On Moisture Sensors for plants
Moisture sensors suck. This link is an excellent deep dive into why the sensors on the market right now aren’t great. Use nails. This guys doesn’t literally use nails, but he demonstrates the circuit you would need. For my own plants, since they are indoors and my living conditions are quite stable, I won’t be bothering with moisture sensing at all. I’ll rely on a timer. It’s true that this will require testing and calibration, however, calibrating a timer to give the right amount of water is the same level of tedious as calibrating a moisture sensor would be.
If you’re interested in automatic watering systems, have a look around youtube. There are literally hundreds of tutorials that will guide you through all the steps
I’m using a standard arduino nano, the same relay module as this guy, wired to the power supply of an LED sting and an air pump, all of which I acquired from amazon, but can also be purchased more locally from places like spikenzie labs, Abra, and in the case of the air pump, any pet store.
I use an air pump instead of a water pump because it’s more efficient, but a water pump will work just fine.