What makes something a weed?

On a gardening show yesterday, this guy shows a table full of potted plants. Most of them are green leafies, and looked pretty much to me like any other houseplants. One of them even had little flowers, sort of “baby’s breath” type flowers. Lo and behold, it turns out that he is talking about weeds! All these plants are pests, and he starts telling how to kill each one.

Huh? I had always thought of weeds as those green, leafless sticks that look sort of like wheat stalks, but in general have no aesthetically redeeming characteristics. So, why is the handsome plant with the little flowers a weed?

As told to me by an old greenskeeper “Anything that appears on your lawn that you don’t want there is a weed.”

Benlormat has it spot on. Although various definitions of weeds are floating around by far the most widely accepted one, and the only one that works, is “a plant where it is not wanted”.

And it really is that simple. Far from being plants with no redeeming characteristics many of the world’s worst weeds are plants of great beauty. It was there attractiveness that led people to move them from their natural environment in the first place, and in many cases once they had been moved they rapidly became weeds.

However weeds can also be indigenous to an area. Most of the world’s weeds fall into that category. An oak tree in a wheatfield is indisputably a weed, which is why so much effort was spent eliminating them before cultivation.

And as you can see there are various categories of weeds. There are economic weeds such as the weeds that compete with commercial crops and cost money in a very direct sense. There are environmental weeds like the punkwood invading the everglades that don’t cost money directly but that destroy the ecological value of land. There are aesthetic weeds like crabgrass that are unwanted simply because they are considered unattractive. There are medical weeds like poison ivy that are unwanted because they pose a physical risk to people or animals. There are also several other possible classes of weeds that don’t fit neatly into any of those categories.

The simple fact that a plant is attractive doesn’t in any way stop it form being a weed. An attractive plant can even manage to be an aesthetic weed, as odd as that might seem. While baby’s breath might seem pretty in isolation I’m sure you would think differently if your entire lawn were choked with it.

The usual cliché is ‘any plant that grows somewhere that the gardener doesn’t want it is a weed’ (or something like that), so potatoes could be considered weeds if they grow from leftover tubers, in the middle of this year’s carrots.

However, the general characteristics of ‘problem’ weeds would be; fast, persistent or invasive growth, a tendency to choke other plants, prolific reproduction, unattactive appearance or thorns/spines etc.

There is no botanical disticntion though; ultimately, all garden plants are derived from wild ancestors; some through a process of intensive cultivation, but some with little or no change from their wild counterparts.

One man’s ‘invasive creeping weed’ can very easily be another’s ‘ideal ground cover’.