Yacon (Smallanthus sonchifolius) is a tuberous root vegetable native to the Andes Mountains, known for its sweet, crisp texture, often likened to a water chestnut or apple. The plant stores much of its carbohydrate content as fructooligosaccharides (FOS), a type of inulin, which the human body does not fully digest, contributing to its low-calorie sweetness. Achieving the highest yield and maximizing the conversion of these starches into sweeter, more palatable sugars depends entirely on precise timing for a successful harvest.
Identifying the Right Time
Yacon is a late-season crop that requires a long growing period, typically needing six to seven months in the ground to produce a good yield. The plant’s goal is to store energy for the following season, and this process accelerates dramatically toward the end of the growing cycle. Harvesting is usually timed for late autumn or early winter, depending on the local climate.
The most reliable visual indicator of readiness is the senescence, or dying back, of the foliage. When the large, leafy stalks turn yellow and begin to shrivel and droop, the plant is signaling that it has finished its above-ground growth and has begun translocating energy reserves down to the underground storage roots. This process naturally maximizes the size and density of the edible tubers.
The ideal moment often coincides with the first light frost, which signals the plant to halt leaf activity and rapidly move sugars into the roots. A light frost kills the top growth but does not freeze the soil deeply, benefiting the harvest. If a hard, deep freeze is anticipated, harvesting must occur immediately beforehand to prevent tuber damage. In frost-free climates, growers rely solely on the foliage dying back, but plants can be left in the ground longer until natural senescence.
The Harvesting Process
Once the foliage has fully died back, the first step in harvesting is to cut the remaining stalks down to just above soil level. This clears the area and helps the grower identify the central crown from which the roots radiate. Because the edible tubers are brittle and easily damaged, they must be dug up with caution.
A spading fork or a shovel is the appropriate tool, inserted wide of the central stem—at least 12 to 18 inches away—to avoid slicing into the delicate roots. Working around the circumference of the plant and gently levering the soil helps to lift the entire root ball intact. The goal is to remove the entire cluster of tubers and rhizomes as a single mass.
The next step involves carefully separating the two distinct types of underground structures: the larger, brown, edible storage tubers and the reddish, knobby rhizomes. The rhizomes, which are located closer to the base of the stem, contain the growing buds for the next season’s crop and must be handled delicately for propagation. The edible tubers are typically removed by twisting or snapping them cleanly away from the central crown and rhizome mass.
Post-Harvest Handling
After the edible tubers are separated, they benefit from a process known as curing, which maximizes sweetness. Freshly harvested yacon is high in fructooligosaccharides (FOS), which are not intensely sweet, but curing converts FOS into simple sugars like fructose. This conversion occurs naturally during storage but is accelerated by exposure to warmth and light.
The tubers should be brushed clean of excess soil, but not washed, and then laid out in a warm, bright area, such as a sunny windowsill or a greenhouse, for one to two weeks. The mild heat and light encourage the enzymatic breakdown of FOS into sweeter monosaccharides, increasing the total sugar content. This curing step also allows the skin to dry and harden slightly, improving long-term storage ability. For long-term storage after curing, yacon tubers should be kept in a cool, dark, and slightly humid environment, ideally between 37 and 50 degrees Fahrenheit (3 to 10 degrees Celsius). Storing them layered in a medium like sand, sawdust, or peat moss helps maintain humidity and prevents the crisp tubers from drying out.