Plant problems

Why Are My Ozothamnus Leaves Curling?

Q: Why are my ozothamnus leaves curling?

Ozothamnus (everlasting daisy shrub or rice flower) leaves curl most commonly in UK gardens because of waterlogging and root rot in wet, poorly drained conditions (ozothamnus comes from freely draining, open, rocky or heathland habitats and has no tolerance of saturated soil), cold damage in hard winters (most ozothamnus species are only moderately hardy and the small, aromatic, silver-grey or white-felted leaves curl and brown in hard frost), or drought stress in very hot, dry summer conditions in containers or shallow soils. Ozothamnus is a genus of around 50 to 55 species of aromatic evergreen shrubs in the daisy family (Asteraceae), closely related to Helichrysum (everlasting flowers) and from similar habitats in Australia, New Zealand, and New Guinea. Several species are grown in UK gardens; the most significant for general garden use are: Ozothamnus rosmarinifolius (rosemary-leaved everlasting), a compact, upright shrub with small, dark green, rosemary-like leaves that are white-felted beneath, and dense clusters of small, white, button-like flower heads with a honey scent in June to July; it is the most widely grown species in UK gardens and is considered one of the hardier forms (to approximately -10 to -12°C in freely draining conditions). Ozothamnus ledifolius (kerosene bush) is similar with slightly different leaf shape and a distinctive kerosene-like scent when the leaves are bruised. Both species are excellent in a sunny, free-draining position and produce an attractive, grey-silver effect throughout the year.

Q: How do I grow ozothamnus in the UK?

Ozothamnus rosmarinifolius and O. ledifolius grow best in full sun in very well-drained, lean, neutral to slightly alkaline, poor to moderately fertile soil; the rock garden, gravel garden, raised bed, or the base of a south or west-facing wall are ideal positions. The plants come from open, rocky, heath-like habitats in south-eastern Australia where drainage is excellent, the soil is poor, and rainfall is seasonal; do not add compost or feed heavily, as rich, fertile, moist growing conditions produce soft, lush growth that is less cold-tolerant and less silvery in appearance than the harder growth of lean conditions. Add coarse grit generously to heavier soils to improve drainage. A grit or gravel mulch around the base prevents crown rot and maintains the dry conditions the plant prefers at the root collar. Prune in spring (April to May): trim back the previous year's growth by about one third to encourage compact new growth and prevent the plant from becoming leggy and bare at the base; do not cut into very old, bare wood as this does not regenerate reliably. A second light clip after flowering in July maintains tidy appearance. Take semi-ripe cuttings in July to August; the cuttings root readily in gritty compost and young replacement plants grow quickly to flowering size. Propagation by cuttings provides insurance against winter losses and also provides a means of renewing old, woody plants that are past their best.

Q: What is the difference between ozothamnus and helichrysum?

Ozothamnus and Helichrysum are closely related genera in the daisy family (Asteraceae) from similar Australasian and Mediterranean habitats, and many species that are now classified as Ozothamnus were previously placed in Helichrysum; the taxonomy of this group has been revised substantially and plants may be encountered under either name in UK nurseries and garden literature. The key distinguishing features between the two genera are botanical (details of the flower head structure and phyllary arrangement) and are not practically relevant to garden use; the cultural requirements and garden characteristics are similar for the grey-leaved, aromatic, Australasian species in both genera. The most significant former Helichrysum species now classified as ozothamnus in UK gardens is Ozothamnus rosmarinifolius, which was widely sold as Helichrysum rosmarinifolium for many years and may still be encountered under this name; it is the same plant regardless of the name used. The other important distinction is between the shrubby, woody ozothamnus species (O. rosmarinifolius, O. ledifolius) and the more widely grown and familiar annual or perennial Helichrysum bracteatum (strawflower), which is a completely different plant used for its papery, everlasting, colourful flower heads and is grown as an annual from seed in UK gardens. These two groups share only the daisy family and some superficially similar flower head structure; their habit, cultural requirements, and garden use are entirely different.

Ozothamnus is a genus of aromatic, silver-grey evergreen shrubs from Australia closely related to Helichrysum; Ozothamnus rosmarinifolius (rosemary-leaved everlasting) is the most widely grown UK garden form, with rosemary-like, white-felted foliage and honey-scented white flower clusters in June to July. Hardy to about -10°C in perfectly draining conditions, it thrives in rock gardens, gravel gardens, and raised beds. Waterlogging is the most common cause of failure; cold combined with wet is particularly lethal.

Waterlogging

Waterlogging is the most common cause of ozothamnus failure in UK gardens; the roots rot rapidly in saturated soil, causing the silver-grey leaves to yellow, curl, and drop, and the plant to collapse suddenly. The problem is most severe in heavy clay soils, in low-lying positions, and during prolonged wet UK winters. The combination of wet soil and cold temperatures is particularly lethal; ozothamnus in wet soil is killed by frosts that would be survived comfortably in dry, gritty conditions.

What to do

Plant only in very freely draining soil; add 30% coarse grit by volume to heavier soils. A rock garden, raised bed, or gravel garden provides the ideal drainage. Apply a grit mulch around the base rather than bark mulch; bark retains moisture at the root collar. Do not water in autumn or winter; reduce irrigation to a minimum from September to April. Avoid planting in low-lying, clay-heavy, or north-facing positions.

Cold damage

Cold damage browns and curls the small, white-felted leaves of ozothamnus in hard UK winters; Ozothamnus rosmarinifolius is the hardiest commonly grown species (to about -10 to -12°C in dry conditions) but is significantly less tolerant in wet conditions. Cold wind causes desiccation of the small leaves and produces browning similar to frost damage. After hard winters, the plant may be cut back considerably but often regrows from surviving buds if the rootstock has remained dry and the damage is not too severe.

What to do

Ensure perfectly draining conditions before winter; this is the single most effective protection. Position in full sun in a sheltered spot; a south-facing slope or raised bed provides both drainage and exposure. Wrap young plants in fleece from November to March in colder areas. Do not cut back until April or May; surviving buds may not be visible until new growth emerges. Take semi-ripe cuttings in July to August as annual insurance.

Drought stress

Ozothamnus is drought-tolerant once established in well-drained soil; the small, white-felted leaves are adapted to reduce water loss in dry conditions. Drought stress causing leaf curl is primarily a problem in containers (where the limited root volume dries out rapidly) and in the first season after planting. Established plants in the ground in average UK summer conditions rarely need supplementary watering. The characteristic silver-grey or white appearance of the foliage is most intense in dry, lean conditions; plants in moist, fertile soil look less silvery and more green.

What to do

Water container-grown plants when the compost is almost dry; allow the surface to dry between watering. Water newly planted specimens in their first summer; established in-ground plants need watering only in prolonged dry spells. The plants recover quickly from moderate drought stress. Lean, dry conditions enhance the silver-grey appearance of the foliage; avoid overwatering or over-feeding.

Frequently asked questions

Why are my ozothamnus leaves curling?

Ozothamnus leaves curl most commonly because of waterlogging in wet UK conditions (the roots rot rapidly in saturated soil; the most common cause of failure; plant in gritty, perfectly draining conditions), cold damage in hard winters (brown curled leaves below -10°C, especially in wet soil; dry conditions significantly improve cold tolerance), or drought stress in containers or newly planted specimens (water when the compost is almost dry; recover quickly when watered). Cold combined with wet is the most lethal combination.

Is ozothamnus hardy in the UK?

Ozothamnus rosmarinifolius is hardy to about -10 to -12°C in perfectly draining, lean conditions and is reliably perennial in most of England and Wales in a suitable dry, sunny position. In wet soil, cold tolerance is significantly reduced and plants may be killed at much milder temperatures. Take semi-ripe cuttings in July to August annually as insurance. The rock garden, gravel garden, and raised bed are the most reliable positions.

How do I grow ozothamnus in the UK?

Grow in full sun in very freely draining, lean, neutral to slightly alkaline soil; add generous grit to heavier soils. Do not add compost or feed heavily; lean soil produces the hardiest, most silvery growth. Apply a grit mulch around the base. Prune in April to May by one third to maintain compact shape; take semi-ripe cuttings in July to August. The honey-scented white flower clusters in June to July are attractive to bees; the silver-grey foliage provides year-round interest in a gravel garden setting.

What is the difference between ozothamnus and helichrysum?

Many species sold as Helichrysum have been reclassified as Ozothamnus following taxonomic revision; Ozothamnus rosmarinifolius was previously sold as Helichrysum rosmarinifolium and may still appear under this name. Both genera are in the daisy family with similar aromatic, grey-leaved characteristics and similar cultural requirements. Note that Helichrysum bracteatum (strawflower), grown as an annual for its papery coloured flower heads, is an entirely different plant in both habit and use.