Now that the circuit has been built and tested, it was time to put everything together:
I plugged in the 5v power supply and everything worked like a charm! The pump fed water to the plant until the sensor got wet (notice the LED on the right which lights up). Also, the very top of the soil was moist, which is perfect for the grass.
I’m super happy with the results. I’m planning to make a video on how to make this, an Instructable, and maybe a larger version (for an actual plant!).
I finally made a video on how to make one of these, complete with part lists and more. Here is an Instructable with more info!