I hooked up soil moisture meters whose data is exposed in an API, which is read by an arduino board that activates micro pumps from a reservoir after a threshold (customized per plant).
> We had a fight and they moved out
These aren’t Arduino brand arduinos just like your office xerox isn’t necessarily made by Xerox.
Where do you get them?
They’re cheap to make (basically just a small PCB with a few passives and a connector) and while they don’t last a long time in some soils, they’ll last long enough for you to learn what you want and then decide if you want to change sensors every year or three, go higher quality, or find another way to estimate evapotranspiration and water based on open loop control and monitoring (which is what most people likely end up doing, either technically or by human approximation).
If you (or anyone else) is in, or willing to go to, the edge of Cambridge, MA, I’ll set a couple aside for you for free.
But I use different moisture sensors: https://www.amazon.com/dp/B0896R33V8
And extra wiring/tubing because of my distance requirements