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Sieve compost

Updated: 21.10.2026

The heap looks finished until you fork it and find twigs, eggshells and lumps the size of a walnut. You want to know whether to sieve compost, which opening is enough, and what to do with the pile that will not go through. Sieving evens the crumb. It does not make home compost safe for seed, and a fine mesh on a damp heap mostly clogs. The sieves themselves, with prices and review counts, are on the [garden sieve comparison](/hub/garden-tools/garden-sieve). This page stays with the bin. We did not run a lab test. A qualifying purchase through our links can earn a commission at no extra cost to you.

The heap looks finished until you fork it and find twigs, eggshells and lumps the size of a walnut.

Our top picks

Spear & Jackson Spear & Jackson steel riddle

Best overall

Spear & Jackson Spear & Jackson steel riddle
9.2/10about £14.95
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johgee johgee garden sieve with tools

Alternative

johgee johgee garden sieve with tools
7.1/10about £27.44
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Flatro Flatro stainless sieve, 5 meshes

Best value

Flatro Flatro stainless sieve, 5 meshes
7.3/10about £14.95
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On this page
  1. 1.When the heap needs a riddle
  2. 2.What falls through, and what goes back
  3. 3.Seed compost is a different job
  4. 4.A damp heap and a small frame

When the heap needs a riddle

You do not have to sieve finished compost for a bed or a mulch. Garden Organic says a cool home heap rarely gets hot enough to kill weed roots or seeds, and that lumpy compost is still usable. A riddle is worth setting up when you want an even crumb for potting. The RHS treats a riddle as the way to sort finished compost, not as a test the heap must pass. Finished means dark, crumbly and smelling like earth, not a wet mat of last month’s peelings. Sieving a heap that is still cooking only blocks the mesh. Sieving does not make the compost sterile. The millimetre bands in full are on garden sieve mesh size.

What falls through, and what goes back

About 6–10 mm is enough for a home heap you will use on beds or in rough potting. A 10 mm plate lets a coarse crumb through and holds twigs. UK reviews use the Spear & Jackson riddle on compost and still see small stones pass, so 10 mm is not a filter for grit. Finer than that is the wrong default for a whole heap. The overs go back on the bin. The RHS says so, and Garden Organic says to put the large bits on the next heap. They are not a reason to buy a 3 mm mesh and grind them through. Knock them off the sieve into a trug and tip the trug into the top of the bin. If you see plastic, glass or a perennial root you recognise, that piece comes out of the cycle. A second, finer pass is only for the bucket you are about to pot with, not for the barrow. How full to load the frame is on how to use a garden sieve.
Spear & Jackson Spear & Jackson steel riddle

Testsieger

Spear & Jackson Spear & Jackson steel riddle
9.2/10about £14.95
View offer

Seed compost is a different job

Sieved home compost is still home compost. The RHS says peat-free seed compost is more reliable for germination than a home-made mix, and that unsterilised soil can carry weeds, pests and diseases. Sieving does not change that. A 3 mm disc makes a finer texture. It does not reach a temperature. Do not pot soil that contains oxalis, horsetail or ground elder. If you sow small seed, use a bought peat-free seed compost for the tray. A thin sieved layer over small seed is a covering, usually no deeper than the seed. The RHS says not to compost rhizomes, taproots, bulbs or seedheads at home, because a cool heap may not kill them. A sieve then spreads them evenly. Leave those pieces out when you fill the bin.

A damp heap and a small frame

Wet compost sits on the mesh because the crumbs stick to each other and to the wires. Three millimetres on a damp heap blinds in one spadeful. Ten millimetres may still pass a moist crumb and hold the twigs. If the bin is sodden, leave the cover off on a dry day, or sieve a forkful that has sat on a sheet, rather than changing down a mesh size. A thinner layer, moved across the mesh, is the whole technique. A small frame is tedious on a heap even when the opening is right. Armo’s table is 20 × 20 × 1 cm, the opening is not stated, and many UK reviews say the large title did not match. You can sieve a pot through 20 cm. You will not enjoy a full bin. A sieve that is honestly 10 mm, which you then find too coarse for a seed tray, is the wrong opening, not a broken tool.

Common questions

Do you have to sieve finished compost for a bed?
No. Lumpy compost is still usable on a border or as a mulch, which is Garden Organic’s line on a home heap. Sieve when you want an even crumb for pots or you are picking out twigs and rubbish. The bed does not need a 3 mm texture.
What opening is enough for a heap, and what is too fine?
About 6–10 mm for the bulk of a finished heap. A 10 mm plate holds twigs and lets small stones through. About 3 mm is too fine for a damp bin and belongs on a small, drier volume. One millimetre is a dust mesh, not a compost riddle.
Where do the twigs and lumps go?
Back on the bin, as the RHS and Garden Organic both describe. Keep out plastic, glass, and any weed root or seedhead you can recognise. Do not grind the overs through a finer disc to make them disappear.
Can sieved home compost go on small seed?
Not as the compost you rely on for germination. The RHS prefers a peat-free seed compost, and sieving does not sterilise a heap or remove weeds, pests and diseases. A thin sieved layer as a covering is a different, much smaller use.
What must not go into the bin in the first place?
Rhizomes, taproots, bulbs and seedheads. The RHS says a home heap may not get hot enough to kill them. Oxalis, horsetail and ground elder are the potting warning in the same spirit. A sieve will not sort those out later.

Related pages

Garden sieve buying guide

Garden sieve

Best garden sieve for stones, and who should skip it

How to use a garden sieve: load, rock and clear it

Garden sieve mesh size: stones, crumb and seed cover

Sources

Public UK sources used for this comparison. Listing prices, stars, and review counts are the amazon.co.uk lines in the product rows. A 20 October 2026 search snapshot is a price-band rule of thumb only, not a second check of these ASINs. We did not run a lab test.

  1. RHS — How to make your own potting mix (retrieved 20.10.2026)
  2. RHS — Four steps to perfect compost (retrieved 20.10.2026)
  3. RHS — John Innes potting compost (retrieved 20.10.2026)
  4. RHS — Sowing in pots (retrieved 20.10.2026)
  5. BBC Gardeners' World Magazine — How to make a soil sieve (retrieved 20.10.2026)
  6. Spear & Jackson — Garden riddle (retrieved 20.10.2026)
  7. HSE — Good handling technique (retrieved 20.10.2026)
  8. Consumer Rights Act 2015 — notes on goods remedies (retrieved 20.10.2026)