Ultra dwarf fruit trees are very small trees that produce edible fruit. Most ultra dwarf trees are well under 6 feet tall and grow in an 18-by-18-inch pot. In some ways, growing a dwarf fruit tree is similar to growing a bonsai. Frequent weak fertilization and frequent watering give the tree the resources it needs to produce fruit. Like bonsai, a root trim every two or three years will help to limit the overall size of the tree.
Water your ultra dwarf fruit tree frequently. How often will depend on your climate, but plan to water two or three times a week. Soak the pot until water drains out of the bottom. Never let your ultra dwarf dry out. However, do not allow the roots to stand in water.
Fertilize your ultra dwarf often. Potted trees require more fertilization than trees growing in the ground. For ultra dwarf citrus trees, fertilize with one-half strength fertilizer every two weeks with a good, balanced citrus fertilizer in the spring and summer. Although you should start fertilizing every two weeks, watch your tree for signs of over or under fertilization and adjust accordingly. An over fertilized plant will have lots of green growth that occurs at the expense of fruiting. An under fertilized tree may not have good green growth nor fruit well.
Watch your pot for a white buildup around the rim or on top of the soil. This white buildup indicates over fertilization. If you see a white buildup, thoroughly water the plant to flush the excess fertilizer from the soil. If the buildup is extreme and doesn't respond to flushing, re-pot your tree in new soil.
Remove your dwarf citrus from the pot in winter every two years. Trim one-third to one-half of the roots with a pair of sharp pruning shears to limit its size. Re-pot your tree using a good, well draining potting soil.