I am sorry for this delayed reply to your gardening question. We are transitioning to a new Q&A system and your question was unfortunately lost in the transition. I have discovered it now and hope this reply is not too late to be of help.
Your zone is a bit far north for ficus to be planted in the ground. The only exception will be if you are able to cover them and provide a heat source beneath the cover and even at that it is a risk. You can put them in pots and the ultimate size will be determined by the size of the pot. The more confined the roots the smaller the tree. You can also prune them back to maintain a more compact size.
Thanks for the question. Please stop in again soon!
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