Koubachi's Wi-Fi enabled plant sensor, which launched at CeBIT, has started shipping its first pre-order units across Europe. The roughly €125 gadget goes in the dirt around a plant and connects to a Wi-Fi network. From there, it measures temperature, light, and soil moisture, then sends the data to an iOS or web app, which can tell you to mist, water, or move the plant. The app also contains some more detailed non-sensor information about most plants, so it can give you advice on fertilizing or otherwise caring for them. You can alternate it between pots or beds to develop a profile of each plant, so you should be able to get away with only buying one.
In principle, Koubachi isn't so different from "smart home" gadgets like Samsung's Wi-Fi oven, but it's quite a bit simpler and more immediately useful, especially since it's a standalone device rather than a whole appliance. It can be ordered online through Koubachi's store or bought through resellers in some countries.