Just a reminder that if you have trees in the active growing period already, or have trees you’ve recently repotted, be sure to protect them from frosts and freezing. Long roof eaves will protect from frosts, and garages are very handy for the stronger snap freeze in late spring. Be very wary of temperatures in springtime lower than 27 degrees F.
Try not to get into that comfortable, ‘Oh it will be all right’ attitude for bonsai already out on the benches. Trees that normally have high resistance to extreme cold, such as alpine species, begin to lose that ‘antifreeze’ when they begin to grow. Even spruce and pine can be damaged.
You might remember that story from the Little House on the Prairie series, when on the farm an alarm goes off early in the morning, well into springtime, and the little plants were already growing strongly. It was a frost. Everyone got up and splashed a little water on each plant before the sun hit. The frozen water protected them.
Again, only those trees that are actively growing (leafing out) or that you’ve recently repotted need much consideration. Fall freezes are different; those are beneficial to some degree (except for such odd trees as needle juniper, Juniperus rigida, which can freeze but is sensitive to frost.)