There are a few myths out there stating how purple cannabis can be a sign of nutrient deprivation, but that isn’t true. Furthermore, other myths say that you can turn cannabis purple by freezing it or adding food coloring, both of which definitely aren’t suggested.
Purple plants are nothing more than genetics and, at times, a lowered pH level. Some strains have the capability to grow in low pH soil, which will not affect the plant when harvested.
So, if your plants begin turning purple, chances are you’re growing a purple strain with anthocyanins, or the growing temperature is slightly cooler and reduces visible chlorophyll.