Biodegradable Mulches

“I value my time too much to want to spend it ripping up plastic in the fall,” is Andrew Frankenfield’s reason for trying biodegradable mulches. Andrew is a Penn State Extension educator in Montgomery County, and he is also a farmer. He tried a half acre of biodegradable mulch this year for tomatoes. “So far it looks good, it is starting to degrade along the sides but the weeds are not breaking through,” he told a group of 50 farmers at a field day at Trauger Farms in Kintnersville, PA this month. As we looked at the four biodegradable mulches planted to tomatoes I heard a great discussion of the benefits and disadvantages.
We all know the benefits of plastic mulch. Not only does it keep the weeds down, it warms up the soil giving us earlier (and more) tomatoes, peppers, eggplants and other heat loving veggies. But it costs us. Farmers estimate it costs $25-100 an acre for labor and disposal of plastic mulch.
A possible alternative to black plastic mulch is biodegradable film mulches that look and act much like black plastic, but instead of ripping them up in the fall, you till them into the soil and the microbes degrade the material, leaving you a clean field (hopefully) in the spring.
Good biodegradable mulches are made from starch (corn or wheat). The starch is food for the microbes. They eat it and turn it into CO2 and water. The material will break down fastest when the microbes are most active – when the soil is warm and moist. An important thing about starch based mulches is they become sticky and adhere to the soil as they break down, instead of becoming brittle and blowing around like some of the older technology.
Some of you may have experienced biodegradable mulches in the past and say no way –too hard to lay with the plastic layer – stuck around for ages – too expensive. . . . .Well it may be time to look again. Some of the new mulches are performing well in research trials. One product (Biotelo) had good soil stretch and field application similar to plastic. The soil temperature and yields for muskmelon were similar to plastic according to a study by Dr Rangaragan at Cornell. In a more recent trial from Dr Orzoleck at Penn State in pepper, cantaloupe, eggplant, zucchini all had as good or better yields with biodegradable mulch films (various brands). Even though the film began to degrade before the crop matured, there was no weed growth or competition.
But the question remains – are the biodegradables economical? I sat down with my neighbor to run a few numbers. He figures he uses about 7,000 feet of plastic per acre (1,000 ft rows, 6 ft centers). For the cheapest of the biodegradable mulches I found that is a little less than one 8,000 ft roll at $349/ A for biodegrable mulch. Regular plastic mulch runs him $95 per 4,000 ft roll. At two rolls per acre it costs him $200/ A for plastic mulch. But that does not take into account the cost of ripping up the plastic and disposal. He just pulled up an acre this morning. In two hours for three guys, plus the tractor operator, it cost him about $100 per acre. Disposal in this area is about $50/ Ton. For about 400 lbs/ A of plastic disposal is another $10/ A. Including these extra costs that is $310/ A for plastic mulch plus removal and disposal. That does not include the time and hassle to dispose of it.
I don’t think the final word is in on biodegradable mulches. But it looks like they are worth experimenting with.
Orzolek, M. D. 2007, 208, 2009. Metabolix Field Research; Center for Plasticulture, Penn State University. mdo1@psu.edu
Orzolek M. D. and B. Dye 2008. Paper Mulch Evaluation Study; Dept. of Horticulture, The Pennsylvania State University. mdo1@psu.edu
Sorkin, L. 2006. New biodegradable mulch is cheaper than plastic when removal and disposal costs are also Considered. Cave Moose Farm SARE Project. lauraglenn@hotmail.com

Rangarajan, A. Ingall, B. 2006. Biodegradable Mulch Product Testing. Department of Horticulture Cornell University. ar47@cornell.edu