This is a circuit that will remind you to water plants when the pot is dry, this circuit is mainly meant for the indoor plants that are the unfortunate ones that don’t even receive rainfall.

The Circuit consist of two probes( You can use nails or just strips of uninsulated wires) When the probes are shorted the LED will be turned off. When the soil is wet the resistivity of soil is so low that the LED is turned off, when the soil is dry the resistivity of soil is high and it does not conduct.

In this circuit Q1 and T1 form an astable oscillator and T2 acts as a switch that turns on and off the astable oscillator. A buzzer can be used instead of the LED. The pot can be used to adjust the sensitivity of the device.

Parts List

Part     Value
C1       100nf
R1       100k
R2       470k(Pot or Preset)
R3       1M
Q1       BC328
T1       BC107
T2       BC107
LED      (Or buzzer)
Battery  9V
Battery clip
Wires, solder,pcb etc