Gadenin日本語Get the appYou plant the crown, not the tuber
This is the single thing that ruins more yacon crops than anything else, so take it slowly. A yacon plant makes two completely different things underground. Out at the edge of the plant, on the ends of short stalks, sit the storage tubers: large, smooth, tapered, pale brown or pinkish, often a pound (450 g) each. Those are what you eat. They have no growth buds anywhere on them and they will never sprout, no matter how you treat them. Plant one and it simply rots.
At the center, directly under the old stems, sits a knobbly reddish or purple mass about the size of a fist or larger, covered in small pink and white growth points. That is the crown, sometimes called the corona or the rhizome. It is woody, unpleasant to eat, and it is the entire propagation stock of the plant. Every new yacon plant comes from a piece of crown carrying at least one of those buds.
Look at a lifted plant and the difference is obvious once you have seen it. The eating tubers are smooth-skinned and detach cleanly with a little stub. The crown is lumpy, tightly congested, has visible pink shoot points, and everything is fused together. If you cannot see a bud on a piece, it will not grow.
| Part | Where it sits | What it looks like | Use |
|---|---|---|---|
| Storage tuber | Outside ring, 8 to 18 in (20 to 45 cm) from the stems | Smooth, tapered, pale brown to pink, no buds | Eating only, never replants |
| Growing crown | Directly under the old stem bases | Knobbly, reddish purple, visible pink shoot points | Propagation, saved and stored frost free |
| Old stem stubs | Top of the crown | Hollow, dry, snap off easily | Trim to 1 in (2.5 cm), keep as a handle |
| Fibrous roots | Throughout, threading between tubers | Thin, stringy, white to brown | Discard |
Timing: a long season with frost at both ends
Yacon needs roughly six to seven months of frost-free growing, around 180 to 210 days, to fill its tubers properly. The tops are killed outright by the first light frost, so the season ends when it ends and there is no extending it. That means everything depends on starting early enough at the other end.
Plant out after the last expected frost, once the soil has reached about 55F (13C) at planting depth. Yacon is not remotely hardy as a growing plant and a shoot caught by a late frost sets the whole crop back weeks even if the crown survives. In a short-season garden, start the crown pieces in pots four to six weeks before that date, in a frost-free place at 60 to 70F (16 to 21C), and set out rooted plants instead of dormant pieces. Those weeks come straight off the harvest date.
- Wake the crowns first Bring the stored crowns out into the light and warmth in late winter, before you divide them. Within two or three weeks the buds swell and color up, which is what lets you see where to cut. Dividing a cold dormant crown is guesswork.
- Divide into pieces with buds Cut with a clean sharp knife into pieces roughly two to three inches (5 to 8 cm) across, each carrying two or three visible buds. Fewer buds is a slower start; a huge undivided crown makes a congested crowded plant, not a bigger one.
- Dry the cut faces Leave the pieces in a dry airy place at room temperature for two to three days so the cut surfaces callus over. Planting a wet cut face into cold soil is the main cause of pieces rotting before they shoot.
- Pot up or plant out Pot into a four to six inch (10 to 15 cm) pot of ordinary potting mix, bud just under the surface, or plant straight out if the soil is above 55F (13C) and frost is genuinely past. Keep barely moist, not wet, until shoots appear in two to four weeks.
Space, depth and soil
Give each plant three feet (90 cm) in every direction, with rows three to four feet (90 to 120 cm) apart. This looks absurdly generous when you are setting out a piece the size of an egg, and it is exactly right by midsummer, when the plant stands five to seven feet (1.5 to 2.1 m) tall with broad rough leaves and a two foot (60 cm) spread of tubers underneath. Crowded yacon makes plenty of stem and a poor tuber crop.
Set the crown piece so the buds sit about two inches (5 cm) below the surface, no deeper. The crown works its way upward as the plant grows and the tubers swell, which is why earthing up matters later, but burying it deeply at planting only slows emergence in cold soil.
The soil wants to be deep, loose and free-draining, because the tubers are brittle and swell horizontally: a compacted pan at spade depth gives you short stubby crooked tubers. Dig or fork the planting station to a full spade's depth and mix in a bucket of well-rotted compost per plant. Yacon is not a heavy feeder and does not want fresh manure, which pushes stem growth at the expense of tubers, but it does want the ground open. Slightly acid to neutral soil suits it; it is unfussy about pH otherwise.
If your ground is heavy clay, plant on a low ridge or in a raised bed rather than trying to improve the whole plot. Yacon tolerates poor fertility far better than it tolerates a wet, airless root zone.
Write it down at planting
Record the date you set the plants out, the position of each plant, and how many buds each crown piece carried. Yacon crowns multiply every year, so within three seasons you will have far more planting material than you need, and the only way to know which stock is worth keeping is to have written down what you planted where.
Also note the soil temperature on planting day and the date the first shoots broke ground. The gap between those two, compared across seasons, tells you plainly whether you are planting too early into cold ground or leaving free growing weeks unused at the start of a season that frost will close at the other end.