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How to use peat-free compost

Updated: October 2026

The bag is open on the patio, the surface looks pale, and you are about to water the whole pot until it shines. How to use peat-free compost, for the first fortnight, is mostly a refusal to do that. Many peat-free and wood-based mixes look dry on top while the root zone is still wet, and a rich bag such as All Mix is on a different feed clock from a light one. Which bag you should have bought stays on the [best organic compost](/hub/fertiliser-soil-and-bark-mulch/bio-compost/sub/bio-compost-best) page. The [bio compost comparison](/hub/fertiliser-soil-and-bark-mulch/bio-compost) holds the five prices. This page is the first two weeks after you cut the sack. It is not a personal trial.

The bag is open on the patio, the surface looks pale, and you are about to water the whole pot until it shines. How to use peat-free compost, for the first fortnight, is mostly a refusal to do that.

Our top picks

BioBizz BioBizz Light Mix 20 L

Best overall

BioBizz BioBizz Light Mix 20 L
9.4/10about £10.44
View offer
BioBizz BioBizz Light Mix 50 L

Rank 2

BioBizz BioBizz Light Mix 50 L
10.0/10about £17.15
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BioBizz BioBizz All Mix 20 L

Alternative

BioBizz BioBizz All Mix 20 L
8.6/10about £10.70
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On this page
  1. 1.Before the plant goes in
  2. 2.Watering in the first weeks
  3. 3.When to feed
  4. 4.Flies, mould, and leftovers

Before the plant goes in

All Mix is the bag with a wait. BioBizz tells you to moisten it and leave it 36 hours before planting. The amazon listing calls it a strong pre-fertilised soil and does not repeat the 36 hours, so the wait comes from the maker. One reviewer lost tomato starters and described the mix as too rich. DIVCHI is a compressed block: add water in stages until the centre is damp. The listing does not state a jug size.

Watering in the first weeks

Water by the root zone, not by the colour of the surface. Push a finger in, or lift the pot. The RHS advice for peat-free compost is little and often, rather than a weekly soak. If it sheets off the root ball, stand the pot in a tray for a short drink, then tip the tray away. Constantly wet surfaces are where fungus gnats breed.
BioBizz BioBizz Light Mix 20 L

Testsieger

BioBizz BioBizz Light Mix 20 L
9.4/10about £10.44
View offer

When to feed

Light Mix is the early feed. BioBizz describes it as lightly fertilised and expects liquid feed from early on. All Mix is the later feed. BioBizz says the heavy pre-fertilising covers about a couple of weeks. Feeding on day one, on a bag the listing already calls strong, repeats the tomato-starter problem. Which? and Garden Organic use about four weeks as a rule of thumb for many composts. Use the couple of weeks for All Mix if you are following BioBizz. The two bags are compared on Light Mix versus All Mix.

Flies, mould, and leftovers

A few fungus gnats on a wet windowsill are a watering and storage problem. Let the surface dry and close the sack. A whole bag that is crawling when you open it is a different case. Contact the seller and do not sow the rest of the tray into it. Do not tip leftovers on the border. The RHS tells gardeners not to use potting compost on beds.

Common questions

Do I water peat-free compost more often?
You water little and often, which can mean more frequent small drinks and fewer deep soaks. The RHS puts it that way for peat-free mixes. The surface dries and looks needy while the roots are still damp, so a daily flood is the mistake. Lift the pot or use a finger under the surface before you add water. A mix that has fully dried can shed water until you rewet it slowly.
How do I know if the pot is actually wet?
Check under the surface, or weigh the pot in your hand. A pale top on Light Mix, All Mix, or a peat-free houseplant bag is not proof the root ball is dry. A glossy surface is not proof the middle is wet. If water runs straight down the gap at the pot wall, the root ball has shrunk and needs a short soak, then a drain. Do not leave the pot in a full saucer.
When do I start liquid feed on Light Mix versus All Mix?
On Light Mix, BioBizz expects feed from early on, because the mix is lightly fertilised. On All Mix, the maker says the pre-fertilising covers about a couple of weeks, after a 36-hour wait before planting. Which? and Garden Organic use about four weeks as a rule of thumb for many composts. That four weeks is not these listings' analysis. Do not feed All Mix on day one on top of a bag already sold as strong.
How do I expand a compressed block without a dry core?
Break the DIVCHI block up and add water in stages, then wait and check the centre before you pot. Reviewers describe expansion, and some say the result looks short of the 10 litre claim. The listing weighs 680 g and does not print a water volume, so this page will not give you one. Stop when the crumbs are damp through. More water will not create litres the block does not contain.
What do I do with the compost I do not use tonight?
Close the sack and keep it cool and dry. An open bag in a warm room is the storage Which? ties to fungus gnats. Do not leave a wet trug of All Mix uncovered for a week and then call the mould a defect. Use the closed sack in pots. Do not spread it as a mulch on the border.
Are fungus gnats a sign the bag is faulty?
A few gnats after a wet week are usually a surface-moisture problem, and Westland and Light Mix reviews both mention them without every buyer reporting them. Let the top dry and close stored compost. If you open a new bag and the whole sack is infested, or plants collapse at once, stop using it and take it up with the seller. A star rating does not prove a bag is free of gnats.
Can I tip the leftovers on the border?
No. The RHS says not to use potting compost as a mulch on beds. It is mixed for containers, not for blanketing soil. Leftover Light Mix or All Mix belongs in another pot, or in the closed sack until you have one. Garden compost from a heap is the material for the border, and it is a different product from these bags.

Related pages

Bio compost comparison

Best organic compost UK

Light Mix versus All Mix

Organic compost buying guide: size, feed and labels

Is peat compost banned in the UK? What is in force

Sources

Public UK and maker sources from the research digest, used for this page in October 2026. Prices, stars and review counts are the amazon.co.uk figures stored for these five listings. Organic wording is not a certifier. All Mix's peat line is the maker's blend article, not a test of the bag in your hand. No ban on amateur peat sales is in legislation.

  1. Defra, horticultural peat announcement, 27 August 2022 (retrieved 19 October 2026)
  2. RHS, peat-free choices (retrieved 19 October 2026)
  3. Peat Free Partnership, legislation timeline (retrieved 19 October 2026)
  4. Environment Agency, compost resource framework (retrieved 19 October 2026)
  5. Soil Association, approved and verified inputs (retrieved 19 October 2026)
  6. Garden Organic, garden compost or potting compost (retrieved 19 October 2026)
  7. BioBizz, behind the blend (retrieved 19 October 2026)
  8. Which?, fungus gnats (retrieved 19 October 2026)