There are several ways that you can tell if a plant needs water, touching the soil to see if it’s dry or looking to see if the leaves are drooping are just a couple. Or you can look at your Plant Monitor and see if it’s flashing!
It’s an electronic sensor that can tell if the soil requires moisture and I built one from a kit from Maplin yesterday. The kit included a circuit board and components which needed to be soldered together.
The circuit board with some resistors placed
The back of the board showing some of the soldering
I’ve soldered kits before like the Crab Bot which I would link to here but I can’t find the post where I first mentioned it! D’oh!
Soldering in progress
Soldering can appear scary but it really isn’t. Doug taught me how to solder but if you have a HackSpace near you, you may be able to learn there.
And here’s  the Plant Sensor in situ.
Sensor in plant pot