@Peter, Thanks for your answer because it has opened another possibility that I had not contemplated.
My fisrt idea was try to do a wireless system with 9V baterry for control valve. I posted this thread where I explain it. I think it is impossible to do without adding a solar panel and I find it easier to have a power supply.
As I have a ESP8266MOD in my jumble case. Can you share your arduino code? I think it is compatible with my ESP. Time ago I fashing it with Arduino IDE. I’ll be very grateful to you.
P.D: Maybe it would be better to continue this conversation in your post about indoor watering system