If you're worried about unruly weeds, this simple cardboard trick might just solve your dilemma – without the need for harmful chemicals.

This cardboard gardening hack, also called ‘sheet mulching’ or used as part of ‘lasagna gardening’, is a cost-effective and sustainable way to keep weeds at bay by blocking sunlight and slowing down their growth.

'Weeds can be really frustrating throughout summer, as plenty of sunlight helps them photosynthesise and grow rapidly,' Chris Bonnett, horticulturist and founder of Gardening Express explains.

While some weeds have their uses (the humble dandelion is an early-season pollinator, and its fluffy seed heads provide a food source for birds), an abundance of weeds can quickly become unsightly, competing with other plants for nutrients, water and sunlight – a particular challenge during the hot summer months when plants need all the resources they can get.

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'There are many tricks and tips out there to get rid of or prevent weeds, but some can actually cause problems for the rest of your garden, especially when chemicals are involved,' Chris continues.

As cardboard is biodegradable, it will naturally break down over time, making it a useful temporary weed suppressant. 'This method allows you to recycle old boxes while helping the soil as the cardboard naturally decomposes,' Chris explains. 'After a few months, the cardboard will also begin to decompose, benefiting the soil as "brown" matter, helping to create a healthier growing environment for the rest of your plants.'

There are some caveats when it comes to using cardboard to suppress weeds, however. Luke Newnes, gardening expert at Hillarys, explains: 'Cardboard is generally very safe to use around established plants, but placement is key. One mistake I often see is people piling cardboard right up against the base of plants or shrubs.

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'This can trap excess moisture around stems and crowns, increasing the risk of rot, particularly during wetter periods. I’d always recommend leaving a small gap around the plant itself so it can breathe while still benefiting from the weed suppression around it.'

You might also struggle with certain weeds, Luke explains. 'Cardboard is highly effective against many common annual weeds, but it can struggle with particularly persistent perennial weeds,' he continues. 'Plants such as bindweed, horsetail and Japanese knotweed have extensive root systems and impressive regenerative abilities, meaning they can sometimes find their way around or even through barriers over time.'

The simple cardboard trick that will help suppress weeds

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  1. Choose the right cardboard and remove any plastic or stickers. Be wary of cardboard that's heavily printed or has a coating, as these will introduce non-biodegradable materials into the soil.
  2. Cut back existing tall weeds before you lay down your cardboard, but there's no need to completely clear the area.
  3. Measure the area you want to cover and cut the cardboard so it fits neatly over the weeds. If you’re using several smaller pieces, overlap each section to prevent gaps. 'The biggest mistake is not covering the area thoroughly enough. Gaps between pieces of cardboard allow sunlight through, giving weeds the opportunity to keep growing,' Luke explains.
  4. Wet the cardboard lightly first as this can help it soften and mould to the shape of the ground more easily.
  5. Lay the cardboard on the weeds and press down the edges where weeds are more likely to grow.
  6. Secure the edges with mulch, soil or compost. 'I always advise overlapping sheets generously and then weighing them down with compost, mulch or soil,' Luke explains. 'Not only does this keep everything in place, but it also helps the cardboard break down naturally, improving soil structure and encouraging healthy microbial activity beneath the surface.'

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