Lysimachia, commonly called loosestrife, is a diverse genus of moisture-loving perennials ranging from the tall, upright Lysimachia clethroides (gooseneck loosestrife) with its elegant arching white flower spikes, to the low-growing Lysimachia nummularia (creeping Jenny) used as a ground cover, and the cheerful yellow-flowered L. punctata. Most species are vigorous growers in moist conditions and are valued for their ease of care and long season of interest. The different species vary considerably in their requirements, but most share a preference for consistent moisture and react similarly when that preference is not met. Leaf curl is the first visible symptom of most problems on lysimachia and, once identified correctly, is almost always straightforward to fix.
1. Drought stress
Most lysimachia species evolved in moist habitats and prefer consistently moist to wet soil in the garden. When the soil dries out, the oval or lance-shaped leaves curl inward and develop a dull, slightly yellow-green appearance. Lysimachia clethroides and L. punctata, both tall, vigorous species, have high water demand and show drought curl relatively quickly. Lysimachia nummularia (creeping Jenny) is slightly more tolerant of brief dry spells but still performs best with consistent moisture. Golden-leaved cultivars such as L. nummularia 'Aurea' are particularly sensitive, as their lower chlorophyll content gives them less capacity to regulate water stress.
What to look for
- Leaves curling inward along their length or cupping upward
- Dull, slightly yellow-green colour rather than the normal bright or golden green
- Soil dry when probed below the surface
- Symptoms worsening rapidly in hot weather or dry spells
- Quick recovery after deep watering
How to fix it
Water deeply at the base of the plant to wet the full root zone. Apply a generous mulch layer to retain moisture. Lysimachia in full sun in dry conditions may need watering every two to three days in hot spells. Moving sun-stressed plants to partial shade greatly reduces drought sensitivity. Lysimachia planted beside water features, in bog gardens, or in naturally low-lying, moist positions rarely needs any irrigation once established.
2. Aphids
Aphids are the most common insect pest of lysimachia, forming colonies on stem tips, flower buds, and leaf undersides from spring through summer. The fast-growing new stems provide abundant soft tissue for aphid colonies to exploit. On L. clethroides, the arching flower spikes are often targeted as they develop. Feeding causes distortion and curling of young leaves, sticky honeydew deposits, and sooty mold. In most gardens aphid infestations on lysimachia are self-limiting by midsummer, but on plants already stressed by drought or disease the colonies can be more persistent and damaging.
What to look for
- Clusters of insects on stem tips, developing flower spikes, and leaf undersides
- Young leaves curled, distorted, and sticky
- Black sooty mold on foliage below heavy infestations
- Ants tending colonies on the stems
- Distorted or stunted new growth on heavily infested stems
How to fix it
Knock aphid colonies off with a firm jet of water. Apply insecticidal soap to heavy infestations every five to seven days. Control ants on the stems to allow natural predators to access colonies. Lysimachia is robust enough to tolerate moderate aphid pressure without lasting harm, and natural predator populations usually manage colonies effectively in established gardens.
3. Rust
Rust (Puccinia or Uromyces species) can affect lysimachia, producing the characteristic orange-brown pustules on leaf undersides alongside yellow patches on upper surfaces and leaf curl. It is more common on some species than others and tends to appear from midsummer in cool, damp conditions. Lysimachia punctata appears more susceptible than the creeping or gooseneck species in most garden settings. Rust spreads by spores in wet conditions and overwinters on plant debris.
What to look for
- Orange or rust-brown pustules on leaf undersides
- Yellow or pale spots on upper leaf surfaces
- Leaves curling and dropping prematurely
- Infection spreading upward through the plant in wet conditions
- Orange powder visible on tissue wiped across the leaf underside
How to fix it
Remove infected leaves immediately and dispose of them away from the garden. Apply a copper-based or triazole fungicide to protect remaining foliage. Clear all plant debris from around the plant in autumn to remove overwintering spores. Avoid overhead watering. Divide overcrowded clumps to improve air circulation and reduce the humid microclimate that favours rust spread.
4. Slugs and snails
Slugs are highly attracted to lysimachia, particularly to the low-growing and ground-covering species such as L. nummularia. The combination of moist habitat, soft leaves, and low-growing stems makes lysimachia an easy target. Slug feeding creates ragged holes and eaten margins that then curl and deteriorate. On creeping Jenny used as a ground cover, slug damage can be severe enough to open large bare patches in the mat. Spring growth and any new growth after cutting back are most vulnerable.
What to look for
- Ragged holes in leaves with eaten margins
- Leaf edges curling around damaged areas
- Silvery slime trails on and around the plant
- Damage worst overnight and after rain
- Ground-cover forms developing bare patches in severe infestations
How to fix it
Apply iron phosphate slug pellets around the plant in early spring and after any cut-back or renovation. A nematode drench in moist soil conditions provides sustained biological control. For ground-cover lysimachia, spreading a thin layer of sharp grit over the mat deters slugs from crossing to reach the leaves. Check under the foliage mat at night and handpick slugs regularly in wet periods.
5. Powdery mildew
Powdery mildew can affect lysimachia in crowded plantings or following drought stress, though it is less common than on related moisture-loving genera such as filipendula. The white powdery coating appears on leaf surfaces alongside upward curling and yellowing. It is most likely to appear on L. punctata in sheltered, poorly ventilated positions in late summer. Drought-stressed plants are significantly more susceptible, and the combination of dry soil followed by cool nights creates ideal mildew conditions.
What to look for
- White or grey powdery coating on leaf surfaces
- Leaves curling upward around infected areas
- Yellowing and browning of affected foliage
- Infection starting on older lower leaves
- Problem worse in crowded plantings or following dry spells
How to fix it
Divide overcrowded clumps to improve air circulation. Maintain consistent soil moisture as the primary preventive measure. Remove infected foliage and apply potassium bicarbonate spray if mildew is spreading. Cutting the plant back to ground level in midsummer stimulates a fresh, mildew-free flush of growth.
6. Root rot
While lysimachia prefers moist conditions, stagnant waterlogging in compacted or anaerobic soil can cause root rot. The stoloniferous or rhizomatous root systems become brown and soft, and the plant shows drought-like wilting and leaf curl despite wet soil. This is most likely in heavy clay soils during prolonged wet winters, and more likely on the taller, upright species than on the shallow-rooting creeping forms.
What to look for
- Wilting and curl despite moist or wet soil
- Yellowing from the base of the plant upward
- Soft, brown, or foul-smelling roots when lifted
- Problem developing after prolonged wet or cold periods
- Plant loosening in soil or lifting easily from the ground
How to fix it
Lift and divide the clump, removing all rotten tissue. Replant healthy sections in improved soil with better drainage. Incorporate grit and organic matter to create moist but freely drained conditions. Avoid replanting in the same waterlogged position without significant drainage improvement.
Quick diagnosis checklist
| Symptoms | Most likely cause | First action |
|---|---|---|
| Inward curl, dull yellow-green, dry soil | Drought stress | Deep water + mulch |
| Sticky tips, insect clusters, sooty mold | Aphids | Water jet + insecticidal soap |
| Orange pustules underneath, yellow spots above | Rust | Remove infected leaves + copper fungicide |
| Ragged holes, slime trails, bare patches in ground cover | Slugs | Iron phosphate pellets + nematode drench |
| White powder, upward curl, crowded planting | Powdery mildew | Divide clump, potassium bicarbonate spray |
| Wilt in wet soil, brown roots, clay or waterlogged site | Root rot | Lift, divide, replant with drainage improvement |
Frequently asked questions
Why are my lysimachia leaves curling?
Lysimachia leaves most often curl because of drought stress (most species prefer moist to wet conditions) or aphid infestation on new growth. Check soil moisture first and inspect new shoot tips and leaf undersides for aphid colonies. Lysimachia is generally vigorous and recovers well once the cause is addressed.
Is lysimachia invasive?
Some lysimachia species are significantly vigorous and can spread aggressively in moist conditions. Lysimachia punctata (yellow loosestrife) and L. clethroides (gooseneck loosestrife) spread by stolons and rhizomes and can become dominant in moist border conditions. L. nummularia (creeping Jenny) is a useful ground cover but can spread widely. Site these species where their spreading habit is managed by division every two to three years or physical barriers.
Can lysimachia grow in sun?
Lysimachia tolerates sun well if the soil stays consistently moist, but in dry conditions it performs better in partial shade where transpiration demand is lower and drought stress is reduced. Lysimachia nummularia and the golden-leaved cultivars are particularly prone to scorch in full sun without reliable moisture. Most species thrive in light shade to full sun when water is not limiting.
Why are my lysimachia leaves turning yellow and curling?
Yellowing alongside curling on lysimachia most commonly indicates drought stress (yellowing follows curl in dry conditions), rust infection in cool damp weather, or root rot in waterlogged soil. Check the soil: if dry, water deeply. If consistently wet, inspect roots for rot. Rust is distinguished by orange or brown pustules on leaf undersides rather than uniform yellowing.
Does lysimachia need to be divided?
Yes, vigorous lysimachia species such as L. punctata and L. clethroides benefit from division every two to three years to prevent them becoming too dense and to maintain vigour. Overcrowded clumps develop reduced air circulation that encourages disease, and the innermost growth of very dense clumps receives insufficient moisture and nutrients. Divide in spring or autumn, replanting healthy outer sections.