Man I love these lil raspberry pi things, you can use em for damn near whatever and they only cost $35-45.
Im about to try to make an irrigation system so I dont have to water plants no more.
moisture/humidity sensor, prob need a longer probe (nogrimprophet)
There is already some cod× out there to run it. When sensor detects an absence of a certain amount of moisture it triggers an electronic pulse to open a valve for however many seconds I want.