To keep the peace in any garden, you must be unafraid to let slip the dogs – and shovels – of war. By Helen Razer.

War of the weeds

Old-fashioned manual techniques are the best way to remove weeds.
Old-fashioned manual techniques are the best way to remove weeds.

There are just two sorts of people who will tell you that gardening is peaceful. These are (a) those who never held a trowel, and (b) heiresses who do not so much garden as tell the groundsman to be a dear and pop that Rothschild’s orchid beyond the ornamental canal. Gardening is not peace. It’s war. Or cold war, really. The garden knows I can kill it and I know very well that the garden can snuff my spirit with a single season of bad tomatoes. It is in this climate of mutually assured destruction the garden and I consent to limit our losses.

I have agreed to let the garden annex all of my time. The garden, in turn, has agreed to let me kill some of its dissenters. Which is to say, its undesirable plants. After a recent summit, we decided on the sacrifice of a sweet autumn clematis. If a weed is a plant not wanted, this was the flowering mother of all that is unwelcome.

Sure it was a fleetingly pretty vine. But it was also needy and selfish. It robbed my other plants of light and nutrients and demanded a difficult annual prune that would punish me with backache and accelerated growth. 

In the front yard with my pruning shears, a shovel and dreams of freeing a space occupied for years by a white, fleecy thug and filling it with manure and tulips, I set about the difficult murder. “What are you doing?” exclaimed the lady from No. 4. No. 7, whose partiality to concrete and native grasses gives her no diplomatic validity, just said, “How could you?” And while it is true that the floral display of this vine was quite decent, it is an invasive dissident better suited to the confines of a pergola than free rein in the modest garden bed of a compact front yard.

Plants, as neighbour and horticultural savant Iris knows, have to earn their keep. A few years back, I was walking past the spectacular garden at No. 10 and saw its caretaker hacking away at a well-established salvia. “Disease?” I said. No. The plant, which was crowding out its smaller neighbours and dropping babies like a Mormon Pez dispenser, was not earning its keep. 

We must continually ask ourselves what a plant contributes to the nervous peace of the garden. Does it, like a sweet pea or a lupin, nourish the soil? Is it beautiful? Can I eat it? Always ask: does it earn its keep? This is how we make the painful assessment of which plants to keep, or repatriate to the backyard, and which plants to destroy. This is an unpleasant but necessary labour of war whose frequency accrues in inverse proportion to the size of one’s territory. Balcony and other small-space gardeners are those who most often ask, “Must I kill?” Those of us with yards can afford a little lenience in our limited warfare. 

And so, I did not take the decision to exterminate the clematis lightly. Certainly, I did not just decide to use glyphosate, best known as Roundup, without first exploring other means. But the mega-weed would just not be dug up quickly enough and I began to spray.

By the time the Monsanto corporation introduced glyphosate in the early 1970s, Iris was already a gardener of some years’ experience and she did not take to the non-selective herbicide readily. Manual weeding, mulch and husband labour are her preferred weapons in the weed arsenal and she says she has only used glyphosate a handful of times on particularly stubborn bushes and couch grass.

Although glyphosate is a non-residual poison and does not affect soil, it is best to follow Iris’s lead and refrain from its use unless absolutely necessary. And by “absolutely necessary” we can mean pathways choked by broadleaf or flat weeds that resist manual removal, crappy lawn, or a colossal vine that gives you cause to lose sleep. 

Organic gardeners say terrible things about Roundup and often cite a study that claims that cows exposed to it are subject to spontaneous abortion. Then again, organic gardeners turn their noses up at my tulips and urge me to make “weed tea”. This is a concoction that sees the immersion of unwanted plants in water to produce a nitrogen-rich fertiliser. It is the worst thing I have ever smelled, and I once attended a drumming circle at ConFest. I don’t believe everything organic gardeners have to say. So, to see if I had committed a grave environmental crime, I asked a horticultural scientist instead of a biodynamic elf: is glyphosate something we must avoid?

John Rayner, lecturer in urban horticulture at the University of Melbourne’s prestigious Burnley campus, says yes. But with qualifications. There are some occasions in which the use of glyphosate products can be justified, he says. Gardeners with impaired mobility can be rationally excused for judicious use of this chemical weeder, as can those who wish to swap their dandelion forest for a proper lawn, or revegetation workers. When clearing unwanted plants from a damaged landscape, the reveg specialist may apply undiluted glyphosate using a painting technique. Using a small brush or dabber, poison is applied neat. For larger plants, a “drill and fill” is used with the injection of poison into deep holes bored at the trunk. But the home gardener, myself included, is better to use manual techniques.

“Get your shovel out, Helen,” was Rayner’s advice.

Rayner says there are questions on two levels about the use of the product. The first is: how does it affect the user? Spray operators need to be more careful than they generally are, he says, and must always use safety gloves. (Pets and small gardeners should not be permitted near wet glyphosate at all and drying time is contingent on a number of factors.)

The second question is to the potential long-term effects of these chemicals on the natural environment. Glyphosate may not persist in soil but it doesn’t behave so nicely in groundwater. In agricultural use, it has produced some broadacre crops that become resistant over generations. This mutation is unlikely to occur in a domestic garden but does not really excuse my use of glyphosate on the mega-weed. Which I probably could have dug up.

Any product that promises death to plant life for an extended period should be completely avoided. The pre-emergent herbicides of lawn care “weed and feed” products are not, apparently, much chop and the soil sterilants in long-term path-weeding products should, for all their convenience, be given a wide berth. And, if you are thinking of salting your garden to prevent growth, don’t. “Sodium chloride is one of the worst things you can do to the soil,” says Rayner.

If you do have both a substantial pathway that vomits weeds and a green urge, you might want to discount the application of household vinegar – with which I have enjoyed a very limited success – whose production is often contingent on petroleum. Maybe think about the hire of a weed-steamer for large areas. Thermal weed-control techniques are used in many European cities where civic use of contact herbicides is banned, and this method of beautifying looks like enormous fun. Rayner dismisses the use of hot water from a kettle and has little to say on the matter of propane torches. Which, again, look like a hoot but are less than ideal in our fire-prone nation and would probably lead me and other klutzes to the emergency room.

Another weeding method employing heat is one I have just begun on a vegetable bed. When I harvested the last of my tomato crop, I began germinating my winter brassicas and preparing the soil with the “solarisation” technique. This Middle Eastern agricultural trick involves turning over the soil and then securing a sheet of clear plastic on top for four to six weeks – just long enough to bring your seedlings to planting maturity. So long as the sun still has a sting in it, it should heat the soil to above 50 degrees, killing a range of fungi, pathogens and seeds. “Will it kill my couch grass?” I ask Rayner. He laughs and tells me “almost nothing will”.

As I have counselled before: mulch. This cover is an effective deterrent in the war against weed terror and, as Rayner advises, a general rule of green thumb is to use herbaceous mulches such as sugar cane or straw for herbaceous plants, and a bigger woody mulch for woods plants. And do remember to leave at least 10 centimetres of bare ground around the plant so it can receive any water and nourishment you give it. Mulch is not precision artillery and will kill all collateral it smothers.

 Small amounts of kikuyu and couch grass and associated demons are best cut and hand-weeded. Clover and other troubles, which can even make their way through the man-made jungles of glass and concrete to your balcony garden, should also be manually yanked. While this is a bit more work than a contact chemical, it does have the bonus of really acquainting you with the needs of the good plants in your garden. Slithering about with my weeding gloves, I noticed that some of my late summer flowers, such as the open-pollinated coneflower and snapdragon and viola, had begun to produce pods, and so I have now collected the seeds from these reliable parents. 

But note well, not all flowering plants produce great issue. Disappointment will likely ensue if you do this with your sweet peas. They suffer such great loss in colour and talent so that I nicknamed this year’s drab crop grown from saved seeds “Drew Barrymore”.

I don’t enjoy pulling creeping grass out of my beds and pots daily but my plants and I benefit from the intimacy. There are always moments of warm diplomacy. Even in a cold war.

This article was first published in the print edition of The Saturday Paper on March 21, 2015 as "War of the weeds".

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Helen Razer is a writer and broadcaster. She is The Saturday Paper’s television critic and gardening columnist.

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