Plant problems

Why Are My Chimonobambusa Leaves Curling?

Q: When does chimonobambusa produce new culms?

One of the most unusual and distinctive characteristics of Chimonobambusa (the genus name means 'winter bamboo') is its autumn culm production calendar, which is the opposite of the spring culm production that is typical of most temperate bamboos including Phyllostachys, Fargesia, and Semiarundinaria. Timing: Chimonobambusa tumidissinoda produces its new culms primarily in autumn, typically from September through November in the UK; the culms emerge from the soil and extend upward rapidly in the autumn months rather than in the spring period when the vast majority of other UK temperate bamboo species are producing their new culms. Why this matters in the UK: this autumn culm production calendar creates a significant risk in UK conditions because the new culms are at their most tender, young, and unhardened at exactly the time when the UK's first autumn frosts begin to occur; a sharp frost in October or November can kill the tender new culms that have been produced in September and October, before they have had the opportunity to harden and mature; this is a significant limiting factor on the success of chimonobambusa in colder UK regions where early frosts are more common and more severe. Visual display: the autumn culm emergence is itself a very attractive feature of the plant for gardeners who grow it in sheltered positions where the new culms are not frost-damaged; the distinctive, prominently swollen nodes are at their most dramatic and cleanly defined on the newly emerged, fresh, bright green culms of autumn and early winter before they age and the surface texture changes. Spring growth: unlike the dramatic culm production of spring-producing bamboos (which is the main growth event of the year for genera like Phyllostachys), chimonobambusa does not produce a major flush of new culms in spring; instead, leaf and branch growth develops on the existing culms in spring as the plant emerges from its winter dormancy.

Chimonobambusa tumidissinoda (walking stick bamboo, thick-noded bamboo) is a Chinese ornamental bamboo prized for its extraordinary culms, where very short internodes and dramatically swollen dome-shaped nodes create a walking-stick-like knobbly appearance unique among bamboos. It produces new culms in autumn rather than spring. Leaves curl from cold stress and winter damage (it is less cold-hardy than most commonly grown UK bamboos), drought combined with heat, or frost damage to the tender new autumn culms.

Cold stress and winter damage

Considerably less cold-hardy than most commonly grown UK garden bamboos; hardy to approximately -10 to -12°C in sheltered positions. In temperatures below -10°C, leaves curl, yellow, brown, and drop; culms turn yellowish-brown or tan and may die back. The plant can regenerate from the underground rhizome system in spring in mild areas if the rhizomes survived. Most reliably hardy in sheltered gardens in Cornwall, coastal Devon, South Wales, mild urban gardens in southern England.

What to do

Position against a south or west-facing wall that provides additional warmth and shelter; in borderline-hardy areas, wrap culms in horticultural fleece in winter during forecast cold spells and apply a very thick mulch (15 to 20 cm) of composted bark or straw over the root zone to protect the rhizomes from freezing; do not cut back damaged top growth until spring after the last frost risk has passed; even if all top growth appears dead, the rhizomes may have survived and will regenerate new culms from the soil surface in spring.

Drought and heat stress

Adapted to the moist, humid forest understory of south-west and central China; in a dry, hot UK summer in a sunny, exposed position on thin, freely draining soil, the leaves roll inward and may yellow and drop from July to September. Chimonobambusa in containers is particularly vulnerable as the compost volume dries rapidly.

What to do

Plant in a sheltered, partially shaded, moisture-retentive, humus-rich position; incorporate large quantities of well-rotted compost and leaf mould into the planting hole; apply a deep mulch around the base; water thoroughly in dry summer periods; check containers at least daily in hot weather; a partially shaded position on the south side of an established hedge or shrub planting, where the plant receives some direct sun but is sheltered from the full heat of midsummer, is ideal.

Frost damage to autumn culms

Chimonobambusa produces new culms in autumn (September to November), unlike virtually all other temperate UK garden bamboos, which produce culms in spring. These tender new autumn culms are at their most vulnerable at exactly the time when the UK's first autumn frosts begin; a sharp October or November frost can kill the new culms before they harden and mature, causing them to collapse, yellow, and die.

What to do

In areas where early autumn frosts are common, protect the new emerging autumn culms with horticultural fleece draped over the plant during forecast frost nights from October onwards; this is most critical for the young, unhardened culms in their first few weeks of growth; once the culms have hardened and the growing tip has stopped extending (typically by November or December), they are more frost-resistant; in very cold-susceptible areas, the unusual autumn culm calendar of chimonobambusa makes it a difficult plant to manage successfully compared with the spring-culm-producing fargesia or phyllostachys.

Frequently asked questions

Why are my chimonobambusa leaves curling?

Chimonobambusa leaves curl most commonly because of cold stress and winter damage (hardy to approximately -10 to -12°C; considerably less cold-hardy than most commonly grown UK bamboos; leaves curl yellow brown and drop in temperatures below -10°C; culm die-back; south or west-facing wall position; fleece wrapping in cold spells; thick mulch over root zone; do not cut back damaged top growth until spring), drought and heat stress (forest understory species adapted to moist humid conditions; leaves roll and yellow in dry hot UK summers from July to September; sheltered partially shaded moisture-retentive humus-rich position; deep mulch; water thoroughly; check containers daily), or frost damage to autumn culms (unusual autumn September to November culm production; tender new culms at their most vulnerable at first UK autumn frost time; fleece protection during forecast frost nights from October onwards; particularly difficult in areas with early or regular autumn frosts).

Is chimonobambusa tumidissinoda hardy in the UK?

Hardy to approximately -10 to -12°C in sheltered positions; significantly less cold-hardy than Fargesia murieliae (to -20°C), Phyllostachys aureosulcata (to -22°C), or Semiarundinaria fastuosa (to -20°C). Reliably hardy: sheltered gardens in Cornwall, Scilly Isles, coastal Devon, coastal South Wales, Gulf Stream coastal areas of west Scotland, sheltered urban gardens in southern England. At risk: the Midlands, northern England, most of Scotland, inland Wales, and exposed rural sites anywhere in the UK. Protection in borderline areas: fleece wrapping, south or west-facing wall, thick mulch over root zone to protect rhizomes. The unusual autumn culm production adds further frost risk in colder UK areas.

When does chimonobambusa produce new culms?

Autumn: primarily September through November in the UK; the opposite of virtually all other UK temperate bamboos which produce culms in spring. Why it matters: new culms are at their most tender and unhardened at exactly the time when UK first autumn frosts begin; a sharp October or November frost can kill new culms before they harden; a major limiting factor in colder UK regions. Visual display: distinctive prominently swollen nodes are most dramatic and cleanly defined on newly emerged fresh bright green autumn culms. Spring growth: unlike spring-producing bamboos, chimonobambusa does not produce a major new culm flush in spring; leaf and branch growth develops on existing culms as the plant emerges from winter dormancy.

What are the swollen nodes on chimonobambusa?

Culm nodes are the solid disc-like dividers that separate the hollow internode sections of a bamboo culm; the points from which branches emerge. In Chimonobambusa tumidissinoda: nodes are very dramatically swollen into prominent rounded dome-like structures much wider than the internodes above and below them; internodes between nodes are unusually short (5 to 10 cm); the combination of very short internodes and very prominent large swollen nodes gives the culm an extraordinary knobbly walking-stick-like appearance quite unlike any other bamboo; the specific epithet 'tumidissinoda' means 'most swollen nodes' in Latin. Cultural use: in China the culms are harvested to make highly prized walking sticks, umbrella handles, and decorative items; naturally swollen knobbly nodes provide a comfortable grip for walking sticks; culms also used as unusual decorative garden stakes and plant supports in the UK.