I noticed that they use Pro-Mix BX at Shaw Nature Reserve so that is the seed starting mix and potting soil I’m going to use for most seeds and plants.
They do make similar products, but what you want in the product is MYCORRHIZAE.
According tho their website, it improves fertilizer uptake; reduces fertilizer costs increases plant’s resistance to stresses; reduces maintenance costs.
Some products which look very similar don’t have the MYCORRHIZAE
I’be been told that the HP variation stands for High Porosity and just has more perlite. It is more expensive.
2016 – I found the BX product at the Bayer Garden Centers. $36.99 for a 3.8 cu. ft compressed bale
Note – this brand does NOT have fertilizer so you will need to add some Osmocote when you transplant.
I also found Pro-Mix at Menards, but it does not have the Mycorrhizae.