Why Are My Yacon Leaves Curling?

Drought

Yacon grows rapidly in summer and its large, hairy leaves lose water quickly in warm, sunny conditions. In a dry spell, or during the first 2 to 3 weeks after transplanting when the root system is still establishing, the leaves curl upward at the margins and wilt noticeably in the afternoon. This is not a disease: it is the plant regulating its water loss in response to demand exceeding supply. Well-established yacon in open ground with a deep root system is quite drought-tolerant, but newly planted or container-grown yacon is much more vulnerable.

What to do

• Water newly transplanted yacon generously until it is established (3 to 4 weeks). Apply a thick mulch around the plants to retain soil moisture. Water during dry spells, particularly in July and August when the plants are at their largest. Yacon in containers needs daily watering in hot weather.

Slugs

Slugs cause the most damage to yacon in spring, when the young shoots emerge from the crowns and the leaves are soft, fresh, and highly attractive to slugs. Slug damage produces irregular holes in the leaves; when the leaves subsequently expand, the undamaged tissue curls and puckers around the holes, creating the appearance of distorted, curling foliage. Once yacon reaches its full summer size, slug damage becomes relatively minor compared with the plant's vigour, but in spring it can set plants back significantly.

What to do

• Apply nematode slug control (Phasmarhabditis hermaphrodita) to the soil around emerging yacon crowns in spring. Check plants in the evening and remove slugs by hand. Delay planting out in cool, wet springs until the growth is more robust. Copper tape around container rims reduces slug access to pot-grown plants.

Aphids

Aphids (particularly peach-potato aphid) colonise the growing tips of yacon in summer, causing the younger leaves at the shoot tips to curl and pucker around the colonies. Large, vigorous yacon plants tolerate aphid pressure well, and natural predators (ladybirds, hoverfly larvae) usually control colonies on the outdoor plant without intervention.

What to do

• Inspect growing tips in July and August. Apply insecticidal soap to heavy infestations on the growing tips. In most cases natural predators resolve the problem without treatment. Avoid using broad-spectrum insecticides that kill beneficial predators.

Botrytis (grey mould)

In a cool, wet summer, botrytis (Botrytis cinerea) can affect the lower leaves of yacon, particularly where leaves touch the soil or where damaged tissue provides an entry point. Affected leaves develop water-soaked patches that turn brown and papery, with a grey-brown fuzzy mould in damp conditions. The dying leaves may curl as they collapse. Botrytis is rarely a serious problem on yacon in a normal UK summer but can be significant in an exceptionally cold, wet year.

What to do

• Remove affected leaves promptly. Improve air circulation by thinning surrounding plants. Avoid overhead watering. The dense canopy of yacon plants in close proximity can create damp microclimates that favour botrytis; adequate spacing and removing lower leaves that touch the ground reduces risk.

Frequently asked questions

Why are my yacon leaves curling?

Yacon (Smallanthus sonchifolius) leaves curl and wilt most commonly because of drought, slug damage to young plants, or aphid infestation. Yacon is a vigorous, tall-growing plant (up to 2 to 3 metres in a good UK summer) with large, soft, hairy leaves that transpire substantial amounts of water in hot weather. In drought conditions or during establishment after transplanting, the large leaves curl upward at the margins and wilt in the afternoon heat as water demand exceeds supply from the roots. Slugs cause extensive damage to the soft young leaves of yacon in spring, leaving irregular holes and sometimes curling the undamaged margins around the damaged areas as the leaf expands unevenly. Aphids colonise the growing tips in summer, causing the youngest leaves to curl and pucker around the feeding colonies. Botrytis (grey mould) in wet conditions can cause the lower leaves to rot and curl as the affected tissue dies.

How do I grow yacon in the UK?

Yacon (Smallanthus sonchifolius) is a South American perennial from the Andean highlands, grown in the UK for its sweet, crisp, apple-like tuberous roots. Start rhizome offsets (propagating crowns, not the edible storage roots) in pots under cover in March to April, and plant out after the last frost (late May to June) into a sunny, sheltered position in fertile, well-drained but moisture-retentive soil. Space plants at least 75 to 90 centimetres apart; they become large, leafy plants by midsummer. Yacon tolerates the UK growing season well and requires less heat than many Andean crops. It grows vigorously once established and requires minimal care beyond regular watering in dry spells. In autumn, the aerial growth is killed by the first frosts but the roots and crowns survive in the ground in most UK regions (except the coldest upland areas). Dig the roots after the first frost kills the tops; the tubers can be eaten immediately or stored in a cool, dark, frost-free place. Save a portion of the crown for replanting the following spring.

What does yacon taste like?

Yacon tubers have a crisp, juicy texture similar to jicama or water chestnut, with a sweet, mildly fruity flavour sometimes described as a cross between apple and watermelon. The sweetness comes primarily from fructooligosaccharides (FOS), a type of carbohydrate that is not metabolised by the human digestive system in the same way as simple sugars; this makes yacon a low-glycaemic food that has attracted attention for its potential benefits for blood sugar regulation, though it should not be eaten in very large quantities at once as excess FOS can cause digestive discomfort in some people. Yacon can be eaten raw (sliced into salads or juiced), roasted, or stir-fried. The leaves can also be brewed into a tea that is consumed in parts of South America for purported health benefits, though there is limited clinical evidence for these claims. The flavour of freshly harvested yacon is mild; leaving the tubers in sunlight for a few days (a process called curing) increases the sweetness.

Is yacon frost-hardy in the UK?

Yacon's roots and crowns (the thick, compact propagating structures at the base of the stems) are frost-hardy to approximately -5 to -8°C and will survive UK winters in the ground in most regions without lifting, provided the soil does not freeze solid for extended periods. The aerial parts of the plant (stems and leaves) are not frost-tolerant and are killed by the first autumn frost, but this is normal and expected: the plant is a perennial in its native Andes, dying back to the roots each autumn and resprouting in spring. In very cold or exposed positions in northern England or Scotland, or in gardens with heavy clay soils that become waterlogged in winter, lifting the crowns and storing them frost-free in slightly moist compost gives more reliable results. In mild areas of the south and west of England and Wales, yacon can be left in the ground year-round with a thick mulch for protection.