Gadenin日本語Get the appWhat is actually happening under the soil
Yacon builds outward and upward at the same time. The growing crown at the center of the plant enlarges each season and sits progressively higher, so a crown planted two inches (5 cm) down in spring is often part-exposed by late summer, with pink buds visible at the surface. Meanwhile the eating tubers swell out sideways from the crown and shoulder the soil upward and apart, cracking the surface into a low dome around the stems.
Both of those create the same three problems. The crown, which is next year's entire planting stock, is left sitting in the open where an early frost can reach it. Tubers pushed into the light develop hard green or purplish patches and a bitter flavor under the skin. And the plant, top-heavy on a shallow crown, becomes far easier for wind to lever over.
Hilling, or earthing up, is simply drawing loose soil from between the rows up around the base of each plant to fix all three at once. It is the only routine physical job the crop asks of you, and it takes a few minutes per plant, two or three times in a season.
When to hill and how much
Start once the plants are around a foot (30 cm) tall and repeat as the season goes on. Do not do it all at once at the start: burying a small plant deeply chills the crown and slows it. Build the mound gradually, so that by late summer you have a broad mound six to eight inches (15 to 20 cm) high and eighteen inches (45 cm) across at each plant, with the sides sloped rather than heaped steeply.
| Stage | Plant height | Soil to draw up | What it is doing |
|---|---|---|---|
| First hilling | About 12 in (30 cm) | 2 to 3 in (5 to 8 cm) around the stems | Steadies the young plant, buries early weeds |
| Second hilling | About 3 ft (90 cm) | Another 2 to 3 in (5 to 8 cm) | Covers the rising crown, anchors the stems |
| Third hilling | Full height, before autumn winds | Top up to 6 to 8 in (15 to 20 cm) total | Keeps swelling tubers dark, protects the crown from frost |
| After heavy rain | Any stage | Repair washed-out sides only | Stops the crown being exposed again |
Use a draw hoe and pull soil from a wide area rather than digging a trench beside the plant. Tubers run out to eighteen inches (45 cm) from the stem and a hoe blade driven in close will slice through them without you feeling it.
Mulch instead of soil, where soil is short
On a raised bed, in a container, or on thin ground where there simply is not loose soil to spare between the rows, a thick mulch does the same job. Pile six to eight inches (15 to 20 cm) of straw, leaf mold or coarse compost around the base and top it up as it settles. It keeps light off the tubers, insulates the crown, and holds moisture through the hot weeks when the tubers are filling.
The trade-off is that a straw mound gives slugs a permanent damp shelter within reach of shallow tubers, and it does not weigh anything, so it contributes nothing to holding a top-heavy plant upright. On an exposed site use soil for the first two hillings and mulch only for the final top-up, and pull the mulch back from the stems in autumn once the tops are dead.
In a large container, aim for a pot at least fifteen to twenty gallons (55 to 75 liters) and leave three inches (8 cm) of headroom at planting specifically so you can top it up during the season. A container yacon that cannot be earthed up ends the season with its crown sitting proud of the compost.
Hilling and support are the same job
A yacon plant at full height carries a heavy head of large leaves on hollow, brittle stems, anchored on a crown only a few inches down. A well-built mound of firmed soil is a real anchor and settles the question on most sheltered sites. On open ground it is not enough on its own.
Where wind is a factor, drive a stake alongside each plant at the second hilling, while you can still get to the base without breaking stems, and tie loosely at three feet (90 cm) and again at five feet (1.5 m). Do it then rather than later: once the plants close over, walking into the row snaps stems, and a snapped yacon stem does not recover, it simply stops.
A plant blown flat in early autumn is a real loss, because yacon puts on a large share of its tuber weight in the last month before frost. Losing the leaves at that point costs weight you cannot get back.
Note the dates of each hilling and whether the crown was showing when you got there. If it was already exposed at the second pass, you are hilling too late for your site and should bring the whole sequence forward a few weeks next season.