Shohin and mamé, or smaller size trees, should be under cover – this allows for better control of moisture levels.
Probably one of the worst times of the year for your bonsai. During the winter, most trees need to be well protected from long periods of freezing temperatures. Place in a cold greenhouse or polytunnel or cover them with insulating material such as horticultural fleece. If there is little or no rain, occasional watering should keep them moist but not wet.