Brunnings Perlite, what it does and when to use it

March 31, 2025

Perlite is the white stuff you see through a bag of potting mix, and plenty of people assume it's a filler or some kind of plastic bead. It isn't. It's volcanic glass that's been heated until the water trapped inside it turns to steam and pops it, a bit like popcorn, and what you're left with is a lightweight particle full of air.

What it actually does in a mix

Roots need air as much as they need water, and that's the part people miss. A mix that holds water everywhere and air nowhere suffocates roots, which is what root rot usually is underneath all the fuss. Perlite holds its shape when it's wet, so the gaps between the particles stay open and water can drain through instead of sitting. It doesn't feed the plant and it doesn't hold much water itself, and that's exactly its job.

It's also inert and it stays that way, so it isn't breaking down over a season and turning back into mush the way a lot of organic material does in a pot.

Where it earns its place

Pots and containers, first and foremost, and particularly anything that's been sitting in a mix that's got old and compacted. Propagation is the other big one, because cuttings want a medium that stays open and damp without going waterlogged, and perlite mixed with something that holds moisture is the standard answer for that. It's also worth having on hand for the plants that genuinely hate wet feet, so succulents, cacti and most of the fussier indoor plants.

Where it does not earn its place

Working perlite through a heavy clay garden bed sounds sensible and it does not really work. You'd need an enormous quantity to change the structure of a bed, it's light enough that it works its way up to the surface over time, and you've spent a lot of money on something that has largely floated away. Clay gets fixed with organic matter, and with gypsum where the clay is the dispersive kind, and those are different products and a different job. Perlite is a potting mix ingredient rather than a soil amendment, and it's worth being clear about that before you buy four bags.

The safety bit, and it's a real one

Dry perlite makes a fine dust and you do not want it in your lungs or your eyes. So dampen the bag before you start working with it, which knocks the dust down completely, and wear a dust mask if you're mixing a decent quantity. It's a two second job and it's the sort of thing nobody mentions until you've had a face full of it.

How much to use

For general potting, somewhere around a fifth to a quarter of the mix by volume is plenty, and you're aiming to lighten the mix rather than replace it.
For cuttings and anything that wants sharp drainage, go heavier, and half and half with a moisture holding material is a common starting point.
Mix it right through rather than layering it, because a layer of anything in a pot creates a barrier and makes drainage worse rather than better.
Don't put a layer of perlite or gravel in the bottom of a pot for drainage. That is an old idea that has been tested plenty and it raises the wet zone rather than lowering it.

Shop related products

Brunnings Perlite 5L. The standard bag, which goes a long way through a potting mix.
Brunnings Vermiculite 5L. The other half of most propagation mixes, and it holds moisture where perlite holds air.
Brunnings Seed Raising Mix 5L. Already blended, if you'd rather not mix your own.
Brunnings Peat Moss 5L. The moisture holding partner for a homemade cutting mix.

Did you know we also keep perlite in the bigger 25 litre bag in the shop, which is not on the website, and we've got P2 dust masks on the shelf a few aisles over, so give us a ring on (08) 8536 4333 to check what's there before you come in.

The potting mixes and the propagation gear are all in our garden centre, and if you tell us what you're potting up we'll tell you honestly whether you need to buy anything extra at all.

More on soil and pots

I am the sort of person who tips perlite straight out of the bag on a windy day and then wonders why I'm coughing, so learn from the general direction I am pointing rather than from my technique.

Candeece