I suggest that you plant it. It's not like a cordyline or a palm. Conifers that are not dwarf need to go in the ground and need more real estate for their roots.

I had never heard of this tree before so I did some research. I found this interesting site on them. It turns out they are not a pine at all but a very old species that is just put in that catagory for want of a better place. Take a look at the site--very interesting reading.

http://awaytogarden.com/beloved-conifer-japanese-umbrella-pine