But only in spring... now all trees are going (or gone) dormant for the winter.

Yes you can graft them, but in late spring like larke said. If the sucker shoots are still softwood (don't have an aged hard bark)which they probably are since they are fresh shoots I would recommend propagation through cuttings which is way easier than grafting. If propagating by cuttings its best to do so in late spring to early summer.

Larke and Mike,

Thanks for your replies. Yep, the suckers are still soft wood. They are long enough to have plenty of cuttings to root and, to hurry a good nebari, I was considering playing with a graft in addition. It'll definitely be spring or later here before any grafting takes place, and I'll need to prepare the rootstock first as well. The actual "tree" has a good root base, but I'll be leaving part of the suckers on the tree for a while as sacrifice limbs, to thicken it and the trunk further.

Betty