Moisture sensor
sensoricon
port: Grove: A1 (C16, C17)
interface: analog
output values

dry soil: 0 - 300
damp soil: 300 - 700
Water: 700 - 950

Further information: http://wiki.seeedstudio.com/Grove-Moisture_Sensor
Order: https://www.conrad.de/de/p/seeed-studio-101020008-feuchtigkeitssensor-1369548.html

With the class set for SEK I there is the possibility to develop a plant station. Here, for example, the moisture sensors can be used to check the moisture in a flower pot and water can be added with a pump (or a small container attached to a servo motor) as soon as it is determined that the plant in the pot is too dry.