Outdoor: The most important thing is to water the trees. The second most important is water. Heat and drought can have a major effect on our bonsai. In the sun, a tree in a bonsai pot can dry out surprisingly fast. Check the trees as often as possible and water them thoroughly whenever you water them. Spraying water onto the foliage late in the afternoon can help cool the foliage and container and reduce water loss. Reduce or suspend fertilization. If you are not seeing new growth on your trees, it is best to stop fertilization. You may restart when new growth is evident. Wiring and pruning may be done at this time. Do not repot. Provide shade for thin-leaved trees such as maples that may burn in full sun.
Indoor: If these trees are spending the summer outdoors, treat them as the above outdoor trees. If they are indoors, water as needed. You may fertilize trees that are indoors that show new growth. You may transplant tropical trees but provide shade and adequate moisture after transplanting. One other thing; water, water, water, and, oh yes, water!
Works Cited Editor. (Vol. XII, Number 7, August, 2005). Things To Do This Month. Bonsai Hai . Prairie State Bonsai Society