Using Arduino board to connect from the analog A0-A0, Vcc-5 v, Gnd-Gnd 
principle is to compare the resistance of the two legs will be translated from A To D is from 0-100% 
By the time there are no measuring value is 0 if the humidity is below 30% will order Relay to work
Then the relay will order to the pump and solenoid valve , watering until the humidity up to 50%, it will stop the water.