If you are currently trying to plant trees in order to shade your garden, you will probably want something that grows very fast and provides plenty of shade. With the many types of trees available, you will have no problem finding a variety that will grow extremely fast and provide all the shade that your garden needs to survive. There are also many things you can do to speed up the growth of trees.
Generally trees are separated into two categories: long lived and short lived. If you are just looking for some temporary shade for your garden, you should stick to a short lived tree. But if you plan on keeping it for years, go for a long lived tree.