Blue Clock Vine, a Favorite Thunbergia
It's hard to remember when I first started growing the blue clock vine. It has been a star in my garden for several years. However, it takes a bit of understanding and familiarity with its habits to make it really shine.
Blue clock vine (Thunbergia battiscombei) is somewhat a misnomer, as the plant is more like a rangy shrub than it is a vine. No holdfasts, tendrils, or other vinelike structures hold it in place. It doesn’t twine or twist around its support. It just grows long, lax stems that would fall down unless a support of some kind was provided for it to grow up through or to lean on. It might best be described as a weak-stemmed herbaceous perennial.
Thunbergia battiscombei is a member of the Acanthaceae (acanthus) family and is native to tropical Africa. Other common names include scrambling clock vine, blue boy, blue glory, clock vine, and various derivatives of these names. Several species of Thunbergia are desirable garden plants and will be discussed in another article.
For several years now, in my Zone 8b garden, the blue clock vine has bloomed all summer long. Wave after wave of brilliant bright blue-purple flowers hang down and then curve up and flare out somewhat like an excessively flared saxophone. Clusters of flowers originate at each axil, so as long as the plant is growing and producing leaves, more and more flowers spring forth. Each flower is highlighted by a golden throat that is a perfect example of a complementary color scheme, or one that makes both colors show to their greatest advantage. Five- to seven-inch diameter heart-shaped, deeply-veined green leaves arranged oppositely on the stem are attractive in and of themselves. Lighter green, fuzzy two-part sepals heavily veined with darker green enclose the buds and bases of each flower. The attractive sepals remain for a time after the flower has fallen.
Blue clock vine, a native of tropical Africa, likes the heat and humidity of the Deep South. It needs, at the very least, morning sun. However, the very hot afternoon sun will cause it to wilt. The plant will grow in full shade, but flowers will be fewer. Farther north, clock vine can flourish in full sun.
Blue clock vine will grow in almost any well-drained soil, but most of us are not quite happy if a plant merely lives; we want it to thrive. Rich, moist, but well-drained soil and occasional sprinklings of complete fertilizer (or infrequent applications of slow-release fertilizer) will keep it growing and blooming profusely.
Since blue clock vine is root hardy to 20°F, gardeners in the Deep South can grow this plant as an herbaceous perennial. In areas with colder winters, it will need winter protection, or it can be grown as a summer flowering annual and replaced each year. In tropical areas like Zones 10-12, blue clock vine is hardy year round.
Blue clock vine is easily propagated from cuttings or by removing plants that root naturally at the enlarged nodes when stems touch the ground. Starting from seed is reported to be easy, too, if seeds are purchased from a supplier. In Florida, seeds are not formed on the plants. Possibly the pollinator species is absent.
Uses/How to Grow
Left alone, blue clock vine will flop over and form a scrambled mound of stems. This, to my way of thinking, is not the best way to grow the blue clock vine. It needs a support, such as a tomato cage or a cage constructed of concrete reinforcing wire or other sturdy material. Once this is understood, the gardener will find any number of places where this plant will excel. As long as something is there to tie the plant to or for it to lean against or grow up through, it will hold its flowers up and furl them out to give the best view to the observer.
Blue clock vine is not one of those scrambling vines that climbs to the top of any support and holds its flowers up and out of range of the viewer, or that engulfs a trellis or fence. It rarely grows as tall as six feet; more usually four or five feet tall. Therefore, its flowers are more likely to be at or below eye level.
Some of mine are in the ground and have come back from roots faithfully for many years. Others are in containers that can be moved around the landscape as needed. They, too, come back year after year, and I do not move them to the greenhouse in winter.
Practically pest free and blooming so constantly throughout the summer, this plant is highly recommended. Look for it at your favorite garden center, or if you have a friend or acquaintance that grows it, ask for a cutting or rooted sprout. However you find it, it is sure to delight you with many years of glorious purple blooms.