Shan Yao, or Chinese wild yam (Dioscorea opposita, Dioscorea oppoistifolia, Dioscorea batata) is both a nutritious food and a medicinal herb, tonifying the Spleen, Lung and Kidney qi. The dried herb can be bought and used in cooking or in raw herb formulas, but you can also find the fresh tubers in many Asian grocery stores. Better yet, grow the hardy, easily propagated perennial in your garden!
The tubers can be boiled, baked, fried, mashed, grated or added to soups or stews. They have a nice mild flavor reminiscent of a floury potato, though superior in both taste and nutrition to the potato. They store well for an extended time, but can also be left in the ground to be harvested as needed during the winter season. In some regions of Asia, they are eaten in quantity and grown as a staple food crop, as well as grown for harvest to be dried and sold in herb stores.
Many people think of yams as tropical plants, therefore unsuitable for cultivation in this country, however there are a few species that come from temperate zones that thrive well here. Dioscorea opposita is a native species found growing wild in the mountains of northern Japan and on the sunny slope of hillsides in many regions of China. These species tolerate temperatures down to about -15 F, are hardy to zone 5, and easily grown outdoors in most parts of North America.
Growing Shan Yao in the Garden
Dioscorea opposita, or batata, is easily grown, preferring a sunny location, though it will do fine in part shade and can survive in almost any situation ranging from full sun to full shade. In the wild, it grows best in the intermediate light levels along forest edges and stream banks.
The plant is very hardy and can grow and propagate in a variety of different habitats and environmental conditions. It likes fertile, rich, loamy soil where the root can grow down deeply. In good conditions, roots can grow up to 3 feet long and weigh 4 pounds or more.
A vigorous, twining, climbing plant, it can reach 8 feet or more in height, sending out long shoots each year. It may be grown like runner beans up a frame or bamboo trellis, or if you have a good deal of space, the shoots may be left to grow on the ground. They can be trained to grow almost anywhere, along the fence or wall, meandering along any terrain, or allowed to climb into surrounding shrubs and trees.
Plants should be watered regularly and soil kept moist, but not over-watered. Soil pH requirements are broad and plants do well in conditions from ranging from mildly acidic (6.1 to 6.5) to neutral (6.6 to 7.5), or mildly alkaline (7.6 to 7.8).
Chinese wild yam is also sometimes grown for its ornamental value and the twining vine is attractive grown on arbors, trellises, and porches. The flowers are pale pink to white, blooming in late summer to early fall with a cinnamon-like fragrance, hence its common name "Cinnamon Vine". The flowers are dioecious (individual flowers are either male or female, with only one sex found on any one plant) so both male and female plants must be grown if seed is to be harvested for propagation.
Propagation is quite simple, achieved by either 1) replanting the top portion of the root, 2) planting the small tubercles formed on older plants, or 3) by stem cuttings taken in the late spring.
In the first method, after harvesting the root in the fall, cut off the top few inches of the root and store in a cool, dry place for the winter. This piece can then be replanted in early spring, while the rest may be cooked for food. It is best to wait to remove the top portion until you want to eat the remainder of the yam, it stores better when kept in one piece.
Another easy method of propagation is achieved by harvesting the small tubercles (pea-size baby tubers that look a little like small bulbs) formed in the leaf axils along the stems (see photo). These can be treated like seed. Collect them in late summer or early fall, once they are easily detached and fall freely from the plant. Store in a cool, frost-free place over the winter being careful not to let them dry out, or they can be potted immediately and left in an unheated greenhouse or cold frame, keeping the soil moist but not wet. They will remain dormant in the winter and come into growth in the spring. Plant seedlings in the ground in the summer when they are in active growth.
Plants grow easily propagated by either method, from tubercles or from a piece of the main root, and will produce harvestable tubers of over a pound in weight after the first year of growth. If the plants are left in the ground, the second year tubers will increase to 5 or more pounds.
Because Chinese yams produce a very vertical root, it is possible to grow a number of plants quite close to each other, spaced about 8-12 inches apart. Leaving the plants in the ground for 2-3 years will increase the overall yield per plant considerably. Exceedingly high yields are possible, certainly quite a bit higher than potatoes and with none of the disease problems associated with that plant.
The tuber grows in the shape of a club, about as thick as an adult's finger at the top, thickening to the size of an arm at its base. Harvesting the root is the most difficult challenge with the plant as the roots are large and grow quite deep. The tubers can be dug in the fall, like most root crops, since at this time the plant has stored its nutrients in its roots for the winter. Or it may be left in the ground to be harvested as needed during the winter season. It is recommended to leave plants in the ground to grow for a second year when possible, as they will become considerably larger, achieving full maturity in 3-4 years.
Because one has to dig down quite far to retrieve the tubers, this can cause disturbance to other nearby plant roots, so should be taken into consideration when choosing a planting site. Dioscorea opposita (or batata) is considered a very good potential commercial crop, the main obstacle being the development of a simple harvesting method for the deep growing tubers.
Cautionary Planting Practice
The plant is fast growing and can become invasive if left unattended for many years. The twining vine has the ability to rapidly invade wild habitats, with both quick growing vegetation and prolific asexual reproduction via the small tubercles that seed themselves easily.
Be careful that it does not outgrow other garden plants as it can create a thick blanket, competitively excluding light. Without occasional thinning and care it may also weight down and break the branches of large trees and shrubs. In the wild, an entire stand of native shrubs may become covered by Dioscroea opposita, causing total shade conditions and eventually killing the stand.
Precautionary practice requires harvesting the tubers in the fall within the first few years of growth, and deadheading plants to keep the leaf tubercles from propagating volunteer seedlings, creating the next season's runaway crop. If these measures are taken, the plant is easily controlled and will be a joy in the garden and kitchen.
Shan Yao tonifies the qi of the Spleen, Lungs and Kidneys. As a Spleen tonic it is particularly useful for treating diarrhea, chronic loose stool and poor appetite, and is a key herb in the formula Shen Ling Bai Zhu San. It also treats cough and wheezing due to Lung qi and yin deficiency and is commonly used in formulas for diabetes. It is an ingredient in many Kidney tonic formulas as it is neutral in temperature and non-cloying, therefore easy to digest. Due to its mild astringent nature, it is also used in cases of urinary frequency, spermatorrhea, and excessive vaginal discharge.
As a "food herb" Shan Yao is fairly mild, and has no significant side effects. It gently tonifies deficiencies, slowly over time, rather than giving the quick physiologic results of some herbs with stronger and more specific natures. Long-term consumption as a medicinal food increases strength and vitality over time.
The tuber is also used externally, applied to ulcers, boils and abscesses. It contains allantoin, a cell-proliferant that speeds the healing process, and the leaf juice can also be used to treat snakebites and scorpion stings. (Plants for a Future 1997, Tu, 2002). The roots contain diosgenin, a compound used in the manufacture of progesterone and other steroid drugs, and commonly used in naturopathic medicine in the treatment of various disorders of the female reproductive system.
Buying Plant Seeds and Starts
Generally found in plant nurseries specializing in Chinese herbs, Shan Yao is usually sold as a small plant in the spring or early summer. Below are a few reputable sources that carry this and other high quality Chinese herb plants.
Stir Fried Shan Yao (Chinese Wild Yam)
"Chinese Herbal Medicine Materia Medica" by Dan Bensky, Steven Clavey, Erich Stoger, 2004
"Growing At-Risk Medicinal Herbs: Cultivation, Conservation and Ecology", by Richo Chech, 2002
"Planting for the Future: Saving Our Medicinal Herbs", edited by Rosemary Gladstar and Pamela Hirsch, 2000
"Plants for a Future: Edible Medicinal and Useful Plants for a Healthier World" by Ken Fern, 1997
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