I have yet to see one of our grows that did not exhibit purple petioles. Sometimes most of the stems, sometimes a scattering of stems.
NOTE: Do not confuse purple/brown petioles with purple leaves and buds which often occur during cold weather, especially in indicas that really are kushy (as opposed to allegedly kush or afghan or pak).
(Hydro grows, all indica)
Purple petioles 002.jpg Purple petioles 008.JPG
Purple Kush (PK) in 12/12 week 1. Maybe her buds will be a nice purple, maybe not. We'll see.
Since our winter grows are always uber healthy and perky, I've not considered the purple petioles a problem. However, it's time for me to learn to fine tune nutrition and during research have found that purple petioles may be the result of inadequate pH levels or nutrients or micro-nutrients or only God knows what.
I've read that:
The condition is an indication of low magnesium or phosphorus.
It is common with Indicas, don't worry about it.
The pH is too low; raise to around 6.0.
Raise the air temp; the plants are too cold and will grow slow.
If the plants are otherwise healthy, don't worry about it.
The roots are too cold.
It's Daffy Duck's fault.
Which of the above, if any, is correct? If "none", then what is correct?