Most gardeners know that compost applied to perennial beds helps the soil and plants in many ways. Usually the added compost is tilled into the soil before planting. Now research from the Washington State University at Puyallup questions whether that's necessary.
Researchers applied a 3-inch-thick layer of compost to silty loam soil test plots. Some of the plots were tilled to a depth of 7 inches, while others were left with the compost on the soil surface. Red osier dogwood shrubs were planted throughout the test area. After six years of measuring growth rates and fertility levels, researchers concluded that the difference in growth rates in shrubs in the tilled and untilled sites was minimal. Both treatments improved soil quality and leaf coloration. The tilled-in sites did have slightly higher levels of carbon and nitrogen in the soil. Researchers concluded gardeners shouldn't get too concerned about tilling in the compost when applying it to perennial plantings.
For more information on this research and to obtain a pdf file of this report, go to: Washington State University.