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As a garden crop yacon is remarkably untroubled. The leaves are large, rough and slightly resinous, and nothing routinely strips them. There is no equivalent of the pest that reliably finds your brassicas or your potatoes. If you have come to this expecting a spray schedule, there is not one, and that is genuine rather than an omission.
The consequence is that almost every yacon failure is caused by handling, water or temperature rather than by an organism. The list below is short and it is worth reading as a list of your own likely mistakes rather than of enemies.
| Problem | First sign | What to do |
|---|---|---|
| Bruising at lifting | Soft brown patches days after harvest | Cull affected tubers, lift more gently next year |
| Crown rot in store | Soft, dark, foul-smelling crown in midwinter | Cut back to firm tissue, dry the box, reduce damp |
| Crown dried out in store | Shriveled crown, buds shrunken and dead | Add slightly damp packing material, check monthly |
| Slug and snail grazing | Shallow holes in exposed tubers, rasped stems | Hill up so tubers stay covered, pull mulch back in autumn |
| Wireworm or grub tunnels | Narrow holes through tubers, common after grass | Cut out damage, use those tubers first |
| Late frost on young shoots | Blackened growing tips in spring | Recut nothing, re-cover, crown usually reshoots |
| Wind damage | Snapped hollow stems, plant leaning | Stake early next season; snapped stems do not recover |
| Green patches on tubers | Hard greenish or purplish skin, bitter taste | Trim off, hill up earlier next year |
Bruising is the biggest single loss
More yacon is lost to careless handling than to everything else put together. The tubers are thin-skinned and hold a great deal of water, and they bruise the way a ripe pear bruises. A knock that would not mark a potato leaves a patch that goes brown and soft within three or four days and then spreads until the whole tuber is lost. The damage is usually invisible at the moment it happens, which is why people do not connect the losses found in store weeks later with the way the crop was handled at lifting.
Everything follows from that. Do not tip yacon into a bucket. Do not stack it in a deep heap where the weight of the pile bruises the bottom layer. Do not carry a plant by its stems and let the tubers swing. Do not scrub soil off with a brush. Lift onto a sheet, carry in shallow wide trays, and move each tuber individually with two hands if it is a big one.
Sort strictly before storing and put anything marked, cut, or with a torn neck into the pile you will eat this week. One rotting tuber in a tray will take the ones touching it.
Losing the crowns over winter, which loses you the crop
The crowns are the propagation stock and they are stored quite differently from the eating tubers. They are not frost hardy, so they cannot stay in the ground anywhere that freezes, and they are alive rather than dormant in the way a seed is, so they can be killed by drying out just as easily as by rot. Losing them means starting over from bought material next spring, whatever kind of harvest you had.
Lift them with the crop, trim the stems to about an inch (2.5 cm), and leave a little soil clinging rather than cleaning them right down. Pack them in barely damp sand, coir, leaf mold or old potting mix in an open box, and keep them somewhere frost free and dark at around 40 to 50F (4 to 10C). Barely damp means the packing holds together if you squeeze it and no water comes out. Too wet and the crowns rot; bone dry and the buds shrivel.
Check the box once a month through winter. Cut away any soft, dark, foul-smelling patch back to firm white tissue and let the cut dry; a crown can lose a third of itself and still produce good plants. If the packing has dried out, mist it lightly. If the crowns feel wet or the box smells sour, repack in drier material and improve the airflow.
A far simpler alternative, where winters are mild enough that the ground does not freeze, is to leave one or two whole plants undug in a well-drained spot, mulched deeply, and lift them in late winter for dividing. Do this as insurance alongside a stored box rather than instead of it.
Losing every crown is recoverable if you catch it early: order or beg replacement crowns in late winter while other growers are dividing theirs. Discovering it in late spring means missing the planting window and losing the whole year.
Frost at both ends of the season
Yacon is caught by cold twice. In spring, a late frost blackens the young shoots. This is rarely fatal, because the crown sits below the surface and usually pushes new shoots within two or three weeks, but those weeks come out of a season that already needs six or seven frost-free months. Cover young plants with row cover or an upturned pot if a late frost is forecast; it takes minutes and buys back a fortnight.
In autumn, the first frost ends the season and starts the harvest. That is not a hazard, it is the signal. The hazard is the hard freeze that follows it, which can reach down and damage tubers left in the ground. Once the tops are blackened you have roughly a week of grace in most climates, less if a serious cold spell is forecast. If in doubt, lift.
The other cold hazard is at the storage end: a garage or shed that stays above freezing in an ordinary winter but not in a cold snap. Frost in the store kills the crowns outright and turns the eating tubers to mush. A minimum-maximum thermometer in the storage space, checked when you check the boxes, is worth the small cost.
Keep a record of what you lost and when
Note how much of the crop you culled at sorting, how much went soft in store and in which month, and how many crowns survived to spring out of how many stored. These three figures, tracked over two or three years, tell you which part of your process is actually failing, which is almost never the part people assume.
Note the date of the last spring frost and the first autumn frost as well. Yacon lives entirely between those two dates, and having your own site's numbers written down is worth more than any general advice about when to start.