Title image above is copyright © Kristi Ellinopoullos

First published 19th January 2025

Should you ever get sticker shock looking to buy succulent potting medium in bulk, and you think “It really is about time I made my own”, then maybe this post is for you!

Please note that I’m talking about bulk amounts — if you only have a small number of small plants in need of repotting, then it may be simpler and easier to buy whichever size of a quality commercial mix suits you best.

And if all you have are succulents, and small numbers of them, and you don’t have compost or regular potting mix lying around then it is also probably best to stick to a commercial mix.

But for everyone else, here is my recipe:

  • three parts potting mix or two parts compost
  • two parts coarse sand or poultry grit
  • one to two parts perlite (NOT vermiculite!)
    ** please see very important note below about handling perlite **

A ‘part’ is a measuring unit of whatever suits you — it could be a scoop or a measuring cup, but for me, a ‘part’ is a standard 9 L bucket, and the above proportions fill a roughly 60 L tub.

Why These Materials?

Potting Mix or Compost

This is to provide organic matter — nutrients for the plant in other words. It also stimulates a microbial community (a rhizosphere microbiome) to develop, which assists in getting these nutrients to the plant.

Potting mix is less rich in organic matter than pure compost, which is one reason why I suggest the different amounts above.

The other reason is that compost, being pure organic matter, holds both water and nutrients very well, and this isn’t necessarily ideal for plants evolved to cope with arid and/or nutrient-poor conditions. Having less compost overall dilutes its effects so to speak.

Having said that, I prefer compost, partly because I make my own and always have it to hand, but mostly because of my soil microbiology background. It is an excellent slow-release fertiliser not only because of its nutrient-dense and nutrient-retaining properties, but also because it is rich in beneficial soil microbial life which make those nutrients bio-available.

But there is nothing wrong whatsoever with potting mix. There is also nothing wrong with some mix of both either, especially if that is all you have!

Coarse Sand or Poultry Grit

Either is just as good as the other, so long as it is coarse. You want largish, rough particles to encourage good drainage of water. I use poultry grit as it is more convenient for me, but the soil microbiologist in me also thinks that the minerals in that grit may also be being made bio-available by the microbes present in the compost (specifically by the lithotrophs).

Perlite

Perlite is a naturally occurring volcanic mineral of around 70% silicon dioxide. It has a high water content, and on heating, this water escapes as vapour, which causes the perlite to expand. It has a brilliant white appearance after expansion.

Perlite is extremely lightweight, has high permeability, low water retention, and prevents soil compaction. These properties make it very useful whenever increased drainage and aeration is required.

Vermiculite is another silicon-containing natural mineral of high water content, which also expands on heating. There is more magnesium, iron and aluminium in vermiculite than silicon however. Like perlite, it too is lightweight but has a more brown-grey dull appearance. You may have seen it used as packing material, and if you’ve seen very light, tiny pieces of what looks like greyish packing material in commercial potting mixes, then that was probably vermiculite.

Like perlite, vermiculite loosens soil and increases aeration. Unlike perlite, vermiculite increases water and nutrient retention. These are normally ideal properties in a potting mix, but the opposite of what is required for succulents.

Use perlite for succulent mixes where you need drainage, and vermiculite everywhere else where you want water and nutrient retention.

The reason I say one to two parts perlite is to take into account your own environment. I use two partly because it’s easier to remember two parts of each of the three different materials, but mostly because we get a lot of rain and I add extra perlite to compensate for this. This also balances with the use of the richer compost over regular potting mix.

A very important note concerning the handling of perlite:
Please use a dust mask rated for filtering silica particles whenever handling loose perlite. Googles are also advised. The bag will contain very fine dust, an unavoidable consequence of the larger particles abrading during handling and transport.

Please take this warning seriously as you will fully understand why inside of three seconds of opening the bag! I also strongly recommend handling perlite outdoors only. Standing upwind of gentle breezes, with the mixing tray upwind of you again is also very helpful in blowing the fine dust away from you.

The dust is only really a problem when a volume of perlite is disturbed. It is so lightweight that any movement of air is enough to send it upwards. The problem goes away once the perlite is incorporated into a mix and watered into a pot —  do ensure it is wetted thoroughly prior to future disturbance of the mix when repotting.

On Mixing

You can mix small amounts in a bucket, bu be sure to get right down to the bottom to incorporate the heavier grit and potting mix or compost particles which have settled there. Also be especially careful when leaning over it on account of the perlite dust. I use a cart with a large, flat and shallow tray for the quantities I make, as this minimises the heavier particles concentrating at the lower depth. The larger surface area removes the dust more effectively too. An alternative could be a kiddie’s wading pool — if dedicated for the purpose and not actually used by kiddies!