Scorzonera (Scorzonera hispanica) is one of the most rewarding and most underrated root vegetables in the UK garden. It produces long, black-skinned roots with a sweet, nutty flavour sometimes compared to oysters, and it can stay in the ground over winter and into the following spring, harvested as needed. The strap-like leaves are edible when young. Because the plant spends many months in the ground, pests and diseases that damage the foliage have a long window in which to reduce the plant's ability to build the root. When scorzonera leaves start to curl, pucker, or distort, the cause is almost always aphids or rust.
What causes scorzonera leaves to curl?
Scorzonera belongs to the Asteraceae family (the daisy and chicory family), which means it shares some pests and diseases with close relatives such as salsify, chicory, and lettuce, but its pest profile is distinct from brassica crops. In UK conditions, the two causes that most reliably produce curling, puckered, or distorted foliage on scorzonera are aphid infestations and rust fungus. Both are more likely to become serious in crowded beds with poor air circulation, and both are made worse by overhead watering. Drought stress, leaf spot diseases, slug damage to young growth, and poor soil causing nutrient stress round out the other possible causes, but aphids and rust account for the overwhelming majority of cases.
1. Aphids
Several aphid species feed on scorzonera in UK gardens. The willow-carrot aphid (Cavariella aegopodii) is one of the more commonly recorded species on plants in the Asteraceae and Apiaceae families, migrating between willow trees as its primary host and various herbaceous plants as secondary hosts. Other umbelliferous and composite feeders may also colonise scorzonera when conditions are favourable. Whatever the species, the damage pattern is similar: colonies of small, soft-bodied insects establish on the undersides of young leaves and on growing tips, removing plant sap continuously as they feed. The affected leaves respond by curling downward and inward, often tightly enough that the colony is completely concealed inside the curl. Young leaves at the growing tip may be too distorted to open at all.
As the colony grows, the aphids excrete a sticky clear liquid called honeydew onto the leaf surfaces below. Honeydew encourages the growth of sooty mould, a black fungal coating that blocks light from reaching the leaf surface. On scorzonera's long, strap-like leaves, patches of sooty mould spreading down from aphid colonies higher on the plant are a useful indicator that an infestation is established and growing. Heavy infestations in early summer reduce the plant's ability to photosynthesize during the period when it is building root reserves, which can translate to a smaller, less-developed root at harvest. Aphids on scorzonera may also transmit plant viruses, though this is less well documented than on crops like lettuce and broad beans.
How to fix it
Check the undersides of young leaves and the growing tips of scorzonera from late spring onward, when aphid populations begin to build. Small colonies can be rubbed off by hand or dislodged with a firm jet of water directed at the leaf undersides. For larger infestations, apply insecticidal soap or a diluted neem oil solution to the undersides of all affected leaves, repeating every seven days for two to three applications. Neem oil has the advantage of disrupting aphid life cycles as well as killing adults on contact. Avoid broad-spectrum insecticides, which kill the natural predators (ladybirds, hoverflies, lacewings) that provide effective biological control of aphid populations through summer. Encouraging these predators into the kitchen garden by growing nectar-rich companion plants near the scorzonera bed provides season-long support. Ants farming aphid colonies on your scorzonera, carrying aphids to new growth and protecting them from predators, are worth controlling with a grease band or similar barrier around any raised bed structure if you notice their presence.
2. Rust
Rust on scorzonera is caused by Puccinia scorzonerella or closely related Puccinia species specific to plants in the Asteraceae family. It is a fungal disease that is immediately recognisable once you know what you are looking for: the leaf undersides develop raised, powdery, orange or rust-brown pustules (technically called uredinia, the spore-producing structures of the fungal life cycle), while the upper surface of the same leaf shows corresponding yellow or pale green spots or discolouration directly above each pustule. Affected leaves curl, pucker, and in severe cases turn yellow and collapse. The spores are carried on the wind, which is why rust can appear suddenly and spread quickly through a bed even without any obvious source of infection. The disease is worse in damp, humid conditions with poor air movement around the plants, and in years with a wet spring and summer it can become a significant problem.
Unlike some rusts, which alternate between two entirely different host plants to complete their life cycle, scorzonera rust appears to be capable of completing its cycle on Scorzonera hispanica alone, which means infected plants left in the ground through winter can provide a source of overwintering spores for the following season. Rust does not make the root inedible, but a plant that loses most of its foliage to rust in summer will not have built the root reserves to produce a satisfying harvest, especially if you are growing scorzonera as a two-season crop for larger roots.
How to fix it
Remove rust-affected leaves as soon as you spot the first orange pustules. Do not compost them; put them in the general waste bin to prevent spores spreading back to the bed. After removing affected leaves, avoid wetting the remaining foliage when watering; water at the base of the plant or use a seep hose rather than overhead irrigation. If plants are densely crowded in the row, thin them to give better airflow between the remaining plants. There is no fungicide approved for rust on scorzonera for home garden use in the UK; cultural control (removal of infected leaves, improved airflow, and dry foliage) is the main management approach. At the end of the season, clear all plant debris from the bed before winter to reduce overwintering spore loads. Rotate scorzonera to a fresh bed in subsequent years rather than growing it in the same position, as spores can persist in soil and plant debris.
Other causes to consider
Leaf spot diseases, caused by various fungal pathogens, can produce small brown or tan spots with yellow halos on scorzonera leaves. In severe cases the spots coalesce and the leaves curl, yellow, and drop. Leaf spot is most prevalent in damp, humid conditions and on plants in crowded positions with poor airflow. Remove affected leaves promptly and water at the base rather than overhead. Good plant spacing and crop rotation reduce incidence.
Drought stress causes scorzonera leaves to curl inward along their length and take on a slightly dull, grey-green tone as the plant reduces water loss. Scorzonera is reasonably drought-tolerant once established, but it prefers consistently moist, deep soil and will show stress symptoms in a prolonged dry spell, particularly if the bed is shallow or the soil is light and sandy. Mulching the bed after sowing and watering during dry periods in summer prevents the worst stress. Adequate soil moisture during the main growing season also produces longer, more evenly developed roots.
Slugs can devastate young scorzonera seedlings and also damage emerging leaf growth on established plants. The damage is ragged notching or removal of leaf tissue rather than the cleaner curling or spotting of pest and disease problems, and the slime trails slugs leave are usually visible on or near the affected plants. Use slug pellets approved for kitchen gardens, or lay physical barriers such as copper tape or grit around the bed, particularly when seedlings are at their most vulnerable in the weeks after germination.
Nutrient stress from poor soil produces slow, pale, weak growth and leaves that fail to develop fully, which can cause a degree of curling or cupping in the foliage. Scorzonera produces its best roots in a deep, fertile, well-drained loam. If your bed is thin or impoverished, incorporate well-rotted garden compost before sowing and apply a balanced general fertiliser in early summer. Avoid fresh manure, which causes roots to fork.
How to keep scorzonera healthy
- Sow scorzonera in spring (April to May in most UK regions) into a deep, well-prepared, weed-free bed in full sun. The soil should be loose, fertile, and free-draining to allow the roots to develop straight and long without obstruction.
- Thin seedlings to around 15 cm apart to give each plant adequate space and airflow. Crowded scorzonera is more susceptible to rust and aphid problems and produces inferior roots.
- Mulch the bed after the seedlings are established to retain moisture through summer. A weed-free, moisture-retentive bed keeps the plants growing steadily and reduces drought stress that predisposes them to pest and disease attack.
- Water at the base of plants rather than overhead. Wet foliage encourages rust and leaf spot. A seep hose laid along the row is ideal.
- Inspect the undersides of young leaves and growing tips weekly from late spring. Removing a small aphid colony by hand takes seconds; dealing with a large, established colony and its associated sooty mould takes much longer.
- Remove rust-affected leaves immediately and dispose of them in the general waste, not the compost heap. Prompt removal limits spore production and slows the spread of the disease to healthy foliage.
- Rotate scorzonera to a fresh bed each season. Because the crop stays in the ground for many months and sometimes for two full seasons, rotating it away from the same patch after each harvest reduces the buildup of soil-borne disease and overwintering pest populations.
- Leave roots in the ground over winter if you want to use the soil as natural cold storage. The flavour improves after frost. Mark the row clearly before the foliage dies back so you know where to dig through winter and into spring.
Frequently asked questions
Why are my scorzonera leaves curling?
The two most common causes of scorzonera leaf curling in UK gardens are aphid colonies (particularly the willow-carrot aphid, Cavariella aegopodii, and related species) and rust (Puccinia scorzonerella or related Puccinia species). Aphids cluster on young growth and cause leaves to curl and pucker as they remove sap. Rust produces orange pustules on leaf undersides with corresponding yellow spots above, and affected leaves can curl and distort. Drought stress and leaf spot diseases are secondary causes worth checking if no insects or pustules are visible.
What are the orange spots on the underside of my scorzonera leaves?
Orange or rust-coloured powdery pustules on the underside of scorzonera leaves are the spore masses of a rust fungus, most likely Puccinia scorzonerella or a related Puccinia species. The corresponding upper surface shows yellow or pale green spots or patches above each pustule. Rust spreads by wind-borne spores and is worse in humid, damp conditions with poor air circulation. Remove affected leaves promptly, avoid overhead watering, and increase spacing if plants are crowded. There is no fungicide approved for rust on scorzonera in the UK for home growers; hygiene and removal of infected material are the main management tools.
Can you eat scorzonera leaves?
Yes. The young leaves of scorzonera are edible and have a mild, slightly bitter flavour similar to dandelion leaves. They can be eaten raw in salads when very young and tender, or cooked like spinach once larger. Leaves that are heavily infested with aphids, badly distorted by rust, or coated in sooty mould are best discarded rather than eaten, but mild pest or disease pressure on individual leaves does not make the rest of the plant inedible. The root is the main crop and is unaffected by leaf-level pest and disease problems unless the foliage is so badly damaged that the plant cannot photosynthesize efficiently.
When do you harvest scorzonera?
Scorzonera sown in spring in the UK is typically ready to harvest from autumn of the same year, but the roots are still relatively slender at this stage. The flavour is often said to improve after frost, and many growers leave the roots in the ground over winter and harvest through autumn, winter, and into the following spring. Scorzonera can also be left to grow for a second season to produce thicker, more substantial roots. The roots can be dug as needed rather than lifted all at once, since the ground acts as natural cold storage. This long growing window makes keeping the foliage healthy throughout the first growing season particularly important.
Why are my scorzonera plants not growing well?
Poor growth in scorzonera usually points to soil conditions rather than pest or disease pressure. Scorzonera needs a deep, loose, fertile, well-drained soil to produce long, straight roots; in shallow, stony, compacted, or waterlogged ground the roots fork, stay short, or rot. Nutrient-poor soil produces slow, weak top growth and undersized roots. If the plants look pale and grow slowly but show no pest or disease symptoms, incorporating well-rotted compost before sowing and applying a balanced general fertiliser in early summer usually restores momentum. Scorzonera also responds poorly to competition from weeds, which crowd the root zone and reduce the moisture and nutrients available to the crop.