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How to use Seramis granules

Updated: October 2026

The bag is in the hallway and the plant is waiting. How to use Seramis granules depends on what you actually bought: a closed-pot clay fill, a Hydroleca or pumice job, or a compost that only names Seramis. Those three water cycles do not share a calendar. The ten packs are named on the [Seramis granules comparison](/hub/fertiliser-soil-and-bark-mulch/seramis-granules). Why expanded pebbles dry at the top while open-pore clay stays wet is on [Seramis granules or LECA](/hub/fertiliser-soil-and-bark-mulch/seramis-granules/sub/seramis-granules-or-leca).

The bag is in the hallway and the plant is waiting. How to use Seramis granules depends on what you actually bought: a closed-pot clay fill, a Hydroleca or pumice job, or a compost that only names Seramis.

Our top picks

COMPO COMPO pumice granules 6 L

Best overall

COMPO COMPO pumice granules 6 L
9.4/10about £29.78
View offer
Westland Westland orchid mix 4 L

Best value

Westland Westland orchid mix 4 L
9.2/10about £7.29
View offer
Westland Westland Hydroleca 10 L

Rank 3

Westland Westland Hydroleca 10 L
9.2/10about £13.55
View offer
On this page
  1. 1.Check what you actually bought
  2. 2.Closed-pot clay method
  3. 3.Hydroleca, LECA grit and pumice
  4. 4.Seramis-named composts

Check what you actually bought

Read the bag before you pick a pot. Branded Seramis is a watertight pot, soil ball left on, red and blue indicator. Hydroleca 10 L and Invigortex 1 L are a top, a crock, a mix, or a humidity tray. COMPO pumice 6 L is 2–5 mm grain, used neat, at up to 25 per cent, or as a 2–3 cm top. Westland orchid, UK GROW houseplant, UK GROW cactus and Topline citrus are compost. Pot them as compost. A watertight pot of Hydroleca, watered like Seramis, leaves a wet base. Pour dry clay or LECA in a ventilated room and do not inhale the dust. Labels and litres are on the Seramis granules buying guide.

Closed-pot clay method

Use a clean watertight pot about a third larger than the root ball. Fill about one third with granules, set the plant with most of the soil ball left on, and fill around it to about two thirds granules. Fit the indicator so you can read it in place. The first drink is about a quarter of the pot volume. Wait until the indicator is fully red. Blue means wait, and the colour can lag two to four hours. Outdoors, put holes 3–6 cm up the wall. A wide hole in the base is not this method. Replace tired granules on a 12–18 month rule of thumb. Black, soft roots on a large plant are a nursery job.
COMPO COMPO pumice granules 6 L

Testsieger

COMPO COMPO pumice granules 6 L
9.4/10about £29.78
View offer

Hydroleca, LECA grit and pumice

Use Hydroleca as a decorative top, a crock before compost, about one part pebbles to three parts compost, or a humidity tray. The brand page also uses a 2 cm moist layer on a greenhouse bench. Rinse a dusty bag. Ball size in the 10 litre bag varies. Invigortex grit blends at 20–50 per cent or sits as a top layer. Rinse, sterilise and reuse it. That is drainage, not a Seramis closed fill. COMPO pumice is neat substrate, up to 25 per cent in a mix, or a 2–3 cm top, and grain colour is the wet or dry cue. Check the grade: some bags arrived finer or coarser than 2–5 mm. If you bought pebbles, use pebble jobs. A sealed cachepot is the open-pore method, not this one.

Seramis-named composts

Water until it just appears at the holes, then empty the saucer. No quarter-volume drink, and no indicator, unless you bought one separately. Orchid mix: fill about one third, do not firm it, spring repot after flowering, 4 litres for a 14 cm pot. Not houseplant compost, and not ericaceous. Dense bags got fines sorted or perlite added. Houseplant mix says feed after about six weeks. Ignore a 14 cm line on the 20 L and 40 L. Cactus 4 L is peat-free. Topline is two 10 litre bags. Compost is not reusable. Gnats are on Seramis granules for houseplants. Do not strip the soil and pot into dry mineral with no feed plan.

Common questions

Do I keep the soil ball?
Yes, on the Seramis closed-pot method. The manufacturer tells you to leave most of the compost on the roots and fill granules around it. Stripping every scrap is a last resort for a badly rotting ball, and it leaves you with no feed in the pot. Hydroleca as a top or crock does not ask you to bare-root the plant.
How much water after a Seramis repot?
About one quarter of the pot volume for a closed mineral fill, then stop. That figure is the manufacturer rule of thumb, not a millilitre table for every pot. Compost mixes that name Seramis are watered like compost: until water just appears at the holes, then empty the saucer.
When do I water again?
When the indicator is fully red, after the two-to-four-hour lag. Blue means wait. Do not put the plant on a weekly calendar. Hydroleca and compost mixes do not use that stick. They use a dry top, a light pot, or water at the holes.
Can I use a pot with a hole?
For Hydroleca, pumice mixes and the compost bags, yes. That is the normal drained pot. For branded Seramis, the method assumes a watertight pot. Outdoor Seramis pots use holes 3–6 cm up, not a wide hole at the base. A large drainage hole plus water until it runs through is not the closed-pot method.
How do I mix Hydroleca into compost?
Westland’s listing ratio is about one part Hydroleca to three parts compost. Invigortex grit says 20–50 per cent in a blend. COMPO pumice says up to 25 per cent. Those are different minerals. Pick the ratio on the bag you hold, not an average of the three.
Do compost mixes that name Seramis follow the closed-pot method?
No. They are potting composts. Pot them, water them, and empty the saucer. The Seramis in the blend is an ingredient, not a licence to fill a watertight pot and pour a quarter of its volume.
When do I add liquid feed?
On UK GROW houseplant mix, the bullet says after about six weeks. On a Seramis-type mineral fill, use a weak liquid on a watering once the plant is settled, because most of the old compost is still there and the new volume is inert grain. Orchid and cactus mixes follow their own on-bag feed lines.

Related pages

Best Seramis granules

Seramis granules

Seramis granules buying guide: type, litres and peat

Clay granules for houseplants: caps, gnats and trays

Seramis vs LECA: open-pore clay or expanded pebbles

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 ten amazon.co.uk listings in the stored pages. A gnat, watering or CO2 line is the manufacturer's claim. Peat-free means those words on that listing. This is not a laboratory test.

  1. Seramis, granules and hydroponics (retrieved October 2026)
  2. Seramis, common questions (retrieved October 2026)
  3. Seramis 15 L granules on amazon.co.uk (retrieved October 2026)
  4. Westland Hydroleca clay granules (retrieved October 2026)
  5. Westland orchid potting mix (retrieved October 2026)
  6. RHS, growing media for houseplants (retrieved October 2026)
  7. RHS, peat-free compost (retrieved October 2026)
  8. Written answer on peat sales, 19 March 2026 (retrieved October 2026)