Hi,
I have installed a couple of soil moisture sensors in my garden and built two different
kind of end devices mit ATMega328 and RFM95 (4 channel analog voltage input and 8 channel
analog voltage input). I use the sensors shown below (SMT50 by Truebner) since they are reasonable low cost and fully water proof for long term operation.
The system is just for monitoring soil moisture after experience with severe drought last summer in Germany. I will add valves later and work on a complete controll system.
I do have similar nodes and a weighing scale with HX711 AD converter for monitoring my beehives.
Maria