I got a new Chinese Elm bonsai a couple of months ago, and it's been doing well until this week. I noticed some of the leaves turning yellow and dropping, which is making me nervous. Is this normal in spring? My other plants are sprouting new growth, but this elm seems like it's shedding instead. I've read that they can be semi-deciduous depending on climate, but I'm not sure if I'm over or under-watering it. Any advice from those who've had them before?