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I'm not sure how many members we have on this forum but I'd bet that there are at least that many recipes for succulent potting mixes. Hopefully others will add their comments. Some use a different mix for different plants. Some mixes are an exotic combination while others are pretty basic.
All of my succulent plants are outdoors year round. I am a lazy gardener and I also tend to over water potted plants so I want a an easy, one size fits all, fast draining, soil mix. For this purpose I use a commercial cactus / succulent soil from Home Depot or Lowes and mix it 50% with pumice.
To supply some level of nutrients, I apply tomato plant food diluted 50% once a year.
Is this the best mix???? Most likely not but it has worked well for me. Others are much more refined at that magic of the correct mix so lets see what other comments we get.
Good luck as you move forward with growing succulents.
I think you can do the same for succulents, just add more aggregate. The main thing is that the mix drains fast. What you use depends on what's available in your area. Perlite and pumice serve some of the same functions. I use cactus mix alone or usually with added pumice, up to about 25% for most plants.
What are you growing?
If you're using clay pots then you can get away with less rock. Be aware that varying the amount of rock will affect the watering interval, as well as the need for fertilizer, so it's good to be consistent. For a given type of plant anyway. I try to set different plants up so that they will all need water at roughly the same time, for the sake of convenience, because I'm a lazy person.
These days I fertilize most plants in the sun every month or so with a 1/4 strength fertilizer (50 ppm N). They definitely don't need it but I like the results. We have a very even, mild climate. Some fast-growing plants may benefit from low-strength fertilizer at every watering. As a general rule succulents aren't particularly needy that way, so try growing them without fertilizer before you experiment. Avoid fertilizer right after repotting and when plants are dormant.
Pumice is volcanic glass which is full of little air pockets. Vermiculite is processed from a mineral which expands when heated. Pumice is much heavier, holds less water, and has a lower cation exchange capacity. Otherwise they perform roughly the same role in soil mixtures, though they are definitely not interchangeable.
I'll add...vermiculite holds more water than pumice, and vermiculite breaks down relatively quickly (considering that some of our plants grow slowly). All my C & S plant idols say vermiculite is fine for tropicals (it's great for rooting houseplant cuttings). But for C & S, use pumice, scoria or perlite (depending on what you can get, price, and their differences). Perlite's lighter and cheaper (good) but it floats and creates more dust (bad), and its other growing properties are somewhat different from pumice. Perlite's air bubbles are sealed in a heating process; pumice's are permeable. Scoria (basaltic spongy lava) is heavier still and breaks down faster than pumice (granitic spongy lava). I grow okay in scoria, but some folks say it can be quite alkaline (high pH). Perlite's an okay lightener and filler, and it retains a bit more water than pumice.
Now that I've written that, it looks like it would be much clearer in a table or matrix.
In the east, pumice is not readily available. Chicken grit, which is crushed granite, is cheap and available at feed stores. Heavier than pumice, but does the job. I abhor perlite aesthetically. The container plants forum on this website has sticky links at the top to excellent discussion of drainage in potting soil by Tapla.
Yes, my favorite is pumice and, luckily, out here in Phoenix, I can still get it. It has become harder to get a good size quantity and much more expensive than in the past. I still search it out though. It has all the qualities I want for my C&S.
Baja_Costero wrote:Pumice is volcanic glass which is full of little air pockets. Vermiculite is processed from a mineral which expands when heated. Pumice is much heavier, holds less water, and has a lower cation exchange capacity. Otherwise they perform roughly the same role in soil mixtures, though they are definitely not interchangeable.
many growers of succulents here in California use pure pumice as their 'mix' and just add a dilute fertilizer to the water either weekly or sometimes with every watering. Nearly impossible to rot a plant growing in just pumice.
I used chicken grit for awhile and didn't think the plants responded well planted with it. It is heavy and seems to compact the medium. But maybe others have better results. I am back to perilite since pumice, which would be my first choice, is expensive to ship back to Georgia.
Thanks Baja, I use lots of scoria with the cactus mix I buy (about 50/50) and if in the ground I dig deep and then fill with the mixture and then surround the top of the hole with decent size rocks and fill more soil mixture so the depth can eaily be over 1 foot. After planting I surround the plants with small or less small rocks. Despite all the rain most of the plants survive year after year. (some die). Xuling
I also read that scoria (red lava) is aerated basalt and can be fairly alkaline, while pumice is felsic (largely feldspar and silica), and is more neutral in pH.
Chemically they are not the same. Though I have success in both, I've definitely failed more often in scoria than in pumice.
Some plants just don't seem to thrive in scoria, even though I like the visual color contrast. Because of that, I'm more likely to use it as top dressing than primary growing medium. I even think my acidification routine moderates the alkalinity of the scoria, but it is still not as successful as pumice.
These are just my personal observations. Of course this isn't scientific; my idiosyncrasies may the the culprit. Maybe if I did something differently, scoria would be just as good or better than pumice.
I like the look of scoria better, but it is definitely much more effective at retaining water, and that can be really bad for some succulents. I find it's pretty good for cycads and palms, though... but I avoid its use for potted succulents for the most part now. I restrict my use of scoria to when I am ammending a garden soil, or making large raised planters where I do not want the white color of pumice or perlite to stand out. Then I just add a LOT of it and less organic material. Still, things stay wetter longer for me (which can be good, too, in hot summers). I certainly do not find them comparable though. Even perlite and pumice are much different (in a different way) and hate having to use perlite (not heavy enough and creates a toxic cloud of microparticles that make me gag when I use it... floats to the top of the pot, too and does not make a good top dressing... always have to add some rocks or large sand when using perlite in pots).