The Small Farm Future Blog

Weeds: Four Definitions

Posted on June 9, 2013 | 4 Comments

With the growing season now at its height, what better time to reflect on that hardy perennial close to every gardener’s thoughts – weeds? As Shakespeare nearly wrote, ‘what’s in a name – a weed by any other name would still reduce your yields’. So here’s four definitions for the botanically unloved.

The first hails from way back in the dark ages before anyone had invented permaculture and agroecology. In this view, weeds are much like their animal counterparts, vermin. They’re just born bad, like serial killers or planning officers, and there’s nothing you can do about it. Rehabilitation is hopeless – the only good weed is a dead weed…

The second definition – a well known one – evinces a more modern liberal sympathy. Weeds are ‘plants in the wrong place’. The nice thing about this one is its emphasis on the relativity of weediness – a nettle in the vegetable bed may be a weed, but in the corner of the garden it’s useful for compost, beneficial insects and food. Of course, from the nettle’s point of view it’s not in the ‘wrong’ place at all in a garden bed (though it may have chosen a poor location for an easy life). Still, at least the definition hints at this wider relativity – a weed is no more than what somebody chooses to define it as.

The third definition comes from Patrick Whitefield’s excellent book, The Earth Care Manual (which sadly seems to have gone missing from my bookshelf, so I’ll have to do this from memory). Weeds in Patrick’s definition are not so much plants in the wrong place as in the wrong quantity. This is even better than the previous definition because it emphasises tradeoffs – there are certain plants that certain people don’t want for whatever reason, but to get rid of them involves work, and some benefits may accrue from their presence. So there’s a balance to be struck between the pros and cons of the plants and the pros and cons of investing effort to get rid of them – only when that balance gets tipped too far in favour of the plant should we speak of ‘weeds’.

But maybe there’s something missing from each of these individual definitions that is better captured by combining all of them. There are certain plants that quickly occupy the spaces we cultivate, and sometimes even shapeshift so that they become almost indistinguishable from the plants we actually want. An example: many wild (weed) cereals closely resemble their cultivated cousins, but shatter and spread their seeds just prior to the harvesting of the cultivars – Indian scientists developed a reddish-leaved rice so that farmers could easily distinguish crop plants from the (green-leaved) weeds, but within a few years the shatter-prone weeds were also sporting reddish leaves…Yet another illustration of the power of natural selection.

So even though it’s true that weediness is relative (what counts as a weed partly depends on where it is, how much of it there is and who’s defining it) nevertheless there are some plants like dandelions that are just, well, weedy, whereas there are others like daffodils that aren’t, even though I personally have more time for dandelions than daffodils. This weedy habit involves rapid reproduction, quick occupation of bare or disturbed ground, a tendency to form monocultures, a responsiveness in growth to high fertility, and rapid evolutionary adaptation to the agroecosystem. In other words, it’s basically all the characteristics that we seek in crop plants, only without the payback we expect of crops. Indeed, certain crops like oats and rye were originally weeds of wheat and barley fields and only later became domesticates in their own right.

What I take from these definitions is that in any given cultivation system there are plants which from a human point of view are just bad ‘uns however you cut the deck (definition one), but they’re probably only bad in the context of that system and they may bring some benefits (definition two), so it’s worth thinking carefully about control strategies and keeping those strategies in proportion (definition three). Like death and taxes in human life, weeds are a certainty in every cultivation system – if your system has no weeds, then I’d hypothesise you’re spending an irrationally large amount of time/money/other resources on eliminating them. Either that, or I’m just jealous. So my fourth definition would be something like ‘weeds are plants of a weedy disposition (OK, OK, I know that’s circular, how about fast-growing, fast-reproducing, spreading and nutrient-taking habit) growing in such quantities as to impair the overall productivity of a given agroecosystem’.  It’s not as snappy as the other definitions, I admit. But brevity isn’t always a virtue.

The weedy habits of both crops and weeds have major agricultural implications, and in particular suggest to me some limitations of a potential perennial agriculture, a topic that I’m currently working on. But that’s for another time.