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Green Corner: Cardboard Weed Block

Looking for an economic and environmentally-friendly way to block weeks in your garden? Try recycling cardboard!

Cardboard sheets can be used under a layer of mulch or rocks to stop upward growth of unwanted weeds. Cardboard serves as an effective barrier to keep unwanted weeds from sprouting or growing. Over time, the cardboard will biodegrade and feed the soil below it with organic matter.

It is recommended to start early in the season, laying the cardboard in a sufficiently thick (but not too thick!) layer under your new season’s mulch. Use plain cardboard, because printer ink can be toxic and problematic for plants, and two to three stacked sheets (as opposed to five or six) is optimal. As the cardboard moistens through natural processes (including rain), it will begin to break down. Provided you use clean cardboard without a lot ink on it, the cardboard will boost the soil’s nutrient content as it biodegrades. You can position the cardboard around areas where plants you want to grow are located, or cut a hole through it to place new plants into cut-out opening(s). And, you should remove all staples and tape before use.

Be careful not to put down too thick of a cardboard layer, especially against your home’s exterior or in areas where tender plants are located. Too thick a layer may harbor the growth of plants, and too much against your home’s structure might unintentionally invite pests such as termites and moles to nest underneath. Be sure to anchor your cardboard (placing mulch or rocks on top works well), so that it does not become dislodged or blow away before it is moistened.

When well-planned and well-maintained, cardboard sheets can serve as an excellent alternative to plastic weed barriers as well as an excellent alternative to herbicides. With an appropriate layer thickness, you can help your garden without the use of chemicals and ultimately save time from weeding by hand or dealing with expensive weed block. Typically, an appropriate layer of cardboard may last for two or three seasons.

Happy gardening!


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