Organic lawn care experts recommend top-dressing your lawn with compost to improve the quality and health of your grass. But application guidelines are not always readily available. Researchers at Cornell University examined the effects of top-dressing established turf grass with compost made from dairy and poultry manure. They chose to conduct this multiyear study on four sports fields in New York State. Compost was top-dressed at 1/4-inch and 1/2-inch rates one time the first year and twice a year in years two and three of the study.
The compost applications were found to increase the soil's organic matter content, bring the pH closer to neutral, and reduce compaction. On some sites the lawns greened up sooner in spring. However, there were concerns about increased phosphorus runoff, high salt buildup, and more weed seeds due to the compost being immature. The quality ratings of the turf grass went up at one site but didn't improve at other sites that were used more frequently. It appears that top-dressing with compost could not overcome poor lawn construction and overuse.
Researchers found compost applications were most effective when the lawn was aerated before and after top-dressing. They suggest using finished compost with the particle size of 3/8 inch for easiest spreading. For best coverage, the compost should also be moist, but not so wet that it clumps.
For more information about this study, go to: Cornell Waste Management Institute.