Wow that is pretty. I love the shape. It's a shame you have to cut it! Think you can get one more year out of it in your garage?

I'm sure I can, last winter I allowed it to go dormant and it did just fine. My best case scenario would be to keep it and allow it to grow as tall as it can get, but I really don't know how that is possible when I live in a temperate climate.

As long as you can fit it inside over the winter, whether your garage or interior, I say let it grow! Some people even carefully lay them sideways to get them to fit. Just make sure your garage doesn't get below freezing, and you should be fine!

my preference is to prune and root in the spring. So if you expect to need it cut by winter 2018 then its Spring 2018 to prune. That to me looks like it can easily fit through a doorway. Be sure to place the plant on a thermal break (not directly on the concrete).

You could use a frost blanket and incandescent pin style Christmas lights to keep it outside longer during the fall. Use pin lights only....the screw in bulbs will burn the plant. Cover it up in the evenings and turn on the lights. Then uncover during the day. This can be done while lows hover in the upper 30s. Once lows go beyond that then its best to bring in for the season.

You can always bring it in once the nighttime temps get to 45 and let it go semi dormant for the winter. Those branches can be pulled together to make it manageable to make it fit through a doorway. You can use twine or even old panty hose to tie it up and make it thinner to place somewhere out of the way for the winter.

I bring in many trees for the six month dormant period ( I live in Virginia) and some are stored sideways in my greenhouse. They are placed on pallets to keep them off of the cold stone floor. The heater that will come on to keep them around 50 degrees will allow the air to circulate under the container. I also bring trees inside the house ( 100 or so ) It's better to keep them off of the floor if left in a garage or greenhouse like I do. Just lift them . I also use hooks that are used to hang containers. I'll place them on racks and place the hooks under the base stem and another on some other large branches to hang them . It works.

It's best to prune like K mentioned next season.

Good Luck!! You have a beautiful tree!!

Laura