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Peat-free soil blocking: how to stop cubes crumbling

Updated: October 2026

You sieved a bag of peat-free compost, pressed four cubes, and they crumbled on the tray or slumped in the bath. Peat-free soil blocking is a binder problem, not a reason to put the press back in the drawer. Bagged peat-free mix is built for pots. It is often barky, short of clay, and sold at potting damp, so a cube has nothing to knit with. The fix is a sieve, a simple home ratio, and water past that potting feel. Peat is not already illegal in UK garden centres. Cards stay on the [Soil blocker comparison](/hub/fertiliser-soil-and-bark-mulch/soil-blocker). Nobody here ran a cube trial. A qualifying purchase can earn a commission at no extra cost to you.

You sieved a bag of peat-free compost, pressed four cubes, and they crumbled on the tray or slumped in the bath. Peat-free soil blocking is a binder problem, not a reason to put the press back in the drawer.

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On this page
  1. 1.Why the bag crumbles
  2. 2.A working home mix
  3. 3.Watering and feeding peat-free cubes
  4. 4.Peat policy in 2026

Why the bag crumbles

A peat-free multi-purpose bag is full of woody fragments so a pot drains. In a 50 mm cell those chips are fault lines. The cube splits on eject. The RHS wants a fine mix for seeds and cuttings, but a seed bag is usually too dry, and short of mineral fines, if you tip it straight in. A little loam is the binder most bags omit. Perlite stops that loam and the extra water turning the cube into a pudding. A UK home pointer is three parts sieved peat-free, one part perlite, one part loam. Skip the weep and no ratio holds. Garden soil alone brings weed seed and can set like a brick. Use a little bagged or sterilised loam. Tiny cubes want a finer, less rich blend.

A working home mix

Sieve peat-free compost through about 6 mm. Mix three parts of that with one part perlite and one part loam, then add water until a squeezed handful holds and weeps. If the loam is heavy, cut it. If the cube still cracks, you are dry, not short of a branded additive. A fine seed bag can work without the full 3:1:1 if you wet it to a weep. Unsieved multi-purpose fails first. Nursery recipes exist, and this page will not turn them into grams. Micro 20 cubes are about 2 cm. Do not fill a 20 mm cell with lumpy multi-purpose. Peat-and-grit scoop lists are one grower's system, not a UK requirement. When a handful holds, charge twice, scrape, and eject. That sequence sits on how to use a soil blocker.
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Watering and feeding peat-free cubes

The RHS peat-free note says the surface can look dry while the core is still wet, and barky blends can grow toadstools. Poke below the surface. If the finger comes out damp, wait. If it comes out dry, stand the tray in water for 10-15 minutes and empty it. An overhead rose strips the fines you just sieved. Feed after true leaves, not on sowing day, at the weak end of a seedling feed you already trust. Stop if edges brown. A 20 mm cube on a heat mat may need potting on more than a feed. Damping-off is hygiene and wet faces. Clean the tray and empty the bath. Toadstools on a cube you will plant soon are a moisture check, not a reason to bin the press. If cubes stay wet and collapse, add perlite next time or empty the tray. If they dust apart, you skipped loam or the weep.

Peat policy in 2026

A retail peat ban has been proposed. As of the March 2026 written answer, the government line is to legislate when Parliamentary time allows. That is not an enacted nationwide shop ban. Garden centres and amazon.co.uk still sell peat and peat-free side by side. A peat bag you already own is not illegal. The same sieve-and-weep rules apply if you use it. Northern Ireland's product-safety file for tools, from 13 December 2024, is about the press, not the bag. BS 3882 is a topsoil specification, not a soil-blocker mix standard. Do not hang a home 3:1:1 on that number. Method versus modules sits on soil blocker or module trays.

Common questions

Can I block straight from a peat-free bag?
Sometimes, if it is a fine seed compost and you wet it to a weep. A barky multi-purpose usually needs a 6 mm sieve and a binder. Straight from the bag at potting damp is the mix that crumbles on eject.
What is a simple home ratio?
A UK rule of thumb is three parts sieved peat-free, one part perlite, one part loam, then water until a handful weeps. It is not a lab recipe. Cut the loam if it is heavy. Other nursery mixes exist and are not copied here as grams.
Why add loam?
Loam brings mineral fines that help the cube smear and hold. Peat-free bags often rely on bark and fibre, which drain a pot and split a cube. Garden soil from the border is not a substitute: it brings weed seed and can set like a brick.
Is peat already banned in garden centres?
No. A retail ban has been proposed. As of 2026 the line is to legislate when Parliamentary time allows. Peat and peat-free bags are both still sold. Do not treat a peat bag you already own as illegal.
When do I start feeding?
After true leaves, following the RHS seed-and-cuttings note. Do not feed the day you sow. Use a weak peat-free seedling feed and pot on a 20 mm cube before you try to feed it into a tomato.
Can I use garden soil alone?
No. Stones, weed seed, and a set that is too hard for a 50 mm cube make it a poor whole mix. A small fraction of bagged or sterilised loam is the binder, not a trowel of the bed.
Why do peat-free cubes look dry but stay wet inside?
That is the RHS peat-free surface trap. Bark and wood fibre pale on top while the core stays damp. Poke below the surface before you bathe again, and empty the tray so cubes do not sit in water.

Related pages

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How to use a soil blocker so the cubes do not crumble

Soil blocker vs seed trays: cubes or plastic cells

Sources

Public UK and maker sources from the research digest, used for this page in October 2026. Prices, stars and review counts are from the seven amazon.co.uk listings in this set. A German review line is not a UK sample. Ladbrooke prices are market context from the maker's site. A nationwide shop ban on peat compost has not been enacted.

  1. RHS, how to garden without plastic (retrieved October 2026)
  2. RHS, peat-free compost for seeds and cuttings (retrieved October 2026)
  3. Ladbrooke soil blocker hand tools (retrieved October 2026)
  4. Garden UK, soil blocking in the UK (retrieved October 2026)
  5. GOV.UK, General Product Safety Regulations 2005 (retrieved October 2026)
  6. GOV.UK, product safety advice for businesses (retrieved October 2026)
  7. Blackberry Lane, soil blocker notes (retrieved October 2026)
  8. Consumer Rights Act 2015 (retrieved October 2026)