The best time to water plants is usually in the early morning, both to maximize the efficiency of water used and to promote healthy flora.

Mornings tend to be cool and without strong winds, so the amount of water lost to evaporation is much less than during the middle of the day. Yes, evenings are typically similar, but if plants stay damp overnight they are more likely to be damaged by fungal and bacterial diseases. Ideally, use a drip or soak system instead of a regular sprinkler, which wastes a lot of water and drenches the leaves, which are prone to damage as well as disease— Good Housekeeping Magazine