These easy to grow perennials make a bright combination in a sunny border. Blooming together in early summer, the masses of yellow sundrop flowers at the base of the yellow flag tie the plants together. The tall flower bearing scapes and linear leaves of the yellow flag give a vertical thrust to the garden while the sundrops provide an anchor. The differences in both plant and flower shape and size provide contrast. The combination, however, may be difficult to achieve; both plants grow well in medium moist soil but sundrops prefer dryer soil and yellow flag prefers wetter soil. Both grow well in full sun although yellow flag tolerates some shade.
Four Angled Sundrops(Oenothera tetragona)
This short-lived perennial is native to eastern North America where it is found in open places and along woodsides. The plants are well branched with hairy, reddish brown stems, and has red tinged buds that open into cup-shaped, four petaled flowers 1- 1½ inches across. Plants tolerates heat and some shade and drought, but are often short lived in the garden so are treated as a biennial. If the foliage becomes unattractive during the summer the stems can be cut back to the basal rosettes. Several cultivars are available that vary primarily in height from twelve to eighteen inches tall.
Bloom Time: Late spring to mid summer
Size: 1-3’ H x 1’ W
Hardiness: Zones 3-8
Yellow Flag Iris (Iris pseudacorus)
Tall and slender, this rhizomatous, non-bearded iris is native to wetlands in Europe, the Middle East, northern Asia and northern Africa. It is an adaptable plant and although does best when growing in water or constantly moist soil, can grow in dryer areas if watered during dry spells. The bright yellow flowers are about two inches wide and often have brown veins and brown blotch on the falls. The leaves are sword-shaped, two to three feet long, and bright green. The large fruit capsules are attractive in dried bouquets.
Bloom Time: Late spring to early summer
Size: 1-3’ H x 2’ W
Hardiness: Zones 5-9
