Plant problems

Why Are My Dianella Leaves Curling?

Q: Why are my dianella leaves curling?

Dianella (flax lily or blueberry lily) leaves curl and brown most commonly in UK cultivation because of cold damage in hard winters (dianella is of variable hardiness depending on species and cultivar; most commonly grown UK garden dianellas such as Dianella tasmanica and D. caerulea cultivars are borderline hardy and the long, strap-like, arching leaves curl, go limp, and brown at the tips and margins after exposure to temperatures below about -5 to -8°C; the rhizome base is somewhat hardier than the leaves and often survives temperatures that kill the top growth, sprouting new leaves in spring), drought stress in hot UK summers (the long, arching leaves curl along their length and develop brown tips when the root zone dries out; container-grown dianella and plants in sandy, free-draining soils in a sunny position are most at risk), or wind desiccation in exposed winter positions (cold, drying wind strips moisture from the evergreen leaves faster than the roots in cold soil can replace it, causing rolling, browning, and tip dieback similar to frost damage). Dianella is a genus of around 40 species of evergreen, rhizomatous perennials in the asphodelaceae family from Australia, New Zealand, Africa, and the Pacific; they are grown in UK gardens for their elegant, sword-shaped or strap-like, arching, blue-green or variegated leaves, small star-shaped blue or white flowers in spring, and the striking, vivid blue-violet or purple berries that follow; the berries are the plant's most distinctive ornamental feature and are particularly attractive in autumn and winter.

Q: Is dianella hardy in the UK?

Dianella hardiness in the UK varies by species and cultivar; the most commonly grown garden dianellas are borderline hardy and best treated as half-hardy to marginally hardy rather than fully reliable perennials in most of the UK. Dianella tasmanica (Tasmanian flax lily) is one of the hardier species, tolerating approximately -8 to -10°C in freely draining conditions in a sheltered, south-facing position; it can be grown outdoors year-round in the mild UK coastal gardens of Cornwall, west Wales, western Scotland, coastal west Ireland, and sheltered London gardens. Dianella caerulea and its cultivars (such as 'Little Rev', 'Clarity Blue', and 'Breeze') are generally somewhat less cold-hardy. In most UK inland and midland gardens, dianella is most reliably grown in containers that can be moved under frost-free cover from November to late March, or in a very sheltered, south-facing border with a generous dry bark or gravel mulch from November. The rhizomes are typically harder than the above-ground leaves; even if the foliage is damaged or killed, new growth from undamaged rhizomes often appears in May or June.

Q: How do I grow dianella in the UK?

Dianella grows best in a warm, sheltered, sunny to partial-shade position in freely draining, moderately fertile, slightly acid to neutral soil. The plants prefer the kind of conditions found on the rocky, well-drained slopes and coastal margins of Australia and Tasmania from which most UK garden species come; they do not thrive in heavy, wet, cold clay or in waterlogged conditions over winter. In mild UK coastal gardens, plant in a sheltered south-facing border in freely draining soil with a generous bark or grit mulch applied from November. In colder UK inland gardens, grow in containers (minimum 25 to 30 cm diameter) in freely draining, slightly acid compost (ericaceous or standard potting mix plus 20% perlite or grit) and move under frost-free cover from November to late March. Water moderately through the growing season from April to September; allow the compost to approach dryness between waterings in summer. Reduce watering in winter. Feed monthly from April to August with a balanced liquid fertiliser. The small, starry blue or white flowers appear from late spring to early summer, followed by the vivid blue-violet berries that persist through autumn and winter. Divide congested clumps or pot-bound containers in spring to propagate; dianella divides easily from the rhizome.

Q: What are the blue berries on dianella?

The vivid blue-violet or deep purple berries of dianella are the plant's most distinctive ornamental feature and appear after the small starry flowers have finished from late summer through to winter; they are held on slender, branched flower stalks (panicles) above the foliage and remain on the plant for many weeks. The berries are genuinely blue (a colour rare among berry-producing plants of the northern hemisphere garden palette), and in species such as Dianella tasmanica and D. caerulea the colour is a vivid, polished deep blue-violet that is immediately eye-catching in a winter border. The berries are toxic and should not be eaten; dianella berries are not related to blueberries despite the common name 'blueberry lily'. The plant's common name 'flax lily' refers to the flax-like appearance of the long, narrow, arching leaves rather than any connection to flax plants (Linum). For the best berry display, grow in a position with adequate sun (at least partial sun rather than deep shade) and avoid over-watering or rich feeding, which promote leaf growth at the expense of flower and berry production. The berries are most visible and longest-lasting from September to December, providing valuable late-season ornamental interest when little else in the garden is producing fruit or colour.

Dianella (flax lily or blueberry lily) is an Australian and New Zealand evergreen perennial with elegant, sword-shaped, arching leaves and striking vivid blue-violet berries from late summer to winter. Borderline hardy in most of the UK; most reliably grown in containers moved under frost-free cover from November to March. Cold damage and drought are the primary causes of leaf curl in UK conditions.

Cold damage

Cold is the most common cause of dianella leaf curl and browning in UK cultivation; the long, arching, strap-like leaves curl, go limp, and develop brown tips and margins after exposure to temperatures below about -5 to -8°C. In a hard UK winter, the entire above-ground foliage can be killed while the rhizome base survives to produce new leaves in May or June. The most sensitive cultivars can be damaged by temperatures as mild as -3°C if the cold is accompanied by wet soil around the crown.

What to do

Move container-grown dianella under frost-free cover from November to late March; a cool greenhouse, frost-free porch, or unheated conservatory is ideal. In outdoor border plants in mild UK gardens, apply a generous dry bark or gravel mulch (10 to 15 cm) from November to insulate the rhizomes, and wrap the foliage in a single layer of fleece on nights when temperatures are forecast to fall below -3°C. Remove damaged foliage in spring once new growth begins from the rhizome base.

Drought stress

Drought causes dianella leaves to curl along their length and develop brown tips; the arching, strap-like leaves lose tension and droop when the root zone dries out. Container plants and those in sandy, free-draining soils in sunny positions are most at risk during a hot UK summer. The drought response is visible quickly in dianella, making it a reliable indicator of when watering is needed; the leaves uncurl within a day of thorough watering if damage has not progressed to browning.

What to do

Water moderately from April to September; allow the compost or soil to approach dryness between waterings but do not allow complete desiccation. Container plants need more frequent checking than in-ground plants; water when the top 2 to 3 cm of compost feels dry. A bark mulch over in-ground plants reduces moisture loss from the soil surface. Reduce watering significantly from October to March when the plant is growing slowly.

Wind desiccation

Cold, drying winter wind strips moisture from the evergreen dianella leaves, causing them to curl, bleach, and brown at the tips even when temperatures have not fallen below freezing. The leaves dry out because the roots in cold or frozen soil cannot supply moisture fast enough to replace what is lost through the leaf surface on a windy day. In exposed, windy UK garden positions, wind desiccation can cause as much visible damage as frost.

What to do

Position dianella in a sheltered spot protected from prevailing winter winds; a south or west-facing position sheltered by walls, fences, or dense evergreen shrubs is ideal. In exposed gardens, grow in containers that can be moved to a sheltered position or brought under cover from November. Temporary windbreak netting around vulnerable plants in late autumn significantly reduces wind desiccation damage through winter.

Frequently asked questions

Why are my dianella leaves curling?

Dianella leaves curl most commonly because of cold damage below -5°C (leaves curl, brown at tips, go limp; move containers under frost-free cover from November; mulch outdoor plants heavily), drought stress (curl along the length with brown tips; water when the top few centimetres dry out; mulch the root zone), or cold wind desiccation in exposed positions (browning from moisture loss even above freezing; shelter from prevailing wind; bring containers under cover). Cold combined with wet is particularly damaging to the rhizome base.

Is dianella hardy in the UK?

Dianella tasmanica is the hardiest commonly grown species, tolerating approximately -8 to -10°C in sheltered, freely draining conditions; D. caerulea cultivars are somewhat less hardy. In mild UK coastal gardens, outdoor year-round growing is possible with generous mulching. In most UK inland gardens, container growing moved under frost-free cover from November to March is the most reliably successful approach. The rhizome typically survives temperatures that kill the foliage and produces new leaves in May.

How do I grow dianella in the UK?

Grow in a warm, sheltered, sunny to part-shade position in freely draining, slightly acid to neutral soil or compost. In mild gardens, plant in a sheltered south-facing border with deep bark or gravel mulch from November. In colder gardens, grow in containers (minimum 25 to 30 cm) in free-draining compost plus 20% perlite, moved under frost-free cover from November to March. Water moderately spring to autumn; reduce in winter. Feed monthly April to August. Divide in spring to propagate.

What are the blue berries on dianella?

The vivid blue-violet or deep purple berries are dianella's most distinctive feature, appearing from late summer and persisting through autumn and winter on slender panicles above the foliage. The colour is a genuine deep blue, rare among berry-producing garden plants. They are toxic and should not be eaten despite the common name 'blueberry lily'. For the best berry display, grow in at least partial sun; deep shade reduces flower and berry production. Berries are most visible from September to December.