Growths from a main trunk
The main tree is a parent 'something' onto which was grafted a knotted, curly-wurly willow. We lost the grafted top after three years when the storm snapped the top off. This spring the remaining stump (3 feet) sprouted growth from 3 'warts' up its trunk. They've grown very quickly - and tall. Bright green but the leaves are nothing like the original grafted willow. What should I do now? I wish to keep the new bush-looking growth as, while it's nothing like I bought, it is attractive and fills a space. Hope this makes sense - difficult being unable to show you! The tree/bush has added another 3 feet in height to the 3 foot high trunk.
The parent, or "root stock" was probably also some type of willow, because grafts need to be done between closely related species. It was probably not as decorative as the "scion," which is what you lost. Now your root stock has started to grow. Keeping it as a bushy shape is easy enough, all you need to do is keep pruning the shoots to encourage bushy growth. Here is a good article on pruning: http://pubs.ext.vt.edu/430/430-459/430-459.html