What is the best soil for growing cannabis?

There are a few ways you can achieve a good result. My choice if I had to grow in soil, would be some good composted soil. The darker the better.

Dig some holes and fill them with a great (bought) soil.

Add some perlite to aerate it, and make good drainage. That also help against salt build up, as the drainage become improved.

An important thing is the PH. A good soil PH is essential, so the nutrients can be used by the plant without problems. No lock ups.

So use some dolomite lime in your soil mix. And make sure it’s mixed good into the soil. Then you have made sure there will be no problems with the PH.

It will keep the PH inside the values where the plant can make use of the nutrients without problems.