Promix is what our local nursery uses and it become obvious that seeds started ( and seedlings) in high quality potting mix ( and hanging flower pots!) Do better with Promix. I have used the "usual" mixes ( Miracle grow) and find more and more odd chunks of ? And I was tired of buying something that claims to "feed plants for months", when the seedlings look starved until I add fertilizers ( yes diluted). I had wanted to get the bulk bundle of the Promix commercial bales, but our local stores did not have them and shipping costs are high. Our local nursery sells them in the Spring (the large bags), but I wanted to start seeds this winter and missed out on the final bags of mix before they closed the greenhouse. Healthy plants start as healthy strong seedlings...