As the weather warms up, many of us are spending more time in the garden, getting borders and beds ready for summer. However, one common problem quickly returns at this time of year: weeds.
Thankfully, one of the simplest solutions might already be sitting in your recycling bin: cardboard.
'Consider using cardboard when establishing new borders for your gardening or new no-dig beds, as it can help eliminate weeds and improve the soil by creating rich organic matter,' says Matthew Wilson, gardener and CEO of Handy Gardeners. 'Cardboard is a great, low-cost option when compared to synthetic membranes used as weed barriers.’'
Below, we explain why it’s an excellent idea, as well as how to use cardboard in your garden correctly.
How does cardboard prevent weeds from growing?
Weeds need sunlight to grow, and cardboard acts as a barrier that blocks light from reaching the soil beneath.
'If a plant cannot photosynthesise, it will be unable to produce the food it needs for energy and growth, leading to it withering and dying,' explains Richard Barker, horticultural expert and commercial director of LBS Horticulture.
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Weed seeds need to be in contact with the soil to sprout, and the layer of cardboard separates them from the soil, preventing seeds from sprouting and taking root.
'The cardboard will gradually break down in the soil, creating an area of nutrient-rich compost,' Richard adds. This will improve soil structure and even encourage beneficial organisms such as earthworms.
Remove any tape and labels first
Before laying cardboard down in the garden, it's important to prepare it properly by removing any packing tape, staples, and labels.
'Brown, uncoated cardboard works best, as coated, printed, or glossy cardboard can contain plastics or chemical additives that may leach into the soil,' says Richard.
Breaking boxes down into flat sheets will also make them easier to work with and ensure better coverage.
Lay it directly over weeds
One of the biggest advantages of cardboard mulching is that you don't need to dig out every weed beforehand. Simply cut back any tall growth and place the cardboard directly over the affected area.
'I recommend overlapping the edges by a few inches so that weeds cannot grow through the gaps,' says Richard.
Taking the time to overlap the layers properly can make a big difference to the barrier's effectiveness over the coming months.
Wet the cardboard thoroughly
Dry cardboard can be difficult to keep in place, especially on windy days. This is why, when laying it down, it’s important to soak it thoroughly with a hose or watering can.
'This will help to mould it to the ground and stop it from blowing away,' Richard explains. 'It also encourages worms to begin breaking down the cardboard.'
Wet cardboard is also easier to cover with mulch and less likely to lift or shift before it has settled.
Cover it with mulch
For the best results, add a layer of organic mulch over the cardboard, ensuring it fully covers the cardboard. A layer around 5-10cm deep is usually enough to provide good coverage.
'Use compost or bark chips, as these will help to keep it in place and hide it, improving the appearance of the area,' says Richard. This also helps keep the cardboard in place and provides additional weed suppression.
Cardboard won't eliminate weeds overnight, but it can dramatically reduce them over time. Depending on the weather and the thickness of the cardboard, it may take several months to fully break down.
You'll be left with healthier soil and significantly fewer weeds to deal with, making it one of the easiest low-effort gardening tricks to try.
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