Right now this system uses Electric Imp's infrastructure for data transmission; all readings are sent via HTTPS to their servers and then queried from there. Since this all fits into the definition of an IoT Node of No Security Consequence, I'm alright with the information belonging to them for the time being, and re-evaluating as I add more functionality.
The source code for the Agent and the Device, the two pieces of the Electric Imp infrastructure, are included below.
The source code can be found at my GitHub page: https://github.com/jcjones/garden-imp
This software is released under the MIT License.