These days, we all get busy and soon a week (or month) has gone by. Then we remember: water the plants! Run over to the plants and the soil is like a desert and we apologize to the poor plant.
This situation can be averted through a simple project using the Adafruit Circuit Playground Express. The amount of moisture in the soil can be measured by the board and indicators used to show if the plant needs watering.
All you need is a nail and an alligator clip cable. Adafruit carries a kit with the materials or you can buy the pieces separately.
A nail is a common piece of metal to use but it could be any metal that isn't too broad that can stick into the soil of the pot with a decent depth. The metal/nail does not need to reach the bottom of the pot, only be an inch or two (2.5-5 cm) down in the soil.
The Circuit Playground Express can detect the capacitance (the ability to store an electric charge) on an analog pin (in our case, analog pin
A1). As the moisture around a nail in the plant's pot increases, the value increases (we're creating a bigger capacitor). Dry soil doesn't work as well for electricity (like most dry materials except metals) so the value read by the Circuit Playground Express will be lower.
This project works best on indoor plants in a pot or indoor window bed. Outdoor use would require wanterproofing and the "water me" indication wouldn't be obvious if it was outdoors.
The plant in my example is a baby Maple tree in a smallish pot. As it grows, it'll need a bigger pot!
You will need to spend a few minutes with your chosen plant to get a good idea of when it is wet and dry to provide a good, accurate measurement. So pick out your plant and do not water it before starting.
You might want to look on the Internet as to what type of soil moisture makes the plant flourish best. You can adjust the moisture values in your program to "dial in" the best values for your particular plant.