I have a five-variety dwarf apple tree that is doing well, but seems to be developing a very strong central leader. (I planted it last year.) Is this going to be a problem? I seem to remember hearing that I shouldn’t let it do this, but I can’t find any information about how to prune this type of apple tree.
As I suspected, the answer to your pruning question was lurking in the pamphlet I received many years ago with my Raintree Nursery tree order. Here is what they say about “combo fruit trees” and their care:
“Combination fruit trees with several varieties on the same plant can be a fun way to grow lots of varieties in a limited area. They can be somewhat challenging too. Often one or more varieties (branches) will be much more vigorous than others. If this problem isn’t carefully addressed, then the tree can become more and more lopsided and the most vigorous varieties will overgrow the others and dominate the tree. Prune back the most vigorous branches upon arrival (if we haven’t already done so) to even out the branch lengths. Prune the most vigorous branches back again in the summer to maintain a balance. The most vigorous branches are the most upright. Spread the branches if they are supple enough to spread without breaking. If you keep any upright branches and they are too stiff to spread, cut them back, if possible to the lateral side branches. The combos should be grown as open center trees. On most combo trees, the varieties are named on the plastic label attached to the tree with the bottom budded variety listed first, the second from the bottom listed second and so on. Missing varieties are crossed out on the label.”
University of Minnesota Extension has information on open center pruning.
Oregon State University Extension has a good general guide by Jeff Olsen to Training and Pruning the Home Orchard.