Cape Leadwort (Plumbago auriculata)

Cape Leadwort, Cape plumbago

The Blue Plumbago is a hardy and easy-to-care-for shrub with a great tolerance for drought. An excellent outdoor plant choice for a groundcover in any landscape design.

I. Appearance and Characteristics 

Plumbago auriculata, the Cape leadwort, blue plumbago or Cape plumbago, is a species of flowering plant in the family Plumbaginaceae, native to South Africa and Mozambique.

The specific epithet auriculata means “with ears”, referring to the shape of the leaves.

Plumbago auriculata is an evergreen shrub, often grown as a climber, ascending rapidly to 6 m (20 ft) tall by 3 m (10 ft) wide in nature, though much smaller when cultivated as a houseplant. The leaves are a glossy green and grow to 5 cm (2 in) long. The stems are long, thin, and climbing. The leaves alternate and are 2–5 cm.

The corolla with five petal-like lobes is about 2 cm wide and can be pale blue, blue or violet in color. There are also variations with white (P. auriculata var. alba) or deep blue (P. auriculata ‘Royal Cape’) flowers. The flowers are complete and bisexual, and are arranged in corymb-like racemes. The sepals and petals are connate while the pistil is adnate. The ovary of the flower is superior and the flower has regular symmetry. It has basal placentation, with 1 locule and 5 carpels. It flowers mostly in the summer, but in the right conditions it can bloom year-round.

It is visited by various butterflies. Their leaves serve as food for the caterpillar of Hummingbird hawk-moth. Conversely, the sticky sepals sometimes catch animals up to the size of a housefly. It is believed that the plumbago species living today are very similar to the first ancestors of Drosera and other carnivorous plants.

In temperate regions it may be grown outside in frost free areas, otherwise under glass. It grows best in full sun to part shade.

The species and the white-flowered form P. auriculata f. alba have both gained the Royal Horticultural Society’s Award of Garden Merit.

Plumbago auriculata can be propagated sexually by seeds and asexually by cutting in summer. It needs well-aerated soil and light and prefers acidic soil.

II. How to Grow and Care

Sunlight

As native to sub- to tropical regions of the world, cape leadwort is used to grow bathed in full sunlight. Thus, it will best grow in your garden in an exposed position.

If growing indoors, it can tolerate partial shade, however, at the expense of its flowers. The less sunlight you provide to this plant, the fewer flowers it will sprout for you. The best position for an indoor cape leadwort then would be a bright windowsill.

Temperature and Humidity

The optimum growth of the blue plumbago plant is attainable in USDA Hardiness zone 9-11. It adores warmer weather which is at least 60-80 degrees Fahrenheit (15 – 26 °C)

Although this evergreen shrub can handle a bit of a colder temperature, one must still avoid extreme colds because it is quite vulnerable to freezing injury. Particularly if temperatures drop below 32 °F (0°C). In light frost, the plant may lose some of its leaves, but they later grow back in spring.

A plumbago plant grows favorably under a humid climate. This proves to be beneficial during the blooming period. The recommended humidity level for growing plumbago is at least 55 – 60 %.

As a houseplant, the plant may be raised in cooler climates. The typically dry air of most households can be corrected by the use of a humidifier and by setting up a pebble tray.

Watering

Recently planted cape leadwort plants must be watered once or twice per week, depending on the amount of the rainfall your garden receives and the exposition regarding the sun. When the root system is established, which is about 6-7 weeks after planting it in the ground, the watering regime can be reduced to once per week.

For potted cape leadwort, water when the topsoil is dry (which should be more frequent than in the garden) and best to use lukewarm water, in order not to shock the roots.

Soil

To encourage the best growth and the amplest bloom of the cape leadwort plant, grow it on a slightly acidic to neutral soil (pH 6.1-7.3). Some species of Plumbago genus can grow in slightly alkaline soil, such as Cape Leadwort (Plumbago auriculata) and Doctorbush (P. scandens), however, some might suffer from yellowing foliage. Cape leadwort will grow happiest in a well-drained, rich pot-mix type substrate. As it needs good drainage, best mix your soil with some sand or (and) place a layer of clay pebbles at the bottom if you are growing cape leadwort in pots.

Fertilizing

Cape leadwort is a light feeder and needs a fertilizer application twice yearly, however, regular and timely fertilization encourages vigor and maximum blooming each spring. A balanced slow-release fertilizer (N-P-K: 10-10-10) will do just fine. Apply the fertilizer to your cape leadwort in early spring and then again in late autumn. Water-soluble fertilizers should be only applied if your soil has deficiencies of micronutrients such as manganese or iron.

Planting Instructions

The cape leadwort is perfect to be grown as a tall border plant as it rambles. Grow it along a fence, lining a deck or a patio, as a pool cage, or along the property border as an informal fence are all good. The cape leadwort will also look stunning as an ornamental in a large clay or wooden pot.

You can start to grow your cape leadwort out of seeds, which is usually widely available in most garden stores as well as online. Use clean, peat-based soil or compost for each seed. Sow it at a depth of 6 mm, mist the soil with water and firm to increase the contact. Best to place the pots on a sunrise facing window for warmth and maintain light moisture of the top 2.5 cm soil during the germination process. Don’t over-water to prevent mold infestation. The germination lasts roughly three to four weeks, and after that, you can transfer your seedlings into the ground, preferably during spring (for full later bloom).

Pruning

Cape leadwort will benefit from a full pruning during its dormant winter season. Additionally, periodic deadheading and shaping (to your desire) during the growing season will result in its optimum health and visual appearance. During the winter, remove each dead branch back to its base, by making a cut of 6 mm above the stem’s base. Broken branches should be cut at least 2.5 cm below the break. Always use sharp tools for clean cuts, try to wear gloves for your protection, and remember to disinfect your pruning tools between the cuts to minimize the risks of cross-contamination.

Propagation

There are several methods to propagate plumbago plants and the most common of which involve the use of root and stem cuttings, as well as seeds.

Seeds are best sown during early autumn, especially if will be used as ground cover for a garden landscape.

For stem cuttings, be sure to select a healthy stem with 3-4 leaves, and cut at least 2-3 inches long. You may also use a rooting hormone to hasten the root formation.

For root division, choose a plant at least 2-3 years old and split in fair volume. Water beforehand so the roots become hydrated. This will also make uprooting relatively easier.

Transfer to a small pot and make sure the potting soil stays moist but not soggy.

Seeds will germinate within 2-3 weeks, and cuttings may develop roots within 21-28 days. Oftentimes, propagation through the roots has a higher success rate.

Other tips: Transplant your new plumbago plants when the soil temperature is at least 50°F. Repot your old plumbago plants as the roots may become compacted over time. Transfer to a pot that is twice the size of its current container, and place under partial sun.

Overwintering

You can set it up in your garden if the climate is mild enough. Double-check that this is possible, because plumbago is vulnerable to frost and will suffer if temperatures drop below 32°F (0°C).

Where freezing isn’t too harsh (light frost), plumbago will lose its leaves. They grow back in spring, with the blooming.

  • In temperate climates, winter is a dormant period. It won’t bloom when temperatures start cooling down.
  • Conversely, in tropical climates where temperatures are warm year-round, plumbago will bloom continuously!

Pests and Diseases

While cultural management proves to influence the overall and long-term health of the Plumbago auriculata, some symptoms may occur which signifies the presence of garden pests and pathogens.

But rarely do plumbago suffers from a disease. Frequently, the cause of wilting, bud dropping and stem molds is related to either an ongoing or impending infestation. The most common pests that you may encounter are whiteflies, scale insects, spider mites, and larval insects, such as those of the Cassius blue butterfly.

Feeding insects, in their most severe form, can cause leaves to shrivel, turn brown and drop prematurely. These insects suck sap from the leaves, leaving wounds that may become a passageway for fungal and viral infection. If they remain uncontrolled, they can weaken the plant and may lead to decaying tissues.

Control: Spray the plumbago shrubs with horticultural oils or soaps diluted with water. You may also concoct your natural insect spray using chili pepper and citronella extract.

III. Uses and Benefits 

Ornamental uses

Cape leadwort can be used as flower beds and border shrubs. Commonly used as a shrub or groundcover plant, it is prized for its blue flowers. It can also be trained to climb a trellis. A good fit for Mediterranean gardens, it is often planted with Imperial Delight, whose showy blooms make a good visual complement.

Medicinal uses

  • Plumbagin, an antifungal compound found in this helpful herb, supports the body cells’ ability to fight off numerous infections.
  • It functions well as a heart tonic as well. Due to its cardioprotective properties, this herb shields our hearts from the risk of certain illnesses.
  • Additionally, the plant possesses qualities that support your body cells’ ability to combat malignant cells.
  • Additionally, it works well for curing excruciating toothaches.
  • It is an anti-haemorrhagic substance that makes it simple to halt heavy bleeding. Additionally, it has qualities that can combat malignant cells.
  • Indigestion and hyperacidity can both be effectively treated with root extract.

Cape Leadwort (Plumbago auriculata) Details

Common name Cape Leadwort, Cape plumbago
Botanical name Plumbago auriculata
Plant type Annual
Hardiness zone 9a, 9b, 10a, 10b, 11a, 11b
Growth rate Medium
Height 6 ft. 0 in. - 15 ft. 0 in.
Width 6 ft. 0 in. - 15 ft. 0 in.
Sunlight Full sun (6 or more hours of direct sunlight a day)
Soil condition Sand
Flower color Blue
Leaf color Green