I've just finished writing-up an instruction sheet for my IoT students on sensing soil moisture in a plant pot.
I've purchased 6-off of the inexpensive resistive moisture sensors. I've been told they are liable to corrosion so the program I have running in the Wemos D1 Mini uses "rules" and an NPN transistor to switch the 3V3 supply to the sensor on for 8 seconds every 15 minutes (which will hopefully reduce the corrosion effect).
Hope you enjoy reading this article as much as I enjoyed writing it.
Cheers from David
I've just updated the flow to version 2.
This version will check and report if the Wemos D1 Mini is off-line or disconnected from a power source.
It will also send a simple message to a Telegram bot saying the plant needs watering.
There is a "test inject point" to check the "needs watering" condition/path. You can obviously remove this.