This is a time of year when our trees are almost dormant. The more or less constant high heat has caused the process of photosynthesis to slow down. There is an optimal growing temperature for all trees, and each is a little bit different. Pines, Junipers, Cypress and other conifers should be showing a lot of brown/yellow needles or scale growth due to the fact that they are putting a lot of their energy into forming new buds. As the new growth is formed the older growth must be abandoned because it is simply not as efficient as the new growth. Remove the brown needles with your hands or tweezers and your bon- sai will look a lot nicer.
For our deciduous trees the leaves are beginning to tire. They have been working hard since March/April to produce more tree and the molecules that conduct photosynthesis are starting to wear down. During this time it is possible to repot maples, elms, oaks, beech, crab apple, wisteria, and many other deciduous bonsai. As long as the roots are not treated too harshly the trees will still have time to make leaves before the weather gets too dark and cold for them to produce the proteins, carbohydrates and sugars the tree needs to grow. If repotting is needed remove all the leaves and go ahead. In October/November the leaves will begin to change color with most of them falling by December here at the nursery.