Soil compositions for succulents?
Curious if any of the succulent-lovers on Tildes have any tips/tricks for soil composition. I've been using the basic succulent mix from my local hardware store for years, but I've had some issues with rot. Reddit seems to think that soil composition is at fault for just about all succulent ills, so I've adjusted my mix to be about 50% perlite/sand 50% organic (a.k.a the basic succulent mix).
Still seems like the new mix doesn't dry out quite as fast as the internet thinks it should, though. Does going even more inorganic make sense? My guess from a few years of reading about succulents is that they would probably be happy in even 80-90% inorganic soil to keep their roots dry, as long as they were watered when they needed it. No clue if that's right, though.
My understanding is that too much organic is far more often the problem than too little when it comes to succulents, so decreasing that may be the way to go. Another thing that came to mind is the sand -- how coarse is it? You want to be using pretty coarse sand (the stuff I used for my succulent mix was also sold as aquarium pebbles). Wish I remembered the ratio I used, but I haven't repotted it in a long time!
I definitely used too fine of sand in this recent mix I came up with... I'll have to remedy that when I get a chance!
I have always just used regular organic potting soil (the kind without additives like guano or whatever) and have never had any problems. I just water very rarely (less than 1x month) and use ceramic pots. I do live in the US high desert, so ambient humidity rarely cracks 30%. this method works fine for me for aloe, Christmas cactus, zyzyphus, and cholla.
I do the same, using whichever potting soil or garden bed soil I have sitting around. And I'm in a much more humid area (<5 miles from ocean) and it works here too.
With bonsai, it's common to pot trees in 0% organic potting substrate, so organic definitely isn't a requirement.
One inexpensive inorganic substrate common in bonsai is using sifted oil-dry diamataeous earth (the kind you can find in automotive part shops that they throw down to help absorb spilled oil on concrete). You'll want to sift out the smallest parts and rinse the dust before mixing it into your soil, though.
But I really don't think your issue is the soil...
"Root rot" is a misnomer; the roots rot because they die, and they die because they don't get enough oxygen, which is most often due to waterlogged soil. Typically, when the water is absorbed by the roots, it draws in oxygen (hydroponics use aerated water); so, if you're having root rot, it's probably because you're simply watering too much. So, probably an obvious question, but how are you gauging when it's time to water?
What kind of pots do you use? Terracotta pots will allow far better oxygen exchange than plastic ones.
Do you make sure you're emptying the drip tray after watering? Anything that runs through the potting soil should be dumped for succulents.
Thanks for the tip on the diatomaceous earth! I'll definitely check that out.
I usually decide to water them when the leaves are starting to either be visibly parched or get softer. Typically every 2-4w. I've got a mix of ceramic and terracotta pots (rot does seem to have been more common in the ceramic ones...), and I do let the pots sit without their drip trays for a while before I put the plants back in their usual spot.
It's actually been really interesting learning about how the roots die and rot - I've been doing plenty of research on it recently since the one plant that started to rot that I couldn't save was my very first succulent ever. On previous run-ins with rot, I'd guessed that it was disease somehow, but it's fascinating to learn that it's just the roots drowning essentially.
Having read everything people have said here, I think my plan is to slow down watering even more, slowly switch to terracotta across the board, and try to get to a coarser, more inorganic soil mix.
If your current mixture is retaining moisture too long for the species you are growing in the locations you are growing them, you can definitely reduce the organic material in your potting mix even further. You could also swap out fine organic material with a different organic material that retains less water, such as orchid bark and horticultural charcoal. Just be aware that well-draining soil will also lose nutrients faster, so you may need to fertilize a little more than previously.
I would also recommend experimenting with smaller pots (in my experience, most succulents do well in pot bound conditions) and with pots that dry out more rapidly, such as terracotta.
As always, also consider the lighting conditions that your plants are growing in. If conditions are too dark for a given succulent species, it may never perform well no matter how you care for it. But if it has plenty of sunlight, you may find it's actually a water hog and prefers a more moisture-retaining soil.
To give you an idea, I have succulents growing in a very hot West-facing window, and I have to give them a very moisture-retaining potting mix and water them twice a week in high summer just to stop them from parching, which is quite a lot more water than even my ferns require. (Note, however, that I do not water any of my succulents at all in the winter, whereas I do continue watering my ferns.)
I'm glad to know about needing to fertilize a little more if I go for something coarser and increase the drainage speed. Not sure I would've realized that.
I'll definitely look into smaller pots, too. I've started over the last few weeks to move my fastest growing plants into my larger pots and keep the smaller ones in my smaller pots to help them to get to that point of being root bound. Mine have definitely seemed happy when they can fill up the whole pot with their roots.
Given the lighting conditions where I live, I think I'm going to have to just get all of mine a better grow light. I got an underpowered basic one to nurse them through the last two winters, and it seemed to work well for that, but they're definitely still not getting enough light with the windows that I have available to me.
Thanks for all the advice!