You can begin the final defoliation of your deciduous trees. If the leaves are brown, grey and faded now is a good time to remove them. Be careful because there are a lot of small buds at the base of those leave that are going to make your new branches next year. With trees whose leaves are still green you can apply a bit of 0-10-10 once a week for the next month at 1/2 strength to provide potassium and phosphorus that is so important for root growth. This application can also cause brighter color in many of the trees. If your bonsai are showing great fall colors (Amur Maples, Tridents, Gingko, Crabapples, and Elms are yellow, orange, red and gold right now), relax and enjoy them.
For conifers and junipers it is a good time to wire them. Remove all the old needles and leave 5-10 bundles of needles at the end of the branch. Protect the new buds which are growing at the very tip end of the pines. On the junipers you can let the new distal growth run but remove those nasty little groups of pincushion needles that are emerging at branch divisions and in the crotch of leaf separations. Because these trees are beginning to slow down bending is easier than in the Spring and Summer. Use sealer to repair any damage where the branch cracks or splits.
The weather keeps getting stranger and stranger so keep your fingers crossed and don’t let your bonsai dry out.