Tree Dormancy causes a lot of worry for many newcomers to bonsai. It can be scary to start seeing your tree start to have yellow leaves or even drop them altogether.
Luckily this is very normal and a necessary part of your tree’s cycle. Every tree will go into a dormant period during the cold season. This applies to deciduous, tropical, and even evergreen trees. During this time, every aspect of your tree will slow down. Your tree will not push as much energy and will conserve itself to stay alive. For deciduous and tropical trees, the leaves will begin to turn yellow and fall. For evergreen trees, the tree will still slow its growth but will not lose their leaves.
Many people will try to force a tree from entering it’s dormancy period. This is typically done by using a greenhouse or bringing it inside. With some species of bonsai, this will not affect the tree too greatly. However with others, this will interrupt the natural growth cycle of your tree and may prevent correct growth patterns. These patterns are usually what we use to train a tree to develop branches or pads.
Just remember, once it starts to warm up and spring begins, as long as you have maintained your tree correctly during the winter, you will see fresh new green sprouts appear. Once the sprouts appear, they will develop very quickly and you will have a tree with full foliage once again.