Plant problems

Why Are My Illicium Leaves Curling?

Q: Why are my illicium leaves curling?

Illicium (star anise shrub) leaves curl and drop most commonly in UK gardens because of cold damage in hard winters (most illicium species are only marginally hardy in the UK and the large, glossy, aromatic, evergreen leaves curl and drop in hard frost below about -8 to -12°C depending on species), alkaline or chalky soil (illicium requires acid to neutral soil and the leaves yellow from lime-induced chlorosis, then curl and drop in alkaline conditions), or hot, dry, sunny exposure (illicium dislikes hot, direct sun and performs best in light shade or dappled light; hot afternoon sun causes leaf scorch and curl). Illicium is a genus of about 40 species of aromatic evergreen shrubs and small trees from south-east Asia, eastern North America, the Caribbean, and Central America; they are related to the commercially important Chinese star anise (Illicium verum) from which the spice is derived, and share the same characteristic anise-scented foliage and distinctive star-shaped flowers. Several species are grown in UK gardens, primarily for their architectural, glossy, evergreen foliage and their interesting spring flowers; the species most commonly seen include Illicium anisatum (Japanese star anise), an evergreen shrub with strongly anise-scented, dark glossy leaves and small, creamy-white, multi-petalled flowers in spring; Illicium floridanum (Florida star anise), a larger shrub with strongly scented leaves and interesting dark red, spider-like flowers with many narrow petals in late spring; and Illicium simonsii (from Yunnan, China), which is considered one of the hardiest species. All parts of Illicium anisatum and I. floridanum are toxic if ingested; they should not be confused with the culinary Chinese star anise (I. verum) despite the similar anise scent of the foliage.

Q: Is illicium hardy in the UK?

Illicium hardiness in the UK varies significantly by species; Illicium simonsii from Yunnan is considered one of the hardiest, surviving to approximately -12 to -15°C in sheltered conditions, and can be grown in much of southern and western England and Wales. Illicium anisatum (Japanese star anise) is hardy to approximately -10°C in sheltered conditions and is reliably perennial in mild UK gardens (south-west England, sheltered coastal and urban positions). Illicium floridanum (Florida star anise) is somewhat less hardy (to about -8 to -10°C) and requires more shelter or protection in most of the UK. Cold, drying wind causes more damage to illicium than still frost of the same temperature; shelter from north and east wind is important for all species. Acid, moisture-retentive soil also improves cold hardiness by keeping the plant in good health throughout the growing season; stressed or alkaline-soil-weakened plants are far less cold-tolerant than healthy, well-grown specimens in acid conditions. In the right conditions (sheltered, lightly shaded, acid, moist soil), illicium is a handsome, long-lived, low-maintenance evergreen shrub that provides year-round architectural interest with its glossy, aromatic foliage.

Q: How do I grow illicium in the UK?

Illicium grows best in a sheltered, lightly shaded position in moist, acid to neutral (pH 5.0 to 6.5), humus-rich, freely draining soil; a sheltered woodland garden position, a north or west-facing wall base, or a lightly shaded border in acid-soil conditions provides ideal UK growing conditions. The plants are from humid, semi-shaded woodland habitats and dislike hot, direct sun; in a sunny, exposed position the large, glossy leaves scorch and curl, and the plant performs poorly. Add leaf mould or ericaceous compost to improve soil acidity and moisture retention; mulch annually with composted bark. Water with rainwater in hard-water areas; tap water in alkaline regions gradually raises pH and harms the plant. Do not plant in alkaline or chalky soil; the plants cannot tolerate alkaline conditions. Prune minimally; illicium does not require regular pruning and responds poorly to hard cutting back. Remove any dead or damaged growth in spring. The anise-scented foliage is the principal year-round feature; the flowers in spring are interesting rather than showy. Illicium anisatum and I. floridanum are toxic if ingested; plant in positions where children and pets cannot access the foliage or berries.

Q: Is illicium the same as star anise?

Illicium is the genus that includes both the culinary star anise and the ornamental garden star anise shrubs grown in UK gardens, but the culinary spice comes from a different species (Illicium verum, Chinese star anise) from the ornamental garden species (Illicium anisatum, Illicium floridanum, Illicium simonsii). Illicium verum is the source of the spice used in cooking and is grown commercially in southern China and Vietnam; it is not reliably hardy in the UK and is rarely grown as a garden ornamental in this country. The ornamental garden species share the same characteristic anise fragrance of the foliage (from anethole compounds in the leaves) as the culinary species, but their fruits and other parts are toxic and must not be used in cooking or for any culinary purpose. Illicium anisatum (Japanese star anise) is particularly toxic; in Japan its seeds were historically burned as temple incense, but ingestion of any part of the plant causes serious poisoning. The distinctive fragrance of the leaves of all illicium species when bruised is one of the ornamental pleasures of the genus in a UK garden: the clean, fresh, anise-liquorice scent released when a leaf is gently rubbed is a delightful unexpected quality of an otherwise understated foliage shrub, and is particularly strong on warm days in early summer.

Illicium (star anise shrub) is a genus of aromatic evergreen shrubs with large, glossy, anise-scented leaves and distinctive multi-petalled spring flowers. Related to culinary star anise but toxic (do not confuse with the edible I. verum), the most garden-worthy UK species are I. anisatum, I. floridanum, and I. simonsii. Cold damage and alkaline soil are the most common causes of leaf curl; sheltered, lightly shaded, acid conditions are needed.

Cold damage

Cold damage curls and drops the large, glossy leaves of illicium in hard UK winters; most species are damaged below about -8 to -12°C depending on species and conditions. Cold, drying wind causes more damage than still frost at the same temperature; the large evergreen leaves lose moisture through transpiration faster than frozen roots can replace it. Illicium simonsii is significantly hardier than I. anisatum or I. floridanum and is the best choice for colder UK positions.

What to do

Position in a sheltered spot protected from north and east wind; a west-facing wall base or sheltered woodland position is ideal. Wrap young plants in fleece from November to March in cold areas. Maintain the plant in good health through acid soil and consistent moisture; healthy plants are significantly more cold-tolerant than stressed ones. Do not remove apparently dead material until April when the extent of regrowth is clear.

Alkaline soil

Alkaline or chalky soil causes lime-induced chlorosis in illicium; the glossy leaves yellow between the veins, then curl and drop as the plant becomes progressively less able to take up iron and other micronutrients at high pH. The condition weakens the plant over time and makes it more susceptible to cold damage and disease. Illicium cannot be grown successfully in the long term in alkaline conditions without raised ericaceous growing medium.

What to do

Test soil pH before planting; acid to neutral conditions (pH 5.0 to 6.5) are needed. In alkaline gardens, plant in a large raised bed of ericaceous compost and leaf mould; water with rainwater only. Mulch annually with composted bark or pine needles to maintain acidity. Apply a sequestered iron feed in spring to alleviate chlorosis symptoms while underlying conditions are improved.

Hot sun exposure

Illicium dislikes hot, direct sun; in a sunny, exposed south-facing position the large, glossy leaves scorch at the margins and curl in hot summer conditions. The plants are from humid, semi-shaded forest understorey habitats and are adapted to moderate, filtered light rather than full sun. Lightly shaded or semi-shaded conditions in a sheltered position produce the healthiest, most vigorous growth and the glossiest, most attractive foliage.

What to do

Position in light dappled shade or bright indirect light; a north or west-facing position, a sheltered border behind taller plants, or a lightly shaded wall base all provide appropriate light levels. In western UK gardens with naturally overcast summers, a more open position may be tolerated. The glossy, aromatic foliage is most effective and most attractive in a slightly shaded setting where the large, reflective leaves catch and amplify the available light.

Frequently asked questions

Why are my illicium leaves curling?

Illicium leaves curl most commonly because of cold damage (the glossy leaves curl and drop below -8 to -12°C; cold wind is often more damaging than still frost; shelter is essential), alkaline soil (lime-induced chlorosis causes yellowing and curl; needs pH 5.0 to 6.5; ericaceous raised beds in alkaline gardens), or hot, direct sun (the large leaves scorch and curl in hot, exposed positions; lightly shaded, sheltered conditions are needed). Healthy plants in good conditions are significantly more cold-tolerant.

Is illicium hardy in the UK?

Illicium simonsii is the hardiest species (to about -12 to -15°C in sheltered conditions) and is a good choice for most of southern and western England and Wales. I. anisatum is hardy to about -10°C in sheltered conditions; I. floridanum to about -8°C. Cold, drying wind is more damaging than still frost. Acid, moist, sheltered conditions maximise cold tolerance; stressed or alkaline-soil-weakened plants are much less cold-hardy.

How do I grow illicium in the UK?

Grow in a sheltered, lightly shaded position in moist, acid to neutral (pH 5.0 to 6.5), humus-rich soil. Add ericaceous compost and leaf mould; mulch annually with composted bark; water with rainwater in hard-water areas. Prune minimally. All parts of I. anisatum and I. floridanum are toxic; do not confuse with the edible culinary star anise (Illicium verum). The anise-scented foliage when bruised is the signature ornamental quality of all illicium species.

Is illicium the same as star anise?

Illicium is the genus containing both the culinary star anise (I. verum, the Chinese spice) and the ornamental garden species (I. anisatum, I. floridanum, I. simonsii). The garden species are toxic and must not be used for cooking; only I. verum (not hardy in the UK) produces the edible spice. All species share the characteristic anise fragrance of the leaves when bruised, which is one of the ornamental pleasures of growing illicium in a UK garden.