Bali has two seasons: dry (May–September) and wet (October–April). The best time to visit Ubud is during the dry season, when the rice terraces are at their greenest in June and July and rain is infrequent. August is the busiest month — prices are higher and accommodation fills up. If you want Ubud at its most relaxed, come in May, June, or September.
The wet season brings heavy rain in the afternoons and evenings but the mornings are often clear and warm. Ubud is more accessible in the wet season than the beach resort areas, and the landscape is lush and intensely green. The cultural life of the town continues year-round — dance performances, temple ceremonies, and arts events do not slow down with the rain.
Nyepi, the Balinese Day of Silence, falls in March or April (on the Saka new year). The whole island shuts down completely for 24 hours — no traffic, no activity, complete silence. It is a remarkable experience if you are in Bali for it, though it does mean a full day of staying in your accommodation.