Clerodendrums
January 14, 2022
By Karen Maxwell, Horticultural Specialist
In the array of tropical plants we grow, a most fascinating group is the family Clerodendrum and though it still hasn’t found its way into many southern gardens, Clerodendrum thomsoniae* has been at the Edison and Ford Winter Estates for at least 90 years, based on the plant inventory for Seminole Lodge, dated 1931. In the Moonlight Garden, we grow seven varieties, most of which bloom throughout the winter months and several that bloom almost year-round, which speaks highly of its value for seasonal gardeners who desire gorgeous flowers during the winter months.
The family includes shrubs, small trees and vines, some of which are aggressive enough to be used to create a colorful border fence, but because the grouping is so diverse, there is probably a Clerodendrum perfectly suited for your garden or planter. It’s not only gardeners that should be excited by this plant group, but scientists around the world have recently focused more closely on the potential medicinal value of several species of Clerodendrum as it is indigenous to some of the most heavily populated regions of our planet – Africa, China and Pacific rim countries as well as Australia.
According to the “Journal of Traditional and Complementary Medicine,” an international forum for medical researchers, there is growing excitement to expand exploration of the 280 chemical constituents of this family, including 43 flavonoids which have been isolated (things in fruits and vegetables that keep us healthy). Clerodendrum compounds have been widely used in traditional Chinese medicine and the international medical community is looking to understand and evaluate the merits of research that indicate these plants may be able to play a significant role in the treatments of inflammation, cancer, bacterial infections, obesity and much more.
Clerodendrum are classified in the Lamiaceae (mint) family, making them cousins to lavender, basil and rosemary whereas they were formerly part of the Verbena family (lantana, porterweed, and verbena). Now this makes no sense to me, as I once learned that plants in the mint family were easily identified by their square stems, aromatic qualities and often medicinal uses. The very name Clerodendrum breaks down from the Greek — klero for chance because no one was previously sure if these plants had any medicinal value and dendron, meaning tree.
Sometime during the 1990s, taxonomists decided to reclassify the genus Clerodendrum and at the same time, reduce the number of known species from 400 to about 150 and re-group many former Clerodendrum to the genus Rotheca – plants known for a stinky quality when the stem is crushed. The purpose of pointing this out, is that many books upon which we horticulturists rely on for identification, still erroneously call some of these beauties Clerodendrum. In the end, it was not merely the physical characteristics that are easily observed, but it is the plant’s DNA that has the final say. In the count of seven Clerodendrum in the Moonlight Garden, at least two are now Rotheca (the Blue Butterfly Bush and the Musical Notes, which are discussed further below).
Why grow Clerodendrum? Because they have spectacular flowers! When not in bloom, most Clerodendrum do not offer much in the way of plant structure or foliage – for that reason, when they are added to our gardens at Edison Ford, they are often placed behind more attractive foliage or blended well into the landscape where the sometimes deciduous shrubs can hide until they are ready to burst forth with a symphony of flowers. Clerodendrum have origins in tropical Asia and sub-Saharan Africa and for the most part, the species share the same care regimen and are right at home in 9b-11 USDA zones. They will flourish in rich soil, but it must be very well drained as they require lots of water, particularly during our dry winter months. Morning sun in Southwest Florida is fine, but they should be protected from direct, western sun, especially during the summer.
Many Southern gardeners are already familiar with the Starburst Clerodendrum or Fireworks Clerodendrum (Clerodendrum quadriloculare).* Reaching the size of a small tree, its distinctive foliage with dark green on top and purple underside is enhanced when it’s bright pink starbursts open in early spring. If your garden can support a small tree-sized Clerodendrum, then Starburst, a favorite of hummingbirds and butterflies should be included. We do recommend that you give it a good pruning after the completion of flowering to prevent this handsome shrubby tree from becoming top heavy.
Both Flaming Glory Bower* (Clerodendrum splendens) with its bright red blooms and red Bleeding Heart Vine,* (Clerodendrum x speciosum) which has dark glossy foliage and a rich combination of red and pink flowers can sucker easily and spread rapidly in their happy place. According to Leu Gardens in Orlando, the red Bleeding Heart Vine is found in many old landscapes in South Florida but is not commonly offered for sale. It is believed that Mina Edison may have initially planted this vine here at the Edison homestead and it is presently in bloom along the southern wall of the Moonlight Garden where it pairs beautifully with a Brazilian Red Cloak* shrub (Megaskepasma erthrochlamys).
As tropical plants, many Clerodendrum species may appear to die to the ground in the event of a frost, though they will return in the warmer summer season. If you would prefer a less vigorous Clerodendrum for your landscape, there are several other species worth considering that are small shrubs or gentle vines, all with stunning flowers. The Bleeding Heart* (Clerodendrum thomsoniae) is an excellent perennial to grow in a large pot, especially with a trellis. Like many fast-growing plants, it loves water, a well-drained pot, and for best blooms, regular feeding. Prune after blooming to shape your plant, and a light prune throughout the season will keep it attractive. This Clerodendrum does well when slightly pot-bound and is not known to have any toxic effect on people or pets. The Northern version of Bleeding Heart, (Dicentra spectabilis) cannot be grown as a perennial in Southwest Florida. Pagoda Clerodendrum* (Clerodendrum paniculata) is another good choice for a planter. With bright red, pyramidal shaped flowers, this Clerodendrum can be aggressive in the ground, but is easily controlled in a pot. Blooming from spring to fall, and featuring very large leaves, this is a sure conversation starter.
Clerodendrum produce their flowers in a raceme form, also called a panicle, akin to a cluster of individual flowers. They may be upright or pendulous and their common names frequently refer to the flower’s appearance before blooming or after blooming. For example, Clerodendrum minahassae, can be called Fountain Clerodendrum* based on the appearance of its flowers and Starfish Clerodendrum, for the remaining starfish of sepals with a dark blue center seed pod after the petals have all fallen. The size of a large shrub, the Fountain Clerodendrum is found just outside the back door of Thomas Edison’s study. Originally brought to the United States by David Fairchild from Minahas Province in China in 1940, this Clerodendrum is also known as Fairchild’s Clerodendrum.
With the intention of the Moonlight Garden to feature lots of white flowers, the inclusion of Bridal Veil *(Clerodendrum wallichii) was a must in this garden, as it is the site of many intimate weddings. In the far corner of the garden, there is a high reaching vine which has entangled itself beautifully with the pink Bougainvillea and purple Queen’s Wreath and is one of a few plants in nature with a true-blue color – the Blue Butterfly Bush* (Rotheca myricoides Ugandense, formerly Clerodendrum ugandense) named more for the shape of its flowers than as a butterfly attractant. It is a lanky vine that best blends into a landscape, rather than be featured as a stand-alone plant. Its beautiful panicles of dark and light blue flowers will burst through, most of the year, except during the coldest weeks. Musical Notes,* another white species, receives its common name from the appearance of its unopened flowers; and again, it is now Rotheca microphylla (formerly Clerodendrum incisum). No doubt all these names can clog the brain, but we aim to provide the most accurate information we can – especially when our gardeners visit nurseries and growers and will encounter both names being used interchangeably.
Henry Ford liked to visit his friend and often joined in celebration of Edison’s birthday on February 11. So, it is quite fitting, that from December through June, there is a curtain of cascading racemes that resemble hanging light bulbs before reaching a full bloom along the exterior east wall of the Moonlight Garden. Known by many common names, such as “Indian Beads,” or “Chains of Glory,” we prefer to know Clerodendrum schmidtii (interchangeably called Clerodendrum smithianum) simply as the Lightbulb Clerodendrum.* This tall shrub border is just beginning to develop its flowers, so be sure to visit us this month and bring your camera!
