First of all there is a question. Why would anyone want a plant at home if nobody is gonna even look at it? And if you’re keeping eye how it grows, blooms – poring some water shouldn’t be a problem. Well I see one reason why would you want automatic watering – it is when you leave a house for a longer time. You can say that automatics help keeping soil moist just right what plant needs. No argue with that… So randofo just made an automatic plant watering device based on Arduino.
Practically there is nothing unusual in such system. Two metal screws serves as soil moist probes. Arduino takes the reading and activates relay switch once plant needs water. Relay simply turns on non-submersible water pump which delivers water from reservoir. Simple, effective and probably it could save several plants if you don’t like to look after frequently.