A gentleman in Greece showcased on HN his Arduino code he wrote for his father to do just this thing, just a month or two ago:

http://www.stavros.io/posts/arduino-powered-irrigation-syste...

I live in Illinois and my grandmother lives in Central Florida. I installed a Nest thermostat, Protect sensors, as well as an IP-enabled sprinkler controller (http://www.roslen.com/products.html). I can manage her entire home remotely for her, so when she calls, its "click click all done".

The "Internet Of Things" is already here.