I have a small mint plant that a friend grew from a cutting and gave me. He had it in a tiny pot, so I transferred it to another pot in pretty short order, and it's certainly been growing. I have not yet used any sort of fertilizer on it. Recently, I've noticed some of the stems are purple, and those purple stems have dead leaves. Here's a picture:
One possible cause that I'm aware of is that it's gotten too much water. I generally keep it out on a window sill, but it's been raining a lot the past few days. Would it be better to keep it inside until the weather clears up (or at least until the soil dries out a bit)?
But more to the point, should I actually be worried about this at all, or is this considered normal behavior for mint?