Soil moisture-sensing by hacking a solar light
Putting it all together
I kept the same PCB found in the pathway light and rewired the solar panel directly to the board. I added some wires straight from the PCB to lead down to my circuit board probes that I hot glued to the pathway light stand. This worked for me, but you could certainly use a new board in the pathway light to make soldering the parts together easier, though space is a constraint.
There are many other things you could add to this simple circuit if you like. The main constraint is due to the fact that it's running off of a solar panel and battery, and it can not produce a whole lot of current. Keep that in mind if you decide to build your own version.