Why Are My Ornithogalum Leaves Curling?

Waterlogging

Waterlogging is the most common cause of ornithogalum decline in UK gardens. Ornithogalum is native to the Mediterranean and Middle East, where soils bake dry in summer and drain freely in winter. In persistently waterlogged, anaerobic UK clay soils, the bulbs deteriorate rapidly. The strap-like leaves yellow and curl as the rotting bulb base cannot support normal growth. This is most likely during a wet winter in poorly drained heavy clay, in low-lying positions that collect water, or in containers without adequate drainage.

What to do

• Plant ornithogalum in well-drained soil. In heavy clay, work generous amounts of coarse grit and organic matter into the planting area before planting.
• Ornithogalum umbellatum is quite adaptable and tolerates a range of conditions, but still performs best in reasonably well-drained soil in full sun or light shade.
• Ornithogalum nutans prefers woodland-edge conditions with good drainage and dappled shade.
• In containers, use a gritty, free-draining compost and ensure multiple drainage holes. Raise containers off the ground in winter to allow free drainage.

Vine weevil

Vine weevil larvae attack ornithogalum bulbs from late summer through winter. The c-shaped cream larvae feed on the outer scales and basal plate of the bulbs, causing the leaves to curl and wilt in spring. In severe cases the bulb is completely consumed and no growth appears in spring at all. Container-grown ornithogalum is much more at risk than border plants. The adult vine weevil feeds on leaves at night, leaving characteristic irregular notch-shaped holes along leaf margins in summer, which is a warning sign that eggs may have been laid in the compost or soil below.

What to do

• Apply nematode biological control (Steinernema kraussei) to containers and susceptible areas in late summer to early autumn when soil temperatures are above 5 degrees Celsius.
• When emptying containers after the season, inspect the compost thoroughly for c-shaped cream larvae and destroy any found.
• Use a vine weevil killer drench in containers where the pest is a known or recurring problem, applying in autumn before the larvae cause significant damage.

Bulb rot

Fungal bulb rot causes ornithogalum to produce curling, yellowing leaves in spring. The bulb scales become soft and brown and the basal plate deteriorates. This is most common in bulbs planted in wet soil, stored incorrectly before planting, or purchased in poor condition. Ornithogalum umbellatum in particular produces numerous small bulblets that are vulnerable to rot when stored damp.

What to do

• Purchase plump, firm ornithogalum bulbs and plant promptly in autumn. Inspect before planting and discard any that are soft, discoloured, or smell of decay.
• Dust bulbs lightly with sulphur powder before planting to provide some protection against fungal pathogens.
• Ensure good drainage: this is the most important preventive measure against ornithogalum bulb rot.

Aphids

Aphid colonies on ornithogalum leaves cause the strap-like leaves to curl and distort. Aphids congregate on the undersides of leaves and on the emerging flower stems, extracting sap and causing the tissue to curl inward as cell growth becomes uneven. In addition to physical distortion, aphids excrete honeydew that promotes sooty mould growth on the leaf surface, weakening photosynthesis further. Aphid infestations on ornithogalum are most common during warm spring weather as the plants are in active growth.

What to do

• Check ornithogalum regularly in spring for aphid colonies on the undersides of leaves and on emerging flower stems.
• Knock aphids off with a strong jet of water, or spray with an insecticidal soap solution. Repeat every few days until the population is controlled.
• Encourage natural predators by providing habitat for ladybirds, lacewings, and hoverflies. These consume aphid colonies rapidly once they establish in the garden.

Overcrowding

Ornithogalum umbellatum in particular can spread very aggressively, producing numerous small bulblets that eventually fill and overcrowd the available space. Heavily overcrowded plants produce increasingly narrow, curling leaves and flowering declines as individual bulbs compete intensely for resources. In naturalised grass plantings this can self-regulate to some extent, but in borders the dense bulb mass can become unmanageable.

What to do

• Divide overcrowded ornithogalum every three to four years in late summer or early autumn when the bulbs are dormant. Lift the entire clump, separate bulbs and bulblets, and replant at wider spacing.
• Discard excess bulblets of O. umbellatum if the colony is already spreading beyond its intended area. This species can become invasive if left unchecked in borders.
• Consider confining O. umbellatum to areas of rough grass or naturalised ground cover rather than mixed borders, where its spreading habit is less of a problem.

Frequently asked questions

Why are my ornithogalum leaves curling?

Ornithogalum leaves curl most often from waterlogging or vine weevil damage. The strap-like leaves yellow and curl when the bulbs are damaged by wet, anaerobic soil conditions. Vine weevil larvae feed on the bulbs through autumn and winter, and in spring the damaged bulbs produce weak, curling leaves that wilt rapidly. Both problems are most severe in containers.

Is ornithogalum (star of Bethlehem) invasive?

Ornithogalum umbellatum (common star of Bethlehem) can become invasive in garden borders, spreading aggressively by producing large numbers of offsets and self-seeding prolifically. Once established in a border it can be very difficult to eradicate because the small bulbs break apart when dug up and any fragments left behind regrow. It is better treated as a wildflower suitable for rough grass or naturalised areas rather than a cultivated border plant. Ornithogalum nutans (drooping star of Bethlehem) is less aggressive and makes an excellent woodland-edge naturaliser.

When should I plant ornithogalum bulbs?

Plant ornithogalum bulbs in autumn from September to November at a depth of 5 to 10 cm, depending on the size of the bulbs. The larger the bulb, the deeper it should go. Ornithogalum umbellatum tolerates a wide range of conditions including partial shade and poor soil, making it useful for difficult areas. Ornithogalum nutans prefers dappled woodland shade in humus-rich, well-drained soil where it naturalises elegantly.

Is ornithogalum poisonous?

Yes, all parts of ornithogalum are toxic if ingested, containing cardenolides and other compounds. The bulbs, leaves, and flowers should not be eaten. When handling ornithogalum bulbs, wear gloves as some people experience skin irritation from the sap. Keep plants away from children and pets. The toxicity of ornithogalum has been known since antiquity and is why the plant features in historical accounts of livestock poisoning in areas where it grows in pasture.