Can I use cardboard and newspaper as mulch on my organic farm?
Answer: Materials that are used to produce and handle organic crops under the USDA’s National Organic Program (NOP) must be selected for compliance and used in the context of organic principles for farming and handling practices. For more information, see the ATTRA publication Organic Materials Compliance at https://attra.ncat.org/attra-pub/summaries/summary.php?pub=157. Among other information, this publication discusses three basic steps to ensure that materials use is compliant with organic standards and certification.Regarding the use of newspaper and cardboard, both can be useful materials used in organic crop production for suppressing weeds, retaining moisture and adding organic matter to your soil. NOP regulations allow the use of newspaper or other recycled paper as an “allowed synthetic” with the provision that it be “without glossy or colored inks” (refer to NOP regulations 205.2, 205.601(b)(2), and 205.601(c)). It does take some work to separate out the newspapers that are neither glossy nor use colored inks. Also, there are fruit, vegetable, and meat cartons that are water- or grease-resistant and therefore coated with other types of materials, such as waxes, or impregnated with fungicides. These would also be prohibited for use in organic production. ATTRA has not found any research studies to establish the impact of black ink used in the printing on newspaper, or whether the inks and glues used in cardboard are completely safe. However, there is abundant anecdotal and experiential evidence that suggests the use of brown cardboard as mulch is very effective as a weed barrier and that it biodegrades and does not appear to pose any substantial threat to the health of the soil and soil organisms. Many organic gardeners and farmers and ecological landscapers use cardboard often and say that it makes great sheet mulch. A few years ago, ATTRA did research on the different substances that go into making cardboard, as well as the glues, inks, and coatings that may be used. Based on the information available then, the basic components of corrugated cardboard seemed to be relatively benign. Brown corrugated cardboard appears to be the least processed paper product. It therefore would have the lowest number and smallest quantity of chemical substances, compared to white, glossy, highly printed, waxed or otherwise coated cardboard, paperboard, and papers. If you want to remove some of the variable of other unknown substances used in their production, avoid white cardboard (these may require the use of bleach), waxed boxes, paperboard (such as cereal boxes), and any material with colored ink (may contain heavy metals of other substances) or glossy coatings. There is an abundant supply of relatively plain (minimally printed), brown corrugated cardboard that can be obtained for free in most areas of the United States. Using this, many people can fulfill their mulching needs without the use of riskier materials.