Someone (Ken_S) managed to build a really nice Garden Monitoring system to automate the watering. You would think just measuring moisture is all you have to do, but check out his site to see why it wasn't enough, and what he did about it. This is what the device can measure:
http://www.geocities.com.nyud.net:8080/Gar.../GardenMon.html
- Sunlight Intensity at the Surface
- Temperature at the Surface
- Humidity at the Surface (w/ temperature compensation)
- Temperature at three inch depth
- Moisture content at three inch depth (w/ temperature compensation)
- Temperature at two foot depth
- Moisture content at two foot depth (w/ temperature compensation)
http://www.geocities.com.nyud.net:8080/Gar.../GardenMon.html