I've got a fairly mature diy Zigbee moisture sensor working well based on this board I make, paired with a standard capacitive soil moisture sensor...
For $25 you can get a battery powered Zigbee board, soil moisture, and air temp. Plus there's 2 more adc inputs and 3 more digital inputs available for adding other sensors.
Hubitat driver works great.
Let me know if you're interested... I can make an ebay listing.
