Plant problems

Why Are My Romneya Leaves Curling?

Q: Why are my romneya leaves curling?

Romneya (tree poppy or Californian tree poppy) leaves curl most commonly in the UK because of transplant shock (Romneya is notoriously difficult to transplant and recently moved plants often collapse), drought stress in their first season before roots are established, cold damage killing the top growth in hard winters, or waterlogging which rots the fleshy roots rapidly. Romneya coulteri (Californian tree poppy or Matilija poppy) is a large, suckering, glaucous-leaved perennial subshrub from the dry, rocky canyons and chaparral of California and Baja California; it produces extraordinarily large flowers (to 15 to 20 cm across), pure white with a large boss of golden stamens, from June to October on upright, glaucous stems that reach 1.5 to 2.5 m in height. The grey-blue, deeply lobed, glaucous foliage and the enormous, crinkled, tissue-paper white flowers make Romneya one of the most dramatic plants available for the UK sunny border; it is also one of the most resentful of disturbance and one of the trickiest to establish successfully. Transplant shock is the primary reason for leaf curl and sudden collapse in romneya: the plant is almost impossible to move once established (it is notoriously difficult even when container-grown), and recently transplanted specimens from garden centres or between positions in the garden routinely wilt, drop their leaves, and die back to the base; the plant may recover from the root if the roots are undamaged, but the top growth is almost always lost in the move.

Q: How do I successfully establish romneya in the UK?

Successful establishment of romneya depends on choosing the right position before planting, using the right planting method, and then leaving the plant undisturbed for several years to establish the deep, spreading root system on which it depends. Choose a sunny, sheltered position in very well-drained, poor to moderately fertile, alkaline to neutral soil; romneya grows in some of the driest, most infertile, rocky soils in its native California chaparral and performs best in UK conditions that replicate this: lean, gritty, freely draining soil at the base of a south or west-facing wall or on a sunny, well-drained slope or gravel garden. Avoid rich, fertile, moisture-retentive soils; romneya in rich soil grows very lushly but is more susceptible to root rot and less drought-tolerant. Planting method: if planting from a container, disturb the root ball as little as possible; ideally cut off the base of the pot with a knife and slide the root ball intact into the planting hole without loosening the roots. Plant in spring (April or May) after the last frost so the plant has the entire growing season to establish before winter. Water only sparingly in the first season to encourage deep root development; over-watering a newly planted romneya produces shallow, surface roots that make the plant more drought-vulnerable and less stable. Do not move the plant after it is established; established romneya is almost impossible to transplant and will typically die or be severely set back. The plant spreads by underground stolons to form an increasingly large colony over the years; unwanted suckers at the colony edges can be dug out in spring (cut through the connecting root with a spade at least 30 cm from the parent plant).

Q: Is romneya hardy in the UK?

Romneya coulteri is hardy throughout most of the UK once established but behaves as a herbaceous perennial in cold UK conditions: the top growth is killed by frost in most UK winters, dying back to the ground in late autumn, and the plant regrows from the rootstock in spring, producing fresh stems that flower in the same season. In the mildest UK gardens (coastal and urban southern England, the Channel Islands), the grey stems may partially survive mild winters, but even here the plant typically benefits from being cut back to the ground in spring to encourage fresh, vigorous, well-flowered new growth. The rootstock is hardy to about -10 to -15°C in well-drained conditions; in very cold, exposed UK gardens (northern England, Scotland), it may be killed in severe winters, particularly if the soil is wet. Protect the rootstock crown with a 10 to 15 cm layer of coarse grit or composted bark in November in colder UK positions. The plant is far more tolerant of cold than of waterlogging; a combination of cold and wet soil can kill the roots at temperatures well above the frost threshold. In freely draining soil in a sheltered, sunny position, established romneya is generally reliably perennial in all but the most severe UK winters.

Q: How do I prune romneya in the UK?

Romneya is cut back hard to the ground in late winter or early spring (February to March) when the previous year's dead stems are removed and the fresh basal growth that has emerged or is about to emerge can be seen. All the old, dead, or dying stems (typically the entire top growth) are cut back to within a few centimetres of the ground; this can be done with secateurs or loppers depending on stem thickness. The fresh new shoots that emerge in March to April grow rapidly on established plants and produce the season's flowering stems; flowers are typically produced from June or July onwards on the current season's growth. Do not be hesitant about cutting the old stems back hard; romneya responds poorly to partial pruning that leaves some old framework in place and much better to a clean, complete annual cut-back. In mild winters where some stems have partially survived, cut all the old growth back regardless; the plant flowers equally well whether cut back or not, but cutting back produces tidier, more vigorous plants. After cutting back, mulch around the base of the plant with composted bark or gravel to conserve moisture (if needed) and suppress weed competition. The plant's vigorous suckering means that the colony extends outward each year; mark the outer boundary of the plant each spring before cutting back so that sucker shoots emerging beyond the desired colony boundary can be removed.

Romneya coulteri (tree poppy or Matilija poppy) is one of the most dramatic plants for a UK sunny border: enormous white flowers to 20 cm across, with crinkled petals and a golden boss of stamens, on glaucous blue-grey stems to 2 m, from June to October. It is also one of the most notoriously difficult plants to establish, resenting root disturbance intensely. Transplant shock and drought stress in the first season are the primary causes of leaf curl and plant collapse in newly planted specimens.

Transplant shock

Transplant shock is the most common cause of leaf curl, wilting, and sudden collapse in romneya: the plant is almost impossible to move once established, and recently transplanted specimens from garden centres or between garden positions routinely wilt and lose their top growth in the weeks after planting. Even plants that have been carefully grown in containers with minimal root disturbance can suffer significant transplant shock. The collapsed plant may recover from the rootstock if the roots were not damaged in the move, sending up fresh basal shoots after a few weeks; but the top growth is typically lost.

What to do

Plant in spring (April or May) when the soil is warm and the plant has the full growing season to establish. Disturb the root ball as little as possible: cut the base off the container with a knife and slide the intact root ball into the planting hole without loosening the roots. Water in well at planting, then water minimally thereafter to encourage deep root development. Do not move the plant again once it is established; romneya should be treated as a permanent planting from the start. If the top growth collapses after planting, do not dig the plant up; leave the root system undisturbed and watch for new basal shoots emerging over the following weeks to months.

Drought stress

Romneya is highly drought-tolerant once established (it grows in some of the driest, most arid canyon slopes in California), but in its first season before a deep root system is established, it is vulnerable to drought stress, which causes the glaucous leaves to curl inward and develop brown margins. The temptation to over-water a newly planted romneya should be resisted; the plant needs to be gently water-stressed to drive the roots deep into the soil, and over-watering produces shallow, surface roots. Once established, romneya rarely needs watering in UK ground conditions.

What to do

Water newly planted romneya sparingly: water in well at planting and then water only when the plant shows clear signs of wilting in the first season. In the second and subsequent years, no supplementary watering is needed in average UK conditions. Never over-water; romneya is more likely to fail from too much water than too little in UK outdoor conditions. Established plants are among the most drought-tolerant in the UK garden.

Waterlogging

Waterlogging is the most serious threat to established romneya in UK gardens; the fleshy roots rot rapidly in saturated, poorly aerated soil and the plant can collapse suddenly after a wet winter on an unsuitable site. Romneya grows in freely draining, rocky canyon soils in nature and has essentially no tolerance for standing water or persistently wet soil in winter. Clay soils, low-lying positions, and any situation where water sits around the roots in winter are unsuitable; the plant must be grown in very well-drained conditions.

What to do

Plant only in very well-drained soil; a sunny, slightly sloping, gravel garden or raised bed is ideal. Add substantial coarse grit to heavy or clay soils, but in genuinely heavy clay it is better to build a raised bed entirely rather than relying on grit incorporation to transform drainage. Apply a coarse grit top-dressing around the crown in autumn to improve drainage at the most vulnerable root-collar zone over winter. Avoid any position that is wet or flooded in winter.

Cold damage

Cold damage kills the top growth of romneya in most UK winters; the glaucous stems and leaves blacken after hard frost and the whole top growth dies back to the base. This is normal and expected behaviour for romneya in UK conditions; the plant regrows from the rootstock each spring to produce the season's flowering stems. In very severe winters below about -12 to -15°C in combination with wet soil, the rootstock itself can be killed; in dry, well-drained conditions the rootstock is more frost-tolerant.

What to do

Do not cut back the dead stems until late winter (February to March) as they provide some insulation to the rootstock below. Apply a 10 to 15 cm coarse grit or bark mulch over the crown in November in colder UK gardens. In spring, cut all old stems back to within a few centimetres of the ground when basal shoots are visible. The plant flowers on the current year's growth and performs well from this annual hard cut-back routine.

Frequently asked questions

Why are my romneya leaves curling?

Romneya leaves curl most commonly because of transplant shock (the plant resents root disturbance intensely; newly planted specimens routinely wilt and lose their top growth), drought stress in the first season before deep roots are established (though established plants are very drought-tolerant), waterlogging which rots the fleshy roots rapidly, or cold damage which kills the top growth in most UK winters (normal behaviour; the plant regrows from the base in spring).

How do I successfully establish romneya in the UK?

Choose a sunny, well-drained position before planting and do not move it again. Plant in spring by cutting the pot base off and sliding the intact root ball in without disturbing the roots. Water in at planting, then water minimally. Grow in lean, gritty, freely draining soil; avoid rich or wet soil. If the top growth collapses after planting, leave the root undisturbed and watch for new basal shoots; the plant often recovers.

Is romneya hardy in the UK?

Romneya is hardy throughout most of the UK: the top growth is killed by frost in most UK winters (normal behaviour) but the rootstock survives to regrow each spring. The rootstock is hardy to about -12 to -15°C in freely draining conditions; wet soil combined with frost can kill the roots at higher temperatures. Protect the crown with a coarse grit mulch in November in colder UK gardens.

How do I prune romneya in the UK?

Cut all old, dead top growth back hard to the ground in late winter (February to March) when basal shoots are visible. Do this completely: leave no old framework. The fresh new shoots that emerge flower from June or July on the current season's growth. Do not prune in autumn; leave the dead stems to insulate the crown through winter. Mark the colony boundary before cutting back to identify sucker shoots to remove.