More than 15,000 plant species from Australia, South Africa, the Himalayas, and especially the western United States compose the horticultural displays in the thoughtfully laid-out theme gardens here. They are at their peak in July and August, when garden enthusiasts could spend half a day here; the tropical conservatory alone is worth an hour's visit in the off-season. Spring brings a brilliant display of wildflowers to the world-renowned rock alpine garden, primarily in late May and early June. The OmniGlobe simulates the climate and atmospheric changes on earth; other environmental attractions include a "green roof" atop the café and a children's garden that covers part of the parking structure. Tea ceremonies take place some summer weekends in the tranquil Japanese garden, and artists such as rock musician Chris Isaak, singer–songwriter Jewel, and blues legend B.B. King have performed as part of the summer concert series.