During winter, certain species of bonsai trees (Chinese Elms and Other Specialty Trees) will lose their leaves. Some bonsai beginners may feel as though their bonsai trees are dying. Fortunately, many bonsai trees are hardy and can sprout new leaves quite easily if they are tricked into thinking it is still spring.
You will need to create a greenhouse atmosphere during the day to keep the tree extremely warm, above 85 degrees F. This can be done with a glass dome or tabletop greenhouses. However, ensure that the tree gets ventilation. Using a humidity tray will also allow the water to evaporate and create a humid environment as well. At night, ensure that the tree does not get below 50 degrees F.
Keeping your tree in these conditions will ensure that your tree will continue to flourish and sprout new buds. If the tree is left in a cold environment, the tree will naturally take its course and become dormant until springtime.