Independent comparisons. We may earn from shop links. More info

How to use potting compost in pots and coir bricks

Updated: October 2026

The bag is on the doorstep, or the brick is still in its wrap, and you want to pot up without drowning the first plant. How to use potting compost is the method page: open the bag safely, pot with a drainage gap, water peat-free mixes by feel, then feed after the starter window. Prices stay on the [potting soil comparison](/hub/fertiliser-soil-and-bark-mulch/potting-soil). The Products Compared editorial team used RHS container advice, Garden Organic's peat-free notes, and the listing steps on the two bricks in this set. We did not pot the plants. A qualifying purchase can earn a commission at no extra cost to you.

The bag is on the doorstep, or the brick is still in its wrap, and you want to pot up without drowning the first plant.

Our top picks

GROWMOOR Growmoor multi-purpose compost 60 L

Best overall

GROWMOOR Growmoor multi-purpose compost 60 L
9.0/10about £13.98
View offer
Miracle-Gro Miracle-Gro houseplant potting mix 10 L

Alternative

Miracle-Gro Miracle-Gro houseplant potting mix 10 L
8.6/10about £8.99
View offer
PLANT!T PLANT!T compressed coir 15 L

Alternative

PLANT!T PLANT!T compressed coir 15 L
8.6/10about £9.86
View offer
On this page
  1. 1.Open the bag and pot the plant
  2. 2.Water peat-free mixes by feel
  3. 3.Feed, store and leftovers
  4. 4.If you bought a compressed brick

Open the bag and pot the plant

Open a sack at arm's length and keep the dust off your face. The RHS says dampen dusty compost, wash your hands, and do not store an opened bag in a hot greenhouse. Use a pot with holes. Set the compost about 5 cm below the rim, firm lightly, and water until it runs out. Loosen a tight root ball and keep the old planting depth. Houseplant Focus prints an 18 to 24 month repot. That note belongs to that listing. Do not fill a 12 cm houseplant pot from a 60 litre sack if the pot cannot drain. Bag size is on the potting soil buying guide.

Water peat-free mixes by feel

Peat-free compost often looks dry on top while the root ball is still wet. The RHS says water differently, not necessarily more. Finger a third of the way down, or lift the pot. Stop when water reaches the holes. If the mix has dried hard, Garden Organic says stand the pot in a bucket, then drain it. Miracle-Gro's three-month line is a feed claim, not a reason to skip the finger test. Water hanging baskets in the morning. Fungus gnats after a wet surface are on houseplant potting mix.
GROWMOOR Growmoor multi-purpose compost 60 L

Testsieger

GROWMOOR Growmoor multi-purpose compost 60 L
9.0/10about £13.98
View offer

Feed, store and leftovers

Which? treats about four weeks as the usual starter window unless the listing claims longer. Miracle-Gro's 10 litre houseplant mix claims up to three months. Growmoor, Munnie, Laeto and the bricks do not print a duration you can copy. After that window, use the rate on the feed bottle. Fold the bag closed, keep it cool and dry, and use it within about three months if you can. An open sack through a wet winter is a gnat risk. Do not tip leftovers on a border. The RHS says potting compost is for containers. Call a nursery for an irreplaceable plant, twisted growth after green-waste compost, or dust you should not handle.

If you bought a compressed brick

PLANT!T says add 6 to 8 litres of water so the brick becomes a claimed 15 litres. The listing says peat-free and nothing added, so you feed it. Break the coir up in a trug until it is evenly wet. DIVCHI lists 680 g for a 10 litre title, and the first 50 reviews describe a block. Add water until it is crumbly, then drain standing water. The organic wording is not a feed schedule. Potting into dry fibre sends water down the side of the pot. Expand the brick, then use the 5 cm rim. Miracle-Gro and Houseplant Focus are the ready bags. The brick is for when you have no room for a sack.

Common questions

How do I pot a plant in bagged compost?
Use a pot with holes, fill with the mix, set the plant so the compost sits about 5 cm below the rim, firm lightly, and water until it runs out. Loosen a tight root ball first. Open the bag at arm's length and keep dry dust out of your face. That is the RHS container method, not a brand ritual.
Why does peat-free compost look dry?
The surface dries faster than a peat mix, so the top can look pale while the root ball is still wet. The RHS says you water peat-free mixes differently, not necessarily more. Finger a third of the way down, or lift the pot. Water the compost, not the leaves.
When do I start feeding?
After the starter window, which Which? treats as about four weeks unless the bag claims longer. Miracle-Gro's 10 litre houseplant mix claims up to three months. That claim is that listing only. PLANT!T's nothing-added brick needs feed from the start.
How do I expand a coir brick?
On the PLANT!T listing, add 6 to 8 litres of water and wait until the block becomes about 15 litres of loose coir. Break it up in a trug so dry pockets do not remain. Then pot and add feed, because the listing says nothing added.
How should I store an opened bag?
Fold it closed, keep it cool and dry, and do not leave it in a hot greenhouse. Use it within about three months if you can. An open sack in a damp shed is a gnat risk. Wash your hands after you handle it.
Can I put leftover potting compost on a border?
No. Potting compost is a container mix. The RHS tells you not to spend it on beds. Keep the leftover closed for the next pot, or share it. Heap compost and soil improver are the products for borders.
How often should I repot houseplants?
Houseplant Focus prints every 18 to 24 months on its listing. That is a useful default for a steadily growing indoor plant, not a law. Repot sooner if roots fill the pot, and later if the plant is happy and the mix still drains.

Related pages

Peat-free potting compost

Potting soil

Best potting compost UK for patio pots or indoor use

How to choose potting compost for pots and baskets

Houseplant potting mix UK for one or two indoor pots

Sources

Public UK sources from the research digest, used for this page in October 2026. Prices, stars and review counts are from the nine amazon.co.uk listings captured on 21 October 2026. Peat-free means the listing prints those words. Organic wording is not a certificate. This page did not measure fill volume or run a growth trial.

  1. RHS, peat-free choices (retrieved 21 October 2026)
  2. RHS, how to plant a container (retrieved 21 October 2026)
  3. RHS, minimising health risks in the garden (retrieved 21 October 2026)
  4. RHS, retail peat-free from 2026 (retrieved 21 October 2026)
  5. Which?, best compost 2026 (retrieved 21 October 2026)
  6. Which?, peat-free compost for patio pots (retrieved 21 October 2026)
  7. GOV.UK, sale of horticultural peat (retrieved 21 October 2026)
  8. Garden Organic, garden compost or potting compost (retrieved 21 October 2026)