I think the growth rates you show are really leaf sizes. I can't speak for 'Manhattan', but I have 'Chris's Dwarf' aka 'Munchkin' and 4-6" is the usual growth rate-sometimes more. Leaves are about 1/2".

As for pruning, you can but I'd let them get established for 2-3 years first.

tj

Interesting, I've questioned rates as well on my "mariken." It's putting on 6"-9" this year and was closer to 12" on the dominant branch last year.

Am I sure it's " mariken?" It came from Iseli 4-5 years ago and looks like every picture I've seen of this cultivar.

I'll be moving or starting to prune it next year. It must be very happy where it is since it grows nearly as fast as my "autumn gold."

I got my 'Mariken' in 2010 in a one gallon and it only grows 3-4" per year for me.

A pic from last year.

tj

Some pictures of my "Mariken."

I think I mistook the previous years green growth as new growth and the new leaves are showing 4-6".

In any case, it's growing faster than I expected. Gets sun until 1 pm, then is completely shaded by the house. I'm not sure what I'm going to do with it, but it's too crowded.

Closer

Perhaps you are right, that the growth rates I anticipated were more relevant to leaf size. In that case, I will certainly have to learn to prune them because I want them to stay small. I really want miniature but that will no doubt be too much to achieve.