You might want to ask this question in the Conifers forum, right here in the gardenweb. Be sure to put your general location in your new posting, too. You can't get useful suggestions without us knowing where you live.

Also, conifers don't just grow to a certain height and then stop. If they average 3" per year in their first decade, they'll continue 3" per year after that. To get a really good appreciation for this (and for a mindbogglingly wonderful experience) visit the Gotelli Conifer Collection at the National Arboretum. You'll see things like 20' versions of cultivars that are listed to have a "mature height" of 3'. Conifers that stop growing are dead. Terms like miniature or dwarf refer to growth rate, not ultimate size.

I visited with one of the persons that developed witches brooms for miniture trees and he told me and the group I was with that what was sold as dwarf blue spruce would stay small for the first 25 years then begin to grow and reach the same height that a normal one has. He had two pictures one of the dwarf one over 25 years showing what happened.

My dwarf blue spruce that came with this house has started to grow and is about 20+ feet tall. The central leader was trimmed sometime in it's life and I now have multiple leaders coming out of the top making a very interesting basket shape. Will have to cut down in future years but right now I enjoy the tree.

"I visited with one of the persons that developed witches brooms for mini(a)ture trees and he told me and the group I was with that what was sold as dwarf blue spruce would stay small for the first 25 years then begin to grow and reach the same height that a normal one has."

While sometimes witches brooms (and other mutations) will revert, that is not what they're "supposed to do". Before dwarf and miniature varieties are introduced, they are studied to make sure they are stable. If they really are stable, they won't exhibit the growth spurt later on as you're describing. Except for reversion (which ideally shouldn't happen with introduced cultivars), conifers should exhibit approximately the same growth rate each year until they reach their terminal size or die.

The really old (and really large) dwarf and miniature conifers, that I mentioned above, in the Gotelli Collection are not big because of a late growth spurt. They gained their size through very long term steady growth (think tortoise in the tortoise and the hare).

I can not remember his first name but he was the person that collected and researched all kinds of dwarf trees many of them started as collected witches brooms. Perhaps you will know of him if you like minitures. The boxwood Morris Midget was named for him.

'Morris Midget' and 'Morris Dwarf' were introduced by the Morris Arboretum in Philadelphia, and my guess is that they were named for the arboretum. I know lots of collectors/propagators from the Conifer Society, Gardenweb, and other venues, but I'm not all that good with names. So even if you knew his name, it might not ring any bells.