Gardeners looking for a chemical-free way to tackle weeds are turning to an unlikely hero: cardboard. According to experts, this humble material can smother weeds effectively while enriching the soil as it decomposes.
John D. Thomas, owner of Backyard Garden Geek, explained: “When planning new garden beds, cardboard is key to weed control. It is thick enough to smother them, but unlike landscape fabric, it'll rot over time. This means that your plants will be able to eventually pull nutrients from your native soil while beneficial bugs such as earthworms will be able to make their way into your garden beds.”
The method is simple: place a large box over the weeds and weigh it down with rocks or bricks. Melody Estes, a landscape design supervisor at The Project Girl, advised: “Ensure that all sides of the cardboard are covered and that it does not come into direct contact with soil.” Gardening experts at Garden Organic recommended slashing down weed growth, laying overlapping sheets of cardboard, and weighting them with compost or manure for six to 12 months.
However, caution is needed. Estes warned: “When using this technique, be sure to place the cardboard carefully so as not to disturb any other plants in your garden.” The cardboard can take up to a year to decompose, depending on the type—recycled paper breaks down faster than corrugated cardboard with polyethylene. As it rots, it releases nutrients, making the soil ideal for new plants.
Experts noted that roots can grow through cardboard if it is moist and placed in a dark, airless environment. Once plants emerge, support structures can help guide them to light and water while preventing pest issues. The water causes cellulose fibres to swell, aiding decomposition and nutrient release.
