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Using Cardboard and Paper Wisely in the Compost and the Garden


Q. I'm a devoted fan of your show looking for composting advice. Many gardening websites recommend adding shredded paper to your compost pile. I'm concerned that the ink on printed paper contains chemicals, and I won't have a truly organic compost come next spring. So should I add paper? Not add paper? Help!
    ---Anne in Doylestown, PA
A. Unfortunately, many people who give composting advice have never actually done it, are not thinking their recommendations through, or both. I've composted for 25 years, tend to think things through maybe too much, and don't like the idea of composting paper for many reasons.

  1. Paper is one of the most easily recycled materials in today's enlightened world. Virtually everyone has an easy way to get old newspapers, magazines and mixed paper into a stream where it gets turned into more paper, tissues, toilet paper or some other essential element of modern society, thus reducing the need for the raw material needed to make virgin paper (otherwise known as 'trees').

  2. While some modern inks (like the soy-based inks that have become popular in newspaper printing) are fairly innocuous, inks that are made for some other purposes still use petroleum and metals in their manufacture. (A good example is slick paper, where soy inks dry too slowly to be practical.) In addition, some paper itself has been bleached with chlorine, a particularly nasty player whose breakdown produces dangerous dioxins.

  3. Most importantly, there is little to no nutrition left in processed paper, and it won't add much—if any—fertilizing or disease-preventing power to the finished product. That's why I'm always yelling at allayouse to collect and shred massive amounts of fall leaves; shredded leaves make the finest disease-preventing, soil-enhancing, plant-feeding compost. If you have a compost pile where the predominant "brown materials" are paper instead of leaves, you are creating the equivalent of a heavily-processed artificial fast food for your plants. Compost made with shredded leaves is minimally processed, high quality slow food—and it's local too!
Q. Mike: I read that burying wet newspapers around plants will prevent weeds from coming up. Should I try this? Could I use old magazines as well? And exactly how would I do this? Regards,
    ---Catherine in Nokesville, VA
Q. My son purchased a home last year that has an unused vegetable garden he and I want to bring back into production. I have gardened organically since the 70's and have never used any paper or cardboard because I believe that both contain chemicals I don't want in my food—so I told him that his idea of mulching with cardboard is a no-go. But how about brown craft paper? He wants to use it in the walkways that we will create between long rows of raised beds to keep down the weeds. I worry that as the paper breaks down it will leach chemicals into the soil which will be taken up by roots that grow near or under the pathways. What do you think?
    ---Sandy in Kutztown, PA
A. The last time I tackled this question in print (back in 2004), I, like you, worried about the possibility of glues and such in cardboard. Afterwards, I received a very thoughtful note from someone in the industry who gently explained that there is no single thing known as 'cardboard'; it's a catch-all term used to cover a wide array of heavy duty paper-based products. He added that he was in the cardboard box business and was pleasantly surprised to learn that corrugated cardboard shipping boxes are very clean—just about all paper, no glues and no bleach. As a result, I have become more enthusiastic over the years about the idea of using cardboard and black and white newsprint as a weed block under soil or mulch. (Note to Catherine: Not just "around plants"; it has to be used correctly.)

(Your 'brown craft paper' is yet another animal. As far as I can tell, it's actually called 'kraft paper', a term ('krafting') that refers to a special manufacturing process that makes the paper very liquid proof, thus befitting its preferred old-time use for wrapping meat and fish. Some kraft paper, I am told, is also oiled or waxed to make it even better at resisting leakage. I'm pretty comfortable with it being used as weed barrier; but you'd have to go out and buy it, whereby most of us have a lot of old cardboard boxes and daily newspapers sitting around, begging for re-use.)

Now, how to use cardboard and newsprint: I recommend that gardeners planning to build raised beds level the soil, mark out the areas for the beds—no more than four feet wide but as long as you want—lay down single pieces of cardboard or entire sections of newspapers over the bare ground and then build and fill the raised bed frames overtop of that. (See this previous Question of the Week for more on raised bed building.)

Same with the walking lanes (which should be two feet wide by the way); lay down cardboard or newspapers and then cover this rustic weed barrier with the mulch of your choice. (Don't waste your precious shredded leaves or compost for this necessary chore; this is one of the only good uses for shredded bark and wood chips.)

Is this plan 100% free of potential chemicals? Of course it isn't. Neither is rainwater, animal manure, or scraps from conventionally grown produce. You pays your money and you takes your choices. I, for instance, will mix some horse manure into my compost piles when it's available, knowing that the horse may have been medicated. To me, it's still a great use of a nutrient rich ingredient, and I accept the small amount of risk.

Whereas I see no benefit and way too much risk in making compost from paper—too many problems; too little nutrition; too many other and better ways to reuse the paper; too much really good compost available elsewhere.

And as previously noted, I've gradually come to the conclusion that it's perfectly acceptable to use cardboard and newsprint (but not slick magazines or mixed paper) as weedblock. You may come to a different conclusion. That's fine—it's your garden.

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