DR. Paul's Research Update
Extending the growing season. . . and the storage life of your harvested produce

Recent research documents quantifies the effectiveness of row covers and the greater shelf-life of organic greens

By Dr. Paul Reed Hepperly

August 16, 2004: Greenhouse production of vegetables and fruits is one approach to season extension in temperate climates. Although greenhouses are effective in this regard, they are often quite expensive. Putting row covers over field transplants is an intermediate strategy between greenhouse and open field production. This method can accelerate early season growth and prevent late frost damage on summer crops at much reduced capital costs to farmers compared to greenhouse production.

Penn State researcher Mike Orzolek reports on his results this year with zucchini under row covers. Early zucchini yield was 10 days earlier under row covers compared to open planting. All plants were transplanted to the field on May 27; covers were installed the same day and were removed on June 16. In the first 7 harvests, 14 varieties of zucchini that had been covered yielded double than those without row covers. Overall, zucchini under covers yielded 25 percent more than exposed rows.

This spring was cooler than normal in State College but these preliminary tests indicate that row covers have potential not only as a good insurance of avoiding late frosts but also a way of stimulating early harvests, which generally get best market prices. Organic, sustainable, and conventional farmers should consider looking at this option as a potential alternative in their cropping system. We suggest farmers get information on how this works from your own small on-farm trial and then run return-on-investment numbers before moving to the system whole hog.

In addition to controlling temperature, row covers can serve as insect barriers. Insect avoidance would be especially important for organic production systems under some conditions.

As you make up your plans for next year, consider trying some covered rows—and let us know what your experience is with this developing method.

Organic Swiss chard keeps better than conventional

Increasing vegetable storage life holds huge advantages for farmers and consumers alike. Farmers want to sell and consumers want to buy fresh products. Highly perishable products such as chard and other greens can degrade before or shortly after arriving in the marketplace, disappointing both producers and consumers.

A group of Argentinean scientists have shown that Swiss chard grown organically can store better than conventional chard. In blind studies, organically produced chard was rated firmer and maintained brighter colors longer than conventionally produced chard. In both conventional and organic chard, the rate of deterioration was indexed at 0.057 per day; however, start of deterioration was at 3 days for conventional chard and 10 days for organic chard.

No significant differences between conventional and organic chards were found for yeast, mold, population levels of assorted bacteria, rate of vitamin degradation, water content, chlorophyll content, or acidity.



Orzolek, Mike. 2004. “Row Covers: Do They Work?” Pennsylvania State University Department of Horticulture, The Small Fruit and Vegetable Gazette 8(7). http://hortweb.cas.psu.edu/extension/vegcrops/vegetable_gazette/2004/august2004.htm#covers

Moreira, M. del R., Roura, S. I. and Del Valle, C. E. 2003. Quality of Swiss chard produced by conventional and organic methods. Lebensmittel-Wissenschaft und -Technologie 36(1):135-141.

Paul Reed Hepperly, Ph.D., is research and training manager at The Rodale Institute.