The best soil for succulents is well drained - the quickest way to kill succulent plants is to put them in rich soil, with manure or other organic matter, which holds moisture. Succulents do not appreciate the kinds of conditions that jungle plants love; moist, nutrient rich compost based soil.
Garden soil on its own, even the very best vegetable garden soil with lots of additional organic matter, is not suitable for succulents in any kind of container or pot; succulent soil should be a lean soil, with little to no organic matter or excess nutrients, and extremely sharp drainage.
This rules out garden soil, as for most garden plants, you actually want moisture retention; for succulents - especially if they're grown in containers - this will be the death of them as it will cause root rot.
However, just because they don't like too much organic matter it doesn't mean you can't add some compost to the soil, just don't overdo it. 10-20% by volume is plenty.
Caution; do not use composted manure because it's too strong - use that for making compost tea or to put on the vegetable garden. Instead, make compost from kitchen scraps or vegetation like leaves to use in your succulent soil.
A soilless mix means you can tailor it to your succulent plants needs by changing the ratio of sand, aggregate and other components.
Fine sand or silt will clog the pores of the soil, so rinse or sieve out dust before you mix the different ingredients.
Hardy succulents grown in ground prefer to have grit and even some rocks to cling to. Their roots will travel quite a distance to seek out moisture, but they can't have any standing water - especially late in the fall if you live in areas where it freezes.
A mulch of stones, lava rock or even a few decorative larger rocks will give the roots somewhere to find a tiny bit of water, even when it's super hot and dry everywhere else.
Their favorite rocks? Anything with a porous appearance, like this sedimentary rock local to my area will work.
The ingredients and ratio - Equal parts by volume of:
For Sempervivum and other hardy succulents potted into containers use some type of commercial bagged potting mix such as Miracle Gro, Sunshine Mix #4, or comparable brand with equal parts Turface, fir bark and chicken grit.
Keep in mind that the Sunshine mixes contain water holding polymers, which hold a lot of moisture, so in most cases, your hardy succulents won't need much additional watering.
A word of caution with mixes that contain a water retaining polymer: this breaks down under freezing conditions, turning it into a sodden, slimy mess. Use these types of soil mixes outdoors with caution.
I suggest smaller pots for Sempervivum especially, and the addition of pumice or small sized lava rock for additional drainage.
After planting top dress with the chicken grit or other mulch like lava rock, crushed granite or pumice.
They come from alpine areas, growing in gritty soil with little organic matter, in a climate that is warm and dry through the short summer growing season and snowy in the winter.
Here’s another succulent soil recipe based on the above, with a few differences:
The turface usually won’t need to be sieved unless it has a lot of fine dust which could clog up the pores in the soil when wet.
For a trial, pot some Sempervivum in:
Plant others in:
In a month or so of growing, compare the plants top growth and also the root structure and see which one does best in your growing conditions.
Some climates are quite wet in the fall and winter, which requires an extremely well drained soil mix.
As alpine plants, many hardy succulents have the ability to cling to any small particles to hold them in place – they’re well adapted to steep terrain and cliff faces.
It’s worth experimenting a bit to find which soil mix your succulents like best for your particular climate.
When you think about where succulent plants originate, very few of them have evolved near trees. So they wouldn't necessarily be happy with leaf mold, compost or bark products because these would hold too much moisture.
The secret is to test, test and then test some more to see what kind of soil works best for the particular plants you're growing, and your climate and conditions.
Tender succulents require a slightly different type of soil, especially if you plan on bringing them in for the winter. The last thing you need is to bring in all kinds of pests, which are sometimes attracted to soils high ratios of organic matter.
Good drainage is usually the one thing missing from most house plant soilless mixes, which are sometimes the only type of soil available. Mix this type of soil half and half with some kind of grit, like turkey grit, or pumice - perlite is another option, but sometimes it's so light that it tends to float right out of the mix.
I use Sunshine Mix #4, and sometimes mix it with a small amount of steer manure, for outside during the summer. This is generally pasteurized, so won't bring in the same kind of pests as compost or other manure based soils.
Look for soilless mix specifically for cactus plants; this has the excellent drainage necessary for all types of succulents.