Ok, so I have 2 young plants, just a few inches tall. They are the same strain, under the same lighting and watering conditions and one of the stalks is a purplish color towards the bottom. I'm using an organic fertelizer but my question is why one has the purple and the other does not. I remember from a past crop long ago and in a far away land that this could be a deficiency? I forget which nutrient though...any help is appreciated.