Dioscorea batatas - Chinese Yam

Young vine (2 years) showing yields of bulbils. Older vines make much more, though this year our largest vine is serving as a trellis for hardy passionfruit. We have a new polyculture planting which we think will optimize production and harvesting of this interesting and tasty crop.

Here's what the roots look like when grown in deep rich soils in raised beds. Often use removable planks on sides of beds for easy harvest of delicate tubers. From an Asian market in New Haven Connecticut.

For years I thought of this as a very minor food crop for perenial polycultures. The roots are a major staple in Japan but are essentially slow annuals: deep delicate taproots that take several years to mature and kill the plant upon harvesting. These taproots are very delicious - if you have too many plants they can be dug (with care) and they are quite the gourmet root crop, growing quite large as well.

The vines are also a great ornamental, with wonderful cinnamon-scented flowers.

The plants produce small aerial tubers or bulbils, which I always assumed were a novelty food or even a nuisance. Eaten raw, they are kind of starchy and mucilaginous. I figured they were just a tease to remind us that we can't grow "real" air potatoes (D. bulbifera). But last year (2008) our vine started producing huge amounts of bulbils and I boiled some up. To my great surprise they tasted very much like new red potatoes, slightly waxy but excellent with butter and salt while still warm.

I think our four year old vine might have made 2 gallons or more of these pea- to chick pea-sized bulbils last year.

Since then I have been imagining production trellis systems. Vines trellised on poles or even pollarded or heavily pruned nitrogen fixing trees or shrubs with wires stretched between. Laying out a tarp underneath would allow for most efficient harvest, as the tubers drop over a long period of perhaps 6 weeks. With some refinement of best production methods this may prove to be a storable tasty perennial no-dig starch crop for cold temperate climates - something in very short supply here. Anyone who wants some ideas on trellis construction etc. pop me an email at toensmeier@gmail.com.

Photo: taproot plus aerial tubers with Felco pruners for scale. Taproot would be much larger in loose, fertile soil (this was compacted construction fill). Estimated tuber yield from one vine 2 gallons in 2009.