Hi,
I am wondering what is the advantage of Opensprinkler or one ot the commercial irrigation controls out there over some HA automations coupled with zigbee plugs and 24v valves? I have rain, wind and temp sensors, would this be enough to implement a HA only irrigation system? My garden is not that big, maybe 6 or 8 valves would be more than enough.
You need to check the search feature of this forum 
There are so much post about this. You can check these for example:
If you have 6 to 8 valves you will need 6 to 8 relays if you want to use them independently.
Yes, I know. But my main concern was not how to implement the irrigation system, but the advantage of a commercial solution over self made.