There are several different kinds of fruit trees to consider, apple, cherry, peach, pear, plum. As we live in northern portion of Illinois, apple is likely the main fruit tree grown in back yards because it is very winter hardy.
When you shop the fruit tree catalogs or visit with your favorite retail garden center to find out what cultivars or varieties they will be carrying this Spring, homeowners should consider dwarf apples as in most cases yard space is limited. Dwarf apple trees are naturally smaller than their full sized siblings, are much easier to train, prune and maintain that a full sized fruit tree. If you have lots of space, full sized fruit trees are always an option.
Fruit trees are dwarf because they are naturally so or because fruit tree growers graft or bud them to a dwarfing rootstock, limiting the size of your fruit tree. If they are naturally dwarf, then the apples listed will be a "spur-type" tree. There are many examples of spurs available to us – Empire, Red and Yellow Delicious, Macintosh, Rome, Winesap, Early blaze are a few. The smallest fruit trees will be a combination of a spur type grafted or budded on a dwarfing root stock. These will need some kind of support as their root systems are limited and can easily be blown over. It should be noted that the catalogs will list a mature size, considerably small than the full sized version, but that ultimate size of your dwarf tree is really up to you. If you start to train too late, or do not prune correctly that dwarf apple tree will be much larger than you wanted or expected, yet still much smaller than a full sized tree.
Another very important key to selecting your fruit trees will be pollination. Fruit tree catalogs will suggest which apple varieties will be the best pollinators for the varieties you wish to grow. It is critical that you have TWO DIFFERENT varieties blooming at the same time in order to get good pollination and a strong fruit set. Apples are for the most part considered to be "self-unfruitful" meaning that pollen from other flowers on the same tree or from another tree of the same variety will not pollinate itself. A possible exception to this rule is if you have an ornamental flowering crabapple in bloom at the same time, pollen from the flowering crabapple will pollinate your fruiting apple trees. So if you live in an established subdivision and you or a neighbor has a flowering crab apple in the front or side yard or an apple tree of a different variety that blooms at the same time, you do not have to plant that second apple tree for pollination purposes, which will free up space in your backyard.