break up and level the base, then lay your 100mm of quality soil over the top.

If you would rather not do the graft, Barrow Landscaping does supply-and-lay: they prep the ground, spread the soil and lay the turf in one visit.

When you are raising a level by more than 150mm, you do not need good soil all the way down. Roots do not reach the bottom of a deep fill, so paying top price for soil that just sits there is money wasted.

Some yards sell a cheap unscreened fill for exactly this, and clean subsoil does the same job lower down. Use that sort of material for the bulk of the depth, then cap it with 100mm of screened topsoil where the roots actually live. TopTurf sells the screened topsoil for the cap, at £70 a bulk bag.

Firm each layer as you go rather than tipping it all in loose. Loose fill settles and sinks, and you end up with dips a few weeks later.

The sum is simple: area in square metres times depth in metres gives you cubic metres. A 40m2 lawn at 100mm is 4m3. Topsoil weighs about 1.5 tonnes per cubic metre, so that is roughly 6 tonnes.

In bulk bags it is easier still. One bulk bag is about 0.7m3 and covers around 7m2 at 100mm, or about 14m2 at 50mm. That 40m2 lawn needs about 6 bulk bags. It is worth ordering a little extra, around 10 percent, because soil settles once it is firmed and watered in.

Delivery from our Leigh base starts at £20, confirmed on your postcode and the size of the order.

Economy fill, where you can get it, is for building up levels and forming a sub-base under turf. It is unscreened, so keep it below the root zone rather than at the surface.

Screened topsoil is passed through a screen so it is fine and free of big stones and lumps. That makes it the one for lawns, seedbeds, borders and raised beds, because it levels cleanly and gives a smooth finish. This is the grade TopTurf sells, at £70 a bulk bag.

Premium BS3882 topsoil is graded to the British Standard, with tested structure and nutrients, and some suppliers stock it for high spec planting. For most gardens a decent screened topsoil does the job.

Top dressing an established lawn is a thin job, not a deep one. You are spreading 3mm to 6mm of fine soil or a sand and soil mix to smooth out bumps and improve the surface, then brushing it down into the grass.

Never bury the grass. More than 6mm in one go smothers the sward and does more harm than good. If the lawn is very uneven, build it up over two or three passes across a season rather than one thick layer.

For this our screened topsoil, or a screened soil and sharp sand blend, works well because it filters into the surface without clogging it.

You need a bed of decent topsoil, at least 100mm, over prepared ground. Turf laid on compacted subsoil, clay or leftover rubble roots poorly and goes patchy. Break up and level the base first, then lay 100mm of screened topsoil and turf on top.

300mm as a minimum for most veg. For root crops like carrots, parsnips and beetroot, go to 400mm or more of deep, stone-free soil so the roots can grow straight and long. A good screened topsoil is the sensible starting point for a productive bed.

100mm of fine, firmed topsoil, with 150mm being better for holding moisture through dry spells. Use screened topsoil so the surface levels cleanly and the seed sits in a smooth, stone-free bed.

One bulk bag is about 0.7m3 and covers roughly 7m2 at 100mm deep, or about 14m2 at 50mm. Work out your area times depth, then divide. For example a 40m2 lawn at 100mm needs about 6 bulk bags. Order around 10 percent extra to allow for settling.