Plant problems

Why Are My Hibanobambusa Leaves Curling?

Q: Does hibanobambusa spread and is it invasive?

Hibanobambusa tranquillans (hiba bamboo) produces running underground rhizomes and spreads horizontally in a manner broadly similar to a moderately vigorous running bamboo; it is neither as tightly clumping as Fargesia nor as strongly, rapidly invasive as the most vigorous Phyllostachys species under UK conditions; however, it does spread and requires active management in gardens where spread beyond the intended planting area would be problematic. Rate of spread in the UK: Hibanobambusa tranquillans typically spreads outward at approximately 30 to 60 cm per year in good UK growing conditions; this rate of spread means it will gradually form an expanding colony over a period of years if not contained; UK gardens planning to grow this bamboo should implement containment measures before planting. Containment options: a 60 to 70 cm deep solid HDPE root barrier installed as a continuous barrier before planting; annual spade cut around the perimeter of the intended planting area in autumn or early spring; container growing in a large rigid container (minimum 60 to 90 cm diameter) which also increases the risk of drought stress due to the limited soil volume. UK invasive species law: Hibanobambusa tranquillans is not listed on Schedule 9 of the Wildlife and Countryside Act 1981 and is not a notifiable invasive species in the UK; it is not in the same legal category as Japanese knotweed. Best uses in UK gardens: as a contained, specimen bamboo in a mixed border or as a screening planting with root barrier management; most effective in a partially shaded position that enhances the variegation contrast and reduces the risk of sun scorch to the white leaf areas; the variegated leaves are very striking in a shade garden or Japanese-style garden.

Q: What is the difference between hibanobambusa Shiroshima and other variegated bamboos?

Several variegated bamboos are available to UK gardeners; Hibanobambusa tranquillans 'Shiroshima' is the most widely grown of these but there are others with quite different leaf sizes, habits, and variegation patterns that UK gardeners may encounter. Hibanobambusa tranquillans 'Shiroshima': broad, paddle-shaped leaves (broader than phyllostachys, narrower than sasa) with irregular cream, white, and green striped variegation; moderately tall (3 to 5 m); semi-running rhizomes; very widely grown in UK specialist bamboo gardens and available from UK bamboo nurseries. Pleioblastus viridistriatus (golden-leaved bamboo, green-striped bamboo, syn. Arundinaria viridistriata): a low-growing (typically 0.5 to 1.5 m), moderately spreading bamboo from Japan with very striking, very bright yellow or golden leaves with fine green stripes; the vivid golden-yellow colour of new growth in spring and early summer is very different from the white-cream-green variegation of 'Shiroshima'; commonly cut back hard to ground level annually in late winter to encourage the production of the brightest-coloured new growth; the leaf colour fades to a more greenish-yellow later in the season. Pleioblastus argenteostriatus 'Okinadake': white or cream-striped, narrower-leaved bamboo; lower-growing than Hibanobambusa; less commonly grown in UK gardens. Sasa veitchii: not variegated in the traditional sense but develops beautiful, natural, pale straw-coloured dried margins in autumn and winter that create a very distinctive bicolour dried-margin effect unique among bamboos. Bashania qingchengshanensis: occasionally seen in UK specialist collections; less widely available.

Hibanobambusa tranquillans 'Shiroshima' (variegated hiba bamboo) is one of the most popular variegated bamboos in UK gardens, with beautiful irregular cream, white, and green striped leaves on moderately tall semi-running culms reaching 3 to 5 m. Leaves curl from drought (the cream areas are especially vulnerable to browning), cold and wind desiccation, or the variegation can decline as reverted all-green shoots are allowed to dominate.

Drought and water stress

The broader leaves of hibanobambusa have a higher transpiration rate than narrow-leaved phyllostachys; leaves roll inward in the characteristic bamboo drought response from July to September in dry UK summers. The white and cream areas of the 'Shiroshima' leaf are chlorophyll-deficient and more susceptible to browning from sun scorch and desiccation than the green areas.

What to do

Water thoroughly in dry periods; apply a deep mulch (10 to 15 cm) of composted bark or leaf mould around the base to retain soil moisture; a position in partial shade or morning sun with afternoon shade protects the cream leaf areas from both sun scorch and the worst desiccation while maintaining sufficient light for good variegation contrast; incorporate well-rotted compost into the planting hole for a moisture-retentive root environment; check containers daily in summer.

Cold and wind desiccation

Hardy to approximately -15°C in sheltered UK positions; normal cold-triggered leaf rolling reverses as temperatures rise. The white and cream areas of the 'Shiroshima' leaf may show slightly more browning from cold, drying easterly winds in February and March than the green areas, and the variegation can appear less distinct when the leaf is rolling in cold stress.

What to do

Provide a sheltered position away from persistent cold easterly winds; a permeable windbreak significantly reduces winter and spring desiccation damage to the cream leaf areas; cut back any dead or wind-damaged culms to ground level in spring after the risk of further frost has passed; new variegated culms regenerate vigorously from the rhizome system in spring.

Reversion to all-green shoots

Entirely green, non-variegated shoots and culms sometimes emerge from the rhizome system alongside the variegated shoots; these reverted green shoots are typically more vigorous than the variegated shoots and if left in place will gradually dominate the planting, reducing the proportion of variegated culms and leaves over time until the planting appears largely or entirely green.

What to do

Inspect the planting at least once in spring and once in summer for entirely green, non-variegated shoots and culms; cut reverted shoots to ground level immediately on detection; do not allow reverted shoots to develop and leaf out; this is the single most important maintenance action for preserving the variegated character of 'Shiroshima' over time. Also cut back older culms (more than three to four years old) in late winter to encourage vigorous new culms with the freshest, most vivid variegation.

Frequently asked questions

Why are my hibanobambusa leaves curling?

Hibanobambusa 'Shiroshima' leaves curl most commonly because of drought and water stress (broad leaves have high transpiration rate; cream and white areas more susceptible to browning from desiccation and sun scorch; water thoroughly in dry periods; deep mulch; partial shade or morning sun with afternoon shade protects cream areas while maintaining good variegation contrast; incorporate well-rotted compost for moisture-retentive root environment; check containers daily in summer), cold and wind desiccation (hardy to approximately -15°C; normal cold-triggered rolling reverses as temperatures rise; white areas may show slightly more browning from cold drying winds; sheltered position away from persistent cold easterly winds; permeable windbreak), or reversion to all-green shoots (more vigorous green reverted shoots gradually dominate if not removed; cut to ground level immediately on detection; single most important maintenance action for preserving the variegated character; cut back older culms in late winter for fresh vivid variegation on new growth).

How do I keep the variegation bright in hibanobambusa Shiroshima?

Light levels: partial shade or morning sun with afternoon shade; gives brightest most distinct variegation contrast and protects cream areas from afternoon sun scorch; deep shade makes variegation less distinct. Remove reverted green shoots: inspect at least once in spring and once in summer; cut all-green non-variegated shoots to ground level immediately on detection; do not allow them to develop. Consistent moisture: cream and white areas more susceptible to browning from drought stress and sun scorch than green areas; moisture-retentive humus-rich soil; deep mulch; consistent watering in dry periods. Cut back old culms: cut older culms (more than 3 to 4 years) to ground level in late winter; newest culms and leaves display the brightest most distinct variegation.

Does hibanobambusa spread and is it invasive?

Produces running underground rhizomes; broadly similar to moderately vigorous running bamboo; less invasive than most vigorous Phyllostachys; more spreading than Fargesia. Rate of spread: approximately 30 to 60 cm per year outward in good UK conditions. Containment: 60 to 70 cm deep solid HDPE root barrier before planting; or annual spade cut around perimeter in autumn or spring; or large rigid container (minimum 60 to 90 cm diameter; increases drought stress risk). Not listed on Schedule 9 of the Wildlife and Countryside Act 1981; not a notifiable invasive species. Best uses: contained specimen bamboo in mixed border or screening planting with root barrier; most effective in partially shaded position enhancing variegation contrast.

What is the difference between hibanobambusa Shiroshima and other variegated bamboos?

Hibanobambusa 'Shiroshima': broad paddle-shaped leaves with irregular cream white and green striped variegation; moderately tall (3 to 5 m); semi-running rhizomes; widely grown in UK specialist bamboo gardens. Pleioblastus viridistriatus (golden-leaved bamboo): low-growing (0.5 to 1.5 m), moderately spreading; very bright yellow or golden leaves with fine green stripes; vivid golden-yellow new growth in spring fading to greenish-yellow later; commonly cut back hard to ground level annually in late winter for brightest new growth; very different from the white-cream-green of 'Shiroshima'. Pleioblastus argenteostriatus 'Okinadake': white or cream-striped, narrower-leaved, lower-growing; less commonly grown. Sasa veitchii: not traditionally variegated but develops ornamental pale straw dried margins in autumn and winter unique among bamboos.