Cactus Soil 101: How to Make a Simple Potting Mix

We’ve got the dirt on Trichocereus. Literally. A good soil mix is the foundation of a healthy cactus, but there are a lot of options out there on what to use and how to put it together. In this guide, we’re going to go over common organic and inorganic materials, how to put a simple mix together, and any extra tips we have on soil for you.

Before We Begin - A Quick Overview

Soil and Potting mix are terms largely used interchangeably at times, but technically speaking, soil is the uppermost layer of earth - what you’d go out and dig up outside. You would not want to take this and plant something in it. Potting mix is a soilless mixture of materials, specially designed to work better for your plant. In this video, when we say soil, we mean potting mix or the materials gathered to make a potting mix.

Trichocereus are very resilient to a lot of different soil types, and they’re typically not fussy when it comes to needing the “perfect soil” to do well. Certain types, like bridesii or scopulicola, may need a more specialized mix to grow best, but for the most part, they are very forgiving plants.

As we move forward, the important thing with any soil mix is that you learn how it acts in your specific conditions and you get familiar with a watering system that works for you. Each ingredient you use will act differently and have pros and cons depending on what you need, so it benefits you to learn to tailor your mix to your own needs.

Organic vs Inorganic

Let’s start with a closer look at the components that make up a potting mix. There are two main kinds of ingredients you will be using: organic and inorganic. Both are important and necessary in creating a potting mix.

Organic: Materials that are derived from living matter, like peat moss and compost. These materials store essential nutrients and better retain moisture.

Inorganic: Materials that are not derived from living matter, such as sand, rocks, and clay. These materials provide better aeration as they retain less moisture compared to organic matter.

Common Materials

Let’s take a quick look at common materials used in cactus potting mixes, what they are, and what their benefits and drawbacks are.

Peat Moss

A natural, organic material harvested from peat bogs.

Pros: Excellent water retention; lightweight; easy to find; helps keep mixes evenly moist
Cons: Harvesting raises sustainability concerns; it can become hydrophobic when fully dry; it compacts over time and reduces airflow.

Coco coir

A natural fiber extracted from the outer husk of coconut shells.

Pros: Renewable and more environmentally friendly; resists compaction; provides good aeration; rewets easily after drying out.
Cons: Holds less water than peat moss; may require more frequent watering

Compost

Decomposed organic matter, often plant residues, sometimes animal manures.

Pros: Rich in nutrients; increases moisture retention; can improve overall soil structure.
Cons: Quality varies widely; it can hold too much moisture for certain plants

Perlite

Lightweight, porous material made from volcanic glass.

Pros: Excellent drainage and airflow; lightweight; inexpensive; easy to mix into soil.
Cons: Floats to the surface with watering; breaks down into fine particles over time; very dusty when dry

Pumice

A porous volcanic rock that is generally bigger than perlite.

Pros: Excellent long-term drainage and aeration; durable and slow to break down; stays evenly distributed in soil
Cons: More expensive; harder to source in some areas

Sand

A granular material composed of finely divided mineral particles.

Pros: Adds weight and stability; improves drainage when coarse grades are used; inexpensive; widely available.
Cons: Fine sand can compact soil, reduce airflow, and retain too much moisture; it adds significant weight to containers.

Decomposed granite

Crushed stone from weathered granite rock.

Pros: Provides excellent drainage; long-lasting; adds weight and stability; works well in gritty cactus mixes.
Cons: Heavier and finer than pumice or perlite; can compact if used too heavily; may be harder to find depending on location.

Each of these ingredients has benefits and drawbacks, and knowing what each does will allow you to better tailor a mix for your needs.

How to Make a Simple Mixture

If buying a store-bought mix, they usually don’t have enough drainage, so you can simply amend with more inorganic material.

If making a mix from scratch, start by choosing your organic material(s) and then your inorganic material(s). Generally, you will want 30%-50% inorganic material in your potting mix, but certain types will want more inorganic, anywhere from 50%-80%, depending on how humid your climate is. Once you have your materials, mix them uniformly.

Mix in at least 30% inorganic material to your potting mix

*Note: every potting mix will act differently depending on what’s in it and your growing conditions. There is no one perfect blend. Try out different mixtures and see what works best for you.

We like to use both perlite and pumice, so that we can get the best of both worlds - nice drainage without too much weight. For more sensitive cacti, we use more inorganic material.

Recommendation - Premade Mix

Sunshine Mix #4 is the most widely used for cacti & succulents. It has generally been found to be a good mix that is ready to use pretty much right out of the bag.

Troubleshooting

Amending soil mixes can help to alleviate many issues found in plants. For example, a TBM with humidity spotting can be helped by adding more inorganic material to its soil mixture. If you have a habit of overwatering or your plants don’t have shelter from constant rain, going with more inorganic material can help here as well.

Soil amendments can help troubleshoot other issues with cacti

If you’re running into these common problems, changing your soil can help in these different ways:

Humidity spots & fungal spotting = add more inorganic material (it will also help with the long-term health of the plant)
Rotting = add more inorganic
Stems shriveling & wrinkling even with frequent watering = add more organic matter to retain more moisture
Soil becoming hydrophobic when dry = add more organic matter

Extra Tips

The amount of inorganic material will affect how much you’re watering your plants. If it’s got a lot of organic material, it’ll stay wet longer and need less frequent watering, and vice versa.
Outdoors in the ground, lean towards more inorganic. Provides relief during the winter, and will help it not get too waterlogged during rainy seasons.
Smaller plants in smaller pots prefer a smaller particle size and vice versa. You can still use smaller particles for larger plants in larger pots, but they usually like a larger particle size.
Don’t overthink it. Stick to a simple mix, and you’ll be alright. You can always amend from there.
Use a heavier mix if planning to keep the plant in that container for a while, as it can get top-heavy when the potting mix dries.

Outro

Taking the time to find a potting mix that works for you can make your life so much easier in the long run. Knowing what organic and inorganic materials suit your needs, and using those to make a simple mix, will be the foundation of healthy, long-lasting cacti.