A: The temperate group is probably the most popular group of trees. The juniper, for example, is a classic temperate tree. These are trees from climates that have a definite change of season, but without very harsh winters.
To replicate their natural environment, they require what’s known as a partial dormancy: they need to have some change in conditions through the winter months. While they don’t have to be subjected to freezing conditions, they will fail to thrive if the temperature is very much the same throughout the year, as it would be in a warm room. They do need some kind of a slow-down period during the winter.
Ideally, these trees should be outside throughout the entire summer. They should stay outside during the early fall and through the season where the temperatures will drop down to the high twenties or low thirties.
This way, the trees are able to follow the natural weather pattern of experiencing a gradual change in the seasons.
A common mistake is to take a tree that has been grown indoors throughout the summer and then, wishing to give the tree a "cold snap" in an attempt to induce dormancy, placing it outdoors into what would be, to the temperate tree, the very sudden and rather severe cold of fall or early winter.
Dormancy is a gradual process, and it takes a couple of months for a tree to ease into it. You can’t just place the tree into a cold place and expect a natural dormancy to occur. The tree has to adjust gradually to the change of seasons, just as it happens in nature.
On the other hand, if you do not give it a place where the temperature will change and dormancy begins, the tree will gradually get weaker and weaker, just like a person trying to function without sleep. That is why trees benefit from being left outside in the fall and early winter.