Why Are My Sasa Leaves Curling?

Drought and water stress

The very large broad sasa leaves create a very high total transpiration rate; in a dry, hot UK summer the leaves curl inward from the margins and the margins begin to dry and brown as the plant struggles to balance water loss through the large leaf surface with uptake from the root system. Sasa in containers and in thin, freely draining soils in sunny exposed positions are most vulnerable; those in cool, shaded, moisture-retentive woodland soils are far more drought-tolerant.

What to do

• Water thoroughly in dry spells, especially in July and August; sasa in a shaded or partially shaded position with moisture-retentive, humus-rich soil needs significantly less supplemental watering than sasa in full sun or a thin, dry, exposed position; check containers daily in summer; a deep mulch (10 to 15 cm) of composted bark or leaf mould around the base retains soil moisture significantly; in a very dry, hot summer on thin soil, sasa may show repeated stress curling that can be reduced by relocating to a moister, more shaded position.

Wind desiccation

The very large, broad sasa leaves present a very large surface area to the wind; persistent drying cold easterly winds in winter and spring, or hot dry winds in summer, strip moisture from the leaf surface faster than the root system can replace it. The leaves curl, the margins dry and brown, and the plant's appearance deteriorates in an exposed, wind-swept position. Wind desiccation contributes significantly to the characteristic dried, bleached-margin effect on Sasa veitchii leaves in winter.

What to do

• Provide a sheltered, wind-protected position; a permeable windbreak (a hedge or living screen) is more effective than a solid fence or wall (which creates turbulence on the leeward side); in an exposed position, a windbreak on the prevailing wind side significantly reduces leaf desiccation damage; for Sasa veitchii, some wind exposure in winter is desirable to enhance and develop the characteristic dried-margin ornamental effect, but persistent severe wind desiccation that causes extensive leaf browning beyond the margin should be reduced.

Cold and frost stress

Sasa species are generally cold-hardy to approximately -15 to -18°C in UK conditions. Like all bamboos, the broad leaves curl and roll inward in cold weather as a protective mechanism; the leaves uncurl as temperatures rise. Severe or prolonged frost may cause widespread leaf browning. The extensive, spreading rhizome system usually regenerates the plant in spring even after severe top growth damage from extreme cold.

What to do

• No action needed for cold-triggered leaf curl in healthy sasa; this is entirely normal behaviour. After a severe frost, monitor in spring; new culms and leaves will emerge from the rhizome system if the root system is undamaged; cut back any dead, browned top growth to ground level in spring to make space for the new growth. In the coldest UK areas, in a very severe winter, covering the root zone with a thick mulch of composted bark or straw protects the rhizome system in the soil even if the top growth is killed back to the surface.

Normal dried margins in S. veitchii

In Sasa veitchii specifically, the natural drying and bleaching of the leaf margins to a pale, straw-coloured, papery, white-looking border is a completely normal, healthy, and highly ornamental seasonal feature; it is not a disease, nutrient deficiency, drought damage, or pest problem. This bleaching begins in autumn and is most pronounced and beautiful in mid-winter; it is one of the primary reasons this species is grown in UK gardens.

What to do

• No action needed; enjoy the feature. The dried margins are replaced by fully green new leaves in spring as new culms emerge with the return of warm weather. Do not treat with any product or cut back in response to the dried margins in winter; this is the plant behaving entirely as intended.

Frequently asked questions

Why are my sasa leaves curling?

Sasa leaves curl and brown at the margins most commonly because of drought and water stress (very large broad leaves have very high transpiration rate; water thoroughly in dry spells; shaded moisture-retentive humus-rich soil far more drought-tolerant than full sun thin dry exposed position; deep mulch retains moisture), wind desiccation (large leaf surface area vulnerable to drying winds; provide sheltered position with permeable windbreak; some wind exposure in winter desirable for S. veitchii dried-margin effect), cold and frost stress (normal protective curling in cold weather; leaves uncurl as temperatures rise; regenerates from spreading rhizome system in spring after severe top growth damage), or the normal ornamental dried-margin development in Sasa veitchii (completely normal healthy seasonal feature; bleaching from autumn to mid-winter; fully green new leaves in spring; no action needed). S. veitchii dried margins are a feature, not a fault.

How do I stop sasa from spreading in my garden?

Root barrier: heavy-duty HDPE bamboo root barrier at least 60 to 70 cm deep (70 to 80 cm for robust species) installed vertically before planting as a continuous contained zone; join carefully; check top of barrier periodically and cut back any rhizomes going over the top. Trench method: open trench 30 to 45 cm deep around the planting exposes rhizomes as they try to cross; inspect at least twice yearly in spring and summer; cut back any crossing rhizomes; less effective than a solid barrier. Annual spade cut: sharp spade cut vertically around the perimeter in late autumn or spring, cutting and removing crossing rhizomes; must be done consistently every year. Container growing: large rigid container (minimum 60 to 90 cm diameter) completely contains rhizomes; repot or divide every 2 to 3 years. Mowing: regular mowing along the boundary kills emerging rhizome tips for sasa used as ground-cover.

What is the white edging on sasa veitchii leaves?

The pale straw-coloured papery white-looking border on the margins of Sasa veitchii leaves is completely normal, natural, and highly ornamental; NOT a sign of disease, nutrient deficiency, drought damage, or pest attack. Natural autumn and winter drying of the outer leaf margins; as temperatures cool and growth slows in autumn, margins lose their green colour, dry, and bleach to pale straw to white papery texture; at its most pronounced in mid-winter: broad bright to dark green central zone surrounded by a wide pale straw to white dried border; a primary ornamental reason S. veitchii is grown in UK gardens. In spring: new culms and leaves produced with fully green, undamaged margins; old dried-margin leaves replaced and drop; fully green in summer before autumn drying cycle recommences.

Is sasa bamboo invasive in UK gardens?

Sasa palmata: very vigorously spreading; can cover very large areas rapidly if unmanaged; can travel under many garden fences into neighbouring gardens. Sasa veitchii: less aggressively spreading but still spreads significantly more than clumping bamboos. Both strongly rhizomatous; not listed on Schedule 9 of the Wildlife and Countryside Act 1981 (not a notifiable invasive species in the way Japanese knotweed is). Best uses: very large gardens where spreading as dramatic architectural ground-cover is acceptable; or root-barrier-contained planting in smaller gardens; not suitable for a small garden without root containment. Alternatives for smaller gardens with large bold leaves: Indocalamus tessellatus (even larger leaves, less vigorously spreading); Fargesia spp. for non-invasive clumping bamboo.