This creative switch is turned on when you water your plant. When the plant is thirsty and needs water, the red LED will let you know you need to care for your plant. After watering, the green LED lets your know your plant is watered. 

What you’ll need:

→ a plant
→ green LED (+/- 2.2v @ 20mA)
→ red LED (+/- 2.2v @ 20mA)
→ 3v battery (CR2032)
→ two 100k resistors
→ two 150 resistors
→ two 100k transistors
→ two nails
→ wire
→ soldering iron
→ solder
→ wire clippers/strippers
→ alligator clips for testing
→ something to solder everything to
→ something to mount everything on

☝ Prototype your circuit first on a breadboard to make sure everything functions

☝ Next, set everything up on the surface you will be soldering to so you have an idea before you begin

☝ Next, solder

☝ Then start to consider where each component will go on the surface you are mounting everything on

☝ An example layout

☝ Attach everything via hot glue or solder

☝ All ready to go

☝ Place the unit inside the plant and insert the nail contacts into the soil. If your plant is dry and thirsty, the red LED will be on