This is a simple circuit that can easily be perfboarded. With just a handful of components you can monitor the water content of your plants soil. The picture is of the new version, have a look at the old version also.


“Circuit Operation:
1) When the soil is very dry, the LED flashes brightly, since the soils resistance is very high.
2) When the soil has been watered a few days before, but is drying, the LED flashes dimly,
3) When the soil is damp because it has been recently watered, the LED is off.
Note that different soils have a different resistance. Also, sometimes, watered soil will continue to have a high resistance until the soil absorbs the water, a delay of about one hour.”