Thank you Sal. You've opened up a great topic.
The soilless mixes are the ones I use consistently. For all my plants, including succulents, I've mixed my own potting soils for 35 years. (I was a weird kid.) After many attempts at potting soils, I found that certain ingredients are to be avoided in pots. First, topsoil should not be used. Some people may be able to grow great plants with it, but growing up in the midwest, I had clay soils that would compact terribly in pots. Later I found out that any clay in a pot eventually loses it's air spaces from the lack of/degraded organic material, the micro-flora dies, and it all compacts into... well... clay. Some soils may have enough organic material to keep the mixture afloat, but as a rule, topsoil should be avoided. The next ingredient I never use is Michigan peat. Unlike sphagnum peat, it is a murky additive that holds water and creates a tight, poorly draining mixture.
Important to remember, potting soils are as different as the people using them. I can mix a soilless potting mix that works well for me, but another person may kill everything they try to grow in it. My personal mixes are too well drained for most people.
My basic potting soil mix:
2 parts coir
1 part coarse perlite
1 part vermiculite (I like to use the coarse, but can't always find it.)
This is the base for nearly all of my plants. I add other ingredients as needed depending on the growing requirements of the plant. For weight, I add very coarse sand, sometime pumices, or other chunky bits. Pine or fir fines, SMALL bark chips may be added for mass and drainage. When using bark products, make sure they are well composted or aged. Fresh bark, or even larger pieces of composted bark will rob nutrients from the soil. A bit of fertilizer with a nitrogen component helps to alleviate the effect.
Lime is used to balance the acidity in sphagnum peat. I don't use it for coir based mixes. Since I fertilize regularly, I don't add other fertilizers to the initial mixture. That comes later and is more dependent on what I have growing in the pot rather than broad spectrum fertilization.
How often do I repot? <<<GULP>>> A succulent I repotted last year hadn't been done in 18 years. I like to repot every three years for most things. Some require even more frequent repotting, especially if they are fast growers and need more room.
So... what works for YOU?
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