Which product
- Topsoil
- Screened mineral soil. It fills and levels, and it is what you want under a lawn or to raise a bed. It feeds very little on its own. Sold graded, and the cheap ungraded kind arrives with stones and weed seed.
- Compost
- Decomposed organic matter. It feeds and lightens but does not hold structure, so a bed filled entirely with compost sinks noticeably in the first year. Best used as a proportion rather than as the whole volume.
- Well-rotted manure
- A richer compost. Powerful on vegetable beds, too strong for seedlings and for most ornamentals if used fresh.
- Potting and multipurpose compost
- Formulated for containers, with a wetting agent and a fertiliser charge that lasts a few weeks. Expensive per litre and wasted on open ground.
A raised bed is usually filled with roughly two parts topsoil to one part compost. Filling one with compost alone is the most common and most expensive garden mistake.
Volume, depth and how it is sold
Soil is sold by volume: litres in bags, cubic metres loose or in bulk bags. Area alone tells you nothing until you choose a depth, and depth is where the volume actually comes from.
| Job | Depth | Per 10 m² |
|---|---|---|
| Topping up an established bed | 5-10 cm | 0.5-1 m³ |
| New planting bed | 15 cm | 1.5 m³ |
| Under a new lawn | 10-15 cm | 1-1.5 m³ |
| Raised bed or root vegetables | 30 cm+ | 3 m³+ |
litres = area × depth in metres × 1000
The crossover between bags and bulk sits at roughly one cubic metre — about twenty 50-litre bags. Below that, bags are convenient. Above it, a bulk bag or a loose delivery is cheaper per litre and saves an enormous amount of carrying, provided there is somewhere it can be tipped.
Two adjustments the arithmetic does not make for you. Fresh compost settles by 10-20% in the first season, so fill slightly proud. And ground is rarely level, so treat any calculated volume as a lower bound.
Grass seed and sowing rates
Seed is sold by weight and applied by rate. A European bag prints grams per square metre; an American one prints pounds per 1000 square feet. One pound per 1000 square feet is about 4.9 g/m², which is worth knowing before comparing two products across a border.
| Job | Typical rate |
|---|---|
| New lawn from bare soil | 35 g/m² |
| Overseeding an existing lawn | 25 g/m² |
| Repairing a bare patch | 40-50 g/m² |
Rates vary considerably with the mix — a fine ornamental blend and a hard-wearing ryegrass are not the same — so the figure on your own bag beats any table. Sowing heavier than the rate does not give a thicker lawn; it gives seedlings competing with each other.
Timing decides the result more than quantity does. Spring and early autumn are the windows, when soil is warm and moisture is reliable. The same seed at the same rate in midsummer mostly feeds birds.
Buying
- Decide the depth before pricing anything. It is the number that moves the total.
- Compare bags and bulk in the same unit — litres against cubic metres — before choosing. A thousand litres is one cubic metre.
- Check access before ordering loose: a tipper needs somewhere to tip, and a bulk bag needs machinery or a lot of friends.
- Buy graded topsoil for anything you will plant into. The cheap ungraded kind costs its saving back in weeding.
- Seed does not keep well. Buy the quantity for the job, not the biggest bag on the shelf.
Depths and sowing rates here are common horticultural practice, not standards, and vary with soil, climate and seed mix. Use the figures on your own product where they differ.