I see from my web site stats that one of the posts that randomly gets hits from the back catalog is one with “Al’s Gritty Mix” in the title, and I suspect that means I’m getting some search engine traffic from people looking for information about it. I decided to make a dedicated post for those people, rather than have them dig the information about my experiences out of a recap of a certain week from months ago.
“Al’s Gritty Mix” originated from a post by a user (hi, Al!) over on the GardenWeb forum, who came up with it and did a lengthy post explaining it’s merits for citrus, cacti, succulents, etc. The short of it is that most commercial potting soils are terrible for succulents and cactus; commercial potting soils are designed to hold water, which is pretty much the opposite of what you want for dry desert plants. Retained water for long periods of time leads to rot, which leads to dead plants.
Instead, you can create a “grit” to pot the plants which has three basic parts:
- Organic material (which should never exceed 33% of the mix)
- Inorganic material (non-water retaining)
- Inorganic material (somewhat water retaining)
I’ll break down what that means — and common ingredients — below.
The material normally used here is pine or fir bark fines. Small chunks of bark that absorb water to a certain degree, and also provide some organic material for the roots to leech from. You can sometimes find pine bark fines at home improvement stores amongst the bags of mulch, but it’s tricky – and you have to read the bags very carefully to find the right material and the right particle size. Simpler solution? Pet bedding.
ZooMed has a product called “Reptibark” that is animal cage bedding that’s made of fir bark pieces that works very well, and is relatively easy to find in pet stores.
Inorganic material (non-water retaining)
Next, you want an inorganic material … preferrably one that doesn’t hold water. Bonus points if it’s porous and airy, and helps keep the soil light and not condensed. The ideal material here is horticultural pumice; however, that’s another material that can be hard to find. Some indoor garden stores will have it, or a man-made equivalent by the name of GrowStones, which is a synthetic pumice made of 90% recycled glass that is essentially the same thing but structurally is more stable (meaning it doesn’t break down as quickly as pumice will). To get the right size, you may want their “Soil Aerator” product.
You can also use crushed granite (Al’s original recommendation), or even small pebbles. The easiest way to find this product is at a tractor supply or livestock feed store (such as a grain elevator) under the name chicken grit.
In a pinch, the most easy to find (and cheapest) alternative here is common perlite, which you can pretty much find anywhere garden products are sold. Perlite has a lot of negative features though, such as: it breaks down quickly, it’s very dusty, it floats, and it has a strong tendency to discolor when exposed to a combination of moisture and air. (First, it grows algae/mold, which then dries out and dies, so it’s going to be either green or rust orange.)
I’ll confess that I do use perlite in my mixes, but mostly towards the bottom of the pots. (Because I’m thrifty.) I’ll use a gritty mix that’s heavier in layers above, or if I use a perlite mix for an entire pot, I’ll make sure to use a top-dressing of stone on the pot so it doesn’t float up and move around every time I water).
Organic material (water retaining)
Finally, you want something that’s a bit moisture-retaining (So the water sticks around long enough for the plant to soak some up) but not going to stay damp for days on end. Basically, there’s a cue from the world of bonsai growers and use high-fired clay.
The preferred product here is something called Turface. It’s a product sold to sports fields, golf courses, etc – that’s a high fired, calcined clay pebbley material they use on, say, baseball fields. It’s the red color. It drains very, very quickly, but still retains a bit of moisture. It can also be tricky to find. Some landscaping companies carry it in fifty pound bags; enterprising individuals will sell it online (check Amazon or eBay) for big markups per pound but in smaller amounts (and then you pay through the nose for shipping), so it depends on how much you think you need. Or if you can order a large bag online and split it with some other growers locally. (Check the succulent subreddit, or your local growers club — you’re likely to find other enthusiasts in your general area.) Locally, I’ve managed to find it at a golf cart dealership that also stocks golf course supplies. Check the manufacturer’s website for local distributors and call around!
One note on turface though — price per 50lb bag will vary greatly. The normal retail price seems to be $35-$45 per 50lb bag. If you’re lucky, you may manage to find it for as low as $9. So it doesn’t hurt to call around if you have multiple distributors in your area.
A popular alternative is a product from Napa (The auto parts store) called Floor Dry. Part 8822! It’s about $9 for 24 quarts, and it’s similar to turface with the exception of the fact that it’s a diatomaceous earth-based product.
Lately, however, Napa has been tweaking the product. If you go this route, check the back of the bag. You want to make sure that what you are getting is “calcined diatomaceous earth” and not “amorphous diatomaceous earth”. The amorphous stuff seems to be the direction they’re going, and it’s not as good — it will break down much faster, and tends to turn back into clay after a while, which can block drainage in your pot, impede roots, and in some cases gets taken up by the plant and then excreted back out the pores of the leaves.
I’ve had this happen (before I knew better) on a few soft leaved haworthias. Jury is out on how harmful it is to the plant, but it definitely is not aesthetically pleasing.
Now, with all this non-soil, you’re going to need to fertilize occasionally. Use a half-strength cactus fertilizer (which tends to be low nitrogen) about once a month, or every other watering. Dynagro Foliage Pro 9-3-6 is also highly recommended by several growers, and Al himself. If you’re using something like the Miracle Gro cactus fertilizer, you may want or need to occasionally also add a bit of Epsom Salt for magnesium. (Something like a quarter teaspoon per gallon of water). You can read more about that in Al’s original post if you’re curious.
And if all else fails….
If you can’t find the materials to make a gritty mix, that doesn’t mean you’re out of luck — just use the commercial based mixes, but add substantially more inorganic material (Such as coarse sand, perlite, gravel). You’ll probably want to do a mix that’s at least 1:1 potting mix to additive. If you go this route, be prepared to water far, far less often.
On the off-chance that you’re still interested in reading more about this, there’s an excellent follow-up on Al’s Gritty Mix over on GardenWeb that you can find here.