Stromboli is at its best from late April through October. June, September, and the first half of October are the sweet spots — warm seas, fewer crowds than midsummer, full ferry service, and reliable weather for the volcano hike. July and August are crowded, hot, and busy at the harbour, though they are also when the village is most alive.
From November to April many restaurants and bars close, ferries run a reduced timetable, and the volcano hike is often closed because of weather. The volcano itself, of course, performs all year.