What are weeds?

woman weeding

What are weeds and why should gardeners care about them?

It is said that gardening is all about the gardener’s efforts to control nature and controlling weeds must be one of the hardest tasks that the gardener has to do.

Weeding and weeds can especially be a challenge when you are new to gardening because it’s not always easy to identify which plants are the weeds and which plants are not. They can also be a challenge when you are re-creating or reviving a garden that has been left unloved.

But, like almost anything in life, the extent to which we are troubled by weeds is largely determined by our attitude towards them.

I confess to having been an anti-weed fanatic in the past, patrolling my garden on the lookout for weeds, head down, shuffling, obsessed. But in recent times I’ve developed a grudging respect for weeds, after all, the reason that they are able so comprehensively to invade our gardens and landscapes is because they are among the most advanced plants in evolutionary terms.

Weeds succeed because they have developed extremely efficient ways of either staying alive or reproducing themselves. They may do this by sending deep tenacious tap roots down into the soil which regenerate whenever the upper parts of the plant are removed, or they may have a fast track life-cycle whereby they germinate, grow, flower and set seed all in a matter of weeks.

Different approaches to weeds

In many respects, a gardener’s relationship with weeds is likely to depend upon whether he or she gardens organically or with the use of chemicals.

The gardener who uses chemicals clearly has some powerful weapons at his disposal in his or her war on weeds.

But as well as exercising some weed control, those weapons are capable of causing a fair degree of collateral damage, whether by harming plants that the gardener wants to keep, or by more broadly damaging the garden’s ecosystem.

If you garden organically, on the other hand, you either have to be willing to accept the presence of some weeds in your garden for at least some of the time or you have to adopt and maintain a more long-term strategy of weed prevention.

Nevertheless, there are plenty of ways that the organic gardener can manage weeds and we’ll look at them in the posts in this weed control series. We’ll also look at some of the ways that weeds can be a beneficial presence in our gardens.

What makes a plant a weed?

In part 2 of this weed control series, I try to answer the simple, but not entirely straightforward, question – what exactly are weeds?

You will often hear gardeners say that weeds are plants growing in the wrong place and, although something of a cliche, this is probably the best working definition there is.

Weeds are plants like any other. They have the same requirements for light, water and nutrients as other plants and they come in the form of annuals and perennials or even trees or shrubs.

Unwanted plants

The real defining feature of weeds is that they are growing where they are not wanted.

They may be plants that we cultivate elsewhere in the garden but which have spread from their allotted place, by stealth or self-seeding. Or they may be plants that were in the garden before we were and which tenaciously hang on to their place.

They may even be plants that we unwittingly introduce – growing from seeds carried in the potting mix of plants we buy in, or from seeds which survive the home composting process and gleefully spring up when we spread the compost on our borders, bursting with the energy that the compost provides.

This explains why you might end up weeding out the tomatoes, beans and other vegetable seedlings that you may occasionally find popping up in your ornamental beds.

Noxious weeds

Weeds are especially problematic, in the garden and in the wider environment, when they are introduced into conditions for which they are supremely well adapted. Many is the plant that grows unremarkably in one environment but rampantly in another.

These are the real problem or noxious weeds that can irreparably harm native environments and cause significant financial loss to farmers and landholders.

verbena bonariensis - weed or not?
Verbena bonariensis – garden plant in the UK

This is well illustrated by my own experience when I moved from the UK to Australia.

I was shocked to see that many plants I was used to growing in the UK, such as Verbena bonariensis (Verbena or, in Australia, Purple Top), Ricinus communis (the Castor Oil plant), Arundo donax (Spanish Reed Grass), are considered to be noxious weeds.

Some are specifically banned from sale on account of the threat they pose to native vegetation and ecosystems. Likewise, Ligustrum spp (Privet) and Lonicera japonica (Japanese Honeysuckle) are respectable garden plants in the UK but on many lists of invasive weeds in the USA.

Why are weeds difficult to control?

verbena bonariensis roadside weed
Verbena bonariensis roadside weed in Australia

What all of this illustrates is quite how location specific the concept of a weed is.

One gardener’s weed is another gardener’s prize bloom because the degree to which a particular weed species is troublesome in a particular area is determined to a large extent by the growing conditions in that area.

Differences in soil type, or the availability of light and/or water that that may be present in adjoining properties or even in different parts of the same garden, can account for the presence or absence of a particular weed in each place.

Broader climatic considerations, such as minimum temperatures and the amount of sunny days, can account for the different growing characteristics in the UK, compared to elsewhere, of a plant such as Privet.

Therefore, the identification of individual weed species is for the most part a local matter.

There are some weeds that are recognised as such, and are widespread, in many parts of the world. However the main purpose of these weed control posts is to arm you with the knowledge and techniques that you can apply to whichever plant or group of plants are growing in the wrong place in your garden.

It is for that reason that you will not find exhaustive lists of weed species here. Instead, I’ll try to point you to some useful resources that can help you with identifying the weeds that may be troubling you.


The Gardening Step by Step weed control series

Weed identification

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