I have found a few units that are basically what I want to build, but each one has specific limitations that our collaboration would solve. 

My favorite is the "Parrot Flower Power" sensor : http://global.parrot.com/au/products/flower-power/

This unit records light period, soil moisture and temperature and saves the data on a timeline you can use to observe long term trends. 

The drawback is that the device is not WiFi enabled and only communicates via short range Bluetooth, which means the user has to manually sync the data to their smartphone while standing next to it, and you are unable to monitor your garden remotely. 

My second favorite unit is the 'Edyn' garden sensor: https://edyn.com/

This sensor also records light intensity, soil moisture and temperature, and it does connect via Wi-Fi. 

It does not save historical data so there is no way to obverve long term trends, and the app is so slow and buggy that it is crippling sales. 

My goal is to get both units and we can hack them and see if we can just use their technology to prove the concept and get some test data - unfortunately these units aren't being sold in local stores and I won't be able to obtain them until the end of the month. 

I am trying to find some digital sensors to play with but perhaps tomorrow should be more of a brainstorming session. What are your thoughts?

-Mario