Make Your Own Cactus Potting Mix With Recipes From Sarah Gerrard-Jones And The BCSS
Elizabeth is a Permaculture Garden Designer, Sustainability Consultant and Professional Writer, working as an advocate for positive change. She graduated from the University of St. Andrews with an MA in English and Philosophy and obtained a Diploma in Applied Permaculture Design from the Permaculture Association.
Reviewed By COLIN SKELLY
Colin is a Horticulturist and Horticultural Consultant with experience in a range of practical and managerial roles across heritage, commercial and public horticulture. He holds the Royal Horticultural Society’s Master of Horticulture award and has a particular interest in horticultural ecology and naturalistic planting for habitat and climate resilience.
Contributions From RALPH BEHRMANN
As the Owner of Clouds Hill Succulents, a small plant nursery based in the Surrey Hills, Ralph cares for a range of succulents that are available to purchase from his online store.
Darren is the Plant Manager at Pugh's Cacti, a wholesale supplier of cactus and succulent plants to garden centres in the UK, based in Worcestershire.
Peter is the Society Secretary and representative of the BCSS. Peter has a massive 68 years of experience growing cacti and succulents. He has written and published academic articles about these plants, appearing in BCSS’ Cactus World, and can be found in some of the videos on the society’s YouTube account, sharing his Manchester-based collection.
Known online as 'The Plant Rescuer' and having published a book with the same name, Sarah is a houseplant enthusiast with a passion and skill for reviving imperfect plants. She has an online following of almost 300,000 people and won a Gold Medal at the 2022 RHS Chelsea Flower Show.
Jane Perrone is a Journalist turned Houseplant Expert who has over 25 years of experience. Jane published a book on Houseplants at the start of 2023 and is the founder of On The Ledge podcast, with more than 250 episodes to date. She is a member of the RHS Advisory Committee on Houseplants.
Growing cacti can be a lot of fun.
Although they can be easy to care for, one non-negotiable is that they do need to be grown in a suitable cactus mix.
Learn how to make the ideal potting soil for cacti in this guide.
Why Cacti Need A Cactus Mix
Most cacti grow in warm and dry conditions.
Our homes can provide the appropriate temperatures for these heat-loving plants, but if we fail to provide an appropriate growing medium then they will not be very happy.
Cacti grown in an unsuitable medium can often suffer from root rot.
Providing a growing medium which is suitably free-draining is essential if you are to grow cacti successfully in your home.
The first thing to understand when choosing or creating a potting soil for cacti is where those cacti come from and the conditions in their native range.
“Cacti in the wild have adapted to the harsh conditions they receive,” says Darren Evans, Plant Manager at Pugh’s Cacti.
“Their roots grow down deep where it’s cooler and more moisture in the soil can be found. The body of the cactus is well established to defend itself from the sun and dry wind.
“A cactus in a small pot needs more care to keep it hydrated and prevent scorching. On a hot day, the water in a pot can evaporate before the cactus has had time to draw it in and replenish the water in its stem.”
Most come from dry, arid areas where rainfall and humidity are very low, so they will need a very free-draining medium and care which mimics these conditions.
However, some cacti come from rainforests and have much higher water and humidity needs.1Hlaba, K. (2021). Rare and exotic tropical cactus from the Amazon rainforest to flower for the first time in the UK at Cambridge University Cambridge University Botanic Gardens. Retrieved March 13, 2023, from https://www.cambplants.group.cam.ac.uk/news/rare-and-exotic-tropical-cactus-amazon-rainforest-flower-first-time-uk-cambridge-university
These are usually provided with a mix more like that used for the majority of other houseplants.
What Is Cactus Mix?
Cactus mix is the name given to commercial potting soil which has been specifically formulated for the growth of typical arid-climate cacti and other similar succulent plants.
It has superior drainage and will dry out quickly after watering.
“Our plants arrive in a special free-draining succulent potting mix,” says Ralph Behrmann, Owner of Clouds Hill Succulents.
“When repotting, it is important to use a free-draining mix too, otherwise there is a risk that roots may root due to the soil not drying quickly enough.”
By choosing a cactus mix which does not allow water to remain around cacti roots, those growing them indoors can avoid issues with root rot or waterlogging, which reduces the health of the plants.
However, a far better option than purchasing a commercial cactus mix is making your own.
Making your own cactus mix can, of course, save you money, but another thing is that a homemade mix may actually be superior for the specific cactus or cacti you wish to grow.
Another thing to consider is that some commercial mixes contain peat, which is not an eco-friendly or sustainable material.
By making your own you can make sure you avoid causing environmental harm through your gardening choices.
Making Your Own Cactus Mix
The basics of creating a cactus mix suitable for growing cacti indoors involves thinking about the qualities of the medium you create.
As mentioned above, a free-draining mix is essential for most cacti and that involves adding plenty of inorganic materials which allow water to drain through easily and quickly.
However, while you want the mix to drain freely, cacti will need some water available, and some nutrients on which to feed.
That means that in addition to these inorganic materials, we also usually need to provide some level of organic material too.
“For the soil, a simple mix of standard garden compost and sharp sand is sufficient and cheap,” says Ralph.
The proportions of inorganic to organic materials in a cactus mix are a matter of some debate.
There are diverse opinions on this, but, to a degree, it will always depend on the specific type of cactus you wish to grow.
The RHS recommends that, in general, desert cacti and other succulents can be planted in a potting mix of John Innes No. 2 with horticultural grit, fine gravel or coarse sand (up to 30% by volume) added to the mix.2How to grow cacti & succulent houseplants. (n.d.). Royal Horticultural Society. Retrieved March 13, 2023, from https://www.rhs.org.uk/plants/types/cacti-succulents/houseplants/growing-guide
However, since a free-draining mix is desired for cacti, it may be necessary to sieve out larger pieces of woody material from your mix.
It is best to avoid peat-based formulations, not only for environmental reasons but also because peat can retain too much moisture, but is also more difficult to rehydrate once it dries out.
Coir-based mixes are an increasingly popular choice for cacti growers.
Our first mix therefore is:
- 70% light, John Innes no 2. compost
- 30% horticultural grit or coarse (not builders’) sand
However, another thing to note is that many cacti growers recommend a much grittier, sandier mix.
The British Cacti and Succulent Society (BCSS) suggest that the vast majority of cacti and other succulents will thrive in a mix with around equal amounts of potting mix and inorganic materials which improve drainage like grit or coarse sand.
The BCSS typical cactus mix would be:
- 50% peat-free compost (with coconut coir, woody material or recycled waste)
- 50% gritty material
The BCSS also notes that for cacti prone to root rotting problems, there is another option: a clay granular substance which is used as a stand-alone growing medium or in compost mixes.3BCSS Homepage. (n.d.). British Cactus and Succulent Society. Retrieved March 13, 2023, from https://bcss.org.uk/
“Cacti and succulents need to be grown in a gritty compost that has no peat in it,” shares Peter Bint, the current secretary of the BCSS.
“The compost ideally should be at least 30% grit and humus-rich soil.”
Sarah Gerrard-Jones, also known online as The Plant Rescuer, has her own recommendation for a simple, sandy cacti mix:
“For cacti and succulents, use 75% grit or sand to 25% potting compost.”
You could also make your own potting mix, without buying a potting mix to work from, for your cacti from:
- 65% sharp sand/grit mix
- 30% sterilised loam or light garden soil
- 5% leaf mould
There are literally thousands of different recipes out there, using a wide range of ingredients for both the inorganic and organic portions of the mix.
For the inorganic components, other options include pumice, perlite, and even chicken grit or cat litter.
For the organic components, some advocate using some worm castings from a vermicomposting system, or other homemade composts in relatively small amounts.
Some use coconut coir, and others use bark fines or something similar.
Which ‘Recipe’ Should You Choose?
It is important to understand that there is not one correct formula when it comes to creating the perfect mix for cacti.
“A bit of research will pay off when thinking about which mix to use,” says Horticulturist Colin Skelly.
“Although all adapted to cope with drought, succulents and cacti vary greatly in where they have adapted to grow.
“Experimentation with different mixes will also allow you to work out what works best for the specific plants and growing environment you have.”
Expert opinions will differ greatly, and while you can create a reasonably effective free-draining medium rather easily, finding the optimal variation will be a much greater challenge.
However, this should not put you off.
The notes above should make it easier for you to find and make a potting mix for cacti which keeps your plants pretty happy and healthy and, over time, you can experiment a little and find your own perfect potting mix recipes for cacti and succulents – as well as for other plants.
“Think about adding extra air and drainage to the soil,” shares Houseplant Expert Jane Perrone.
“I use a lot of expanded clay pebbles, which you can add to the substrate or put underneath the pot to help with humidity.”
Remember, the goal is to mimic as closely as possible the growing conditions where the cacti you are growing indoors are usually naturally found.
As long as you can approximate those conditions then you should still find most cacti relatively hassle-free plants to grow at home.
