So, finally the project is finished! The result is a portable radio controlled plant-waterer with wireless soil moisture and tank level monitoring. I just mounted the sensor on one of the boxes and the result looks like this:
NetHome-server which allows me to control the watering schema with a DayLiteTimer-item so I can also connect the watering times with the sunset and sunrise. The NetHome server also gives me remote access to it, so I can give the flowers some extra water even when I am in my summer house... It is of course possible to control it via the remote control or with any other 433MHz controller like Tellstick. as well.
The water “nozzles” used to spray the water on the plants are done in the simplest possible way. I just mount a flexible plastic tube over the flower pots and make tiny holes in the tube, one hole for smaller pots and two holes for larger. The mounted arrangement looks like this: