Published Apr 29, 2015

RESEARCH REPORT UPDATE: Mulching Comparison for Watermelon and Sweet Potato Production

By Liz Kolbe

Weed management on organic vegetable farms requires a lot of labor and time. Black plastic mulch is the standard option for keeping weed back, warming soil, and retaining soil moisture. However, black plastic leaves a mess to clean up at the end of the season, with few, if any, good options for responsible disposal. Because of this, and a general desire to reduce the use of plastics in production, fruit and vegetable farmers continue to experiment with paper mulch and no cover. This report summarizes the findings of three years of projects on three farms, Grinnell Heritage Farm, Scattergood Farm, and Middle Way Farm.

In 2012, results from Grinnell Heritage Farm and Scattergood Friends School indicated that mulch in either a plastic or paper form results in fewer weeds during sweet potato growth, and the increased labor of laying the mulch may be balanced out by the reduced weeding labor. However, Mark Quee at Scattergood Friends School noted that the mulches tended to blow around, leaving the rows and sometimes damaging the plants.


At both farms, the plastic mulch resulted in the greatest yields. At Grinnell Heritage Farm, however, it also resulted in more cull plants, though this may simply be due to greater production and not a greater percent of cull tubers. Paper mulch did not seem to improve yields in the same way that plastic mulch did, but did reduce weeds equally as well.

In 2013, results from Scattergood Friends School indicates that paper or plastic mulch generally did not seem to improve fruits per plot, total fruit weight per plot and average weight per fruit for either watermelon variety. Mark Quee expressed that after this trial, he is tempted not to use any mulch in watermelon production. However, he also mentioned the importance to evaluate alternatives to black plastic. In addition, an unusually wet spring followed by drought conditions in the summer of 2013 might have impacted the results.

In 2014 at Middle Way Farm, Jordan Scheibel grew sweet potatoes and experienced limitations of the paper mulch and its ability to withstand severe weather events. Jordan says, “I will be moving production of a number of crops to exclusively or almost exclusively plasticulture: sweet potatoes, cucurbits, and tomato family next year. I may also experiment with onions on plastic, which is my most difficult crop to keep weeded and I have heard anecdotally from another young grower in northern Iowa that using plastic on onions has been great for them.”

For more information and project details, read the full report. More trials underway for 2015!