Hello! I'm new to the forums, and joined primarily because of this troublesome issue. I have two healthy white geraniums growing in clay pots on the windowsill in my kitchen. The plant on the left (see photo) is the older one that I grew from seed about five years ago and the one on the right is a descendant that is around two years old. Both were potted with the same soil mix at the same time (two years ago). I never had any problems. They are growing a bit tall for the size of their pots, and probably should be repotted, but these pots fit the windowsill and they seem happy there :) These photos were taken today, with their new Spring blooms. (The blue thing is a glass marble; I put one in every pot for luck, but didn't think to remove it when taking the photos - sorry about that!) My problem is the older plant on the left. As you can see there is a feathery short green layer of what I suspect is moss (and hope very much is not something serious) growing around the plant. I have no idea where it came from! I'm assuming it came through the window via airborn spores but if that was the case the younger plant is closer to the screen and should also be affected. I haven't been able to identify the moss type and I would really like to know if it is harmful to the plant! The plant does seem happy but it isn't holding its water the same and I don't know if the moss affects this?! I have done some looking around on the internet and there seems to be conflicting opinions about moss and houseplants. Some seem advocate to it for a more decorative look, and I have read that it can be beneficial for retaining water (although that doesn't seem to be the case here). This was the reason I left the moss alone when it first started to grow, although it is multiplying quickly now and will soon overwhelm the soil I think. On the scary side, I have read that the moss smothers the soil and blocks the sunlight available to the plant, and that it turns the soil acid and will eventually kill the plant. Any help in identification and advice for elimination (if needed) would be very much appreciated! These two geraniums have sentimental value for me, particularly the parent plant (which I grew from seed for my Grandma for Mother's Day many years ago and ended up taking home when she moved) and I would very much like to save them. Thank you for reading! P.S. I am asking this question here rather than the houseplant forum because I think the invasive moss (?) came in from outdoors and so outdoor gardeners might be more familiar with its nature and how to eliminate invasive plants in general :) Hope that's okay!