The Friends of Honolulu Botanical Gardens will host its spring plant sale from 9 a.m. to 2 p.m. Saturday at Foster Botanical Garden. This year’s theme is “Planting Ideas.”

Free classes on a variety of gardening topics will be offered throughout the day:

>> 10 a.m., learn how to grow and maintain native plants with Honolulu Star-Advertiser gardening columnist Heidi Bornhorst. Her book, “Growing Native Hawaiian Plants: A How-to Guide for the Gardener,” is available at the garden gift shop.

>> 11 a.m., Mark Suiso of Makaha Mangoes and Kalani Matsumura of the Urban Garden Center in Pearl City will discuss mango and other fruit trees and how to choose the right one for your garden.

>> Noon, Sharon Petersen of Sharon’s Plants will talk about bromeliads and tillandsias and demonstrate how to make arrangements.

>> 1 p.m., orchid horticulturist Scot Mitamura will offer tips on growing orchids.

Classes will be filled on a first-come, first-served basis.

The plant sale, co-sponsored by the City and County of Honolulu, includes a large selection of indoor and outdoor plants, native plants, variegated and red geometry trees, orchids, heliconia, ginger, cactuses and succulents, desert roses, air plants, ceramic planters, miniature succulent gardens, handmade hypertufa pots, loose and mounted tillandsias and bromeliads, bamboo, ti plants, fruit trees, ivory nut seeds, egg pots and more than 30 varieties of anthuriums.

Foster Botanical Garden is at 180 N. Vineyard Blvd. The Friends of Honolulu Botanical Gardens have been sponsoring plant sales since 1961.

Admission is free during the sale and includes guided tours of the garden. Call 537-1708.