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Horticultural vermiculite buying guide

Updated: October 2026

A horticultural vermiculite buying guide has to start before the stars, because the bag in front of you may list 5 L, 25 L and 100 L in one title and never state a millimetre grade. You need the flake size for the job, then the litres that will actually arrive. The ranked packs are on the [vermiculite for plants comparison](/hub/ornamental-plants/vermiculite-for-plants). The Products Compared editorial team used the amazon.co.uk extracts and UK growing notes dated 15 October 2026, and did not laboratory-test the flakes. A qualifying purchase can earn a commission at no extra cost to you.

A horticultural vermiculite buying guide has to start before the stars, because the bag in front of you may list 5 L, 25 L and 100 L in one title and never state a millimetre grade.

Our top picks

PLANT!T PLANT!T vermiculite 100 L

Best overall

PLANT!T PLANT!T vermiculite 100 L
8.8/10about £42.95
View offer
UK GROW UK GROW vermiculite bag 25 L

Best value

UK GROW UK GROW vermiculite bag 25 L
8.0/10about £19.99
View offer
Swiftair Swiftair vermiculite 10 L

Alternative

Swiftair Swiftair vermiculite 10 L
4.4/10about £8.99
View offer
On this page
  1. 1.Fine, medium, or a grade the listing never states
  2. 2.Litres in the parcel, not the largest number in the title
  3. 3.Price per litre only after the volume line agrees
  4. 4.What the listing does not prove

Fine, medium, or a grade the listing never states

Fine vermiculite, often around 0–2 mm or 1–3 mm, is the grade that covers seed. Medium, often called V3 and sold around 2.0–5.0 mm, belongs in a potting or cuttings mix. A wide band such as 2–8 mm or 1–8 mm is a mixed flake, and it will not make a thin cover over dust-like seed. UK GROW bags in this set print no millimetres. Swiftair's 10 L title says 2.0–5.0 mm, then one bullet says coarse and another says fine. If the listing is silent, the grade is unknown until you open the bag. Depth for a fine cover is on the vermiculite for seed sowing page.

Litres in the parcel, not the largest number in the title

Read the variant and the bullets, not the biggest number in the title. On PLANT!T B01DYDV6WU the bullets say you receive 25 L boxed from a trade bag, not 100 L, while the title still lists 100, 50, 25, 10 and 5 litres. Reviews say the picture implied 100 L. Topline's listing is titled as two 10 L Gro-Sure bags at £22.99, and the item-volume line says 10 litres, so there is no honest price per litre. The UK GROW 5 L and 20 L buckets share one block of 4.5 from 406 ratings, so the star row may be the parent listing. Without a dry bin, stop at 25 L on the best vermiculite for plants page.
PLANT!T PLANT!T vermiculite 100 L

Testsieger

PLANT!T PLANT!T vermiculite 100 L
8.8/10about £42.95
View offer

Price per litre only after the volume line agrees

Shelf prices in the extracts, dated 15 October 2026, include these bulk figures. UK GROW 50 L is £29.99, the B2C mix is £32.49, and PLANT!T 100 L is £42.95, about 43 pence a litre. From 10 L upward, pure vermiculite here sits around 40 pence to £1 a litre, as a rule of thumb from these shelf prices, not a weighed test. Buy 100 L only with dry storage and a season of use. Otherwise the 25 L bag, about 80 pence a litre with 87 reviews, is the more honest volume. Share sizes are on the how to use vermiculite for plants page.

What the listing does not prove

None of the kept amazon.co.uk extracts print an RHP mark, so do not call these bags certified because another seller uses that logo. A pH-neutral line on the 50 L UK GROW listing, and toxin-free wording elsewhere, are seller sentences with no laboratory sheet attached. The B2C 100 L bag is half perlite, so its price per litre is not a pure vermiculite bargain.

Common questions

Should I buy fine or medium vermiculite for covering seed?
Buy a fine grade, often around 0–2 mm or 1–3 mm, when the seed needs a thin cover. Medium flakes around 2–5 mm suit potting and cuttings, and they leave gaps over dust-like seed. A listing with no millimetres is unknown until you open the bag.
Is the PLANT!T 100 L bag a fine seed cover?
The amazon.co.uk listing for the 100 L PLANT!T bag does not print millimetres. Grow shops call that brand V3 medium, about 2.0–5.0 mm, and reviewers describe chunky flakes and still buy a finer grade for sowing. It can be the right bulk bag for mixing into compost. It is the wrong assumption if you need a 2 mm cover over fine seed.
Should I buy 10 litres or 100 litres?
Buy about 10 L, or a 5–25 L pack, for windowsill trays or a couple of sacks of compost. Buy 100 L if you will use it across a season and can keep it dry. At the extracted prices, PLANT!T 100 L is about 43 pence a litre and a 10 L bag here is closer to 90 pence. The saving disappears if the sack gets damp.
Why does the title list 5 L, 25 L and 100 L?
Amazon titles often carry every size the brand sells. The litres you receive are the variant and the bullets, not the biggest number in the headline. On the PLANT!T split, the bullets say 25 L from a trade bag while the title still mentions 100 L. Reviews say the picture implied the larger sack, so read the bullet before you compare stars.
Is a 50/50 mix the same as pure vermiculite?
No. The B2C 100 L bag is half perlite and half vermiculite, graded 1–8 mm, at £32.49. Perlite opens the mix and vermiculite holds water, so the bag is not a pure seed cover. There is no customer-review line on that extract. If you wanted only vermiculite, choose a pure listing and accept a higher price per litre.

Related pages

Vermiculite vs perlite

Vermiculite for plants

Best vermiculite for plants: the top pick and value

How to use vermiculite for plants in UK compost mixes

Vermiculite for seed sowing: depth, grit and cover

Sources

Public sources used for this comparison. Prices are amazon.co.uk shelf prices from the listing extracts dated 15 October 2026.

  1. RHS seed germination guide (retrieved 15 October 2026)
  2. RHS peat-free advice (retrieved 15 October 2026)
  3. RHS houseplant growing media (retrieved 15 October 2026)
  4. BBC Gardeners' World: how to use vermiculite (retrieved 15 October 2026)
  5. Westland Gro-Sure vermiculite (retrieved 15 October 2026)
  6. HSE COSHH basics (retrieved 15 October 2026)
  7. HSE EH44 dust guidance (retrieved 15 October 2026)
  8. US EPA: horticultural vermiculite in potting soil (retrieved 15 October 2026)
  9. Summit Environmental (UK): vermiculite insulation versus horticultural bags (retrieved 15 October 2026)