Psophocarpus tetragonolobus - not just a name to conjure with, but a useful tropical crop that's commonly known in English as the winged bean. The pods have extravagant flanges from which its name derives and pods, seeds, flowers, leaves and swollen roots are all edible. They say every bit of a hog can be used, from its tail to its squeal - the same is apparently true of the winged bean. If you're interested in its potential, you can read all about it here in a venerable document from the 1970s. Suffice to say, winged bean has generated considerable enthusiasm among researchers and is a member of that elite corps, nitrogen fixing root crops.
Winged bean loves heat and humidity. I've tried to grow it outside here on several occasions, but to no avail. Cornwall is certainly humid, but, although it's said to be the warmest part of the country, this is a partial truth worthy of estate agents and tourist boards. Warmest in winter is more accurate. Even that's not strictly true - it's just less cold than most other parts of the UK. As a corollary, our summers are generally cooler than other areas of southern Britain, due to the moderating influence of the sea.
So growing winged bean outdoors in the UK seems to be an exercise in futility. My guess is that if you have the kind of summers where you can lounge around in a Hawaiian shirt all night and not get in the least bit chilly, you can grow winged bean in your garden. But, even if you are able to provide it with the right climate, most varieties are daylength sensitive and refuse to flower at a sensible time of year when grown away from the tropics. But not all: meet Hi-Flyer, a variety bred by the USDA that has the potential to flower in our long, often-not-so-hot summer days.
I've been fooling around with Hi-Flyer on an occasional basis for more than a decade. I think I last grew it back in about 2003 in an attempt to regenerate my seed stocks. And I was successful in this endeavour - my single plant grew, flowered and formed a couple of pods, all on a not particularly sunny windowsill, in a not particularly warm house. The sky blue flowers were attractive - big and bold and yet somehow rather delicate; I wish I'd taken a picture of them. The pods were a sight to behold too; once again I regret failing to capture their architectural quality.
This year, I thought I'd kill two birds with one stone: replenish my supply of seeds and finally get around to eating the roots. In Papua New Guinea, the winged bean is particularly popular and is known by the Tok Pisin name of "asbin". Asbin roots are considered a delicacy and special sing-sings (festivals) are organised to celebrate the harvest. I wasn't exactly envisaging a lavish shindig: there was only enough space on the windowsill for two small plants. Opinions on the flavour and desirability of the roots vary, but seem to coalesce around "nutty" "beany" and "earthy".
I sowed seeds in about March and plants finally emerged; I potted them on and left them on the windowsill. For a while they grew well, then suddenly they stopped growing and all blandishments in the way of repotting, feeding and watering were as nothing. Not a single flower bud appeared on either plant. Scratching around in the compost, however, it was clear that there were some thickened roots. It's well known that other leguminous tuber crops do better when their flowers and pods are removed; perhaps this is the case for winged bean and I had inadvertently created the right growing conditions for tuber formation. I'm utterly mystified as to why they refused to flower, especially as this has never been a problem in previous seasons.
So, for some unknown reason, Hi-Flyer barely got off the ground and could be said to have nosedived, at least in the case of sexual reproduction.
I'm now debating whether I should spare both roots, plant them next season and delay gratification until fresh seed stocks have been produced, or just plough on regardless, eat the roots and repent at leisure if my remaining seeds prove unviable - Radix's reworking of the Goose That Laid the Golden Egg. Let me know your thoughts: the fate of these two plants lies in your hands. In any case, I reckon Hi-Flyer winged bean might be worth growing in a greenhouse or conservatory as an all-purpose edible plant for those closet permies out there; you know who you are.