Bonsai: Coping with the cold weather
During the winter, it’s easy for your bonsai to get too cold and hibernate. You’ll notice this when the leaves start turning yellow and falling off. However, not all bonsai will do this and there are sometimes ways to prevent this from happening at all.
Generally, the easiest way to keep your bonsai from “catching cold” is to water them during the daytime when the sun is out. This will ensure that the bonsai soil will not get too cold, and therefore bring the temperature of the entire tree down. However, please remember it is still very important to water your bonsai daily if the tree requires it. Otherwise, the tree may actually be dying and not hibernating. If your tree must hibernate because of the climate conditions, watering requirements will decrease sometimes to only once a week. Pay close attention to the soil conditions for best results.
For detailed information on how your bonsai is doing with respect to the temperature, we recommend a soil thermometer. It will indicate when your bonsai may be reaching the lower threshold. Assuming that it is, it may be time to either bring the bonsai into a greenhouse to keep them at their optimal temperature.
Individual bonsai species will vary as to how they react to the cold climate. For example, junipers enjoy living through the snow. Bonsai trees are very hardy. Even if the tree does decide to hibernate and the leaves do fall off, keeping them well watered and maintained will ensure that the leaves return fully in spring.