This circuit above can be used to automatically water your plants (potted Plants) when the soil is dry, or warn you that you need to water you plants.
For warning you to water your plants, you can make the circuit like above where there is an led that will turn on when the water is dry and turn off when the water is wet. You can replace the led with a buzzer or just parallel the buzzer with the led to make a sound when the soil is dry and needs watering.
For automatic watering, you can replace the led with a relay connected to a pump or to the pump directly, where when the soil is dry, the pump will turn on and until the soil is wet, the pump will turn off.
On the left, i have made the circuit and i used a red led to indicate whether the plants soil needs watering.
For R1-470k, you can wire a 10k potentiometer in series with the resistor (like in the circuit below) so that you can adjust when the led/appliance will turn on, at a certain dry/wetness of the soil. Look at the circuit below
