I made this awhile back with an Arduino clone. I got it from banggood.com.
Most of the materials I implemented in this project were all from banggood. Truthfully I should have bought them from eBay for cheaper price but banggood does have some good sale.
Well anyway my system can only water 2 tanks at once due to my limited power at that time.
You can manually tell it to water the plant by pressing a small button on the breadboard or just leave it water itself from time to time.
I added a LED to each of the tank and it has light sensor and everything. So when I turn the blind the LED go off and when it's dark they turn on.
There's really not much to say.
I also attached the coding I used if you're interested.