Plant problems

Why Are My Musa Leaves Curling?

Q: Why are my musa leaves curling?

Musa (banana plant) leaves curl and fail to open fully most commonly in UK cultivation because of cold temperatures (musa leaves emerge tightly rolled and unfurl as they mature; if temperatures fall below about 10 to 12°C during the unfurling stage, the leaf develops slowly and incompletely, and may remain partially rolled, curl at the edges, or develop brown streaks along the midrib as cell damage occurs during cold spells; even in summer, a cold night in a UK garden can damage an unfurling banana leaf), drought stress (the very large leaf surface transpires enormous quantities of water, and the central rolled emerging leaf can fail to unfurl and instead curls in on itself when the pseudostem and root zone are dry; established musa in the ground can deplete a large volume of soil moisture rapidly in a hot UK July), waterlogging in UK winter conditions (the rhizome rots in saturated, cold, poorly draining soil over winter; in spring, the plant either fails to emerge or produces stunted, rolled, yellowing leaves from a partially rotted rhizome), or low humidity in the indoor winter environment (musa kept as a house plant or in a warm greenhouse over winter in centrally-heated conditions loses leaf moisture rapidly to dry air, and the large leaves curl at the margins and develop brown tips from desiccation). Musa is a genus of around 70 species of giant herbaceous perennials in the banana family (Musaceae) from tropical and subtropical Asia and the Pacific; in the UK, the most commonly grown ornamental banana species are Musa basjoo (Japanese or Sichuan banana, hardy to approximately -12°C in the rhizome), M. sikkimensis (Darjeeling banana, hardy to about -5 to -8°C), and M. acuminata and hybrids (dessert bananas, essentially frost-tender and grown as summer patio or greenhouse plants).

Q: Is musa hardy in the UK?

Musa basjoo (Japanese banana) is the hardiest commonly grown banana species and can be grown outdoors year-round in most of the UK if the rhizome is protected from severe frost; it is the standard species for outdoor UK banana growing. The rhizome of M. basjoo is hardy to approximately -12°C in dry conditions with a generous insulating mulch; the pseudostems (what are commonly called the 'trunk', but are actually tightly packed leaf bases) are usually killed to the ground by any hard frost, but regrow vigorously from the rhizome each spring. In mild UK coastal gardens (Cornwall, west Wales, western Scotland, coastal west Ireland, some sheltered London positions), M. basjoo pseudostems may survive winter partially or fully and produce larger plants with more leaves in subsequent seasons. Musa sikkimensis is somewhat less hardy than M. basjoo in rhizome survival but is similar in pseudostem tenderness. For outdoor year-round growing of M. basjoo: cut the pseudostems to about 60 to 80 cm in November; wrap them tightly in several layers of dry straw or bracken held in place with netting or horticultural fleece; and apply a very deep (30 to 40 cm), dry mulch of bark chips or straw over the entire root zone. Remove the wrapping and mulch gradually from late April as growth begins.

Q: How do I grow musa outdoors in the UK?

Musa basjoo and M. sikkimensis are grown outdoors in the UK in a warm, sunny, sheltered position protected from strong wind (which tears the large leaf blades along the veins) in rich, deep, moisture-retentive, freely draining soil. Shelter is as important as sun; a position sheltered from prevailing wind by walls, hedges, or other large plants prevents the tearing and shredding of the large leaves that makes banana plants look ragged within weeks of leaf opening in an exposed garden. Plant from late spring (May or June) after all frost risk has passed; banana plants are not actively growing before this and gain nothing from early planting in cold soil. Dig a generous planting hole and incorporate large quantities of well-rotted manure or garden compost; banana plants are gross feeders and need rich soil for maximum growth. Water generously through the growing season from May to September; in a hot, dry UK summer, established banana plants in the ground need watering at least every two to three days. Feed with a high-nitrogen liquid fertiliser monthly from May to August to fuel the rapid growth of the very large leaves. Protect from frost each November as described; remove protection from late April when growth begins. Over a period of several years in a warm, sheltered UK garden, M. basjoo can reach 3 to 4 m in height.

Q: Will musa fruit in the UK?

Musa basjoo (the most commonly grown outdoor banana in the UK) does not produce edible fruit in UK conditions; the plant is grown as an ornamental foliage plant for its dramatic, exotic effect. The fruit it produces when it does flower (which is rare in most UK gardens) is small, seedy, and inedible. For edible banana production in the UK, a large heated greenhouse or conservatory maintaining a minimum of 15 to 18°C year-round is required, along with adequate space (at least 3 to 4 m ceiling height for a mature banana plant) and sufficient light. Musa acuminata (Cavendish types, the dessert banana sold in supermarkets) and its hybrids require tropical temperatures throughout the year to produce fruit and cannot be fruited outdoors anywhere in the UK. Fruiting is also dependent on the plant reaching full maturity (typically six to twelve months of active growth after flowering begins) and on the variety; some compact varieties bred for container growing (such as 'Dwarf Cavendish' or 'Grand Nain') are more likely to fruit in a large heated greenhouse than full-sized varieties. In practice, UK banana growing is almost entirely ornamental rather than productive; the exotic foliage effect is the reward rather than the fruit.

Musa (banana plant) is a genus of giant herbaceous perennials from tropical Asia grown in UK gardens for their dramatic, large-leaved, exotic foliage. Musa basjoo (Japanese banana) is the hardiest species and can be grown outdoors year-round with winter rhizome protection. The very large leaves are vulnerable to cold, drought, wind tear, and low humidity. Cold during leaf unfurling and drought during summer growth are the main causes of curl.

Cold damage

Cold is the most common cause of musa leaf problems in the UK; the leaves emerge tightly rolled and unfurl over several days, and any cold spell below about 10 to 12°C during this critical unfurling period causes the leaf to remain partially rolled, curl at the edges, or develop brown streaking along the midrib. Even a cool UK summer night can damage an unfurling leaf. Below -2°C the pseudostem is killed; below about -12°C (for M. basjoo with good mulch protection) the rhizome is damaged.

What to do

Do not plant outdoors until late May or early June when soil and air temperatures are reliably above 12°C. In cold springs, cover plants with fleece on cool nights until June. Cut pseudostems back to 60 to 80 cm in November, wrap tightly in dry straw held with netting, and apply a 30 to 40 cm deep dry bark or straw mulch over the root zone. Gradually remove protection from late April as temperatures climb. Do not remove protection too early; a late April frost can kill the emerging growth.

Drought stress

Drought causes banana leaves to fail to unfurl correctly, curling inward and developing brown, papery edges; the emerging central rolled leaf is most sensitive as it needs adequate water pressure to open fully. Established banana plants in the ground can exhaust soil moisture rapidly in a hot UK July through the enormous surface area of their leaves. Container plants are particularly vulnerable and can become fatally dry within a single hot day.

What to do

Water generously from May to September; in a hot, dry UK summer, established in-ground plants need watering every two to three days and container plants may need daily watering. Maintain a deep mulch (10 cm of bark chips) over the root zone to reduce moisture loss from the soil surface. Feed monthly with high-nitrogen liquid fertiliser from May to August; nitrogen-starved plants produce fewer and smaller leaves and are more drought-sensitive.

Waterlogging

Waterlogging in cold UK winter soil rots the musa rhizome; in spring, the plant fails to emerge or produces stunted, rolled, yellowing leaves from a partially rotted rhizome. Even M. basjoo, which is remarkably tough in other respects, can be killed by a combination of cold and wet where the rhizome sits in saturated, cold soil for weeks. Heavy UK clay soils and low-lying garden positions are the most dangerous environments for overwintering rhizomes.

What to do

Plant in freely draining soil; incorporate grit or raise the planting position if drainage is poor. Apply a very deep, dry mulch over the root zone from November that deflects rain away from the immediate rhizome zone as well as insulating against cold. In waterlogged gardens, grow M. basjoo in a large container (minimum 50 cm diameter) moved under glass from November to May. A well-draining container compost (John Innes No. 3 plus 20% perlite) is essential.

Frequently asked questions

Why are my musa leaves curling?

Musa leaves curl most commonly because of cold during leaf unfurling (below 10 to 12°C the emerging rolled leaf fails to open fully; cover with fleece on cool nights; do not plant out until late May), drought stress (enormous leaf surface loses water rapidly; water every two to three days in hot summers; mulch heavily), or waterlogging of the rhizome in cold UK winters (rhizome rots in saturated soil; plant in free-draining soil; apply deep dry mulch from November). Cold is the most frequent cause in the UK context.

Is musa hardy in the UK?

Musa basjoo is the hardiest commonly grown banana, with the rhizome tolerating approximately -12°C in dry, well-mulched conditions. The pseudostems are killed by any hard frost but regrow vigorously from the rhizome. In mild UK coastal gardens, pseudostems may survive winter partially intact. For year-round outdoor growing: cut back to 60 to 80 cm in November, wrap in dry straw, and mulch the root zone 30 to 40 cm deep. Remove protection gradually from late April.

How do I grow musa outdoors in the UK?

Plant M. basjoo in a warm, sunny, very sheltered position (shelter from wind is as important as sun) in rich, deep, moisture-retentive, freely draining soil from late May. Incorporate large quantities of well-rotted manure at planting. Water generously throughout the growing season; feed monthly with high-nitrogen fertiliser from May to August. Protect the rhizome every winter with a deep dry mulch and wrapped pseudostems. Over several years in a sheltered UK garden, plants reach 3 to 4 m.

Will musa fruit in the UK?

Musa basjoo does not produce edible fruit in UK conditions; it is grown purely as an ornamental foliage plant. For edible bananas, a large heated greenhouse maintaining 15 to 18°C year-round is needed, along with at least 3 to 4 m ceiling height. Compact varieties like 'Dwarf Cavendish' are the most realistic candidates for fruiting under glass. UK banana growing is almost entirely ornamental; the exotic foliage is the reward, not the fruit.