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Laidback gardening with Robert Kourik

The limits of paper and cardboard mulch
Laidback gardening with Robert  Kourik
Here Chester Aaron is poking holes in wet blackand- white newspaper to plant garlic, a crop that is best planted now. The newspaper will be covered with straw to make it more attractive.Photo by Robert Kourik

Now is a good time to mulch to eliminate winter’s weeds. One approach is to use newspapers or cardboard. Remember: Do not use organic mulches within four to eight feet of your house’s walls for protection from fires.

I started using newspaper mulch in the early 1970s, when the organic gardening debate was hot about whether it contained lead and thus was not organic. When I discovered that it probably did contain lead, used in the manufacture of the black ink, I stopped.

Sometime in the late 1970s or early 1980s, newspaper printers switched to soy-based inks to print black-andwhite sections to save money. (Not only did these inks cost less, but they also weighed less than the leadbased inks, so they actually had a positive impact on trucking costs.) So, I switched back to using newspaper mulch, with attractive “natural” mulches on top. By this time, I was using drip irrigation in my garden, with newspapers (avoiding the toxic slick colored sections) layered on top, followed by an attractive rice-hull or mushroom-compost cover.

I used this combination for decades, until I paused to consider some new information. It turns out that newspaper or cardboard can create an anaerobic condition that is slightly detrimental to the exchanges of gases between the soil and the atmosphere. According to Dr. Linda Chalker-Scott, cardboard and newspaper mulches may be useful and not detrimental in annual gardens, but perennial plantings are a different story. Her experience (and her site, www.theinformedgardener.com) is my source for the most fascinating truths and myths about gardening.

The obvious: Newspaper layers are not attractive when the covering mulch blows away or moves; so, keep them well mulched.

Dr. Chalker-Scott believes cardboard and newspaper are not as effective as thick layers of organic mulches in keeping down weeds. The cardboard and newspaper layers also harbor earwigs, snails, ants, termites, voles, and gophers. However, a gardener friend found beneficial gopher snakes each spring under large sheets of cardboard.

The most fascinating observation is Dr. Chalker-Scott’s view that, if used on poorly drained wet soils, cardboard/ newspaper layers cause an anaerobic condition. This applies, as mentioned above, primarily to perennial plantings, as yearly cultivation in tilled gardens awakens the exchange of gases. Dry cardboard and newspaper can attract moisture away from the soil in areas exposed to dry summers or where the soil is well drained. This is definitely food for thought, especially if you’re using the cardboard/newspaper mulch in a no-till garden.

Newspaper mulch is not initially ideal for cultivating bacteria and other soil life, but it is pragmatic, as it saves time and kills off weeds. As the newspaper rots, bacteria will repopulate the soil surface.

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