Plant problems

Why Are My Phlomis Leaves Curling?

Q: How do I prune phlomis?

Phlomis fruticosa (Jerusalem sage) benefits from pruning after flowering in July or August to keep it compact and free-flowering. Cut the flowered stems back by about one half to two thirds to a point where young, healthy shoots are emerging lower on the stem; do not cut back hard into old, bare wood as Phlomis fruticosa does not always regenerate well from old leafless stems. Remove any dead or winter-damaged stems completely at the same time. In spring (March to April), lightly trim any stems that have become untidy over winter. Phlomis russeliana, the perennial species, is managed differently: cut the dead stems and seed heads to the ground in early spring (February to March) before new growth begins, or leave them standing over winter for structural interest and wildlife benefit (the whorled seed heads are attractive with frost and provide food for seed-eating birds). Old, woody Phlomis fruticosa plants that have become bare and leggy at the base often do not respond well to hard renovation pruning; it can be better to take cuttings from healthy material in summer and raise replacement plants than to attempt to rejuvenate a very old, poor-performing specimen.

Q: Why has my phlomis gone woody and stopped flowering?

Phlomis fruticosa (Jerusalem sage) naturally becomes woody and bare at the base over time, particularly if it is not pruned after flowering each year; old specimens with thick, bare, woody lower stems produce progressively fewer flowers and look increasingly untidy. The solution is regular post-flowering pruning: cut the flowered stems back by half to two thirds each year immediately after flowering, always cutting to a point where leafy growth is visible; this prevents the plant becoming leggy and maintains a dense, well-furnished shape. If the plant has already become very woody and bare at the base, it is often better to take semi-ripe cuttings from the current season's growth in July or August to produce replacement plants, rather than attempting hard renovation pruning. Phlomis fruticosa can also fail to flower if it is growing in too much shade; it needs a position in full sun to flower well. Poor flowering can also result from a very sheltered, humid position that encourages leafy growth at the expense of flowers; full sun and an open, well-ventilated position are important for maximum flowering. In a good year in a sunny, well-drained position, Phlomis fruticosa will produce multiple tiers of striking whorled yellow flowers on upright stems; in shade or rich soil, the plant grows more lushly but flowers poorly.

Phlomis (principally Phlomis fruticosa, Jerusalem sage) is a sun-loving evergreen Mediterranean shrub with distinctive silver-grey, woolly leaves and whorled yellow flowers produced in June and July; it is one of the most drought-tolerant shrubs for a sunny, well-drained bank or gravel garden in the UK. The woolly leaf surface is a natural adaptation for Mediterranean heat and light; in UK conditions the most common leaf problems are drought-induced curling, winter waterlogging damage, and cold wind scorch.

Drought stress

Despite its Mediterranean origins and excellent drought tolerance once established, phlomis can suffer moisture stress in containers or in very free-draining soils during prolonged hot, dry UK summers; the silver-grey, woolly leaves curl and fold inward at the margins and the plant may wilt. In the ground in well-prepared soil, established phlomis is very rarely drought-stressed; the problem is most common in pots or in very fast-draining, sandy or gravelly soils during extended dry spells. Newly planted phlomis (in the first two growing seasons) needs watering through dry spells until it establishes a deep root system.

What to do

Water thoroughly at the base of the plant during prolonged dry spells in the first two seasons after planting; once established, irrigation is rarely needed. Apply a gravel mulch around the plant to reduce evaporation while maintaining the excellent drainage the plant needs. In containers, check moisture regularly in summer and water when the top 5 cm of compost is dry; use a gritty, well-draining compost and avoid saucers that allow water to pool around the base.

Waterlogging

Waterlogging is the most serious threat to phlomis in UK gardens; the roots are highly sensitive to wet, poorly aerated soil and will rot rapidly if the root zone remains saturated, particularly in winter when root activity is low. Symptoms progress from leaf curl and yellowing to shoot collapse and whole-plant death; the roots are brown and mushy rather than firm and white or cream. Phlomis planted in heavy clay soils or in low-lying positions where water collects is at high risk; damage is most severe after wet UK winters.

What to do

Plant phlomis in very well-drained soil; add substantial grit or coarse gravel to heavy clay soils at planting, or choose a raised bed, bank, or gravel garden where drainage is inherently good. Avoid planting in low-lying positions where water accumulates. In containers, use a gritty compost and ensure drainage holes are clear; do not allow pots to sit in saucers of water in winter. If waterlogged roots are confirmed, dig the plant, trim dead roots, replant in improved drainage, and water very sparingly until new growth appears.

Cold wind damage

Phlomis fruticosa is hardy to about -10 to -12°C in ideal, dry conditions, but the combination of cold temperature and wet conditions that UK winters can bring reduces its hardiness significantly. Cold, desiccating east winds in winter can scorch and curl the leaf margins and tips of Phlomis fruticosa; the woolly leaves brown at the margins and fold inward. Severe or prolonged cold can kill back the tips and outer shoots of the plant, which then look dead and brown in early spring. The plant typically recovers as temperatures rise, producing new growth from the base and lower stems.

What to do

Plant against a south or west-facing wall or fence to provide shelter from cold east winds; this is the most reliable way to prevent cold wind damage in exposed or northern UK gardens. Do not prune cold-damaged shoots until new growth is visible in spring; the dead material may protect the live tissue below. Once new growth is clearly visible (usually April to May), cut back all dead and damaged stems to healthy, leafy tissue. In particularly exposed gardens, protect newly planted phlomis with windbreak netting in the first two winters.

Vine weevil

Vine weevil (Otiorhynchus sulcatus) larvae feed on the roots of a wide range of plants, including phlomis; root damage causes individual shoots to wilt and collapse suddenly, often in summer when the larvae are large and most destructive. The above-ground plant can look healthy until root damage is severe; wilting that does not respond to watering is a strong indicator of root damage. Adult vine weevils notch the leaf margins with characteristic irregular U-shaped cuts in late spring and summer.

What to do

Apply the biological control nematode Steinernema kraussei to the soil around the plant in late August or September when soil temperatures are above 5°C and larvae are small and vulnerable; this is the most effective and targeted control. Water the nematode solution thoroughly into the root zone. Check the root ball of any wilting plant by carefully removing it from the soil; cream, C-shaped larvae in the compost or soil confirm vine weevil damage. Remove and destroy any larvae found. The nematode treatment can be repeated in spring as well as autumn for severe infestations.

Frequently asked questions

Why are my phlomis leaves curling?

Phlomis leaves curl most commonly in the UK because of drought stress (the woolly leaves curl and fold inward during dry spells, especially in containers or newly planted specimens), waterlogging of the roots in heavy or wet soils in winter (the most serious threat, causing rapid root rot and shoot collapse), cold wind damage to the leaf margins in winter, or vine weevil larvae feeding on the roots. Phlomis fruticosa is a robust, easy-care shrub that rarely suffers serious problems in a well-chosen, well-drained, sunny position.

How do I prune phlomis?

Prune Phlomis fruticosa after flowering in July or August: cut the flowered stems back by half to two thirds to where young shoots are emerging, but do not cut into bare old wood. In spring, trim any winter-damaged stems to healthy tissue. Old, very woody specimens often do not respond to hard renovation; raise replacement plants from semi-ripe cuttings in summer instead. Cut Phlomis russeliana (the perennial species) to the ground in late winter or early spring before new growth begins.

Is phlomis evergreen?

Phlomis fruticosa (Jerusalem sage) is evergreen: it retains its silver-grey woolly leaves through winter, though they may look battered after cold, wet conditions. In very harsh winters the plant may lose some leaves but recovers in spring. Phlomis russeliana is a herbaceous perennial and dies back to the ground each winter; its whorled dead stems look attractive with frost and are often left standing for winter interest and wildlife.

Why has my phlomis gone woody and stopped flowering?

Phlomis fruticosa becomes leggy and stops flowering well if not pruned after flowering each year. Cut flowered stems back by half to two thirds annually to prevent bare, woody bases. Very old, bare-stemmed plants are difficult to renovate; take semi-ripe cuttings in summer and grow on fresh replacements. Full sun is essential for good flowering; shade or rich, moist soil produces lush leafy growth but few flowers.