Inula is a genus of bold, yellow-flowered perennials ranging from the towering elecampane (Inula helenium) to the compact golden samphire. The large leaves that make inula so striking in a border are also quick to show stress. Drought is the most common cause of curling, but powdery mildew, aphids, slugs, leaf miners, and root rot each produce distinct symptoms. Identifying the correct cause before treating saves time and protects the plant.
1. Drought stress
Drought is the primary cause of leaf curling on inula. The genus includes species that grow naturally along stream banks and in moist meadows, and the large, often hairy leaves are adapted to moist conditions rather than drought. When the soil dries out, the leaves curl inward along their length to reduce the surface area exposed to the drying air. The curling typically starts with the outermost, largest leaves and progresses inward if watering is not provided. In very severe drought the leaves brown at the margins and tips as well as curling.
What to look for
- Leaves curling inward lengthwise, beginning with outer and lower leaves
- Soil dry several centimetres below the surface
- Brown margins or tips on the most affected leaves
- Worst during hot spells or after several rainless days
- Recovery visible within hours of deep watering
How to fix it
Water deeply, allowing the moisture to soak down to the full root depth. Inula develops a substantial root system and shallow surface watering is rarely sufficient. Apply a 7 to 10 cm layer of leaf mould, bark chip, or garden compost as a mulch over the root zone to reduce evaporation. During dry spells, water weekly rather than waiting for symptoms to reappear. If inula is growing in sandy or free-draining soil, improving the soil with generous amounts of organic matter before planting makes a significant long-term difference to moisture retention and reduces drought vulnerability.
2. Powdery mildew
Powdery mildew is very common on inula, particularly on Inula helenium and similar large-leaved species from midsummer onward. The fungal infection covers the leaf surface with a white powdery coating and simultaneously weakens the cell structure, causing margins to curl upward and the tissue between the veins to pucker. In warm, still summers the mildew can spread rapidly through a clump, coating successive leaves until the whole plant looks tatty and spent well before the end of the season.
What to look for
- White or pale grey powdery coating on the upper and lower leaf surfaces
- Leaf margins curling upward around the mildewed tissue
- Leaves puckering or looking smaller and more distorted than healthy growth
- Worst on dense clumps in sheltered spots with poor airflow
- Spreading through the plant from midsummer onward
How to fix it
Remove all badly affected leaves and dispose of them in the bin. Cut the plant back hard after flowering to remove the bulk of infected material and allow clean new growth to replace it. Water at the base in the morning only. Divide congested clumps every three to four years and space plants generously to improve air circulation. A potassium bicarbonate spray applied to unaffected leaves slows the spread of the infection without harming beneficial insects.
3. Aphids
Aphids cluster on the growing tips and softest new leaves of inula in spring and early summer. Their feeding, combined with the growth-disrupting toxins they inject, prevents young leaves from expanding and unrolling normally. The growing tip curls and the leaves directly below the tip may remain cupped or distorted. Because inula produces large leaves relatively quickly, aphid damage on a growing tip can leave a visible distorted patch on an otherwise impressive plant.
What to look for
- Tightly curled or cupped growing tips in spring
- Aphids visible within the curled tissue, often green or pale yellow
- Sticky honeydew and sooty mould on stems below the colony
- Damage concentrated at the growing tips, not on mature leaves
- Ants farming the colony up and down the stems
How to fix it
Knock colonies off with a firm water jet or apply insecticidal soap directly to the cluster. Pinching out the infested growing tip removes both the colony and the most distorted growth in one action. Natural predators including ladybirds, lacewings, and parasitic wasps control light infestations effectively without intervention. Avoid broad-spectrum sprays that eliminate these beneficial insects. Subsequent growth will be normal once the aphids are removed.
4. Slugs
Slugs target inula most aggressively in spring when the large soft leaves are just beginning to unfurl from the crown. Slug feeding on a leaf that has not yet expanded prevents the tissue from developing normally: the leaf emerges already curled or with irregular holes throughout, and the surrounding healthy tissue puckers around the damage. Large, lush inula leaves provide a substantial meal for slugs, and established plants in moist woodland-edge positions are particularly vulnerable.
What to look for
- Irregular holes through the leaf blade and ragged edges
- Young emerging leaves curled or distorted in an uneven pattern
- Silvery slime trails on foliage and soil in the morning
- Crown area disturbed, with slime visible near the base
- Damage worst after wet nights in spring
How to fix it
Patrol around the crown after dark in early spring and remove slugs by hand. Apply iron phosphate pellets around emerging growth in April and May, renewing after rain. Biological control with Phasmarhabditis hermaphrodita nematodes is effective when soil temperature is above 5 degrees C. Remove debris and loose mulch from immediately around the crown that provides daytime shelter. A ring of coarse grit around the base deters slugs but needs refreshing after rain.
5. Leaf miner
Several leaf miner species can tunnel through inula leaves, creating winding, irregular pale trails through the leaf tissue. As the larvae consume the interior of the leaf, the surface blisters, and the leaf curls or puckers around the mined areas. The distinctive meandering tunnels visible when a leaf is held up to bright light confirm the diagnosis and distinguish leaf miner damage from disease or aphid distortion.
What to look for
- Winding pale or whitish trails running through the leaf tissue
- Leaf surface blistering, puckering, or curling around the mines
- Trails visible from above without needing to turn the leaf over
- Problem from late spring through summer
- No aphids, fungal coating, or soil problem to explain the curling
How to fix it
Remove and bin every mined leaf as soon as you spot the trails. The larva inside continues feeding and pupating unless the leaf is physically removed. Prompt removal limits the adult fly population and reduces the next generation's impact. Because inula leaves are large and few in number compared to many perennials, even a small number of mined leaves is visually conspicuous and worth removing. Chemical control of leaf miners inside the leaf is rarely practical or necessary for a garden plant.
6. Root rot
Inula grows best in moist but well-drained soil and can suffer root rot when planted in ground that stays waterlogged for extended periods. The roots are killed by oxygen starvation and fungal pathogens, and the plant loses its ability to supply water to the leaves even though the surrounding soil is saturated. The leaves curl and wilt in a pattern identical to drought stress, and the only way to distinguish the two is to check the soil moisture and inspect the roots.
What to look for
- Leaves curling and wilting despite wet or waterlogged soil
- Roots brown, soft, and foul-smelling when the plant is lifted
- Crown area soft or discoloured at the base
- Problem appearing after prolonged wet weather or in low-lying spots
- Drought and pest causes already ruled out
How to fix it
Lift the plant and cut away all rotted roots to healthy firm tissue. Dust cut surfaces with sulphur powder and allow the plant to dry briefly before replanting in improved, better-drained soil. Incorporate coarse grit and organic matter into heavy clay soils. Inula does best in soil that is reliably moist in spring but drains well enough to avoid waterlogging over winter. In persistently wet gardens, raise the bed level or plant inula at the top of a gentle slope where excess water drains away naturally.
Quick diagnosis checklist
| What you see | Most likely cause | First action |
|---|---|---|
| Leaves curl inward, soil dry, margins browning | Drought | Water deeply, apply thick mulch |
| White powder on leaves, margins curling up | Powdery mildew | Remove affected leaves, cut back after flowering |
| Growing tips curled, aphids visible, sticky residue | Aphids | Water jet into tips, insecticidal soap |
| Ragged holes, distorted young leaves, slime trails | Slugs | Night patrol, iron phosphate pellets in spring |
| Winding pale trails in leaf, surface blistering | Leaf miner | Remove and bin every mined leaf |
| Wilting despite wet soil, soft brown roots | Root rot | Lift, prune roots, replant in drained soil |
Frequently asked questions
Why are my inula leaves curling and going brown?
Curling combined with browning on inula usually points to drought stress. The large leaves of inula lose water rapidly in dry conditions, and the plant responds by curling leaves inward to reduce the exposed surface area. Check the soil several centimetres down: if it is dry, water deeply and apply a thick mulch over the root zone. Leaves already browned will not recover but new growth will be healthy.
Does inula get powdery mildew?
Yes, powdery mildew is common on inula from midsummer onward. A white powdery coating appears on the leaf surface and the margins curl upward as the infection weakens the cells. Cutting the plant back after flowering removes all infected foliage and encourages fresh growth. Water at the base only and improve air circulation around congested clumps.
Why are the leaves on my inula curling inward?
Inward leaf curling on inula is almost always a sign of water stress, either from drought or from root rot in waterlogged soil. Both deprive the leaves of water: one because the soil is dry, the other because the roots can no longer function. Check the soil moisture and inspect the roots to tell them apart. Drought-affected plants recover quickly after watering; root-rotted plants have soft brown roots and will not.
Should I cut back inula when leaves curl?
Yes, if the leaves are badly curled from mildew, drought damage, or aphid distortion, cutting inula back to the crown after flowering prompts a flush of fresh growth. Water and feed after cutting back. The plant will not reflower that season but the new foliage carries it through autumn in good condition.