*Ceratostigma*, *Chinese plumbago*: plant, prune and maintain

Description and Botany

Ceratostigmas are herbaceous perennials or small spreading bushes with densely branched fine stems from the family of Plumbagos, which they were once named after. The genus consists of eight species, with their cradle located in the Himalayas and the Far East, with one species native to Somalia. They are commonly referred to as Chinese Plumbagos to distinguish them from the Cape Plumbago, a much less hardy shrub from South Africa found in pale blue or white tones often seen along the Mediterranean coast. They belong to the family Plumbaginaceae.

Ceratostigma plumbaginoides (syn. Plumbago larpentae) is sometimes called creeping Plumbago due to its ability to colonise the soil through its reddish running rhizomes. Fast-growing, this herbaceous plant is extremely covering even though it disappears in winter and starts late around May. Introduced to Germany from western China in 1834 by Alexander von Bunge, it made a notable second entry into England in 1846 from Shanghai to the noble Larpent family, who contributed to its spread.

This perennial grows in rather dry, poor, and sunny rocky areas. The plant does not exceed 30 cm in height but is capable of spreading over large distances in cool soil. It is also more frost-resistant (-20°C) than the shrubby types (-12 to -15°C), which can still regrow from the stump.

Ceratostigma plumbaginoïdes – botanical illustration

From its woody stump emerge fine quadrangular stems, often purplish, bearing alternate leaves that are generally ovate with a pointed tip, measuring 3-5 cm long and 2.5-3 cm wide. The lamina is a bright green colour, bordered with dark, brownish to purplish hairs. The foliage often adopts bronze hues and then bright raspberry red with the first frosts from September. It falls quite late in autumn. The intensity of the colours is all the more pronounced when the plant is exposed to sunlight.

The shrubby species are deciduous or semi-evergreen and have a bushy habit that is slightly wider than tall, reaching 80 or 100 cm depending on the species. The Wilmott’s plumbago (C. willmottianum), native to Sichuan, shows a looser habit, more vigorous than Ceratostigma griffitii, native to the Himalayas. Its dark green leaves, golden in ‘Sapphire Ring’, are diamond-shaped, measuring 5 cm and bear fairly long hairs on the edges and both surfaces. They turn orange-red in autumn. Those of griffithi are evergreen in mild climates, pubescent and thicker with a spatulate shape, measuring only 2-3 cm long, a dull green edged with purple and borne on reddish stems. In all cases, the leaves have no petiole and are alternate. The fine, quadrangular stems regrow directly from the collar in case of frost to the aerial parts, knowing that well-drained soil increases the frost tolerance of the leadworts. The leaves turn red in autumn.

Flowering can occur as early as July depending on the climate, particularly for plumbaginoides, a little later for the others, and continues until frost in October-November. The corolla of the leadworts, supported by a reddish tubular calyx with fine teeth, forms a long slender tube ending in 5 triangular lobes marked with a reddish vein that enhances the brilliance of the gentian blue or cobalt blue. The diameter of the flowers ranges from 1 to 2 cm. The flowers arise and succeed each other within axillary corymbs, grouped in loose clusters appearing towards the ends of the stems. They are rich in nectar, attracting butterflies and bees. The stamens and pistils remain inconspicuous. The flower clusters give way to spiny fruits, brownish to rusty in colour.

The genus name Ceratostigma means “horned stigma”, the stigma being the terminal part of the pistil that receives pollen from other flowers. It is divided into 5 parts, a common character among the Chinese plumbagos.

Flowers of a beautiful intense blue from Ceratostigma willmottianum (photo Daderot)

The main varieties of Ceratostigma

Perennial Variety

Shrubby Varieties

Ceratostigma plumbaginoides

Perennial with running rhizomes quickly forming a beautiful ground cover, even in dry and stony soils. Its small star-shaped flowers of an extremely vivid gentian blue stand out from July against the dark green foliage that turns bright red to bronze at the end of the season. Perfectly hardy, it is also an excellent plant for rockeries or sunny slopes.

• Flowering time September to November
• Height at maturity 30 cm

See the product sheet

Ceratostigma griffithii

Prostrate and spreading shrub bearing small cobalt blue flowers on red branches adorned with thick green leaves, marginate with purple. Evergreen in coastal areas, otherwise it regrows from the stump. To be planted in gravelly, rich, and very well-drained soils, in a warm exposure on a dry slope or in a rockery.

• Flowering time September to November
• Height at maturity 80 cm

See the product sheet

Ceratostigma willmottianum

This spreading bush, reaching 1.5 m, produces a myriad of star-shaped flowers in a magnificent intense blue, at the end of summer and in autumn. The cobalt blue flowers with 5 petals and a purplish-red tube form bouquets along flexible branches adorned with small dark green leaves full of delicacy. It can be pruned as desired and tolerates frosts down to -10°C, which sometimes necessitates growing it in a pot.

• Flowering time September to December
• Height at maturity 1 m

See the product sheet

Ceratostigma willmottianum Sapphire Ring

Cultivar with very bright golden foliage.

• Flowering time August to December
• Height at maturity 80 cm

See the product sheet

Young plantation

Where to plant the beak flower?

Plant Ceratostigma in full sun or partial shade, in light, even poor, calcareous and stony soil. They appreciate well-drained, gravelly soils, which are rather neutral to calcareous and adapt very well to summer drought. Choose a sheltered spot to make the most of its late-season flowering, especially for shrubby varieties. They can be planted against a wall, at the foot of a clematis to shade its base even if the soil is poor.

Be sure to limit excessive growth in fresh, rich soil of Larpent’s beak flower by uprooting its easily extracted rootstocks.

When to plant?

Plant Ceratostigma preferably in spring in cold climates or in autumn to ensure deep rooting before facing summer drought.

How to plant?

This plant is easy to grow.

• Soak the root ball in a bucket of water to thoroughly moisten it.
• Dig a hole three times wider than the root ball and aerate the soil around it with a fork’s tines.
• Add a few handfuls of sand and gravel to ensure good drainage around the roots. In heavy soil, opt for planting on a mound or within a rockery.
• Add manure or decomposed compost if the soil is sandy.
• Place the plant in the planting hole.
• Replace the soil and lightly firm it down.
• Water.

In a large terracotta pot, place a layer of clay balls at the bottom and add good potting soil for flowering plants mixed with drainage materials (sand, vermiculite, perlite…). Add slow-release organic fertiliser or in capsule form in spring.

→ Read also: growing a Ceratostigma in a pot.

Ceratostigma (photo Manuel m.v. – Flickr)

Maintenance

Shorten the branches of shrubby plumbagos by a third when growth resumes to thicken the clump. Otherwise, clean the dried stems by pulling them out.

Water in case of prolonged drought, especially the species C. willmottianum, which prefers cool soil, particularly during the recovery period. Growth is generally quite rapid unless it lacks water. Place the pot against a wall that is well exposed to sunlight during winter or move it into a garage.
This plant is not prone to diseases or pests in our gardens. Don’t worry if you don’t see it starting in spring; it tends to be quite lazy in showing its best during mid and late season.

→ Learn more about pruning plumbago in our tutorial: How to prune plumbago?

Multiplication: propagation by cuttings, sowing

The simplest method of multiplication is to divide the clump, but bushy dentate plants can also be obtained by propagation by cuttings of the terminal parts in May-June.

Propagation by Cuttings

Prepare a deep pot by filling it with potting soil mixed with sand.

1. Take 10 cm long tips of herbaceous stems.
2. Remove the leaves located near the base of the cutting.
3. Insert them two-thirds of their length, ensuring they do not touch each other.
4. Gently firm the soil around to eliminate air pockets and ensure good contact between the potting soil and the cutting.
5. Place them in a humid environment in the shade, for example, by covering them with a cut transparent plastic bottle.
6. In autumn, separate the rooted cuttings and plant them in buckets, keeping them under a frame until spring.
7. Plant your plants in spring in the open ground.

→ Learn more in our tutorial: How to propagate Plumbago?

Sowing

Collect the natural seedlings that you can find around the bushy varieties in particular.

Uses and associations

These hardy, low-maintenance ground cover plants can tolerate root competition, making them suitable for planting at the base of a deciduous tree or bush or a climbing plant. For example, Clematis montana ‘Freda’ features lovely, finely cut leaves tinged with purple in spring and again in autumn, providing a delicate backdrop to the lush electric blue and bronze tuft of a Ceratostigma.

An example of a combination for a colourful border: Ceratostigma plumbaginoides and red Salvia microphylla, like the variety ‘Royal Bumble’ with its beautiful dark red

Sunny rockeries, slightly ungrateful slopes, low walls, path edges, and the base of shrubs planted in the ground or in large pots provide opportunities for Ceratostigmas to thrive and overflow generously. Shrubby species can form low, free-standing hedges combined with dromedary shrubs such as Caryopteris, Perovskia, Potentilla, Rosemary, Cistus, or summer Spiraea… Create modern pot displays that are flashy and graphic in autumn by pairing Ceratostigma griffithii or willmottianum with grasses, asters, phormiums, Nandina, Sedum spectabile, silver foliage from wormwood or santolina, and blue salvias (Salvia nemorosa Caradonna, guaranatica, uliginosa)…

→ More ideas for pairing with Plumbago in our advice sheet!