Crabapples make excellent pollenizers. I heard it's a good idea to have a couple around if growing apples.

To make a crabby apple into a good apple just figure out why it's in a bad mood.

5 inch diameter sounds like a sizeable tree. Maybe you could graft new varieties onto dome of the existing branches interspersing the new among the old.

Could be an interesting project.
Mike

This post was edited by mes111 on Fri, Jan 10, 14 at 21:02

I think it could be a great idea if the existing trees have a good framework to start from....otherwise they are gonna look awful for a long time if you have to cut them back hard and graft to water sprouts.
It allows for more varieties in a restricted space as well

I used to prune and graft for money when in college, and there were a number of farmers who wanted to switch apple or pear varieties (I was hired as part of a team, not doing orchards by myself). The method was hard cutting to 5 or 7 main branches (for vase or espaliered trees), then three grafts on each branch. It depends how tolerant of bad looks the owner would be, but in two years the tree looks full and is productive (you need to return and summer prune suckers a few times), so the bad looks are only in the first year. In three years, fully productive. It would be advisable to graft two varieties that pollinate well, compatibility in pollen and time of blooming, and also early season late season cropping for harvest extension.

A crabapple tree will make a good rootstock for an eating type apple. I have had good luck with this. It is not necessary to save any of the branches. Just cut it off at three feet or higher and graft away. Rind grafting will be the easiest method if the crab is cut this way. Have a good piece of conduit ready to drive into the ground for use as a supporting stake next to the trunk and your successful graft. Perform several rind grafts to make sure you get at least one good take. Just youtube "rind graft apple" to see what I mean. After a few years of training no one will notice it was grafted unless they know what they are looking for. I would wait until march or april to start this work.

Works great, I've converted many naturalized crabs into named varieties and it is far superior to planting new trees. They bear real crops more quickly and require no coddling.

I like to use the water sprouts where I want my permanent branches and graft them and then spread them more horizontally after a couple years of rapid, vertical growth. There are many other ways to do it, however. With water sprouts you can use the simplest of all grafts- the splice.