This is my first time growing lavender, I got a nice sized burpee one about two almost three weeks ago, it was growing fine in a planter next to rosemary and thyme which are all growing alright. Just a few days ago, I noticed the lavender starting to get purplish/brown leaves on one side of the plant and tonight I noticed it has spread it more leaves and branches. So I fear it may be root rot... I didn't quite check whether the plastic windowsill planter I got had sufficient drainage and we had some rain on consecutive days recently with a few days of warm sun that dries out the soil.

I'm wondering whether its possible to pull the plant out of the box and replant in a separate container? I'd rather not do that, bc it might destroy the roots and I have the three plants nicely spaced out in the planter at the moment.

But I'm also wondering whether if its root rot whether it will spread to the rosemary and thyme since I read its caused by a fungus? The rosemary and thyme are growing quite well at the moment.

Thanks for any tips and info you may have!