“But how can i get the Weather Data from my Netatmo Weather Station to OWM?” — I really have no knowledge to tell. You can search ‘Netatmo’ on the forum and I think it has been discussed by other users before. Or Google it to find out if this is an option.
Also, as discussed in other threads, if your Netatmo can send HTTP command (or interface with a server), you can have it or the server it interfaces with send OpenSprinkler command to change the watering percentage. This way, OpenSprinkler doesn’t have to read data from Netatmo, but instead the watering percentage is pushed to OpenSprinkler.