The cheapest way is to use something like this
You can tie the ground through it, and it will open when a sufficient amount of moisture is applied. A more expensive route would be to use an EZIO coupled back to the EZSrve for programmatic control. This is overkill for pretty much every situation.
In regards to the EZSrve and the EZRain (now called EZFlora), under device configuration, select the EZRain module. You can then select config and set your programs / limits / etc…
Under the area screen, select the EZRain, and then select more. You can have individual control for each of the valves and programs.
You can couple as many EZRains together as you would like – a 24 or 32 zone setup with 3-4 EZRains is no problem.
Also, when setting up timers / macros, you can select a program in the module, or a valve for a response – already programmed in. No need to specify individual groups, we have abstracted all of that for ease of use.