Cactus Soil 101
Update 23/11/2022: We no longer recommend adding coarse sand to your soil mix. It provides no benefit over adding additional perlite, and in some cases can lead to clogging of the mixture if the sand is too fine. We’ve also provided additional details around the type and even example brands of potting mixes to use.
Places like Bunnings sell bags of pre-made “cactus soil” but we recommend avoiding it unless you’re really desperate. These mass-produced soils are full of organic materials like bark and sticks, which are very dense and hold a lot of water which is bad news for our cactus.
At Cactus Culture we mostly sell large columnar cacti like San Pedro cactus and Saguaro cactus, which do require significantly higher organic content to their soil than desert species like Echinocactus Grusonii (Golden Barrel Cactus) or Lophophora Williamsii (Peyote), but it still needs to be balanced with an appropriate amount of in-organics for drainage, aeration, and mineral nutrients.
There is a passionate and active community of people who obsess over the perfect soil recipe for each cactus, but we find that an accessible, cheap and simple recipe for most columnar cacti is:
40% coarse perlite;
60% premium peat-based potting mix.
Premium peat-based potting mix products that we recommend in Australia include:
Canna Terra Professional;
Dr Greenthumbs GreenSpace;
If you want to save time and don’t mind the extra cost Dr Green Thumbs also has an excellent ready-to-use soil called Dr Greenthumbs Mineral Based Soil.
If you chose to use a less premium potting mix like Searles or Osmocote you will have to sift it to remove any pieces of bark or sticks that will clog the mixture. Once you discover that about 50% of the bag is sticks and bark you’ll realise that the premium products actually represent better value for money.
Add all the components to a large bucket and mix them together. If you have access to some slightly larger coarse rocks laying around your garden you could add those in too, as variance in the soil structure is helpful in promoting healthy root growth.
Some people swear by adding animal manure to their Trichocereus Pachanoi soil mixture. At Cactus Culture Australia we don’t suggest using any animal manure in your cactus soil. Manure of any kind is a honeypot for bacteria and the moisture-absorbing qualities are not useful in our mixture.
If you really want to geek out on cactus soil we’d recommend checking out our Advanced Cactus Soil guide. Another great resource is The Stone Eaters - an incredible and compregensive guide on cactus soil requirements that makes the case that most cacti can survive on 100% mineral soil mixtures AKA rocks. Although, it does make the distinction that: “some cacti groups – not too many – require something else, apart from the mineral soil. And even fewer are those that do not accept it…some very large-sized columnar plants - Carnegiea Gigantea and Pachycereus Pringlei are nevertheless stone eaters – and some prairie cacti, or forest cacti…are those that absolutely require the presence of the organic component in the soil.”
