your general link.. does not go to a 48 inch box ... so its hard to conceptualize ...

and how big of a tree are your starting with ... as i dont understand how you could take a large one and transplant it.. with no solid ground to stake it in..

what is the wind on the roof ... hard?? .. constant????

more facts please..

ken

I don't think 23x17 is nearly large enough for long term success.
I'd want at least a half barrel size and larger would be even better.
Enormous concrete pots would be best and would last forever.

even if i bought wood.. to make it last.. i would have them potted in plastic and insure there were a lot of drain holes in the wood ... so it stayed as dry as possible ..

so determination of the planter size.. would be a function of the pot size ... if that makes sense ...

so.. at a min.. i would be thinking about a MINIMUM of a 25 gallon black pot ... see link.. no clue if that is a good price.. i got most of mine from recycle bins .... but i dont use them decoratively ... and that one is already 25 inches wide at the top ....

any even in nurseries.. plants of the size you want.. BLOW OVER.. wind and stability are going to be your BIG PROBLEM ... especially if you buy them big ...

and i should also point out.. that conifers have very specific potting media issues.. and what you fill the pot with will also be very important.. and its not going to be your standard bag of potting media ....

i am sure you can do it.. but i doubt you are going to find the info you need here.. with the specificity you wish .... i simply dont think us tree peeps are going to have a lot of specific info for you ... other than to list the variables ....

good luck

ken

ps: winter storage will also be an issue ....

Here is a link that might be useful: link -- you shop price.. i am just showing the pot

Far too small. And you won't keep them at 9-10 feet for long. 3-4-5 trips up the ladder in 2 years to keep them subdued into a "pleasing" geometry will disabuse you of that notion.

So you want a surface area of minimum 48 sf for that plant each, and a total cf volume of roughly 145 cf for how big they will get.

Can you update on what you end up using? I’m trying something similar and would appreciate your experience.