Hi, you haven't said anything about your soil mix (which could well be the problem), or how you water and how much how often, which is just as likely to be a problem. Without knowing those, it's hard to say what's what. Can you post again with more information?

Sure, sorry about that. I water about every third day or so. It depends upon when the top layer of the soil gets a little dry. When it gets dry I give it a good soak until a little water runs out the bottom of the pot. The soil is a mix of some sort of gravel with very dark organic matter (Looks like composted dirt) on top. Sorry, I am new to this so I don't know the name of each component used; however, it was potted at a bonsai shop and the woman assured me it would allow for proper drainage. I have had the tree outside for a few days now, bringing it in at night (temps are below 40) and the yellowing seems to have stopped - but I'm not confident I have it figured out yet.

Well, maybe just try watering a day or so less often and see how it goes.

Ok Thanks for your advice. Do you think a Chinese Elm is a tree I can leave in a sunny windowsill or should I leave it outside all summer?

Outside for LIFE. In winter, you can sink the pot in a large container of mulch, put it in an unheated shed, or just leave it out (in zone 6) and it should be fine. It'll never do well indoors - it's an elm tree, not a hothouse plant.

Thanks, I have the tree outside and it has made a real difference. it is much healthier.