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How to repot a bonsai

Updated: October 2026

A bonsai that has sat for two or three years in fine, spent compost holds water on the surface and circles its roots. How to repot a bonsai, in a British spring, is a short sequence: use a sound open mix, work it between the roots, then shade the tree and water so the pot drains. The bag you buy stays on the [bonsai compost comparison](/hub/fertiliser-soil-and-bark-mulch/bonsai-compost). The Products Compared editorial team followed the Royal Horticultural Society bonsai page, and kept nursery leaflets separate where they disagree. This is not a lab trial. A qualifying purchase can earn a commission at no extra cost to you.

A bonsai that has sat for two or three years in fine, spent compost holds water on the surface and circles its roots.

Our top picks

Miracle-Gro Miracle-Gro cactus, succulent and bonsai compost 6 litres

Best overall

Miracle-Gro Miracle-Gro cactus, succulent and bonsai compost 6 litres
7.8/10about £9.79
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UK GROW UK GROW Bonsai Focus 5 litre bucket

Rank 2

UK GROW UK GROW Bonsai Focus 5 litre bucket
8.6/10about £10.99
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UK GROW UK GROW bonsai potting mix 30 litres

Preis-Tipp

UK GROW UK GROW bonsai potting mix 30 litres
6.6/10about £18.99
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On this page
  1. 1.When to repot in Britain
  2. 2.The sequence
  3. 3.Pines are the exception to a full strip
  4. 4.Do not use a bad bag

When to repot in Britain

Repot in spring, before growth starts. The RHS allows autumn only when the weather is mild and the tree is sheltered. Bonsai2U puts many UK trees in late February to April as the buds swell. That is a shop calendar. If it pulls away from the RHS, follow the RHS. A hard frost overnight is a reason to wait. What the bag should name before you start is on the bonsai compost buying guide.

The sequence

Have compost, mesh, wire and a chopstick ready before you free the tree. Wear gloves and avoid breathing dust. Trim only roots that stop the tree sitting back in. Mendip Bonsai's leaflet suggests cutting about 30 per cent of the root mass. That figure is one nursery's leaflet, not the RHS method. Mesh the drainage holes, and wire the tree if a balcony wind will rock a shallow pot. Chopstick the new compost under the trunk. The RHS says to, because a hollow leaves roots dry while the surface looks wet. Full sun on repotting day dries a trimmed root system.
Miracle-Gro Miracle-Gro cactus, succulent and bonsai compost 6 litres

Testsieger

Miracle-Gro Miracle-Gro cactus, succulent and bonsai compost 6 litres
7.8/10about £9.79
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Pines are the exception to a full strip

Keep some old soil on a pine. Bonsai4me says the fungi on pine roots live in that soil, and washing it off sets the tree back. Mendip's leaflet says wash the remaining soil away. Do not use that as the pine method. Pines also want a drier mix than maples. Akadama with pumice and lava is the club route, and these amazon.co.uk bags do not contain it. See bonsai compost or akadama. An indoor ficus or Chinese elm is on indoor bonsai compost.

Do not use a bad bag

A pack that arrives soaking, smells mouldy, or is full of insects is a reason to buy another bag. Do not oven-sterilise it to fix it. One Focus 5 litre review describes a second tub that smelled mouldy and had insects the buyer thought were springtails. Those insects were not identified in a lab. In the Amazon reviews, Miracle-Gro buyers often mention a wet bag. An open sack in a shed collects fungus gnats. Keep the new compost just moist. The RHS says that, and says not to leave the pot standing in a saucer. Compost is not the fertiliser.

Common questions

When do I repot a bonsai in the UK?
Repot in spring, before growth starts. The RHS allows autumn only when the weather is mild and the tree is sheltered. A UK shop guide places many trees from late February to April as the buds swell. Use that as a window inside the RHS season, not as a different rule. Skip a heatwave, and skip a week of hard frost, even if the compost looks tired.
How often should I repot?
The RHS interval is every two to three years for many bonsai, every three to five years for pines, and every year for birch. A young tree in a small pot can fill with circling roots sooner. Lift the tree and look before you decide from the calendar alone. If the root ball is still open and the compost still drains, you can wait another season.
Do I wash all the old compost off?
On most deciduous trees, clear enough fine old compost for new mix to reach the roots, without scalping the whole ball. On a pine, leave the old soil against the trunk. Bonsai4me warns that washing a pine bare removes the fungi the roots rely on. A nursery leaflet that says wash off the remaining soil is not the method to copy for pines.
How do I get new compost between the roots?
Settle the tree, then poke fresh compost down with a chopstick until the gap under the trunk is filled. Water until it runs from the drainage holes, then let the pot drain. A pot you only top up from the rim often hides an air pocket. Shade the tree afterwards, for about three weeks if you follow the Mendip leaflet, or until it has settled if you follow the RHS wording.
When do I start feeding after repotting?
Follow one source, not a blend of them. The RHS says a low-dose balanced liquid feed every two weeks in the growing season, once any slow-release added at repotting is spent. Mendip Bonsai says wait four weeks, then use their Bonsai Focus feed. The bag of compost is not a feeding plan. Yellow leaves later on can mean the tree is hungry, which is separate from a pot that stays wet.
When should I stop and ask a club?
Ask before you touch an old or valuable tree, a pine whose root ball is a solid mass, a pot with wires you cannot trace, or a tree that is already sour and wilting in hot weather. Those are the cases where a Saturday repot does more harm than a tired mix. A small, healthy garden-centre tree in spring, with a hole in the pot and a bag you have checked for mould, is the repot this page describes.

Related pages

Bonsai compost

Best bonsai compost for the job in front of you

Bonsai compost buying guide: five pre-buy checks

Indoor bonsai compost on a British windowsill

Bonsai compost or akadama, and when to choose

Sources

Public UK sources from the research digest, used for this page in October 2026. Prices, stars and review counts are the figures stored from the eleven amazon.co.uk listings in this set. A drainage line, an all-types line and a peat-free line are listing claims. This is not a laboratory test. Selling peat compost was not shown to be an England-wide offence on 19 October 2026.

  1. RHS, bonsai advice (retrieved October 2026)
  2. RHS, peat-free exhibitor tips (retrieved October 2026)
  3. RHS, retail peat-free from January 2026 (retrieved October 2026)
  4. GOV.UK, Defra peat sales announcement, 27 August 2022 (retrieved October 2026)
  5. UK Parliament deposited paper DEP2026-0072, 29 January 2026 (retrieved October 2026)
  6. Bonsai4me, an introduction to bonsai soils (retrieved October 2026)
  7. Cheshire Bonsai Society, Japanese maples as bonsai (retrieved October 2026)
  8. BBC Gardeners’ World, indoor bonsai tree care (retrieved October 2026)