877 Polymnia sonchifoliaCommon Names: yacón Family: Asteraceae (aster/daisy Family)
Yacón is a coarse textured, robust perennial herbaceous plant with large leaves and little yellow daisy flowers. The plant gets up to 6 ft (1.8 m) tall with an equivalent spread. The stems are thick, hairy and streaked with purple. The leaves are opposite and broad, 8-14 in (20.3-35.6 cm) long with winged petioles. The dainty little flowerheads are about 1 in (2.5 cm) across with yellow rays. They are not very showy and seem a little out of place amongst the huge leaves. Yacón produces spindle shaped storage tubers that can reach 1 ft (0.3 m) in length and weigh up to 5 lbs (2,3 kg), although they are typically less than 0.5 lb (0.2 kg) and 6-8 in (15.2-20.3 cm) in length. They are attached to the swollen stem just beneath the ground surface and point outward like the spokes on a wheel. The tubers have a tan to purplish brown skin and the inside can be white, yellow, violet or orange.
Yacón, Polymnia sonchifolia, is native to the Andes from Columbia and northern Argentina to Peru and Ecuador. It grows in warm-temperate valleys, usually between 2000 ft and 7000 ft (610-2133 m) above sea level, but is cultivated from sea level up to 9000 ft (2743 m). Yacón is a grown as a sweet food crop in Equator and Peru, where children consider the tubers a special treat. In many regions nearly every family has a few plants in their kitchen garden, and yacón has been found in pre-Incan tombs in Peru. Yacón has only recently been introduced to other parts of the world as a novelty root crop and as an experimental source of natural sugars. It is rapidly becoming popular in eastern Asia and New Zealand.
CultureYacón grows fast in loose, well-drained acidic to alkaline soils rich in organic matter. It is daylength neutral for tuber development, but in temperate latitudes, flowers are not produced until daylength shortens in the fall. Some years in Zone 8 we get good tuber development but frost kills the plants to the ground before they bloom. Light: Yacón does well in partial shade to full sun. Moisture: Yacón grows best in a slightly moisture retentive soil with regular watering. The storage tubers allow it to survive periods of drought. Hardiness: USDA Zones 7 - 11. Yacón dies to the ground following frost, but the storage tubers permit it to come back in spring as long as they haven't frozen. Yacón needs about 200 days of frost-free weather before the tubers are ready for harvesting. Propagation: Yacóns in cultivation rarely set seeds. They are propagated from offshoots or "plantlets" removed from the base of the main stem just above the ground; or by dividing the rhizomatous underground stems; or by dividing the the storage tubers; or by rooting cut stems.
In frost free areas yacón tubers can be removed without disturbing the plant which will continue to produce more tubers. After flowering, the yacón plant dies back to the ground for a rest period during the dry season and the tubers are usually harvested then. In frosty climes, harvest the tubers after the plant dies to the ground by groping around with your hands under the plant; don't disturb the main roots and the plant will come back in spring and produce more tubers. Yacón tubers are incredibly sweet. The flesh is white and crispy, a little juicier than an apple, but every bit as sweet as the sweetest Red Delicious. Some say they taste like sweet water chestnuts; others compare the taste to an apple and watermelon combination. The tubers get even sweeter after curing in the sun, but they may not be as crisp. Yacón tubers are usually eaten raw, out of hand like a fruit. They are good sliced and added to green salads, or shredded with carrots and raisins for a sweet slaw.
In Peru yacón tubers are grated and squeezed through a sieve to make a sweet drink, and the juice is concentrated into blocks of candy called chancaca. Tubers are also boiled or baked and the stems and leaves are cooked and eaten as a vegetable. Yacón retains crunchiness during cooking and is just beginning to come into favor for Asian stir-fried dishes. The leaves contain 11-17% dry weight protein and are useful as a livestock feed.
Most roots and tubers store carbohydrates in the form of starch, a polymer of glucose. Yacón tubers store carbohydrates in the form of inulin, a polymer of sucrose that the human body cannot metabolize. Yacón is therefore an acceptable sweet and starchy food for dieters and diabetics. Although it has few calories and little food value, yacón is an easy to grow sweet treat, and a sure conversation starter. Japanese scientists are studying yacón as a source for purified fructose and a variety of processed products such as pickled slices and dried slices.
There are other species of Polymnia native to the U.S., but they do now produce tubers. Jerusalem artichoke, also in the sunflower family, is another plant that produces inulin in its underground tubers.
Steve Christman 12/5/00; updated 10/17/03