I found instructions for several Arduino-based plant sensors online, including the GardenBot, the ArduGarden, and a solar-powered sensor that measures soil fertility and weather conditions.

For now, just moisture. However, there's no reason I can't add more sensors if I want to. pH isn't something that's going to be changing rapidly. I can check that annually and probably be fine.

Soil moisture sensors are cheap and easy to interface with, to the point that combining one with an Arduino and blinking an LED when your potted plant is feeling a bit parched is a common beginners… ...