Hi Don,
Trees in a greenhouse is an awesome plan. I have a 24x38 greenhouse, 10 foot walls with a peaked roof, and we are in zone 6. It is sheathed in triple wall polycarnonate, and is not heated in any way other than passive
solar.
The trees I like best are the oriental persimmons (Fuyu, Hachiya), and I also really like grapes (Ruby, Perlette) trained up into the ceiling trusses. Both of these do really well with winter dormancy, so you still get maximum sunlight Dec-Mar, and these perennials dont suffer any cold damage. They then have very broad leaves in the growing season. In the first years, we grew tomatoes and lettuce wall to wall, but over time, have converted it to a forest jungle of food. I have noticed a 15 degree cooling effect in summer from these large leaved plants, so all the other veggies and such that are grown undernaeath do very well. We grow salad greens and such in the winter and peppers/eggplants/okra in the summer.
The aquaponic component will help to buffer temp swing so that is a good thing as well.
Having a small deck or patio in your greenhouse is really nice as an entry and workspace. Mine gets used tons, both for
gardening and recreation.
Good luck on your plan and feel free to ask any questions that may come up.
