Auto’s in straight promix Hp, any advice?

Hi, I’m planning my 2nd outdoor grow for this spring, going with autoflowering seeds this time, and i want to start them in straight ProMix Hp in 5 gallons grow bag, add some nutrients around week 5 or 6 (dont have any yet but looking to buy something like GH flora series)
Is someone is familiar with promix hp? Should i put something else in it or just go straight and add nutrient when needed ?


Im using promix hp for the first time right now and really like it. Far as the nutrients, im using the fox farm trio.
After I’ve used these up,im going to try out GH though. Check out Bill Ward on YouTube. Thats what he uses and gets awesome results.