The crab apple tree is set apart from other apple trees based solely on the size of its fruit. Trees that produce apples 2 in. or less in size are considered crab apples. In the springtime, crab apple trees bloom with white, red or pink flowers, and crab apples follow in summer and fall. In the fall, the leaves change to intense colors and then fall from the tree, revealing the remaining fruit, which can remain on the tree throughout the winter months.
Prune a crab apple tree before buds appear in the spring. Pruning after the start of the season's growth will disrupt the life cycle of the tree and prevent it from bearing fruit.
Remove any dead, deceased or infested wood, which is easy to spot. Unhealthy wood will fail to produce foliage or will produce less foliage than healthy wood. Branches that rub against each other or against the trunk of the tree should also be removed so they will not sustain bark wounds.
Don't cut away more than a fourth of the branches and limbs in the crown of a crab apple tree in any one season. Crab apple trees depend upon their leaves to convert the sunlight's energy into food energy.
Trim large branches back to the collar--the piece next to the trunk of the tree that is slightly larger than the branch itself. The collar contains natural inhibitors that will cut off sap flow and prevent the spread of disease if the newly cut branch becomes infected.
Prune crab apple trees so that the branches nearest the trunk are 45 degrees away from the trunk. Keep a distance of 18 to 24 in. between main branches throughout the rest of the tree to allow sunlight to penetrate the tree and reach the branches and limbs in the center and on the underside of the crown.
Don't prune a crab apple tree within a year after transplanting it. The extra foliage will allow the tree to absorb the sun's energy it will use to become established in its new location.