The thirst is real! Keep your flora (plants, not the board) happy and hydrated with the Circuit Playground Express Soil Sensor Mini Kit. This kit will teach you all about how to keep your plants in good condition, by measuring the soil moisture content using a nail and alligator clip, then display red or green LEDs on the Circuit Playground Express to tell you the state of your plant
Of course, Adafruit wouldn't leave you with a "good luck!" – check out their learning guide, Soil Moisture Sensor Plotting with Mu and CircuitPython!