Have you heard of Russ Finch, he grows citrus fruit in Nebraska!
I only really know him from this one video. :
https://www.youtube.com/watch?v=ZD_3_gsgsnk
If you're getting the earth moving equipments out you could dig some trenches for the ducts.
I've thought of something similar for here in NC. Here - it would basically just be to keep a few plants going year round. The cool thing about the geothermal is that you can use it to cool in the summer ( It gets hot here in NC )