Glad you found it useful. It would be cool to see an extension of it that logs soil moisture. Keep in mind that our remote sprinkler tutorial is based on a Raspberry Pi + a PiFace, but neither of those support analog inputs.
Here some soil moisture sensors:
In both cases, switching to an Arduino would make more sense: for the first option there's already an Arduino library to read the sensor, while the second option only has analog output (hence the low price).