This is a question asked either by smart-arses trying in some way to catch me out or by those too dim to realise that there can be no single answer and the ensuing discussion will take several hours. The query is closely linked to the second “WHAT DOES IT DO?” I have a colleague who responds by launching into a lengthy spiel about it doing very poor Paul Robeson imitations by the end of which the questioner has invariably wandered off in disgust. Actually for some time I have come up with “Its song and dance routine is a bit sparse, but if it auditioned on the BBC, it would probably get a place in an Andrew Lloyd Webber musical” Obviously all nursery men have independently evolved similar replies. At first sight, this would seem counter-productive but experience has shown that those who ask daft questions rarely want to purchase anything; they simply want a chat because they are understandably lonely.
These days rather than asking, “What’s a herb?” the question frequently takes the form of an aggressive accusation “That’s not a herb” as though I have violated some divine edict that I should never sell anything that fails to conform to the accuser’s naïve preconceptions. Such a person is invariably disappointed when the medicinal and other ethnobotanic functions are explained to her (sorry, worthy bearers of the feminist banner but it’s a statistical fact, not sexism, that the person concerned is always a “she”). Perhaps the politest and best informed discussion of what a herb is may be found in Keith Vincent Smith’s “Illustrated Earth Garden Herbal”, Elm Tree Books 1978, in which Smith quotes Charlemagne as answering Alcuin that a herb is “The friend of the physician and the praise of cooks”. To me, it seems more likely that Alcuin, a Brit of course, provided this clever answer to a question by the Emperor rather than the other way around. My suspicion is that it has been misreported in yet another of those attempts to whitewash the posthumous reputation of the bigoted old proto-nazi.
It seems reasonable then to extend the allegedly Carolingian definition and to accept that a herb is any useful plant, not just culinary and medicinal but one that serves an essential ecological role such as providing nectar and nutrition for caterpillars and other humble members of the food chain. Do that and we shan’t go far wrong in spite of some smart-Alec inevitably trying to chuck a spanner in the works by piping up “what about Bay trees and Coriander seeds, do you count them as herbs?. It seems relevant at this point to mention that my spell-checker, although set to “English” has kept trying to turn “a herb” into “an herb” seemingly having the Americanism “an ‘erb” in its irritating robotic mind. OK then, question to robotic mind “What’s an ‘erb?” correct answer “a right pillock” but then neither the computer nor an American would understand this English colloquialism.