Thryallis is not a plant in my repository of childhood memories. Grandmother didn’t have it in her garden, and I never saw it or was aware of it until a few years back when I saw it growing in a botanical garden. It struck my fancy then, and I looked until I found one for my garden.
Thryallis (Galphimia glauca), native from Mexico to Guatemala, grows as an evergreen shrub in the tropics where it attains a height of about 9 feet tall and wide. In my Zone 8B garden it often gets killed back to the ground by winter’s freezing temperatures and must produce new stems every year. Consequently, it tops out at about 6 feet and is mostly a fall bloomer. In the tropics and areas without freezing temperatures, some bloom can be expected at all times.
Moderately fast growing, thryallis quickly forms a neat rounded shape. Attractive even without boom, the dense mass of light green oblong leaves with slender, reddish stems makes the shrub worth its keep. You won’t be absolutely impressed, though, until you see it in late summer and fall when the shrub is smothered with yellow blossoms. Clusters of ¾ inch flowers borne at the stem tips are a sight to behold. Red stamens and pistils and a flash of red at the base of the petals adds interesting contrast of color. With the cool weather of late fall, the leaves take on bronzy tones.
Usually the shrub gets killed to the ground in my garden and must start over in spring. This past winter, however, was an exception. Even though it lost its leaves during the winter, the stems were not killed. In spring, the stems leafed out quickly. Gardeners in Zone 7 and lower may successfully grow thryallis if it is well protected in winter. Stems should be cut back to the ground after the first killing frost and mulched with a protective layer.
Plant thryallis in full sun for best appearance. Although it will grow in shady areas, plants will be more scraggly and bloom will be less. Well drained soil is preferred. Once established it performs well in dry, sandy soils, although supplemental water may be needed periods of drought. Remove stems that grow out of bounds occasionally to keep the neat, rounded form. Flowers bloom on new wood, so pruning does not inhibit flower production. Fertilize in early spring by sprinkling about ¼ cup of slow-release fertilizer around the base of each plant. Propagate by seeds that follow the bloom or by cuttings taken during the summer.
In the Landscape
Thryallis can be used in several ways in the landscape. In my Zone 8B garden, it is best in a shrub border where its bare winter stems are not objectionable. In Zones 9 and higher, it makes an excellent low hedge that can be sheared to whatever size is
desired. In large gardens, it is ideal as a background plant for perennial beds and borders. In Zone 7 and lower, thryallis can be grown in containers and moved to protected places in winter where it will continue to bloom is light is sufficient. In South Florida and other tropical areas, it is planted on slopes to prevent erosion and provide an attractive mass of color.
Be aware that the stems of thryallis are very brittle, which makes it a poor choice in a yard where children bounce balls that land in the shrubbery or along a pathway where people might brush against the plants. However, this shrub has much to recommend it. If you have not tried it, now might be a good time to add it to your landscape.