Buy two outdoor radios. A pair of the Ubiquitis, for example. One connects to the LAN port on the router and is mounted to the outside of the structure, pointed at the other radio.
The second radio is mounted to the second structure and is configured to connect to the first, much like a laptop connecting to a wireless router. The network cable of the second radio plugs into a router or access point in the greenhouse, and the clients there connect to that AP. The two UBNT radios form a bridge between the two routers, much like a virtual cable. -- db
So, in addition to the Verizon router I have at the new house, I also have a Buffalo Airstation WHR-G125 which I'm using in my current setup with Cox. Unlike the Verizon model, this broadcasts at least half the distance from the greenhous to the house. So this could stay in the greenhouse and be connected to one of the "radios" while the other radio is connected to the ZV router in the house. Have I got it right? Any possible comflicts you think I should be mindful of? Thanks