SparkFun Soil Moisture Sensor w/ Screw Terminals

Seems to work well out of the box. Gives consistent readings which is pretty important. When I used it on 5v, I got readings in coco coir between around 700 and 900 while the actual range of the device is something like 0 - 999 so I wasn't really expecting that, but that's not a bad thing. It is very well put together. The leads are really nice for not having to solder anything. You can find instructions on how to configure it on the SparkFun website. Had it up and running in 2 minutes.

This kind of sensor will only last you a season or two because of the exposed electrodes. If you want a longer lasting solution use the capacitive style sensors. These works have worked just fine for weeks in an outdoor setting. Use some conformal spray on your screws if it’ll be outdoor so they don’t oxidize

This is not working, it is not giving the correct readings. It is always showing wet.