As I was looking up the growth habits of the various legumes that grow wild on the holding here I came across some interesting information about bitter vetch: Lathyrus linifolius. It is a perennial also known as heath pea, and in the gaelic: cairmeal, or corra-meille. As I said before, it’s one of the earliest vetch to flower, coming into bloom during May, but still with flowers to come now in early July. The little bright pink pea flowers fade to blue or beige. As the tiny pea pods ripen, they first swell then shrink a little and turn black before splitting and spiralling the tiny seeds away. The seeds are very tiny, and probably mildly poisonous – a paralysis disease can result from eating significant quantities of other lathyrus seeds unless properly treated, for example leached in water, so I wouldn’t try them.
As a legume, the Heath pea should form relationships with nitrogen fixing bacteria in the soil, so adding to the soil fertility as the plant grows and dies. I was thinking of saving the seed from this and the other native vetches to see whether they would be any use as nitrogen fixing ground covers. Winter tares (Vicia sativa) is sold as an overwintering green manure crop, although it is suggested that it doesn’t like acid soil. Well as I know these vetch grow locally, logically they would make a possible alternative. Anyway, interest seems to have been sparked in Heath pea when the tubers were found by Brian Moffat during an archaeological dig of a twelfth century monastery at Soutra Aisle. His research paper proposed that the monks were using the tubers medicinally. Apparently before potatoes the cairmeal tubers were dug and dried against famine in the Highlands. The tiny tubers were alleged to save people from hunger and enable great feats of endurance, possibly being used by Roman soldiers during battle. I found various online references to this including PFAF, and my Scots Herbal book by Tess Darwin also refers to this. The tubers are said to be sweet like licorice (which is also a legume of course) and were also used to make a drink that prevented hangovers! There were several articles in the mainstream press, including the Mail and the Telegraph, although none caught my eye at the time, the possibility of a Scottish slimming aid being pretty newsworthy. It seems that there has been a bit of research going on in Scotland since. The only paper I could subsequently find online however, found no significant difference in weight change between rats fed the vetch tubers and various controls (http://strathprints.strath.ac.uk/59217/). I only could read the summary, so there may be more significant information in the rest of the article. There is also an entrepreneurial chap in Reading, who appears to be growing and selling seeds and tubers online (under the bitter-vetch tag). He (I think I’m assuming that!) gives a little information about the growing habit of the vetch: a single tuber grows the first year, if left, it bulbs up in subsequent years, and more tubers grow. The plant can be propagated from these secondary tubers as well as from the seed. Weight loss apart, I would be interested in trying the tubers. I’d come across Lathyrus tuberosa, which has larger tubers, but was put off by the fact it is described by several people as being ‘attractive to slugs’. It also prefers more alkaline soils so wouldn’t do so well here presumably. However, I know that Heath pea likes it here, although I would say it appears to prefer the slightly drier soils, possibly because it is slightly small so has less competition from more vigorous plants. I haven’t noticed slugs eating it particularly. It happily grows in grass, but presumably would grow better with less competition.
I couldn’t resist digging this tuber and have planted it in the fruit area amongst my root crops which are due for digging in autumn. There appear to be little tubers (or possibly bacteria nodules I suppose?) on the roots close to the main tuber already. I’ve collected some seed from various plants around the holding, and will try sowing some as green manures (and in pots -why not?) this autumn. If it’s edible, palatable, feeds the soil and grows well, what’s not to like? There may be some scope to increase tuber size to make it more worthwhile as a crop, but as a gourmet snack it is still interesting!