First off, from what I can tell there is no difference between potting soil, potting mix and transplant mix. It’s all the same thing just different names.
The reason that you want to use potting soil is that it allows for aeration and water to flow. If you use traditional soil in a self watering container, the roots would get too compact and not be able to grow. That’s no bueno.
Not being sure which to use, I decided to use both. Screw it why not? That’s part of this whole experience. Trial and error to find out for myself what works best.
Besides the base, the other ingredients are pretty similar. They are vermiculite, compost and some kind of mineralization.
The vermiculite makes the mix lighter and allows for better aeration. The compost provides the nutrients and the minerals, well they provide minerals.
This is coconut coir based, which according to the label is “a sustainable alternative to peat moss.” From some of the articles that I read coconut coir retains water, which is bad for self watering containers. I guess I’ll find out.
I also bought ingredients to make my own organic potting soil – sphagnum peat moss, vermiculite and garden lime. This was mixed up with the compost that I made in my kitchen.
So instead of reading 100 different arguments on which kind of soil to use, I’ll use both and see which one works best and so will you.