Automatic Plant Watering Alarm

  Most plants thrive in high humidity — around 80%. Unfortunately, most homes are much drier, especially in the winter when forced heat can even further drop the humidity.One of the most commonly asked questions in regards to caring for interior plants is the age-old quandary, “How often should I water my plants?”Supplying a plant with too much or too little water are both easy ways to kill our green friends. 

So what can we do about it? It’s simple really. All it needs is for regular checks to feel if the soil in the pot has become too dry. But what is ‘too dry’? Some people just don’t seem to have the right fingers for this task. A little electronics can be used to rid us of this problem forever.

This circuit will sense the presence of moisture in soil and if moisture is not sufficient it will automatically alert you .


Moisture level is sensed by probes which are embedded in the soil. Be careful while inserting the probes they should inserted into a suitable depth and probes should be separated from each other. When there is no moisture in soil then Collector of Q1 becomes high and this signal goes to the base of Q2 and collector of Q2 become low and we are using this signal to turn on the buzzer.

Video – Automatic Plant Watering Alarm

Plant Watering Alarm circuit diagram

plant watering alarm circuit

Plant Watering Alarm-Breadboard Layout

Automatic Plant Watering Alarm breadboard Circuit diagram


  1. R1 = 220R
  2. R1 , R2 = 10k
  3. Q1, Q2 = BC547
  4. LED
  5. DC Buzzer

Plant Watering Alarm component list

Soil moisture detector circuit

Moisture tester calibration and usage

If this circuit does not work with your desired moisture in soil then use 1 mega ohm pot between probe 1 and Q1 base  , change the resistance and adjust sensitivity .

After the previous description it should be clear how the tester should be used. The electrodes should always be kept the same distance apart (between one and two cm), perhaps using a spacer, and the tinned ends should always be completely inserted into the soil.

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