The Thunbergia coccinea, also known as Scarlet Clock Vine or simply Scarlet Thunbergia, is a tropical climbing plant with a semi-woody texture that captivates gardeners and landscapers with its vibrant and abundant flowers. It is native to the tropical regions of the Himalayas, from Kumaun to Bhutan, Assam, Burma, Indochina, and China, growing at altitudes ranging from 984 to 6,561 feet (300 to 2,000 meters). Adapted to hot and humid climates, this plant thrives in dense tropical forests where it can climb trees and other natural structures. Its preference for humid environments and well-drained soils, as well as areas with good availability of indirect sunlight, means it is mainly found in forest edge areas.
The genus name Thunbergia honors the Swedish botanist Carl Peter Thunberg (1743-1828), who was one of the greatest disciples of Carl Linnaeus, the father of modern taxonomy. Thunberg is recognized for his extensive travels and contributions to botany, especially in Japan and South Africa. The specific epithet coccinea comes from Latin and means “scarlet red,” a direct reference to the vibrant color of this species’ flowers.
The Thunbergia coccinea is a vigorous climber that can grow up to 26 feet (8 meters) tall. Its leaves are simple, ovate to lanceolate in shape, measuring between 4 to 8 inches (10 to 20 cm) long and 1.4 to 4.3 inches (3.5 to 11 cm) wide. The leaf surface is pubescent, with palmate venation, usually with three to five main veins. The base of the leaves can be rounded or heart-shaped, while the margins are wavy or toothed, ending in a tapered tip. The petioles (leaf stalks) are grooved and range from 0.8 to 2.8 inches (2 to 7 cm) in length.
The inflorescence of the Scarlet Clock Vine is one of the most striking features of this species. They are raceme-type, pendulous, and long, emerging terminally or in the leaf axils and can reach up to 20 inches (50 cm) in length. Each flower has a tubular shape, with a cylindrical base measuring 0.2 to 0.24 inches (5 to 6 mm) and a throat (inner part of the tube) of 0.6 to 0.63 inches (1.5 to 1.6 cm). The petals are almost round, approximately 0.28 inches (7 mm) in diameter. The calyx is reduced to a tiny margin, about 0.08 inches (2 mm). The flower has lanceolate bracts, with the lower part pubescent and the upper part hairless. The bracteoles are oblong, measuring 0.87 to 1 inch (2.2 to 2.6 cm) in length and 0.43 to 0.6 inches (1.1 to 1.5 cm) in width, with pointed tips.
Similar to the flowers of the Thunbergia mysorensis, they vary in color, presenting shades of orange to scarlet red, with the intensity of the color depending on the temperature conditions. In warmer climates, the color tends to be more faded, orange, while in cooler temperatures, the flowers display a more intense red hue. Its flowering can last all year and intensify in spring if it is well adapted to the climate. In intense heat, it may momentarily interrupt flowering.
It is a fast-growing plant that begins to flower while still young. This species is ideal for covering supports such as trellises, pergolas, arbors, fences, and arches. When grown in pots or planters, it is necessary to provide adequate support for climbing and plenty of substrate. In landscaping, the Scarlet Clock Vine is still quite rare. It can be used to create a significant visual impact in vertical gardens and elevated structures.
Its hanging flowers create an impressive visual effect when grown over pergolas or arches, where the flower clusters can hang freely and be observed from below. Additionally, the flowers attract a variety of pollinators, including butterflies and hummingbirds, adding interest and movement to the garden. The Scarlet Clock Vine is a rustic plant and requires little maintenance, making it an excellent choice for those looking to add color and dynamism to their garden.
The Scarlet Clock Vine can be grown in full sun or partial shade, although it prefers sunny locations. This climber is ideal for tropical and subtropical climates, where temperatures do not drop below 34°F (1°C). It does not tolerate frost and is sensitive to low temperatures. In subtropical areas with harsh winters, the plant may lose its leaves but generally recovers when spring returns. In regions with cold winters, such as in temperate climates, it is recommended to grow it in heated greenhouses to protect the plant from frost and snow.
The ideal soil for Thunbergia coccinea should be well-drained and rich in organic matter. In terms of pH, slightly acidic to neutral soils are most suitable. Although it can grow in pots, its development is favored when planted directly in the ground, where it can deepen its roots without limits. Native to tropical and humid areas, this climber appreciates constantly moist soil, but it is crucial to avoid waterlogging. During the active growth and flowering period, increase the frequency of watering to meet the plant’s high water demand. In hot and dry climates, it is also beneficial to increase the humidity around the plant by using methods such as misting or installing a drip irrigation system.
Fertilize every three months with slow-release fertilizers, such as cote, and organic compost or well-aged cattle manure, to replenish the soil’s organic matter. Thunbergia coccinea is best suited for hot and humid climates typical of tropical regions. Provide balanced fertilizers such as 04.14.08 or others suitable for flowering. Otherwise, excess nitrogen may result in vigorous growth but with few flowers.
This plant does not require frequent pruning. Basic maintenance includes removing unwanted branches, dry leaves, and wilted flowers to keep the plant healthy and aesthetically pleasing. The Scarlet Clock Vine can be propagated by seeds or more easily by cuttings. For this, choose healthy and vigorous branches approximately 10 cm (4 inches) long. Ideally, cuttings should be taken in spring or early summer when the plant is in active growth. Plant the cuttings in a substrate rich in organic matter and well-drained. Keep the cuttings in a warm and humid environment to stimulate rooting. The application of biofertilizer or rooting hormone can speed up the rooting process. As soon as possible, provide support for the seedlings to climb. Transplant to the final location when they reach about 31 inches (80 cm) in height.
