Too hard to answer. It depends on the strain; How you are growing; What nutes; What stage; How frequently you water; and only the plants will tell you when you are messing up.
lmdesade Reviewed by lmdesade on . When do hit max PPM? This is a repost from general growing questions, didn't receive much feedback..so I'll ask the indoor crew (was meaning to spend more time here anyhow!) I usually give them the higher PPM towards the end of the run... in the last three weeks I use my regular flowering nutes as well as "Shoot Powder" which is real high in P to finish em up and then flush them out. I have a friend who told me he hits his peak PPM around five weeks, and then lowers it gradually and finishes in 8.5 weeks. Rating: 5