The average fruit tree can potentially grow 15-20' tall and wide. There are naturally dwarf cultivars that exist, however if you are looking for the best tasting fruit these are not nearly as good. There are dwarfing rootstocks, that will limit the size and/or vigor of the tree they are grafted to. Many apples and citrus can be effectively dwarfed by grafting them to special rootstock. Most rootstocks used, however, are chosen because they make the tree more tolerant of specific diseases or soil conditions. Some rootstocks are even known to produce better quality fruit than the cultivar produces naturally. If allowed to grow full size, most home gardens only have room for 2 or 3 trees. Fortunately, just about all fruit trees can be quite productive when maintained at just a fraction of their normal size. Research trials have shown that the majority produce heavily at just 4' tall and wide with no special pruning skills required.
Pruning during the summer months when the trees are in growth mode does not negatively affect the next year's crop production as it does when pruning is done in winter. Next spring's flower buds develop during the fall. Summer pruning for size control is now common practice on most types of fruit. We still do some corrective pruning in winter.
I maintain the majority of my fruit trees at 7' tall and 4' wide. At this size I can pick fruit while standing on the ground and the plant still looks like a tree.
When I was a bachelor my back yard looked like a mini orchard with trees planted every 7' feet in rows. After I got married, the orchard look was out. I now group my trees.
I planted 11 cultivars of apple trees in my back yard. Instead of planting them singly, 7' apart, I arranged them in three groups of 4,4 and 3 cultivars. Each group is allowed to grow within an 8' wide circular area. The tree's trunks are planted 24" apart in a circle in the center of the designated area. As they grow I made certain that extra vigorous cultivars do not crowd out their neighbors. After growing, each group looks like a single (multi-trunk) tree that is 7' tall and 8' wide. The groups are far enough apart to allow us to plant flowers and shrubs.
There are several advantages of this "grouping" method. The close proximity of trees causes them to "dwarf" each other. Tree growth naturally heads outwards toward open spaces. The branches of different trees in each group operate as if they belong to a single tree. The branches that normally grow 8' long won't suddenly grow 16' or 24' long, just because there is more than one trunk. In other words, a grouping of 4 trees in no more difficult to keep within the 8' area than a single tree.
A single 8' tree could produce about a hundred fruit that would ripen (in the case of apples) within 4-6 weeks. If you grouped 4 trees with 4 different harvest periods, you would still get a hundred fruit, but the harvest period could be greatly extended allowing your family to eat, rather than give away, most of the fruit.
Apple cultivars have some of the most widely distributed harvest periods. The earliest apples can be picked before summer, the latest will hold until mid winter. If you choose the right cultivars you can pick apples for 7 or 8 months of each year!
Citrus fruit generally hold on the tree longer than any other fruit. A navel orange can be edible in December or left on the tree until May. Most citrus cultivars store on the tree for at least 4 months. For this reason I usually plant my citrus singly and allow them to produce hundreds of fruit. Very few are wasted. Lemons and limes are popular because they can bloom several times per year and have fruit available 12 months of the year.
Fig trees have very perishable fruit, however most figs ripen only a few at a time over a 4-6 month period.
You can group unrelated fruit trees, however a group of closely related trees is much more attractive. The types of fruit than I usually group are those that ripen quickly. Peach, nectarine, apricot, plum, pluot, and loquat. I even group slower ripening fruits like apples and pomegranates to get a longer harvest season and more variety.
I've given my avocado group a much larger area, about 12' across. Avocado trees are relatively light producers and I will allow my trees to grow 8-12' tall.
Many fruit trees can be grown as a hedge. Citrus cultivars are easy to shear. Loquats can be pruned into hedges. Apple and pears are often trellised into hedgerows. Don't forget that grapes do well on vertical and horizontal trellises.
