These amazing watermeters are suitable to use with all types of indoor plants. You should use one watermeter per plant.
They are easy to use and accurate.
Firstly push the Sustee watermeter into your plant pot to the correct depth. There are markers on on the stick.

Then water your plant and see the marker change to blue.

Monitor your plant until the marker turns white and then water again. If the marker still appears blue, there is enough moisture in the soil.

The Details
-

pot size 2, 2.5, 3
Diameter 6〜9cm
Pots that can be lifted with one hand.
W10mm×D8mm×H120mm / 4.3g
-

pot size 3.5, 4, 5, 6
Diameter 10〜18cm
Pots that can be lifted with two hands.
W10mm×D8mm×H180mm / 5.9g
-

pot size 6〜12
Diameter 18〜36cm
Large pots that can only be lifted with excessive force.
W10mm×D8mm×H255mm / 8.0g