Lavender is a woody subshrub. I'm betting that the 'purple' color you're seeing is the normal process of the lower part of the stem turning to woody brown. Oregano and thyme can do the same, and especially rosemary, if you've ever grown those--compare the type of color displacement to that?

Most herbs do not need weekly fertilization (or fertilization at all if grown outside in decent soil). Potted herbs should be occasionally fertilized with low-number organic, but not weekly.

Thanks Balloonflower!!! Thats really helpful information. I remember having chocolate mint and the stems being the dark purple color. I was told i had a deficiency but later found out it was normal. So that makes total sense about the lavender.

As for fertilizing, how often would you suggest I fertilize. They are currently in coco coir mixed with vermiculite and compost in red solo cups. They are in a grow tent. I am growing basil and lavender for a recent buisness venture I am doing.

What's the compost amount in them--it should have good needed nutrients. And how long are they staying in the little cups--planting out soon, or just growing in cups? Coir and vermiculite do not have much in the way of nutrient content.

In the solo cups, I would not do more than every other week, with diluted liquid fert. Maybe find a 2-2-2 or similar and go half strength. The babies don't really need a lot. I am not sure about how fert affects lavender, but with basil, it can force too much extra leaf growth, but they won't have decent flavor since it dilutes the essential oils that provide the flavor. That's the case with most store-bought herbs--they're overfertilized to look pretty, but they lose the flavor.

I fertilize my 'adult' potted herbs monthly when I think of it, but it's probably closer to every other month, and not at all generally over the winter when they're more towards dormant.