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Orchid compost buying guide before you trust stars

Updated: October 2026

You have a moth orchid on a UK windowsill, and the amazon.co.uk results all say orchid compost. This orchid compost buying guide is the order to use before you compare stars: which plant you have, what chip size it needs, how many litres you will use, whether the bag claims feed or peat free, and what the price per litre is once the volume field agrees with the title. The [orchid soil comparison](/hub/fertiliser-soil-and-bark-mulch/orchid-soil) holds the eight kept bags and their GBP prices. The Products Compared editorial team wrote this on 21 October 2026 from those listings and from public UK growing guides, with no lab trial. A qualifying purchase can earn a commission at no extra cost to you.

You have a moth orchid on a UK windowsill, and the amazon.co.uk results all say orchid compost.

Our top picks

Westland Westland Orchid Potting Mix 8 L

Best overall

Westland Westland Orchid Potting Mix 8 L
8.7/10about £8.40
View offer
UK GROW UK GROW orchid bark and perlite 5 L

Alternative

UK GROW UK GROW orchid bark and perlite 5 L
8.8/10about £9.99
View offer
Miracle-Gro Miracle-Gro Peat Free Orchid 10 L

Best value

Miracle-Gro Miracle-Gro Peat Free Orchid 10 L
8.5/10about £6.00
View offer
On this page
  1. 1.Start with the plant, not the brand
  2. 2.Chip size and what the listing actually names
  3. 3.Litres, settle, and the unit-count field
  4. 4.Feed, peat-free wording, and price per litre

Start with the plant, not the brand

BBC Gardeners' World splits orchid compost by genus: moth orchids and cymbidiums towards pine bark of about 8–15 mm, other types towards about 5–8 mm. Slipper orchids are a different handmade mix, and a Vanda is often grown with no compost in the pot. Clay pebbles and keiki paste were taken out of this basket because they are not a rooting medium. If the label says Paphiopedilum or Vanda, a default moth-orchid bag is the wrong assumption. One genus in a heated room is on Phalaenopsis compost.

Chip size and what the listing actually names

None of the eight amazon.co.uk titles prints a millimetre grade. Chunky and large pieces are adjectives, not 12 mm. Three retail types remain. Bark plus perlite is the UK GROW pattern, and the Black Soil Society 5 litre mix at £13.99. Bark plus Seramis is Westland, at £7.29 for 4 litres and £8.40 for 8 litres. Miracle-Gro's 10 litre bag is the nutrient-added compost that says peat free on the Amazon title. Seramis in that Westland mix buffers water. It is not a bag of expanded clay balls.
Westland Westland Orchid Potting Mix 8 L

Testsieger

Westland Westland Orchid Potting Mix 8 L
8.7/10about £8.40
View offer

Litres, settle, and the unit-count field

Miracle-Gro's label says volume may fall by up to 10% as the contents settle. The UK GROW 1 litre pouch at £7.99, or the 2 litre bucket at £8.99, can still be the right storage choice beside a 10 litre sack. The UK GROW 1 litre and 5 litre listings both carry a unit count of 1.0 gram. A 5 litre title at 1.2 kg cannot be 1 gram, and a 1 litre title at 250 g cannot either. Black Soil Society's 5 litre title has a unit count of 1,000 g against a 1.7 kg item weight. Do not divide the shelf price by a litre figure the page contradicts.

Feed, peat-free wording, and price per litre

Bark with perlite, or bark with Seramis, is structure unless the listing states a feed. UK GROW's 5 litre file claims essential nutrients and prints no analysis. Miracle-Gro claims 11 nutrients and says to feed after four weeks. Do not copy that line onto a bark-only bag. Westland's saved Amazon bullets do not state a feed. Only Miracle-Gro, at £6.00 and about £0.60 a litre, says peat free on the Amazon title and bullets. Westland's own site describes an 8 litre mix as peat free. The Amazon bullets, at £8.40, do not. Selling peat compost is not already banned in England. Named roles sit on best orchid compost.

Common questions

Is orchid compost the same as multipurpose compost?
No. The RHS says a moth orchid needs loose bark-based compost, not loam or multipurpose compost. Ordinary houseplant compost holds water around roots that are used to drying between waterings. A bag titled orchid compost can still be the wrong texture if it is mostly fines, so the name on its own is not the check. Match the genus first, then look at what the listing actually names as bark, perlite, or clay granules.
What bark size does a moth orchid need?
Gardeners' World points moth orchids and cymbidiums towards about 8–15 mm pine bark, and other orchid types towards about 5–8 mm. Those figures are a grower's split. None of the eight kept amazon.co.uk titles prints a millimetre grade, so chunky on a listing is not 12 mm. Tip a dry handful out. Pieces longer than a little fingernail, with little powder, are nearer the coarser band. Dust will stay wet in a plastic pot.
How many litres should I buy for one supermarket orchid?
One 12 cm plant does not need 10 litres. Miracle-Gro's own line says 10 litres fills six 12 cm pots, one 22 cm pot, or one 30 cm hanging basket, and the label allows the volume to settle by up to 10%. A seller rule of thumb from Allgood Farm is about 1 litre for an 11 cm pot. A 1 or 2 litre pack can be the sensible buy if you have nowhere to keep an open sack, even when the price per litre is higher.
How do I know the bag is peat free?
Read the title and the bullets, not the word bark. In this saved set, only the Miracle-Gro 10 litre listing says peat free on Amazon. Westland's maker page and a B&Q page describe an 8 litre mix as peat free, but the saved Amazon bullets for those Westland ASINs do not. Peat free is an absolute environmental claim under the CAP Code, so it has to be on the pack you are buying. An England-wide retail peat ban was not in force on the Defra update of 12 September 2024.
Why does the Amazon unit count say 1 gram on a 5 litre title?
On the UK GROW 1 litre and 5 litre bark-and-perlite files, the unit count field says 1.0 gram while the titles say litres. The 5 litre listing also shows a 1.2 kg item weight, which cannot be a 1 gram fill. Treat the litre title and the volume field as the claim, and do not calculate a price per litre from the gram field. BS EN 12580:2013 covers declared volume, not bark quality.

Related pages

Orchid bark or moss

Orchid soil

Best orchid compost UK: top pick and best-value bag

How to repot a moth orchid into bark-based compost

Phalaenopsis compost for a UK windowsill moth orchid

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 eight amazon.co.uk listings read on 21 October 2026. A peat-free line is quoted only where the listing or the maker's UK page prints it. A sterilised claim is seller text. Stars are not a laboratory test, and a shared review file is not a second trial.

  1. RHS, Phalaenopsis growing guide (retrieved 21 October 2026)
  2. BBC Gardeners' World, how to care for orchids (retrieved 21 October 2026)
  3. GOV.UK, horticultural peat sale announcement (retrieved 21 October 2026)
  4. Defra written answer, 12 September 2024 (retrieved 21 October 2026)
  5. Westland orchid potting mix (retrieved 21 October 2026)
  6. Miracle-Gro peat-free orchid compost 10 L label (retrieved 21 October 2026)
  7. RHS, minimising health risks in the garden (retrieved 21 October 2026)
  8. Sheffield & District Orchid Society, Phalaenopsis cultivation (retrieved 21 October 2026)