Olearia is a genus of evergreen shrubs and small trees in the family Asteraceae, native to New Zealand and Australia, grown in the UK for their tolerance of coastal exposure, their attractive leathery foliage, and their summer displays of white or lilac daisy flowers. The leaves are typically small to medium-sized, often with a conspicuous silver or grey-green tomentum (a feltlike covering of fine hairs) on the undersides, which gives the plants a distinctive two-tone quality and helps them shed salt spray. Flowers appear in abundance in summer, each a classic daisy form with a central yellow disc and white ray petals.
The key UK species differ considerably in hardiness. Olearia x haastii is the most commonly grown and the most reliably hardy, rated RHS H5, forming a compact rounded shrub that produces masses of white daisies in July and August and tolerates most UK winters without complaint. O. macrodonta, the New Zealand holly, is a larger shrub with striking toothed holly-like leaves that have brilliant silver undersides; it makes an outstanding hedge and windbreak in mild and coastal gardens. O. traversii is the fastest-growing windbreak species, capable of forming a very tall, dense screen quickly in exposed coastal positions, but is significantly less hardy at RHS H3. O. x scilloniensis puts on a spectacular show of white daisies in May and O. phlogopappa offers lilac or white flowers, but both are in the tender H3 category. Understanding which species you have is the first step to understanding why the leaves are curling.
Frost and cold wind damage
Cold damage is by far the most common cause of olearia leaf curl in the UK, and the one most likely to alarm gardeners who have grown used to these shrubs performing well in mild seasons. The symptoms vary with the severity of the cold and the species involved, but the pattern is consistent: leaves curl inward, lose their normal colour and texture, brown at the margins, and in more severe cases collapse entirely against the stem.
The distinction between species matters enormously here. O. x haastii survives UK winters in most parts of the country without significant damage. Planted in a reasonably sunny, open position in central or southern England, it will come through a typical winter looking much as it went in. Even in the north or in a cold inland garden, established plants of O. x haastii suffer only minor leaf curl in hard frosts and bounce back without intervention once temperatures rise. The situation is entirely different for the tender species. O. traversii, O. phlogopappa, and O. x scilloniensis will curl, blacken, and lose significant amounts of foliage in a hard frost. In an exposed inland garden in a bad winter, they may lose all top growth entirely.
Cold drying winds from the east or north cause damage even without a proper hard frost. The combination of below-zero temperatures and wind is more destructive than frost in still air, because the moving cold air desiccates frozen foliage as it begins to thaw. Leaf margins brown and curl first; the centres of the leaves follow if the cold spell is prolonged. This kind of wind damage is the most common winter complaint in coastal gardens that are exposed to cold easterlies blowing in from the sea rather than the warm westerlies that make those same gardens so mild most of the time.
Do not be too hasty in writing off damaged olearia in spring. The bark scratch test is the most reliable guide to what is actually dead and what is not: scrape the bark with a fingernail or penknife at intervals down each affected stem and look for green or white-green tissue directly beneath the bark surface. Brown, dry, or hollow tissue is dead; green tissue is alive. Work from the shoot tips downward. Even if the entire top of the plant looks dead, the lower framework and the crown very often survive, and new growth from the base typically emerges by late April or May in a mild location, perhaps a few weeks later in colder parts of the UK. In most cases, established olearia that looks completely dead in February is simply dormant; the recovery that follows by summer can be remarkable.
In gardens where the hardier species are not performing well in winter, the practical answer is to restrict the planting to O. x haastii or the most cold-tolerant named forms, plant in the warmest available spot (a south or west-facing position, or against a wall that stores daytime heat), and avoid exposing new plants to their first winter before they are properly established. Coastal gardens have a far wider range to choose from, because the moderating influence of the sea makes the temperature extremes much less severe.
Powdery mildew in sheltered inland gardens
In sheltered inland positions with limited airflow, olearia can develop powdery mildew, particularly on the more tender species that are grown in protected spots specifically to reduce their exposure to cold. The disease presents as a white or pale grey powdery coating on the surface of new growth, and the affected leaves curl, pucker, and distort as the mycelium interferes with normal cell development. The distortion tends to be most visible on the soft new shoots of spring and early summer growth, which is when the conditions for mildew are most favourable.
Olearia mildew is most problematic in crowded positions where stems are packed tightly together and warm, humid air circulates poorly. The disease thrives in exactly the conditions that some gardeners create when trying to protect a tender olearia from cold: a sheltered corner with walls on two or three sides, limited airflow, and the higher humidity that results. Paradoxically, the protection from cold comes at the cost of increased mildew risk.
Improve airflow by pruning to open up the centre of the shrub in late spring after flowering. Remove congested stems to allow air to move through the plant. Avoid overhead watering, which wets the foliage and raises humidity around the leaf surfaces. Remove badly affected shoots and dispose of them rather than composting. A potassium bicarbonate spray applied thoroughly to all leaf surfaces at the first sign of white powdery coating will check the progress of the disease; repeat at ten-day intervals for two or three applications. On a well-sited and otherwise healthy olearia, powdery mildew is unlikely to be a serious long-term problem.
Other causes of leaf curl
Whitefly occasionally colonises olearia in coastal or sheltered garden positions, particularly on plants grown against a wall or in a spot with some warmth and protection. The tiny white insects live in large numbers on the undersides of the leaves and feed by sucking plant sap. Leaves on heavily infested plants may show slight yellowing and curl, and the upper surfaces become sticky and blackened with sooty mould fed by the honeydew the insects excrete. Inspect the undersides of leaves in summer, particularly on sheltered wall plants. Treat with an insecticidal soap spray applied thoroughly to the leaf undersides at dusk when beneficial insects are less active, repeating every five to seven days through the active season.
Scale insects can attach to the stems and leaf undersides of olearia in similar sheltered positions, with soft brown scale (Coccus hesperidum) being the most likely species. The symptoms resemble those of whitefly: sticky honeydew, sooty mould, and progressive weakening of the foliage. Treat crawlers in late spring with a fatty acid or neem oil spray, or physically remove adult scale from stems with a soft brush or cloth during winter.
Drought causes newly planted olearia to curl its leaves as the plant reduces moisture loss through its foliage. Established olearia in most UK garden soils is reasonably drought-tolerant, but plants in their first two or three seasons before the root system has fully developed can suffer visibly in dry summers. Water newly planted specimens consistently in their first growing season, particularly those planted in sandy or chalky soils that drain very freely.
Salt spray damage in severely exposed coastal positions causes leaf margin browning and curling that can resemble frost damage. True salt damage typically affects the windward faces of the outermost leaves most severely and is most pronounced after storm events that deliver concentrated salt-laden spray. Olearia is more salt-tolerant than almost any other garden shrub, but plants placed at the very edge of exposed cliffs where they take the full force of every storm can still show marginal leaf burn.
Phytophthora root rot causes progressive wilting and decline in olearia planted in waterlogged clay or in low-lying positions where water accumulates after rain. The symptoms begin as a loss of vigour and a dull, slightly wilted appearance in the foliage; leaf curl and premature leaf drop follow as the root system deteriorates. There is no effective treatment for established Phytophthora infection. Plant olearia in well-drained soil or improve drainage significantly before planting in clay.
Olearia in UK gardens
Olearia deserves to be far better known in UK gardens beyond the coastal southwest where it already has a strong presence. The ability of O. traversii and O. macrodonta to form dense, effective windbreaks in exposed coastal positions where almost nothing else survives makes them genuinely invaluable plants. On the cliffs and headlands of Cornwall, Pembrokeshire, the Outer Hebrides, and the west coast of Ireland, olearia hedges and screens stand between the garden and the full force of Atlantic weather, making it possible to grow a far wider range of plants behind them than the exposure would otherwise allow.
O. macrodonta, the New Zealand holly, is a particularly beautiful plant for this purpose. The leaves are large, deeply toothed, and strongly reminiscent of holly, with a rich green upper surface and a brilliant silver underside that flashes as the wind moves through the hedge. In summer, the whole plant disappears beneath a cloud of white daisy flowers that are highly attractive to bees and other pollinators. As a flowering hedge it has few equals in the coastal UK garden.
For inland gardens in most parts of the UK, O. x haastii is the species to grow, and it rewards the planting generously. The compact, rounded habit suits borders and mixed planting well. The white-daisy flower display in July and August is reliable and attractive to pollinators at a time when many other shrubs have finished. The year-round silver-green foliage is good-looking through the winter months when most shrubs have nothing to offer. This is a plant that genuinely earns its space in any sunny position in a UK garden, and its hardiness means it can be grown from Inverness to Penzance with equal confidence.
Frequently asked questions
Why are my olearia leaves curling?
Cold damage from frost or winter wind is the most common cause of olearia leaf curl in the UK. The less hardy species (O. traversii, O. phlogopappa, O. x scilloniensis) will curl, brown, and shed leaves after hard frosts or persistent cold east winds. Even O. x haastii, the hardiest commonly grown species, can show minor leaf curl in a severe winter in an exposed inland position. Check stems by scratching the bark; green tissue below the bark means the plant is alive and will recover once temperatures rise. Other causes include powdery mildew in sheltered inland gardens, whitefly, drought in newly planted specimens, and Phytophthora root rot in waterlogged soil.
Which olearia species are hardiest for UK gardens?
Olearia x haastii is the hardiest species commonly grown in the UK, rated RHS H5, meaning it will survive temperatures down to around minus 15 degrees Celsius in most UK situations. It forms a compact rounded shrub and flowers reliably in July and August with masses of white daisies. For inland UK gardens away from the moderating influence of the coast, O. x haastii is the only species that can be grown with confidence in most positions without frost protection. O. macrodonta (New Zealand holly) is somewhat less hardy but performs very well in sheltered or coastal gardens. O. traversii, O. phlogopappa, and O. x scilloniensis are significantly more tender (RHS H3 or borderline H4) and are best suited to mild maritime gardens in Cornwall, Devon, Wales, or western Scotland.
Can olearia be used as a coastal windbreak?
Yes, olearia is one of the best plants for coastal windbreaks in the UK and Ireland. Olearia traversii is particularly valued for this purpose: it grows very quickly, tolerates ferocious salt-laden gales, and forms a dense barrier that protects everything behind it. O. macrodonta is also excellent, forming a tough, beautiful hedge with large holly-like leaves that have silver undersides. These two species are staples of exposed coastal gardens on the cliffs and headlands of Cornwall, Devon, Pembrokeshire, the west coast of Scotland, and the whole Irish west coast. They create conditions in which otherwise impossible plants can thrive, and on the most exposed coastal cliffs they will grow where almost nothing else survives.
How do I know if my olearia has died from frost or will recover?
The bark scratch test is the most reliable way to assess frost-damaged olearia. Use a fingernail or penknife to scrape a small section of bark from stems at various heights. Green or white-green tissue directly beneath the bark means that section is alive. Brown, dry, or hollow tissue means that section is dead. Work down from the shoot tips, which die first, toward the base and the crown. Even if all the upper stems are dead, the crown and lower woody framework often survive a UK winter, particularly in established plants. New growth from the base typically appears by late spring. The key is patience: olearia that looks completely dead in February will often produce vigorous new shoots from the crown by May.
Why does my olearia have a white powdery coating on the leaves?
A white powdery coating on olearia leaves is powdery mildew, a fungal disease that causes the affected leaves to curl and distort. It is most common on olearia grown in sheltered inland positions with poor airflow, and on the more tender species that are sometimes planted in such spots for protection. The disease develops in warm, humid air conditions, particularly in late summer, and is made worse by dry soil combined with damp air. Improve airflow by pruning out congested growth in the centre of the shrub. Avoid overhead watering. Remove badly affected shoots. A potassium bicarbonate spray applied to all leaf surfaces at the first sign of the white coating will check the spread. Powdery mildew is rarely a serious threat to an otherwise healthy, well-sited olearia.