Alys Fowler: the best way to beat weeds

Dandelions are beastly weeds. Photograph: Alamy

Weeds are often thought of as being unpredictable, with an ability to turn up anywhere and take over. In fact, they are quite the opposite: entirely predictable and wholly reliable. Give them bare ground and they will appear; thus, the first rule of weeding is cover your work. If you are not going to be back at that spot for a couple of weeks, cover the soil with cardboard, black plastic, mulch, or sow green manure. Don’t give the weeds a new playground.

All weeds exploit two strategies to reproduce: by spreading stems or roots, or scattering seed. If you can’t get round to weeding out the roots, pull off the flower heads. But be nice; pollinators love weeds that are rich in nectar and pollen. If possible, let them flower, then pull off the flower heads before they set seed. Rot the seed heads down in a bucket before adding to the compost, as immature weed seeds will happily mature on top of the compost heap if they are left with enough flower stalk.

Seeds can travel long distances. They hitch a ride on the wind or a visitor, and arrive unannounced in your garden. Annual weeds rely on this strategy to get anywhere, while perennials can fall back underground to keep marching on. We fear this lot.

The beastly types are brambles (rooting stems), buttercups (runners or stolons – stems that creep along the ground), ground elder and bindweed (rhizomes – subterranean stems), dock and dandelion (tap roots), mare’s tail or Japanese knotweed (both rhizomes) and creeping thistles (spreading roots and seed). If you leave bits of root behind as you dig, they will resprout.

The biggest weeds probably will have to be dug out nonetheless. “Lasagne gardening” – where you layer sheets of cardboard and rough organic matter on top of the soil – can defeat them, or at least loosen the soil, so it makes digging them out a more joyous task. The bigger the weeds, the more layers of cardboard you will need.

Lasagne gardening works better than weed-suppressing membrane because it enriches the soil and doesn’t leach petrochemicals into the ground. Worms love lasagne gardening because it provides them with new food; they don’t feel the same about plastic. Both systems work by weakening plants through lack of light. Some plants with very deep roots keep going for longer than you’d expect, so if in doubt, add another layer. This way you will also bury weed seeds, which tend to need light to germinate.
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If that doesn’t appeal, get a goat, rabbits, chickens, or a strimmer. My mother’s battle cry used to be “off with their heads”: eventually, you exhaust the roots.

If your weeds are running through the roots of shrubs or herbaceous perennials, the task is more difficult. Picking at new growth will slow them down, but you must be vigilant to win. Digging up shrubs and perennials in autumn, washing the roots and picking out the offending types is laborious but effective. Glyphosate and the like isn’t nearly as effective as it would like you to think it is.

You should come to your garden in the spirit of generosity to all that grows there.

• Listen to Alys on our gardening podcast at theguardian.com/sowgrowrepeat.

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