Few, if any, home landscapes are complete without an array of trees. Generally, trees are woody plants that grow taller than 15 feet and have a single stem or trunk. There are a few exceptions to this rule, of course, such as small Japanese maples or dwarf varieties but most comply. The key is to research any tree before you place it in your landscape paying special attention to its ultimate, mature height and spread as well as any common insect or disease problems.