P.S. Or maybe there is some other decision instead of this one? Using Wifi? I don’t want to use RF sockets, as it is too bulky and those sockets not intended to use outdoors.
Yes this is supported by OpenSprinkler, by using a 433MHz RF transmitter. You need to get an RFToy, which include a pair of transmitter, receiver, and the RFToy gadget which you can use to decode the RF signal.