Making Your Own Cactus Soil

Soil Mixes

Commercial Packaged Soil Mixes

Custom Soil Mixes

Amendments

Soil Collapse

Acidifying Soil

Commercial Packaged Soil Mixes

Potting Soil

Regular commercial potting soils vary from company to company, but the problem with most is that they hang on to too much water for too long a time for most cacti and succulents. Most commercial potting soils are manufactured for plants that have lush growth and vigorous roots and as a result, tend to use water more quickly than most cacti and succulents. Fortunately, there are amendments that can be added to commercial potting soils to help make them more porous and thus cacti and succulent friendly.

Some potting soils contain peat or sphagnum moss which can cause problems for cacti as peat moss breaks down over time, compacting the soil. If at all possible, try to get a potting soil that doesn't contain peat or sphagnum moss.

Cactus Potting Soil

Commercial cactus potting soils are made to be fast draining and help take the guesswork out for someone who is new to the hobby and is reluctant to try their making their own mix. I've tried a lot of different brands and can say that the only one I don't care for is the one made by Kellogg. I used it for a season with not so good results. Over the course of the following growing season, any plant that was in their soil was repotted with different soil. Uni-Gro, Black Magic, and E.B. Stone are commercial soils I like to use with my plants. I mix extra perlite into all of them to help them drain a little more.

Custom Soil Mixes

Note: The mixes below were taken from a flyer freely available to Sacramento Cactus and Succulent Society members. And 'yes', after bad mouthing peat and sphagnum moss, some of them call for peat and sphagnum moss. Not everyone shares my view about not using peat or sphagnum moss.

50-50 Soil Mix

50% regular potting soil mixed with 50% perlite. (The key to this mix is getting a potting soil that does not contain peat or sphagnum moss.)

Arboretum Soil Mix

30% redwood compost

30% horticultural sand

15% peat

15% scoria

10% perlite

University of California Succulent Mix

1 part ground sphagnum peat moss

1 part redwood compost

1 part horticultural sand

2 parts volcanic pumice

for every one cubic foot of mix add:

5 tablespoons dolomite limestone

2 tablespoons gypsum

3 tablespoons superphosphate

1 teaspoon potassium nitrate

1/2 teaspoon potassium sulfate

Amendments

Perlite

Horticultural perlite is the end product of a process that is transformed from natural perlite. Detailed information about the manufacture of perlite can be found at perlite.net.

Perlite is my choice for making a faster draining soil mix. It is an inexpensive and effective way to go when aeration of soil is needed. It is very light meaning that it won't weigh down a pot. Typically, mixing one part potting soil (or cactus potting soil) and one part perlite serves most of my needs.

Be aware that perlite can have a lot of dust in it. If there are a lot of fine, dusty particles, consider taking a colander and sifting out the very fine grains. If too much fine grained perlite is added to a potting mix, it will act to fill in the air spaces between the soil particles and may cause an amended potting mix to hold more water than just potting soil alone. Whenever using perlite, DO NOT breathe the dust.

Pumice

Pumice is a product of volcanic activity where tiny gas bubbles in lava cannot escape before the lava cools. It's similar to perlite in that it acts to loosen up a soil mix, but unlike perlite, it is mined, processed, and sold in its natural state. It is somewhat heavier than perlite, a little bit harder to find, and tends to cost a little more, but it quite suitable in aerating a potting soil.

The most likely place to find pumice is at a nursery, but it might also be found at a local feed store. It goes by the name of Dry Stall and is used in horse stalls so that horses have some sort of traction underneath them. I've used it as an amendment and like it.

Note: Some growers get passionate about perlite versus pumice. Some swear that perlite, because it's so light, will "float" to the top of a pot after repeated waterings. I've found that a well-mixed soil with perlite works just fine and if there's any "floating" of perlite to the top, it happens during watering where some perlite may move its way to the top because it is so light in comparison to the water and other potting materials. For me, perlite is a bit easier to find than pumice.

Red Lava Rock

Click to view larger image Red lava rock seems to be on par with pumice. The speckles of red lava rock around the base of a plant actually add a nice visual effect to a plant and pot. One drawback to using it is finding it. The only place I've been able to find it in my area is a local rock and gravel company called Cascade Rock.

Horticultural Sand

Horticultural sand is a fancy name for large grain sand. Large grain sand is better than small grain sand for extra drainage. The smaller grains will tend to fill in spaces between potting soil particles and may act to hold onto more water rather than let it pass through. Large grain sands tend to be located near cement products at your local hardware store, so look for it there if you don't see it in the garden section. Note that sand will make a potted plant heavier to tote around.

Peat Moss

Peat moss is good at aerating soil, but it breaks down relatively quickly and its texture changes as it does. In my experience, any concentration of peat in a potting mix break down to the point where the soil in a pot can become a solid, unworkable mass over time. In addition to being unworkable, the soil is hard to rehydrate if it's allowed to dry out completely. Yet another problem that can happen is when the soil dries, it can shrink and pull away from the sides of the pot. So unless plants soaked in a shallow pan or bucket, much of the water will run down the sides of the pot and out the bottom meaning the plant won't get a lot of water. The one saving grace of peat is that it is fantastic for seedlings and cuttings where it's likely plants will be repotted after a short period of time.

Coconut Coir

Coconut coir is the shredded husk of a coconut. It can be used as a soil amendment in place of peat moss. Unlike peat moss however, coir doesn’t break down quickly nor does it have a rehydration issue if it gets completely dry. Peat moss breaks down relatively fast and can actually repel water if it gets too dry.

After reading about adeniums and a few growers having success using coir as an amendment, I decided to give it a try. As of this writing (8/2014), the adeniums that were planted in the mix are doing no better and no worse than those in the other soil mix I use. The coir mix for adeniums I’m testing out consists of one part coir, one part perlite, and one part potting soil (one made without either peat or sphagnum moss). The mix I’ve used for other adeniums consisted of one part cactus potting soil with two parts perlite. There was nothing wrong with the original mix, I just wanted to see if there was a difference with some coir added in. One thing I did notice when I watered for the first time is that the water goes right through the pot. In other words, it’s a more “airy”, looser mix. Time will tell whether or not this is going to work for my adeniums. Just for kicks, I planted a few epiphyllum cuttings into the mix to see how they do.

I found a brick of compressed coir at a local nursery. Hydrating it loosened it up and made for quite a bit of product when the process was done.

On a side note, many small nursery succulent or cactus plants will be sold in containers that are pure peat moss. In August 2014, I bought my first haworthia that was planted in 100% coconut coir.

Soil Collapse

Potting soils are composed of mostly organic materials that were likely composted to some degree before they were bagged and priced. Composting is the breakdown of organic matter by a combination of moisture and micro-organisms. Composting continues at a slower pace while potting soil is in a pot, but the breakdown of organic material does continue. This can present a problem for plants that are in the same potting soil for several years (10+ years), fewer years for potting soils that have peat or sphagnum moss in it. For someone planning to repot every few years it's not an issue, because fresh soil resets the clock on breakdown. But when a mature plant doesn't require repotting for several years, any potting soil or cactus potting soil may cause problems for a grower because the organic component of it may have broken too much. When a potting soil breaks down aeration goes down and moisture retention goes up even if the potting soil has been amended with pumice, perlite, etc.

If you have older plants that won't require repotting for several years, contact a Cactus and Succulent Society about a soil mix that will stand the test of time.

Acidifying Soil

Cactus tend to like their soil a little on the acidic side. This came to light when a commercial grower (who lives about 35 miles from my location) mentioned that he acidifies his water with a touch of distilled vinegar. It appears that the groundwater in this part of California (I'm on a well) is on the alkaline side meaning that eventually the soil in pots will tend toward the alkaline side with each watering.

pH is measured on a scale of 1 to 14 with 1 being an extremely harsh acid and 14 being an extremely harsh alkaline. 7 is considered neutral. With the pH of my groundwater on the alkaline side (near 8), my cactus plants apparently aren't getting the nutrients they need because they were being bound up by the properties of an alkaline environment. The thought is that a touch of acidity in the vinegar-water mixture should free up nutrients for plants to use, and with any luck plants that like slightly acidic conditions will appear to be happier for it. An added benefit of the repeated application of acidic water is the decrease of hard water mineral deposits on pots and plants. To this nursery growers credit, my cactus did perk up. However, a lot of the succulents hated it, especially the stapelias (and the orbeas and huernias). Over the course of a growing season when I started to apply vinegar laced water, they went slowly downhill and it wasn't until I went back to giving them straight water that they started to perk back up. So be aware of what it's doing to your plants if you decide to acidify the water.

Generally speaking, applying a mixture of two tablespoons of vinegar to five gallons of water should suffice in helping acidify soil in pots. If you want to know where you stand in regard to your water's pH, then test the water. Hydroponics stores offer small test kits that cost less than $10 and it's what I used to test my water. Keep in mind that too much vinegar in the mix can lead to a hostile environment for plant roots because it's too acidic. In fact, the roots could burn so try to keep the pH between 5 and 7.