I never heard anything about PM being used to make plants turn purple. Its a flower enhancer not a color enhancer.

I would use 1/2 the recommended dosage maybe a little less just to be safe. I've used bushmaster before and it really worked well other than my plants looking sickly for a few weeks. I used it on a sativa grow and none of the plants got over 3' tall!

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Kali Mist/Colombian Red Haze journal

Here's my last grow AK47 and PPP in hempy journal