Advanced Cactus Soil
Put simply: plant soil needs to strike a good balance between adequate plant nutrition and suitable drainage for the species we are growing. For cacti we need to find a way to achieve high nutrient but fast drainage growing mediums. This can be tricky, as plant nutrients are traditionally found in things like rich composts and animal manure, which are the exact opposite of fast draining.
In our Cactus Soil 101 guide we provided the following recipe for cactus soil:
40% coarse perlite;
60% premium peat-based potting mix.
In this mixture, the cacti get all of their nutrients from the soil. The role of perlite is purely to reduce the organic composition of the mixture and to increase the drainage capacity.
This mixture is great because it’s simple, cheap, and effective and you can source the ingredients easily from most regular garden stores. But if you’re a dedicated cactus nerd like us and want to take your soil to the next level read on.
Quick Tips
If you don’t have time to read the full article but just want a couple of quick tips:
Sand is a dead ingredient, it serves no purpose other than to dilute the organic makeup of the mix. Try and substitute it with something that also contains valuable nutrients like crushed/decomposed granite;
Perlite is also a dead ingredient but it does a great job at aiding drainage. Substitute for pumice which achieves the same purpose but also contains nutrients;
Vary the granulations to achieve good drainage. In nature nothing is uniform and you want to try to recreate this in your mix. For your minerals try and include something 2-5mm, something 5-10mm and if you want to go crazy a few larger pieces as well;
Not all potting soil is created equal, try to find one which is composed primarily of peat moss and/or leaf mould. Try to avoid ones full of sticks and bark and all the other additives;
Avoid heavy organic composts and manures - these will clog the mixture and be a host for bacteria.
What is the Best Cactus Soil Mix?
This is an impossible question to answer succinctly because the best cactus soil is dependent on the exact species of cacti you are growing. All cacti are endemic to the Americas but their natural range is absolutely enormous: all the way from Canada down to the bottom of Argentina and everywhere in between. There are cacti that grow in scorching deserts, cacti that grow in cold mountains, and even cacti that grow in trees.
Below we have shared some examples of soil mixtures we use for different species/types of cacti. In each group, we have included species examples as well as an overarching recommendation for organic/mineral soil composition. Organics are things such as peat, compost, leaf mould and worm castings. Minerals are things such as pumice, perlite, sand, granite, etc.
South American Columnar Cactus
Species examples: Echinopsis pachanoi (San Pedro), Echinopsis peruvianua (Peruvian Torch), Echinopsis terscheckii, Echinopsis cuzcoensis
Recommended composition: 60% organic, 40% mineral
Example Mix: 50% peat moss or sifted premium potting mix, 10% worm castings, 20% 2-5mm pumice, 10% 5-10mm crushed granite, 10% Zeolite 4-6mm
North American Columnar Cactus
Species examples: Carnegiea gigantea (Saguaro), Pachycereus pringlei (Cardon cactus), Neobuxbaumia polylopha
Recommended composition: 30% organic, 70% mineral
Example Mix: 20% peat moss or sifted premium potting mix, 10% worm castings, 40% 2-5mm pumice, 20% 5-10mm crushed granite, 10% Zeolite 4-6mm
Small Mexican Desert Cacti and Taproot Cacti
Species examples: Ariocarpus retusus, Astrophytum asterias, Obregonia denegrii, Turbinicarpus lophophoroides, Lophophora williamsii
Recommended composition: 10% organic, 90% mineral
Example Mix: 10% worm castings, 50% 2-5mm pumice, 20% 5-10mm crushed granite, 10% Diatomaceous Earth, 10% Zeolite 4-6mm
Ball Cactus
Species examples: Echinocactus grusonii (Golden Barrel), Ferocactus, Parodia, Mammillaria
Recommended composition: 30% organic, 70% mineral
Example Mix: 25% peat moss or sifted premium potting mix, 5% worm castings, 45% 2-5mm pumice, 15% 5-10mm crushed granite, 10% Zeolite 4-6mm
