The Brown County University of Wisconsin Extension Office has completed a three-year study of commercially-manufactured backyard composting bins. The study, released in February, tested 12 bins, including a homemade wooden bin, on variables such as rate of composting, ease of handling, cost and size. Of the 12 bins, four received top ranking.

The study resulted from the belief that municipalities that cost-share bins with residents or plan to should know which bins are the best choices. The extension service noted that if a large percent of homeowners in a municipality composted their own yard trimmings, less time and money would be needed for pickup and composting. So some municipalities have concluded that it is cheaper to cost share a compost bin with homeowners than it is to pick up yard trimmings at the curb.

In June 1996, Paul Hartman worked with master gardeners in creating a mix of 2/3 brown material - mostly six-month-old leaves - and 1/3 green material - mainly new grass clippings.

The mixture was put in the bins for testing. Temperatures were taken in the center of each bin and recorded for 15 days to determine thermophilic bacterial activity. Bins that needed tumbling were tumbled and water was added where needed, Hartman reported.

All of the bins had a good amount of composted material after the trial period, but tests were not made for compost maturity.

The data shows a wide variation from bin to bin. The bins that sustained higher temperatures longer were judged to be superior in the rate and extent of decomposition of the compost material during the time frame studied. In the report, however, bacteriologist Richard Albert notes that higher temperatures do not always indicate faster composting. Composting by bacteria, fungi, etc. does continue at lower temperatures.

The highest temperatures recorded were in the Presto and Gardener No-Turn bins - 156 degrees F two days after they were filled.

Almost all bins reached the optimum 130-160 degree F range and held it for four to five days. Only one bin - the Green Magic Tumbler - failed to reach 130 degrees.

The Covered Bridge bin, the Presto bin, the Handy Composter and the homemade wooden bin reached the highest average temperatures and combined for a mean temperatures of 113 degrees over the 15-day period. The others together had a mean temperature of 95.9 degrees.

"This is a statistically significant difference with a 95 percent confidence level," the report says. "If you equate the mean temperatures with advanced decomposition, then (the four higher-temperature bins) initially decomposed more quickly than the rest. This also correlates with nutrients available factor analysis comparing nutrient availability with temperature."

The report noted that the faster decomposing bins were all uncovered bins, so they received more natural water, keeping the compost going longer. Researchers watered the covered bins only as they dried out.

"The largest bins not covered did the best (as decomposition relates to sustaining temperatures)," the report says. "If we had uncovered all the bins we would have had a fair comparison. We didn't do that because we wanted to test the bins as set up by the manufacturers."

The report suggested that most people will not work too hard at composting, so the open bin with the biggest volume (that doesn't dry out) will do the best. Researchers gave the four bins that achieved the highest temperatures the highest rankings.

"We liked bin No. 3 (Covered Bridge) the best because of the expandable volume going up to 40 cubic feet," the report said. "Can we say statistically that some bins worked better than others? Yes, we can, but only for the reasons mentioned above."

The report noted that the costs of the open-topped bins were significantly lower than covered bins.

Bins that were the most trouble to use were the Green Magic Tumbler (small volume, dried out quickly) and the Bio-Orb composter (too heavy to roll), the report said. All of the bins were considered easy to assemble.

"Homeowners can easily compost yard waste in their own yard," the report concluded. "The bins tested looked good, did not occupy much space and were not subject to rodent infestation. Cost and ease of handling would be major factors in choosing a bin." For more information, contact Hartman, at (920) 391-4610.