Hi Arnaud,

Good News ! I've just finished a community app, "Netro for Homey," that does pretty much everything you're describing. It's currently in review for the Homey App Store, and already usable through its test channel.

What it does:
- Per-zone control: see each zone's watering status and start/stop watering per zone, right from Homey.
- Controller actions: set moisture, "no-watering" days, enable/standby, plus online/offline status.
- Whisperer sensor: humidity, temperature and light readings.
- Two dashboard widgets: a zones overview and a quick watering control.
- Insights: per-zone watering history you can graph and stack.
- Flow cards for automation and this is exactly your "external triggers" idea: you can use any Homey device or value (a humidity sensor, a rain-tank level, a rain forecast, etc.) as the trigger, and have it start or stop Netro watering automatically.

It runs on Homey Pro and is available in English and French.

👉 If you'd like to try the pre-release now, here's the test link: [ https://homey.app/a/com.netro.watering/test/ ] (it's the version pending certification — feedback very welcome).

It's a community app (unofficial, not affiliated with Netro). @Netro Support : if there's ever interest in an official integration or collaboration on the Homey side, I'd be glad to talk.

Happy to answer any questions!
Patrick