As leaves drop from semi hardy deciduous trees, wait an extra week or two and then put them in the greenhouse if you have one. Leaves from tropicals (already in the greenhouse) will fall and must be cleaned up immediately. Set out bait for slugs and mice to prevent winter problems. No fertilizing is done in the greenhouse now.
If you have a light room, prepare it for your tropicals and semi-tropicals. Water trees frequently. Many features of a light room include a fan to circulate air and a humidifier to provide moisture. Plastic sheeting can help humidity levels stay higher.
Light can be provided by LEDs or flourescents (grow lights), and reflective foil will increase light. Metal halide lights give intense light but also throw off a good deal of heat which some trees may not like, and they also use a great deal of electricity.
Leaves are falling and temperatures drop. Prepare the winter storage area. A secure place out of the wind for hardy trees (perhaps with some sphagnum or similar to protect roots), and a cold area (above freezing) for frost-sensitive species, like a garage or breezeway. Winter temperatures between 34 and 40 degrees are ideal for many trees.
Stop fertilizing. This is the month to start major work in pines. Pines may be potted but waiting until early spring is best.
Outdoor trees which are frozen require no water, but above freezing do not let them go dry. Cover with snow or ice cubes which melt above freezing.
Indoor hibernating trees require less water than in the growing season, but don’t let them dry out completely.