Brunnings Vermiculite, what it does and when to use it

March 31, 2025

Vermiculite and perlite sit next to each other on the shelf, they're both light, and they're both bits of heated rock, so people treat them as the same thing and they are not. Perlite makes air space. Vermiculite holds water. Once you know which one you're after, the whole aisle gets simpler.

What vermiculite is

It's a mineral with a layered structure, and when it's heated hard the layers expand apart into soft golden flakes, a bit like a tiny concertina. Those layers are what makes it useful, because they hold water, and they also hold nutrients and release them back to the plant rather than letting them wash straight through. That's a genuine difference from perlite, which does neither of those things.

It's sterile out of the bag, which matters for seed raising, and it doesn't feed the plant itself.

Where it's the right answer

Seed raising is the obvious one. Seeds need moisture that stays steady, because a tray that dries out at the wrong moment ends the germination and a tray that sits soaking rots the seed. Vermiculite evens that out, and a thin layer sprinkled over the top of a sown tray holds moisture at the surface without shutting light out.

Cuttings are the second. A propagation mix wants moisture and air at the same time, so vermiculite with perlite is a sensible pairing where each one is doing half the job.

Sandy soil is the third, and in this district that's worth knowing. Sand drains so fast that water and nutrients are through it before the plant has a chance, and vermiculite worked into a small area, like a planting hole or a raised bed, holds onto both. Doing a whole yard is not realistic, so treat it as a targeted thing.

Where it is the wrong answer

Heavy clay, and this one gets recommended a lot. Clay's problem is that it already holds too much water and drains too slowly, and vermiculite holds more water again, so you're pushing in the direction the soil was already going. Clay wants organic matter, and gypsum where the clay is the dispersive kind that goes cloudy in a glass of water. That's a different bag and a different job.

It's also not the thing for a plant that wants to dry out between waterings. Succulents, cacti and most of the fussier indoor plants want perlite in the mix rather than vermiculite, and getting that backwards is a reliable way to rot a plant you were trying to look after.

How much to use

In a seed raising mix, something around a quarter to a third by volume works well, and you're aiming for a mix that holds together damp without staying sodden.
Over the top of sown seed, a thin dusting only. Enough to stop the surface crusting and drying, not enough to bury anything.
In a cutting mix, half vermiculite and half perlite is a fair starting point, then adjust depending on whether things are drying out or going slimy.
Dampen it before you work with it. It throws a fine dust dry, the same as perlite does, and a dust mask is worth wearing if you're mixing any quantity.

Shop related products

Brunnings Vermiculite 5L. The moisture holding half of a propagation mix, and the one to sprinkle over sown seed.
Brunnings Perlite 5L. The air holding half, and the one for anything that hates sitting wet.
Brunnings Seed Raising Mix 5L. Already blended, for anyone who would rather not mix their own.
Brunnings Peat Moss 5L. Another moisture holder, and useful in a homemade cutting mix.

Did you know we keep the seed raising mix in bigger 6 litre and 15 litre bags in the shop, and a block that swells up to 30 litres, and none of those sizes are on the website. There's rooting hormone on the shelf too, in both a powder and a liquid, so give us a ring on (08) 8536 4333 to check what's there.

The propagation gear and the seeds all live in our garden centre, and if your seeds aren't coming up we'd rather work through why with you than sell you a bag of something.

More on getting things to grow

I still have to say perlite for air, vermiculite for water out loud in the aisle like a nursery rhyme, and I am not even slightly embarrassed about it.

Candeece