You can make your own potting mix:
- 30% peat moss or coco coir
- 30% perlite or vermiculite
- 30% compost or soil
From Larry Hall:
Miracle Grow potting mix works great or you can mix your own by using 2/3rds peat moss and 1/3 well rotted manure or compost and a couple of good handfuls of perlite. It lightens the soil. I also add about a cup of garden lime or dolomite, I also throw in a handful of Epsom salts.
A standard batch I will make would be 2 5 gallon buckets of peat 1 bucket of compost or well rotted manure 1 cup garden lime and a handful Epsom salts.
2 five gallon buckets full peat moss
1 five gallon bucket Well rotted horse manure or compost or worm castings
1 and 1/2 cup Garden lime
1 large coffee can full of perlite
1 handful of Epsom salts