I've been using a simple delay sketch to control a 120v pump through a relay. I've had trouble with finding a better code which would allow to maintain my current 10 seconds on every 15 minutes but also turn the pump on for 30 minutes every x amount of loops. This is needed to ensure the nutrients in solution stay mixed well. This setup is for an aeroponic test rig for my peppers, next spring it will be used for a large outdoor garden but I need to work kinks out over the winter.
Make this timer is easy, but first you need to tell which type of arduino are.you using. After you need to.check ph and EC otherwise your roots can be burn from this parameters. And then pumping timing have to change by external parameters, as light and temperature. Then you need control also humidity for external plant grow
I have a vertical hydroponic system, so I can help you, but not giving you the code, but only how can you do it, otherwise you are not push to learn.
Let me know
I'm using a mega board since I had one. I check my ph and tds with separate testers for now since it's what I have. I've been using a 10 seconds on and 15 minute off time using a terrible delay sketch and manually plugging the pump in for a an hour, after two weeks of this my reaper plant looks great. I'm reading several arduino books but still haven't learned how to have a timer with different start stop times and a counter for running my 1hr run after x amount of cycles.
Look at blink without delay in the IDE examples. Then read Robin2's several things at once in the stickies at the top of the main page. You will find what you need there.
I have trouble understanding how to use blink without delay when it seems to only have a single interval. I don't understand which variables to change to have an x second long blink every x number of minutes.
You can generalize blink without delay up to include many events. It is very powerful. Robin2 wrote a super helpful tutorial, http://forum.arduino.cc/index.php?topic=223286.0