I Think, Therefore I Yam

I'm not misquoting the late, great Rene Descartes, natural philosopher and mathematician, whose phrase cogito ergo sum has been spouted ad nauseam by have-a-go intellectuals for years. Nope, that's not what I mean.  Neither am I using the word yam as an obscure verb to describe my penchant for eating in a manner famished, nor as an indication that I am spouting nonsense in an animated fashion. It is true, however, that I can and will do both of these if circumstances demand it.

What I mean is that all right thinking people, gardeners and natural philosophers ought to investigate the edible potential of the Chinese yam (Dioscorea polystachya). This is a member of the great and still thoroughly extant genus Dioscorea, which inludes many other edible species.

The Chinese yam comes from temperate areas of, you guessed it, China, along with Korea and Japan.  It's also found as an introduced (read: highly invasive) plant in the USA and should not be planted in those parts where it is likely to be a problem. It's a dioecious (male and female flowers on separate plants) climber and not unattractive. It's also vigorous, as this picture taken last year at Frank van Keirsbilck's garden shows: estimated height 4 metres. The lack of a suitable pollination partner doesn't bother it one little bit. In lieu of true seeds, the Chinese yam produces large quantities of bulbils, or more correctly, tubercles, in its leaf axils. These drop off and establish new plants, hence its potential as an invasive weed.

My understanding (correct me if I'm wrong) is that the majority of plants under cultivation are male, so true seeds are rarely formed. If and when they do develop, they're probably produced in seed pods that look something like these on  D. caucasica, which I took in Ghent last SeptemberAs well as being consumed as a root crop, it is also used in Traditional Chinese Medicine for numerous complaints.

Strangely, Chinese yams have attracted the attentions of a philosopher of an altogether different ilk: Rudolf Steiner. Steiner, the founding father of Biodynamics, thought very highly of the Chinese yam, due to its unique ability, in his opinion, to store light ether in its roots. According to Steiner, this made its cultivation in Europe essential to maintain human health. He envisaged it replacing the good old spud as a staple, due to the latter's tendency to make both people and animals materialistic. I think he meant the opposite of spiritual rather than an atavistic compulsion to hang around shopping malls.  So what on earth is "light ether"?  To me, all this is not only etheric, but esoteric.  The fact that Usain Bolt, sprinter extraordinary, is supposed to attribute his speed to the Trelawny yams he grew up eating in Jamaica, just adds to the peculiar allure of this plant.  But surely the Trelawny yams aren't  D. polystachya, as some reports I've seen suggest, but D. cayensis. 

Image courtesy of Dr Markus Heyerhoff
The Germans seem to have taken Steiner at his word and are now growing the Lichtwurzel (light root) on a limited scale, particularly in the Bodensee region.  Cultivation practices look somewhat elaborate, involving greenhouses and wooden boxes.  Several companies are now marketing the roots and products derived from them.

I contacted Dr Tobias Hartkemeyer at the University of Kassel, located in the raccoon heartland of Germany, where they have been running a research and development project on the Chinese yam: Lichtyams.  I was keen to know whether they had been able to breed any new varieties. Tobias told me he had managed to get a female plant, but this had failed to thrive and he has been unable to produce any true seed so far.

The young shoots resemble those of black bryony, (Tamus communis) the only native British climber in the same family, the Dioscoreaceae. This seems to occur in every hedgerow hereabouts and has attractive glossy leaves and in the autumn, on female plants, bright red berries.  I really like black bryony, but confusing the roots of the two species is the kind of mistake best avoided. Black bryony's roots, yam-like in appearance though they may be, are powerfully irritant and likely to send the diner on a trip to the local hospital.   Luckily, perhaps, the bryony emerges many weeks earlier than the yam and is unlikely to be confused with it.  I do wish the yam showed the same early growth as the bryony, though - it might yield much better.

I'm no stranger to the Chinese yam, having grown it several times in the past, but, if I'm honest, I've hardly ever eaten it. This is probably a shame as it really is supposed to have beneficial effects on one's intellectual, cognitive and spiritual development - according to Steiner that is. It's also very tasty, something which tends to have a greater influence on my choice of food than considerations of continuing spiritual evolution. The biggest intellectual stimulus I have had from from growing it has always occurred as I attempt to figure out how to extract the long, thin, brittle roots from the soil without breaking them.  As you normally have to wait several years before they reach a harvestable size, they also provide you with ample opportunity to develop reserves of patience.

So with all this in mind, I got myself some yam bulbils - two varieties, species even, described as Dioscorea batatas and Dioscorea japonica. These names are doubtless obsolete synonyms which some obliging taxonomist will delight in pointing out to me in due course. On the left are the somewhat smaller bulbils of D. batatas, on the right those of D. japonica.

I'm not much of a party animal, but it's often possible to pick up a few plastic cups at such events; these make serviceable pots for long rooted plants, at least in the early stages of development. Judging by the appearance of what might be politely described as finger-like protuberances from the bottoms of these cups, potting on is now required. My finger is on the right, in case you're confused. The only discernible difference I can see between the two types (species?) is the greater vigour and precocious bulbil development on the D. japonica plants.

Some American polyculture enthusiasts have abandoned the shovel and are now harvesting the yam bulbils as the main food instead.   The 'yamberries' as they are calling them, seem to yield very well in their climate in New England  giving 3-4 US gallons per plant (I think that's around 12-15 litres) in Holyoke MA.  They're certainly miniscule compared to the the fist size ones produced by the air potato, D. bulbifera, but they seem to make up for this by being produced in large quantities. Lightly toasted on a skillet, or in the oven, they are apparently very good eating. A root crop that doesn't require digging - is there no end to the diverse talents of Dioscorea polystachya?

This is an intriguing plant, with delicious roots and all sorts of associated mystique, half-truths and misinformation.  Aside from the necessity of mining the roots rather than harvesting them, the main problem, in our climate at least, is their late emergence in the spring and subsequent slow maturity. If plants of different sexes can be located, it might be possible to set up a Dioscorea dating agency and breed varieties that are better adapted to our climate.  There are, apparently, numerous sorts found in China, with varying shape, size and number of roots.  So, to any Chinese yam enthusiasts who have male and female plants in their possession, Radix awaits your call.


Crikey! Now I know why I want an Ipad so badly, too many spuds.
Rhizowen said…
Madeline - Overdosing on potatoes is an all-too-common affliction, particularly amongst young people. As responsible adults, we should set an example by our regular and conspicuous consumption of yams in their presence. Every little helps.
Frank said…
nice info there! I'm lucky if I can harvest 100 grammes of small bulbils each plant, and they harvest that much?? I'm impressed...They actually have a very nice taste, and this year they seem to be a bit bigger over here. I'll try and dig up (in one piece!) one of these five or six year old plants, I wonder how big the root will be.
There's also dioscorea villosa that stands our winter. I tried to grow it a few times (even from seeds), but for some strange reason it disappears after planting out. This one is grown in Germany as well, but probably only in small gardens.
Mr. H. said…
So we we have this terribly long list of new things to try in the gardens every year as it never ceases to amaze us what will actually do well in our northern climate. Anyway, next years list has three types of yams from a company called Horizon Herbs on it and I am not sure which one to try or maybe even all of them.

They have Dioscorea quaternata (American wild yam) sold as seeds and dormant roots...these are supposed to be hardy to -10°F. The other two are Dioscorea batatas and japonica.

Any thoughts on whether or not the latter two would be as hardy as the first?
Anonymous said…
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Anonymous said…
I've tried D. bulbifera, D. batatas and D. japonica here in Wales. Batatas and Bulbifera died out the first winter but Japonica is still ticking along and in it's third year now.

It hasn't exactly thrived, but it appears to be getting stronger with each passing season. It may actually produce a bulbil or two at some point, but I'm not holding my breath.

I was hoping that Bulbifera would survive as the bulbils were a much better size, but as it was most likely the toxic form it's probably for the best that it wasn't hardy.
Brianj said…
Mr. H,

I tried growing Dioscorea batatas in southern Maine this past spring/summer. Grown amongst a pile of sticks in silt soil and getting partial sun, the vines didn't grow more than few inches in length. They were attacked by slugs as well.

Plants for a future lists Batatas as hardy to zone 5. Oikos Tree Crops sells them and says -20F.

My guess is that they need sandy soil to grow well and overwinter. They may need high trellising to avoid slug damage.

I have tried to find people with success stories in New england but only found mention of it in the comment section of this post:

Mr. H. said…
Thanks everyone, after much reading and considering our particular gardening conditions (and the price) I ordered 20 Dioscorea Batatas aerial tubers from Horizon Herbs...wish me luck.:) Summer Hill Seeds has them listed as hardy to zone 4...we are in 5b.

"This lovely vine has shining, heart shaped leaves with cinnamon-scented white blooms. Hardy to zone 4, Cinnamon Vine grows from 10-20 feet in full to part sun and well drained soil. Large edible tubers are formed that can reach as much as 3 feet long and deep."
Rhizowen said…
In our climate I find them too slow to get going, which is I presume a function of our cool springs. Slugs can and do eat the emerging shoots which does nothing to speed their growth either. In a greenhouse or tunnel, they are positively exuberant.
C Robb said…
it must be the patience required that leads to spiritual edification.
Anonymous said…
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Bob Willis said…
I believe the problem of the long tuber and being able to dig it up, is resolved by growing it in a 'gutter' of say, 2" plastic pipe cut in half lengthways and maybe 4" below ground level. See BD Growing mag No. 20.

Bob Willis
Anonymous said…
Yams are yummy!Gardening bloggers are funny!