Before you put the Plant Monitor in the pot, you may try gripping the prong in your hand and the moisture of your body should be enough to alter the LED's color as a test.

When placing the Plant Monitor in a plant pot, the front side of the prong should be as close to the edge of the pot as possible. The sensing all takes place from the far side of the prong.

The electronics should be facing out of the pot and the prong of the Plant Monitor pushed into the dirt as far as the white line (but no deeper). It's a good idea to attach the wires you are going to use to connect to the Plant Monitor before positioning it in the plant pot.

Once powered up, the plant monitor will immediately start displaying the level of wetness using the built-in LED. Red on the large LED to the left means it is dry and needs water.

Adding some water to a dry plant provides moisture. The left multicolor LED turns green as it detects the added moisture.