How to sieve compost and use the different grades

Illustration of a wooden compost bay and a garden fork

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Sieving compost is a simple way to turn a rough, lumpy heap into material with a consistent texture suited to specific garden jobs. The process separates compost into grades based on particle size, and each grade has different uses, from fine ingredients for suitable growing mixes to coarser material for mulch.

Table of Contents

Why sieve compost?

Freshly made garden compost often contains a mix of decomposed material, twiggy bits, stones and occasional uncomposted lumps. The RHS guide to making your own potting mix recommends sieving garden soil and organic matter to remove stones, debris and large clumps before mixing. Sieving does the same for compost: it removes unwanted material and creates a more uniform product.

Not all compost needs sieving. For general soil improvement, unsieved compost is perfectly good and retains its coarse structure, which helps open up heavy soils. Sieving becomes useful when you need a fine, even texture for seed sowing, potting mixes or top dressing.

How to sieve compost

You will need a garden sieve or riddle, a wheelbarrow or trug to catch the sieved material, and a shovel or trowel. Choose a sieve with a mesh size appropriate to the grade you want. A 5mm sieve is mentioned in RHS guidance for preparing loam for John Innes compost, and a similar fine mesh is a good starting point for seed-sowing compost. For coarser grades, use a larger mesh.

Work with compost that is moist but not wet. Dry compost can be dusty, while wet compost clogs the mesh and forms balls. Add a shovelful at a time to the sieve, then shake it or rub the material through with gloved hands or the back of a trowel. Do not force hard lumps through; set them aside and return them to the compost bin for further decomposition.

Sieving is easiest when the compost is mature and crumbly. If the material is still fibrous or contains many uncomposted pieces, it will not pass through a fine mesh easily. In that case, use a coarser sieve or leave the compost to mature longer.

Store each grade separately in labelled bags or bins. Fine grade dries out quickly, so keep it covered until you are ready to use it.

The different grades and their uses

By changing the mesh size, you can produce three broad grades from the same compost heap. The table below summarises what each grade looks like and where it is most useful.

Grade	What it looks like	Best uses
Coarse	Larger pieces, twiggy bits, some lumps	Mulching and soil improvement, when sufficiently decomposed
Medium	Crumbly, few small lumps	General potting mixes, raised beds
Fine	Uniform, no visible lumps or stones	Suitable growing-mix ingredients or thin lawn top dressing; not automatically safe for seedlings

The RHS topsoil buying guide describes a similar principle for purchased topsoil: general-purpose grade is sold in different screen sizes, with coarser grades useful for turf laying and finer grades for top dressing lawns. When you sieve your own compost, the same logic applies.

Fine grade

Fine compost passes through a small mesh, typically around 5mm, and has no visible lumps, stones or twiggy bits. Fine particle size is useful in some growing mixes, but garden compost does not become a suitable seed or cutting compost merely by sieving. Nutrient levels, drainage and disease risks still matter; use a suitable purpose-made mix for vulnerable seedlings. RHS guidance on John Innes seed compost specifies sieving loam through a 5mm sieve before mixing, which removes stones and large particles that could hinder germination.

Fine compost can also be used to top dress lawns, where a smooth, even layer is needed. However, because fine sieving removes some of the coarser organic matter, it may not improve soil structure as much as unsieved compost. Use it only where a fine texture is essential.

Medium grade

Medium compost passes through a mesh larger than the fine sieve, leaving a crumbly material with a few small lumps. This grade is a good all-rounder for general potting mixes, raised beds and planting holes. The RHS guide to making your own potting mix suggests sieving organic matter to remove large clumps before mixing with garden soil; a medium grade is usually sufficient for this purpose.

Medium compost retains more structure than fine compost, so it helps with drainage and aeration in containers while still being easy to work with.

Coarse grade

Coarse compost is what remains on top of a medium or fine sieve, or what passes through a very large mesh. It contains larger pieces, twiggy bits and perhaps small stones. This grade is best used as a mulch around established plants, where it will slowly break down and feed the soil. Do not put coarse material in the bottom of a pot as a drainage fix. Use a suitable growing mix and unobstructed drainage holes; return unfinished woody fragments to the compost heap.

Coarse compost is not suitable for seed sowing or fine potting mixes because the large particles can create air pockets and make it difficult for small roots to establish.

Practical limitations

Sieving compost is not always necessary, and it has some drawbacks. It is labour-intensive, especially for large volumes. If you only need compost for mulching or soil improvement, skip the sieve and use the material as it is.

Fine sieving removes coarse organic matter that contributes to long-term soil structure. Over-sieving can leave you with a material that is too fine and prone to compaction in containers. For most garden uses, a medium grade is a good compromise.

Moisture content affects how well compost sieves. Very wet compost will clog the mesh, while very dry compost can be dusty and unpleasant to work with. Aim for a damp but crumbly consistency.

Finally, sieving does not improve the quality of the compost itself. If the compost is not fully decomposed, sieving will not make it ready for seed sowing; the fine material may still contain pathogens or weed seeds if the heap did not heat up properly. Use mature, well-rotted compost for fine grades.

Choosing a sieve

For occasional use, a simple hand-held garden sieve or riddle is sufficient. Look for one with a sturdy frame and a mesh that can be swapped or that comes in different sizes. A 5mm mesh is useful for fine grades, while larger meshes suit medium and coarse grades.

If you sieve large amounts of compost regularly, a rotary compost sieve can speed up the work. These have a drum that you turn, which pushes compost through the mesh while larger material moves to one end. Check that the drum capacity matches the volume you typically handle and that the mesh can be changed.

Whichever type you choose, check the mesh aperture size before buying, and make sure the sieve fits over your wheelbarrow or trug. A galvanised steel mesh is more durable than plastic, but plastic sieves are lighter and easier to handle.

Useful products for this job

The links below open Amazon UK product searches. Check the exact item, seller, current price and compatibility before buying.

Garden sieve or riddle with interchangeable mesh sizes: Allows you to produce different compost grades by swapping mesh panels. Check mesh aperture sizes (a 5mm mesh is useful for fine grades; larger meshes suit coarser grades), frame material, and whether it fits over your wheelbarrow or trug. Search Amazon for Garden sieve or riddle with interchangeable mesh sizes.
Rotary compost sieve: Speeds up sieving larger volumes of compost. Confirm drum capacity, mesh size, and whether it handles moist compost without clogging. Search Amazon for Rotary compost sieve.

Related garden guides

Sources and further guidance

Guidance researched in September 2026. The feature image is an AI-generated illustration. Product guidance is based on published information, not hands-on testing.