Every year I have problems with my elms... In the spring they grow very, very well, but in the summer a lot of leafs (1/3 of them) are yellowing and fall... The soil is not a problem, it is very well drained (Walter Pall recipe ). I usually keep them outside on my window sill all year long, also in winter when temperatures drop down to -20C here in Romania. The big problem is in summer when my window sill is in full sun and the temperature goes well above 40C. This year I moved the trees on my balcony where they are not in full sun, but the temperature here also reaches 40C and the humidity is very low... Could this very high temperature be the cause of the falling leafs in summer? I was thinking to bring the trees inside on the window sill where they will have a couple of hours of full sun, but the temperature will not be that high. Could this be a solution?