Evaluation of Compost Activators for Composting Grass Clippings

The effects of seven manufactured commercially available activators were evaluated for their efficiency in the composting of yard trimmings (grass clippings/wood chip mixture). Two naturally available additives, and a control (absence of activator) were also evaluated. Four measures of composting efficiency were used to compare the overall decomposition response for each activator: weight loss, volume reduction, volatile solids decrease, and oxygen uptake rate. Four experimental blocks were set up in the field, and two experimental blocks were set up in the laboratory. The physical/chemical characteristics of the compost material were monitored as a function of time for each additive. Interrelationships between measures of composting efficiency were also evaluated. Results showed that grass clippings can be composted as efficiently with naturally available materials such as topsoil or mature compost, as with commercially available compost activators, or an unactivated control. The cost of commercially available activators was $1.37 to $9.36 per cubic yard of compostable grass clippings. Naturally available materials such as topsoil and mature compost are available in needed quantities at no cost to backyard composters.