Why Are My Polygonatum Leaves Curling?

Solomon's seal sawfly

The Solomon's seal sawfly (Phymatocera aterrima) is by far the most common and significant problem affecting polygonatum in UK gardens. The adult sawfly lays eggs on the leaves in late spring, and the resulting grey-blue caterpillars feed voraciously on the leaves, causing them to curl, shred, and eventually be stripped entirely from the stem. A severe infestation can reduce the plant to bare stems in less than a week. The caterpillars are unmistakeable: they are a distinctive grey-blue colour, feed in groups, and tend to curl the leaf margins inward as they feed from the edges. The damage typically appears from late May to July.

What to do

• Inspect polygonatum daily from late May onwards for the first signs of sawfly caterpillars. Early detection is essential as the damage can progress extremely rapidly.
• Pick the caterpillars off by hand as soon as they are noticed and drop them into a bucket of soapy water. They tend to fall off the stems when disturbed, so holding a container beneath the stem and shaking it gently is an effective collection method.
• Spray affected plants with an insecticidal soap solution, ensuring the spray contacts the caterpillars directly. This is most effective against young caterpillars in the first two instars.
• Although defoliation looks severe, well-established polygonatum colonies typically regenerate after sawfly damage, as the rhizomes have significant energy reserves. The plant rarely dies from a single year's defoliation, but repeated severe annual damage can gradually weaken it over several years.
• Cultivate the soil around polygonatum in autumn to expose overwintering pupae to birds and frost.

Drought stress

Polygonatum is a woodland plant and requires consistently moist, cool, humus-rich soil. In dry, exposed positions or in unusually dry UK summers, the oval leaves curl inward along their length to reduce moisture loss. The normally deep green leaves also become slightly paler and the elegant arching posture of the stems loses its vigour as the plant struggles to maintain turgor. Drought stress is most common in polygonatum planted in full sun, in shallow soil over chalk or gravel, or in positions sheltered from rainfall by overhanging eaves or dense overhead canopy.

What to do

• Water polygonatum during dry periods through spring and early summer, when the plant is in active growth and most sensitive to moisture stress. The rhizomes have moderate reserves but cannot sustain growth through prolonged drought.
• Apply a generous mulch of leafmould or garden compost around established polygonatum each spring. This retains soil moisture, suppresses weed competition, and enriches the soil simultaneously.
• Ensure polygonatum is planted in a position that receives consistent shade: the leaf canopy of deciduous trees and shrubs significantly reduces soil moisture evaporation and creates the cool, moist microclimate the plant needs.

Slug damage

Slugs feed on polygonatum leaves and on the emerging shoots in spring, causing the leaves to develop holes and to curl around the damage. The damp, shaded conditions that polygonatum prefers are exactly the conditions that slugs favour, making slug damage a consistent problem throughout the growing season. Young emerging shoots in spring are particularly vulnerable, as the tender new growth is easier to damage than the fully expanded leaves later in the season.

What to do

• Apply biological nematode control (Phasmarhabditis hermaphrodita) around polygonatum plantings in spring and again in early autumn when soil temperatures are above 5 degrees Celsius.
• Hand-collect slugs from around the plants in the evening, particularly in wet spring weather. The shaded positions that polygonatum occupies make it easy to check systematically with a torch.
• Iron-phosphate slug pellets are safe to use around polygonatum and do not harm other garden wildlife.

Too much sun

Polygonatum is a shade-demanding plant and performs poorly in full sun, particularly in the afternoon. In sunny positions, the oval leaves curl inward, develop scorched brown patches on the upper surface, and lose their characteristic deep green colour, turning yellowish. The plant may survive in partial sun but rarely thrives, and the defoliation caused by sun scorch compounded by drought stress can prevent the colony from expanding normally.

What to do

• Relocate polygonatum to a shaded position, under deciduous trees or on the north or east-facing side of walls, buildings, or dense shrubs. The east-facing side of a border that receives morning sun but shade from midday onwards is acceptable in moist soil.
• If relocation is not possible, plant taller shrubs or perennials to the south and west to create the shade polygonatum needs in its current position.

Overcrowding

Polygonatum spreads by creeping rhizomes and established colonies can become very dense over time. Heavily overcrowded plants produce progressively smaller stems and leaves that may curl as individual rhizomes compete for resources. The elegant, widely spaced arching stems of a well-established colony at the right density give way to a congested mass of smaller, weaker stems when the planting becomes too dense.

What to do

• Divide overcrowded polygonatum in autumn after the leaves die back, or in early spring before the new shoots emerge. Lift sections of the rhizome mat with a fork, separate into smaller pieces each with several viable buds, and replant at wider spacing.
• Polygonatum divisions establish quickly and reliably. Replant at 30 to 45 cm apart in freshly enriched, humus-rich soil.
• Divisions can be planted in new shaded positions to extend the colony across a wider area of the garden.

Frequently asked questions

Why are my Solomon's seal leaves curling?

Solomon's seal leaves curl most often from sawfly caterpillar feeding or drought stress. The Solomon's seal sawfly (Phymatocera aterrima) is a very common UK pest that strips the leaves entirely, causing them to curl and shred as the caterpillars feed. Drought in dry, sunny positions causes the oval leaves to curl inward to reduce moisture loss, as polygonatum naturally grows in cool, moist, shaded woodland conditions.

How do I treat Solomon's seal sawfly?

Treat Solomon's seal sawfly by picking off the grey-blue caterpillars by hand as soon as they are noticed in late spring and early summer. The caterpillars are visible to the naked eye and feed in groups, so hand-picking is effective and avoids chemical intervention. Check plants daily as the caterpillars can strip the foliage very rapidly. A spray of insecticidal soap is effective against young caterpillars but must contact them directly to work. The damage is largely cosmetic as the plant stores energy in its rhizomes, but repeated severe defoliation over several years can gradually weaken the colony.

What conditions does polygonatum need?

Polygonatum thrives in cool, moist, humus-rich soil in deep shade or dappled shade. It is one of the classic woodland-floor plants, naturalising under deciduous trees and shrubs where most other plants struggle. It performs best in soil enriched with leafmould and garden compost and requires consistent moisture through the spring and early summer growing period. It tolerates dry conditions in summer once fully dormant. Avoid planting in full sun or dry, exposed positions.

When does polygonatum flower?

Polygonatum flowers in May and June, producing its characteristic small, white, bell-shaped flowers that hang in pairs or small clusters beneath the arching stems. The flowers are pollinated by bumblebees and are followed by small, dark berries in late summer. The arching stems and paired oval leaves give the plant a distinctive and elegant architectural quality that makes it one of the most beautiful of all woodland-floor plants even before it flowers.