Native plants have a high survival rate because almost all of them are already adapted to growing in their native climate. Because many indigenous plants have been drought-tolerant, they do well in the drier terms of a container or window box, especially in heat, Mediterranean-style climates.
Native shrubs are more suitable to grow in containers rather than window boxes in which the bushy branches block the view from the window. One native shrub that grows well in a container is that the desert ruellia (Ruellia peninsularis), a native to Southern California in U.S. Department of Agriculture plant hardiness zones 9 through 11. This 4-foot-tall sun-loving plant produces a dense mass of glossy leaves and purple petunia-like blossoms appearing in the late spring. Ocotillo (Fouquieria splendens) is a southwestern shrub that grows in USDA zones 8 through 11. When implanted in the ground, this sun-loving bush attains 20 feet tall with long spiny stems that stay bare during dry spells. This plant quickly grows leaves and crimson flowers after it rains.
Annuals for Containers and Window Boxes
Showy indigenous annuals grow well in containers and window boxes. Pick short- to average-height plants to grow in the window boxes. Native to the Pacific West is that the California poppy (Eschscholzia californica), which reaches about 12 inches tall with ferny green leaves and summer cup-shaped flowers offered in golden-orange, yellow, cream and red. This native annual closes its petals during cloudy weather. Remove the spent blooms to keep the plants out of developing seed pods. Farewell to spring (Clarkia amoena) produces pink cup-shaped blossoms on sprawling 1- to 3-foot-long stems. This summer flower closes at night and opens again in the morning, welcoming visiting honeybees.
Perennials for Containers and Window Boxes
Short native perennials can endure for years in containers and window boxes. Using perennials eliminates the need to replant the containers every year. One creeping indigenous perennial is that the redwood sorrel (Oxalis oregana), which grows in USDA zones 7 through 9. This shade-loving plant produces shamrock-shaped leaves and white or pink cup-shaped flowers from spring through autumn on 6- to 12-inch-tall stems. “Siskiyou” evening primroses (Oenothera speciosa “Siskiyou”) grow pale pink summer blooms in USDA zones 4 through 8, reaching 8 to 10 inches tall in full sun. Pinch off dying flowers to protect against that perennial from reseeding itself.
Window Box Native Vines
Native vines work best in window boxes in which the stems cascade over the edge of the rim. These plants need a little trim to maintain the size of the vines short enough so that they do not hit on the ground. One native vine is that the “Amethyst Falls” American wisteria (Wisteria frutescens “Amethyst Falls”), which grows well in USDA zones 5 through 9. This deciduous vine reaches 8 to 10 feet long, and is covered in purple flower clusters from spring through summer. “Chauga” wild hydrangea vines (Decumaria barbara “Chauga”) create woody stems reaching up to 40 feet long as back. Clusters of snow white flowers appear in the summer and the dark green leaves turn tan-colored in the autumn. This native vine brings butterflies and grows in USDA zones 7 through 9.