Plant problems

Why Are My Perovskia Leaves Curling?

Q: Why are my perovskia leaves curling?

Perovskia (now reclassified as Salvia yangii, but widely known and sold as perovskia or Russian sage) leaves curl most commonly in the UK because of waterlogging, powdery mildew, aphids on the young spring growth, or cold damage causing shoot collapse. Perovskia atriplicifolia is a sub-shrub from the dry, rocky steppes and mountain slopes of central Asia (Afghanistan, Pakistan, and western China); it is grown in UK gardens for its long spires of violet-blue flowers produced from July to October on upright, silver-white stems with aromatic, grey-green, deeply lobed leaves. The plant is very drought-tolerant once established and extremely well-adapted to dry, sunny, well-drained conditions; the main threat in the UK is not drought but the opposite: wet, poorly draining soil in winter that causes rapid root rot. Waterlogging of the root zone in winter (when the plant has died back to a woody crown) kills the crown and roots, and the plant fails to regrow in spring or produces weak, wilting shoots that curl and collapse. Powdery mildew (Erysiphe species) can coat the leaves with a grey-white powdery fungal layer in warm, humid conditions; affected leaves may curl and distort. Aphids can colonise the young shoot tips in spring, causing the emerging leaves to curl and pucker. Cold damage occurs when a late spring frost kills the soft new growth emerging from the woody base.

Q: How do I prune perovskia?

Perovskia (Russian sage, Salvia yangii) is pruned hard each spring when new growth begins to emerge from the base of the previous year's woody stems; this hard annual pruning is essential for keeping the plant compact, well-branched, and free-flowering. In late March or early April in the UK, when you can see the first tiny green shoots emerging from the base of the woody stems or from the lower portions of the previous year's growth, cut all of the previous year's stems back hard to 15 to 20 cm above the ground, always cutting to just above a visible pair of buds or a point where new growth is visible. Do not cut into the underground root zone or crown; cutting the woody stems down to 15 to 20 cm retains a framework of live, budding woody stem while removing the bulk of the old, top growth. The new growth emerging from these cut stems and from the crown then produces the current season's long, silver-white stems and violet-blue flowers by July or August. Do not prune perovskia in autumn; this is one of the most important timing rules for the plant. The old stems, though untidy, protect the crown from frost and excessive moisture entry; cutting in autumn leaves the crown exposed to the worst of the UK's winter cold and wet, which can kill an otherwise hardy plant. Leave all pruning until March or April when new growth is clearly visible. If the plant is still producing flowers in October, delay even the lightest tidying until the hard pruning in spring.

Q: Is perovskia the same as Russian sage?

Perovskia atriplicifolia is commonly called Russian sage in the UK and in horticultural trade, and is widely sold under this common name; however, it is not actually native to Russia, and it is not a true sage. The plant is native to the dry mountain slopes and rocky steppes of central Asia, primarily Afghanistan, Pakistan, Xinjiang, and western Tibet; the common name 'Russian sage' probably reflects a broad association with the central Asian / Russian steppe region rather than a precise geographic origin. In 2017, a major taxonomic reclassification moved perovskia from the genus Perovskia into the genus Salvia (the true sages), renaming it Salvia yangii; this change reflects molecular evidence that perovskia is closely related to the sage genus. In the UK, the plant is still almost universally sold and labelled as perovskia or 'Russian sage' in garden centres and nurseries, and the name Perovskia remains widely used in horticulture despite the official reclassification to Salvia yangii. The plant is a member of the mint family (Lamiaceae) and the aromatic quality of the silver-grey leaves when crushed does recall sage; the flowers are similar to those of Salvia but much smaller and more numerous, arranged in long, airy, branched spikes that give the plant a misty, hazy appearance in late summer. The most widely grown selection in UK gardens is Perovskia 'Blue Spire' (Salvia yangii 'Blue Spire'), which has particularly long, branched spikes of deep violet-blue flowers; it was selected from seedlings raised in the Netherlands and is the standard cultivar available in UK garden centres.

Q: Why is my perovskia floppy?

Perovskia (Russian sage) most commonly becomes floppy and sprawling when it is grown in too much shade, in rich or nitrogen-rich soil, or when it is not pruned hard enough each spring; all of these conditions encourage lush, heavy top growth that the stems cannot support. Perovskia is adapted to grow in very poor, dry, alkaline, freely draining soils in full sun; in better conditions the plant grows more vigorously but the stems become longer and heavier than the plant is designed to support and the whole structure collapses outward. The most effective prevention is hard annual pruning in spring: cutting the previous year's stems back to 15 to 20 cm each March or April before growth begins produces a compact, well-branched plant with shorter, stiffer stems that can support the flowers. A position in full sun (at least 6 hours of direct sun daily) is also essential; shade produces drawn, tall, weak stems that flop inevitably. Avoid nitrogen-rich fertilisers; perovskia does not benefit from feeding and rich soil produces the lush but floppy growth typical of an overfed plant. If a plant is already floppy and in flower, the stems can be tied loosely to short canes placed around the perimeter of the plant as a temporary measure; cut back hard in the following spring to prevent the problem recurring. Some gardeners use the Chelsea Chop (a mid-June hard cut to half the stem length) to produce a more compact, later-flowering plant on perovskia; this produces a second generation of shorter, stiffer stems that flower in September and October rather than July and August.

Perovskia (Russian sage, now Salvia yangii) is a drought-tolerant, aromatic sub-shrub from the dry rocky steppes of central Asia, grown in UK gardens for its long violet-blue flower spikes on silver-white stems from July to October. It thrives on neglect in poor, dry, freely draining soil in full sun; the main threat in UK conditions is not drought but waterlogging, which kills the crown in winter. Powdery mildew and aphids are secondary causes of leaf curl on this usually very trouble-free plant.

Waterlogging

Waterlogging is the most serious threat to perovskia in UK gardens; the plant's roots and crown are adapted to the deep, freely draining, rocky soils of its central Asian homeland and are highly intolerant of wet, poorly aerated conditions, particularly in winter when the plant is dormant. The crown (the woody base from which new growth emerges each spring) rots rapidly in saturated soil; a plant that has survived a summer in apparently good health may fail to regrow the following spring if the crown has rotted during a wet winter. Symptoms of crown rot are failure to regrow in spring or the emergence of weak, wilting shoots that collapse shortly after emergence.

What to do

Plant perovskia in very well-drained soil; add coarse grit or gravel to heavy clay soils at planting, or choose a gravel garden, raised bed, or sloping bank where drainage is naturally excellent. Avoid low-lying positions where water collects. In containers, use a gritty, free-draining compost and ensure drainage holes are always clear; do not allow pots to sit in standing water. Leave the old stems standing over winter to provide some protection to the crown; do not cut back until spring.

Powdery mildew

Powdery mildew (Erysiphe species) occasionally affects perovskia in warm, humid UK summers, coating the aromatic grey-green leaves with a grey or white powdery fungal layer; affected leaves may curl and distort and the growth appears unthrifty. Powdery mildew on perovskia is most common in warm, humid, still conditions with poor air circulation around the plant, and in positions where water stress alternates with high humidity (as is common in sheltered, south-facing walls that become very hot and dry in summer then cool and humid at night). Perovskia's natural preference for open, airy, sunny sites where air circulation is good partly explains why powdery mildew is less common on well-sited plants.

What to do

Ensure the plant is in an open, well-ventilated position in full sun; avoid sheltered, enclosed sites where air circulation is poor. Avoid overhead watering and keep the foliage dry. On plants showing significant mildew, apply a sulphur-based fungicide or a potassium bicarbonate spray to the affected foliage; repeat every 2 weeks. The spring pruning, which opens up the plant's structure and encourages fresh new growth, reduces the pool of infected tissue and improves air movement through the plant. Mildew is rarely severe enough to cause permanent harm on perovskia.

Aphids

Aphids can colonise the soft, young shoot tips of perovskia as they emerge in spring; the new leaves curl around the aphid colonies and may fail to expand fully. Aphid infestations on perovskia are usually light and short-lived; the aromatic, strongly scented foliage is less appealing to aphids than many other garden plants, and natural predators (ladybirds, lacewings) typically arrive quickly. The vigorous new growth rapidly outpaces any early aphid damage and the problem is rarely serious on an otherwise healthy plant.

What to do

No treatment is usually needed; natural predator pressure and the plant's vigorous growth quickly overcome light aphid infestations. Pinch off the most heavily infested shoot tips to reduce colony numbers. Apply insecticidal soap spray to the young growth if the infestation is unusually heavy; the aromatic foliage of perovskia may repel aphids from nearby plants as well as from itself.

Cold damage

Perovskia (Salvia yangii) is hardy to around -15°C in its native dry, continental climate, but this hardiness is significantly reduced in the wet UK winter; the combination of cold and wet that UK winters regularly bring is more damaging than pure cold alone. In a wet winter, even a modest frost can kill the crown of a plant growing in poorly draining soil. Cold damage to the new spring growth, which is soft and tender as it emerges from the woody base in April, causes the young shoots to blacken, collapse, and curl; the plant then produces secondary growth from lower, more protected buds on the crown.

What to do

Leave the old stems standing over winter; they protect the crown from frost and excessive moisture entry. Do not cut back until March or April when new growth is clearly visible. Mulch the crown lightly with coarse grit or gravel in autumn in colder northern gardens; this improves drainage around the crown and provides some insulation. A south or west-facing position in full sun against a wall that provides some reflected warmth and shelter from east winds is ideal for perovskia in colder UK gardens.

Frequently asked questions

Why are my perovskia leaves curling?

Perovskia leaves curl most commonly because of waterlogging (the most serious threat in UK conditions; the crown rots in saturated winter soil and the plant fails to regrow or produces weak, collapsing shoots), powdery mildew (grey-white coating on leaves in warm, humid, still conditions), aphids on young spring growth, or cold damage to soft new shoots in April. In an open, sunny, freely draining position, perovskia is one of the most trouble-free plants in UK gardens.

How do I prune perovskia?

Prune hard each spring in March to April when new growth is just visible at the base: cut all previous year's stems back to 15 to 20 cm above the ground, always cutting to just above visible new buds or growth. Do not cut to the ground; leave a short woody framework. Never prune in autumn; the old stems protect the crown through winter. Hard annual spring pruning produces compact, well-branched plants with upright stems that support the flower spikes without flopping.

Is perovskia the same as Russian sage?

Yes, perovskia and Russian sage are the same plant; in 2017 it was reclassified from Perovskia atriplicifolia to Salvia yangii, though it is still almost universally sold as perovskia or Russian sage in UK garden centres. It is native to central Asia (Afghanistan, Pakistan) rather than Russia. 'Blue Spire' is the most widely available cultivar in the UK, with long, branched violet-blue flower spikes from July to October.

Why is my perovskia floppy?

Perovskia becomes floppy when grown in too much shade, in rich or fertile soil, or when not pruned hard enough each spring. Hard annual pruning to 15 to 20 cm in March or April is the most effective fix; it produces shorter, stiffer stems. Full sun (at least 6 hours daily) and poor, dry, freely draining soil are equally important; rich soil and shade produce soft, heavy growth that inevitably collapses.