Plant problems

Why Are My Astelia Leaves Curling?

Q: Why are my astelia leaves curling?

Astelia (silver spear or kakaha) leaves curl and brown most commonly in UK gardens because of waterlogging in poorly draining soil (astelia comes from moist but freely draining, boggy, mountainous, and coastal habitats in New Zealand and is intolerant of sustained waterlogging; the roots rot in saturated, poorly aerated conditions, causing the long, arching, silver-sheened leaves to yellow and curl at the tips), cold damage in hard UK winters (Astelia chathamica 'Silver Spear' and Astelia nervosa are the most commonly grown species and are generally hardy to approximately -8 to -10°C in well-drained conditions, but the spectacular, broad, silver-sheened leaves are frost-tender below about -5°C; the leaves curl, brown, and collapse when frosted; the growing crown at the base is harder than the leaf blades), or drought stress in very dry conditions (the long leaves curl and lose their characteristic silver sheen when the root zone dries out; astelia prefers consistently moist conditions and performs best in reliably moist but freely draining soil). Astelia is a genus of around 25 species of bold, clump-forming, evergreen perennials in the family Asteliaceae from New Zealand, Australia, and the Pacific Islands; they are grown in UK gardens primarily as dramatic, architectural foliage plants providing a strong, grass-like or sedge-like effect in borders, courtyard gardens, and containers. The most commonly grown species in UK gardens are Astelia chathamica 'Silver Spear' (broad, strongly silver-sheened, arching leaves to 1.5 m in ideal conditions, cream flowers followed by orange berries on female plants) and Astelia nervosa (narrower, bronze-green to silver-tinted leaves, more compact, slightly hardier).

Q: Is astelia hardy in the UK?

Astelia hardiness varies by species; Astelia chathamica 'Silver Spear' is generally considered hardy to approximately -8 to -10°C in freely draining conditions in a sheltered position, making it reliably perennial in most of England and Wales in suitable conditions. Astelia nervosa is slightly hardier and more compact. In mild UK gardens (coastal, south and west, sheltered urban) both species are reliably evergreen and grow vigorously; in colder inland or northern UK gardens, the broad leaves may be damaged or lost in hard winters while the growing crown at the base survives and resprouts in spring. The combination of cold and wet is more damaging than cold alone; a free-draining soil in a sheltered position dramatically improves cold tolerance. In Scotland, northern England, and exposed UK positions, astelia is best grown in a large container that can be brought into a cool greenhouse or conservatory from November to April, or given substantial fleece protection in situ. The plants are significantly more cold-tolerant than their exotic appearance suggests; a well-established plant in a sheltered, well-drained south-facing border in southern England can tolerate most UK winters without protection.

Q: How do I grow astelia in the UK?

Astelia grows best in a sheltered, sunny to lightly shaded position in moist, freely draining, moderately acid to neutral soil; the plants are from mountain grassland, subalpine bog margins, and coastal scrub in New Zealand and perform best in conditions that replicate these: open and bright, consistently moist but never waterlogged. Enrich the growing medium with leaf mould, composted bark, or ericaceous compost to provide the mildly acid conditions the plants prefer; avoid heavily alkaline or chalk soils. Plant in a sheltered position out of persistent drying winds, which damage the large leaf blades; a south or west-facing border with shelter from a wall or large shrubs is ideal. Mulch annually with composted bark to retain moisture and protect the root zone from temperature extremes; apply a generous mulch from November to reduce frost penetration into the root zone. Water regularly during the growing season from April to October; established plants are moderately drought-tolerant but still benefit from supplementary water in dry spells. In cold or exposed UK areas, protect with two to three layers of fleece from November to March or grow in a large container (minimum 40 cm diameter) that can be brought under cover for winter. The silver sheen on the leaves of A. chathamica 'Silver Spear' is most intense in bright light; shade reduces the silver intensity and the architectural effect.

Q: Why are astelia leaves silver?

The silver sheen on astelia leaves is produced by a coating of fine, white, silvery scales (scales belonging to the family Asteliaceae are sometimes called 'stellate scales' or 'peltate scales') on the surface of the leaves; this reflective coating is particularly pronounced on Astelia chathamica 'Silver Spear', where the entire upper leaf surface is covered in a dense, bright silver-white coating that gives the plant its common name and its principal ornamental quality. The silver coating is an adaptation to the intense sunlight and UV radiation of the high-altitude and exposed coastal habitats where many astelia species grow in New Zealand; the reflective scales reduce radiation and heat load on the leaf surface, helping the plant manage temperature extremes in its natural environment. The intensity of the silver effect varies with light levels: plants grown in bright, open, sunny positions develop the most intense silver sheen; those grown in shade or low light have much less pronounced silvering and appear more green. If the silver sheen diminishes noticeably on an established plant, this is often a sign of too much shade, nitrogen-rich feeding (which promotes green leaf growth at the expense of the reflective scaling), or excessive moisture causing soft growth. Moving the plant to a brighter position is the most effective remedy.

Astelia chathamica 'Silver Spear' is one of the most dramatic New Zealand foliage plants in UK cultivation: broad, arching, intensely silver-sheened leaves to 1.5 m create a bold, architectural statement in border, courtyard, or container. Hardy to about -8 to -10°C in sheltered, well-drained conditions, it is reliable in most of England and Wales. Waterlogging and cold are the main causes of leaf curl; bright light maintains the silver intensity.

Waterlogging

Waterlogging is the most common cause of astelia failure in UK gardens; the roots rot in saturated, poorly aerated soil, causing the long, silver-sheened leaves to yellow, curl at the tips, and eventually collapse. The plants come from habitats that are moist but freely draining; sustained saturation, particularly combined with cold in winter, is rapidly fatal. Heavy clay soils and low-lying positions are the highest-risk environments.

What to do

Plant in freely draining, enriched soil; incorporate leaf mould and grit in clay soils. In heavy soils, grow in a raised bed or large container with a gritty, free-draining mix. Apply a composted bark mulch annually to improve soil structure and prevent compaction. Ensure containers have good drainage holes that remain unobstructed.

Cold damage

Hard frosts below about -5°C damage the broad leaf blades of astelia; the leaves curl, brown, and eventually collapse while the growing crown at the base (typically hardier) usually survives to produce new growth in spring. The silver sheen disappears from frosted leaves. In the most exposed positions, several consecutive nights of frost below -8°C can kill the crown as well; fleece protection or container growing under cover prevents this.

What to do

In mild UK areas, wrap the foliage loosely in two to three layers of horticultural fleece from November to March; apply a deep bark mulch over the root zone. In colder areas, grow in a large container (minimum 40 cm) and bring into a cool, frost-free greenhouse or conservatory from November to April. Remove frosted leaves once new growth emerges in spring; the plant readily produces new leaves from the crown once conditions warm.

Drought stress

The long leaves of astelia curl and lose their silver sheen when the root zone dries out in summer; the plants prefer consistently moist conditions and are not fully drought-tolerant despite their bold, architectural appearance. Container-grown plants are most vulnerable; they dry out more rapidly than in-ground plants and the reduced root volume limits the plant's ability to buffer temperature and moisture extremes. Drought-stressed plants also produce fewer and smaller new leaves.

What to do

Mulch the root zone with 5 to 10 cm of composted bark annually to retain soil moisture; water during dry spells from June to September. Container plants need regular watering through the growing season; check moisture levels several times per week in hot weather. The silver sheen recovers once moisture levels are restored and new growth begins.

Frequently asked questions

Why are my astelia leaves curling?

Astelia leaves curl most commonly because of waterlogging (roots rot in saturated soil; plant in freely draining conditions; improve drainage in heavy clay), cold damage below -5°C (leaves curl and brown; crown usually survives; fleece from November; container growing in cold areas), or drought stress in summer (leaves curl and lose silver sheen; mulch and water regularly; container plants need most attention). Cold and wet together is the most dangerous combination.

Is astelia hardy in the UK?

Astelia chathamica 'Silver Spear' is hardy to about -8 to -10°C in sheltered, well-drained conditions and is reliably perennial in most of England and Wales. The leaf blades are damaged by frost below -5°C but the crown survives and regrows. In Scotland, northern England, and exposed positions, grow in a container and overwinter under cover, or provide substantial fleece protection. Astelia nervosa is slightly hardier and more compact.

How do I grow astelia in the UK?

Grow in a sheltered, sunny to lightly shaded position in moist, freely draining, moderately acid to neutral soil enriched with leaf mould. Mulch annually with composted bark; water during dry spells. Apply fleece from November in all but the mildest positions. The silver sheen is most intense in bright sun; shade reduces the silver effect. Feed sparingly in spring; heavy nitrogen feeding promotes green growth at the expense of the silver coating.

Why are astelia leaves silver?

The silver sheen is produced by a dense layer of fine, reflective scales on the leaf surface; this is a natural adaptation to intense UV and heat in New Zealand's high-altitude and coastal habitats. It is most pronounced in bright sun and least pronounced in shade. If an established plant loses its silver sheen, move to a brighter position and reduce nitrogen feeding. Frosted leaves lose the silver effect entirely; new growth is fully silver.