Yacon

Yacon’s strangest quality is what it doesn’t do: unlike almost every other starchy root, yacon doesn’t convert its carbohydrate storage to sugar when you eat it. The sweetness is real - it tastes like apple, watermelon rind, and jicama had a child - but it comes from fructooligosaccharides (FOS), which pass through the human digestive system without being absorbed. The result is a root vegetable that tastes genuinely sweet and contains almost no digestible calories. This is why it’s been adopted by low-glycemic diet communities and sold as a specialty health food at $5-10/lb.

The plant itself is impressive: it reaches 5-8 feet tall with large leaves, produces a clump of tubers at harvest that can weigh 10-20 lb total, and requires almost no pest management. In zones 7-9 it’s one of the more productive food plants you can put in a sunny spot.

What it actually is

Smallanthus sonchifolius is in the daisy family (Asteraceae), native to the Andean highlands of South America. It’s grown from the Andes to Colombia primarily as a fresh food crop - the tubers eaten raw like fruit. It looks like a small sunflower plant above ground; below ground it produces two types of structures:

• Tubers (the edible storage roots): 2-8 inches long, oval to carrot-shaped, pale yellow to purple depending on variety, with crisp, watery, sweet flesh. These are the harvest.
• Rhizome crowns (propagating stems): reddish-purple knobby structures at the crown where the tubers attach to the plant. These are saved and replanted the following spring.

The FOS content is highest in tubers that have been exposed to brief cold (below 50°F) after harvest - this is why traditionally harvested and stored yacon is sweeter than freshly dug. A day or two in the refrigerator after harvest noticeably increases perceived sweetness.

The ROI case

Yacon is a high-yield, long-season root crop with good per-pound value at specialty markets.

Planting	Plants	Yield	Value @$6/lb	Seed cost	Net
3 plants	3	10-20 lb	$60-120	$1.75*	$58.25-118.25
5 plants	5	17-35 lb	$102-210	$2.91*	$99.09-207.09

*Estimated from $3.49 rhizome purchase at 2 rhizomes per plant.

The wide yield range reflects the growing season length and available summer heat. In zone 9, expect the upper numbers; in zone 5-6 with a shorter season, the lower numbers.

Seed cost in year 2+: zero. Save the rhizome crowns from each harvest and replant them. A single yacon planting propagates itself indefinitely.

Growing requirements

Season: yacon needs a long frost-free season - 150-210 days. It’s planted in spring after last frost and harvested before first fall frost. In zone 5, this requires starting rhizome crowns indoors 4-6 weeks early and using season extension at both ends. In zones 7-9, direct planting outdoors works reliably.

Planting: plant rhizome crowns 3-4 inches deep, 24-36 inches apart. Each crown produces a full plant. The plant establishes slowly at first (first 4-6 weeks) before accelerating growth.

Height and support: plants reach 5-8 feet and can be top-heavy with tubers developing underground. A stake or support cage prevents lodging in windy sites. Otherwise no support is needed.

Soil: loose, deeply cultivated, well-drained soil produces the best tuber development. Similar requirements to dahlias (same family). Avoid compacted soil; the tubers need room to expand. Raised beds with 18+ inches of loose soil work well.

Fertilizing: moderate feeder. Generous compost at planting; side-dress with balanced fertilizer when plants reach 3-4 feet. Avoid excess nitrogen, which produces vegetative growth at the expense of tuber development.

Harvest timing: harvest after the first light frost kills the foliage, which signals the plant has stopped growing. The foliage death is natural and desirable - it triggers the final sugar conversion in the tubers. Dig carefully with a fork; tubers can extend 12-18 inches from the plant base.

What goes wrong

Short season failure: zones 5 and north struggle to get full-size tubers before frost. The 4-6 week indoor start is important. Row cover extension in fall adds 1-2 weeks. Even in a shortened season, small tubers are still edible and worthwhile.

Slugs and voles: both attack the tubers in the ground. Vole tunneling is especially destructive - metal mesh hardware cloth buried around the planting perimeter prevents entry. Diatomaceous earth and copper tape around raised beds deters slugs.

Powdery mildew on leaves in late season, particularly in humid climates. Cosmetic; doesn’t affect tuber quality significantly unless it’s severe enough to defoliate the plant before harvest.

Rhizome crown confusion: yacon produces both tubers (eat) and rhizome crowns (save and replant). The crowns look different - smaller, redder, knobby rather than smooth. Label them when harvesting; first-time growers sometimes eat the replanting material.

Skin damage during harvest: yacon skin is thin and tears easily. Handle gently; even small wounds invite mold during storage. Cure briefly (2-3 days at room temperature) to toughen the skin before storing.

Harvest and use

Dig after the first frost kills the foliage. Use a garden fork, loosening the soil in a wide circle before lifting - the tubers can be far from the central stalk. Wash gently; cure at room temperature for a few days.

Storage: yacon keeps 2-4 weeks at cool room temperature; 1-2 months refrigerated. Sweetness increases noticeably after 2-3 days in the refrigerator as FOS converts. Don’t store with ethylene-producing fruit (apples, bananas); it accelerates deterioration.

Saving crowns: select the firmest rhizome crowns with the most growth buds. Store in barely moist sand or peat at 40-50°F over winter. Inspect monthly and remove any that rot.

Preparing: peel the thin skin (vegetable peeler or paring knife). The flesh doesn’t brown significantly after cutting - no need to acidulate. Eat raw within a few hours of cutting for best texture and flavor.

Core preparations:

• Raw sliced: the primary preparation. Peel, slice thin, eat fresh. The flavor is sweet, mildly juicy, somewhere between apple and watermelon rind with a hint of jicama. Eaten as a snack or alongside acidic dishes in the Andes.

• Yacon slaw: julienned yacon dressed with lime juice, cilantro, and a small amount of olive oil or sesame oil. The crunch and sweetness work similarly to jicama in a slaw.

• Stir-fried yacon: brief high-heat stir-fry (2-3 minutes) with garlic and soy sauce. The texture softens slightly but retains some crunch; the sweetness becomes more pronounced with heat. Similar to stir-fried water chestnuts.

• Yacon syrup: boil down yacon juice to a dark, sweet syrup (the commercial product is produced this way). The home version: juice the tubers, simmer the juice in a heavy pot over medium heat for 1-2 hours until reduced and syrupy. Used as a low-glycemic sweetener.

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Related reading: Jicama - fellow crunchy tropical root with similar fresh eating character; Jerusalem Artichoke - another FOS-containing root crop