There are many varieties of crab apples, which produce fantastic blossom followed by – in most cases – a wonderful crop of small fruits, excellent for making crab apple jelly. The fruits which are left on the tree form an important part of the diet of many birds during the winter.
As regards trimming crab apple trees, pruning is very simple. Just make sure that the four main branches of the basic tree structure are well placed to make an open canopy, for unobstructed light entry. After that, let the tree grow without interference. The only operation that may be necessary from time to time is to remove crossing branches, which tend to reduce light entrance into the centre of the tree.