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The Chinese or Hardy Yam

A plant profile on a very promising food source from Brad & Shane Forsythe

Dioscorea batatas (syn. D.opposita); Dioscoreaceae family

After about 6 years of searching private collections and placing an add in the Seed Savers Network’s newsletter, Shane & I finally tracked the plant down a couple of years ago growing in a friend’s garden at Bundanoon, and this winter, we have received a 40cm tuber from them.

yam1 yam2

One of the cold-hardiest species of the Dioscorea genus; in its native of China and Japan, the tuber and aerial bulbils are valued both as an esteemed food, and for their medicinal properties.
The Hardy Yam is a, slender-stemmed twining perennial vine reaching an average height of 2.5-3m, and is said to be easily cultivated in a free-draining, moist fertile soil, growing best in full sun, however, it will tolerate a little shade; and holding true to its vulgar name, the Hardy Yam is apparently quite tolerant of cold winters and is said to grow “as far North as Canada” (Facciola). In very cold areas at least, it seems to die down to ground, and grows anew in Spring.

There are differing reports regarding flowering times, one states that it “flowers in Autumn” (Plants for a Future), and another says “Blooms in Summer, light purple axillary flowers forming spike inflorescence. Capsule [seed] 3-angled and winged.” (A Bare Foot Doctor’s Manual).
Some species of Dioscorea are dioecious (separate male and female plants), therefore, it is necessary to source both, if seeds are wanted (for varietal selection and breeding or genetic variation). If any readers are growing one, Shane and I would love to here from you, so we can offer seedlings, to provide some genetic diversity.
Aerial bulbils are an effective means of vegetative or clonal propagation, and these will resemble the parent, both in hardiness, texture and flavour characteristics, and disease resistance or susceptibility.

The tubers (which grow to 1m) can used in stews, baked, boiled, grated and used in soup, cooked with meat; they are variously described as having an agreeable flavour comparable to that of potato, with a floury texture (Plants for a Future), or sweet potato with a mucilaginous texture (Shipard), and possess good storage qualities.
Tubers can be dug after one year, but left for a few years will be of larger size; there are no references as to whether the tubers become fibrous with age.
“Aerial tubers (bulbils) are eaten in times of scarcity” (Tanaka), this would suggest that they may be of low palatability or quality, however, I have been assured that this is not the case as they have been served as a specialty in a high class restaurant. The aerial bulbils are said to grow about 7-9cm long and 2cm in diameter, and taste somewhat like a good potato.

Tanaka also states that there are two forms of D.batatas recognised in Japan; forma elongata “Naga-imo” and forma tsukune “Tsukune-imo”.

Chinese medicinal usage include stomach and spleen tonic, anti-diarrhoea, chronic enteritis, dysentery, poor indigestion, asthma, et. al., nourishes lungs and complements the kidneys. I have included this only to indicate ethnobotanical usage- consult a professional if considering medicinal uses.

In July, after much arduous and very careful hand digging, Shane unearthed a 40cm long, and 7-8cm thick, a pale-yellowish, white tuber of the hardy yam, covered in a mass of coarse hairy roots.
This we wrapped carefully and took home to plant. Our vegie garden soil is a rich clay loam, made fertile over many years by sheep and chooks, and compost, Shane added a wheelbarrow load of coarse sand, and some more compost for good measure, then the tuber was carefully planted to the correct depth, mulched with dead grass and leaves, and protected from birds, etc.
We hope to see it sprout in the next month or two, and will eagerly await the results of the next 7-9 months of growth, before it goes dormant next winter.
Shane & I would like to thank Howard & Trisha at Bundanoon Village Nursery for allowing us to dig up their only known tuber.

References:
Facciola, S., Cornucopia II
Plants for a Future, Online Plant Catalogue
A Bare Foot Doctor’s Manual – The American translation of the official Chinese Paramedical Manual, (1977),
Running Press, Philadelphia, Pennsylvania.
Shipard, I., (2003), How Can I Use Herbs In My Daily Life, Published by David Stewart.
Tanaka, T., (1976), Tanaka’s Cyclopedia Of Edible Plants Of The World, Keigaku Publishing Co., Tokyo, Japan.

J47 Spring 2005 -Summer 2006