It may or may not fill out. Would need a pic to give better info.

But......., if I understand correctly, you want a large specimen so you don't have to wait but you're asking if there's a chance a tree will fill out after waiting several years? Why not buy smaller in the shape you want?

tj

Pruning back tops would increase amount of time waiting for large tops to be produced. As well as making tops hedge-like. Non-selective top pruning at planting time is an obsolete practice.

It is entirely common for any young tree to have a lanky, often narrow shape and sometimes sparse branching, pretty much regardless of species -- Japanese maples are no exception. The younger they are, the more ungainly they they typically appear. Trees tend not to fill out and spread their canopies until they reach a certain maturity and establishment in the landscape. Much like adolescent humans, they need to grow into their bodies :-) If the overall branching structure is satisfactory, I wouldn't necessarily hesitate to purchase one that doesn't yet show a "classic" Japanese maple form (whatever that is - it will differ widely from cultivar to cultivar) -- it will eventually.

FWIW, Japanese maples offered for sale in containers have typically been grown that way from the start, not field grown and then dug and containerized. And even these tend not to be crowded excessively in the growing field, as doing so tends to increase disease issues unless each receives sufficient sunlight and air circulation.

I'd also agree with the no pruning suggestion, unless the tree was producing some awkward juvenile growth. Any pruning of topgrowth should be done with a purpose in mind - removal of any deadwood, enhancing growth habit, correcting conflicting branching, etc.

Thanks for the advice everyone.

tsugajunkie - The feeling I got from the nurseryman was that these would fill out within two years. They are considerably taller than any other 'nicely shaped' JM trees I've seen for sale at any comparable price, hence my temptation to shortcut.

I think I will go back and look closely for a tree which hasn't been hacked at the top, and which is showing a satisfactory branching pattern already. There were quite a few with overly narrow branching angles off the main trunk.

Vase-like shape, with up-oriented main branches not necessarily a problem - coralbark maple, for instance usually grows this way.