My phals are in glass beakers. When I let them dry out the roots look really sinewy and silvery. I will try doing a soak and then dump out the water. I've been letting them dry out over the weekend (I have them at work) by dumping out all the water on Friday afternoons and putting water back in on Monday mornings. I'm going to try doing the opposite - leaving them dry during the week then soaking them over the weekend.