Posted: 11/12/2014 at 15:54
just off the top of my head and as a idea, after all it's your project not mine.
if you have a raised tank - like a cold water tank in the home - that's fed from the guttering on the g/house, you could use something like these solenoids-
It would be easy for the end-user to drill the necessary holes in the plastic tank and fit as many as needed.
Your control would sense when water was required and deliver a predetermined amount by opening the solenoid for x seconds and let gravity do the work that a pump would do (less cost, less battery drain, less to keep gunk free and maintain).
Also consider that if 1 plant needs watering, then it's likely others do too, so 1 sensor could probably monitor a number of plants using 1 sensor as input and maybe 10 hoses delivering water to 10 plants..
You could also add an additional much smaller tank with liquid fertilizer that would dose the main reservoir.
Sounds like a fun project.
Is it purely a theoretical exercise or does it have to be practical?