EUGENE, Ore. – Digging up sod to start a garden can be difficult, as Michelle Obama demonstrated recently on the White House grounds. The First Lady might have used an easier way to turn lawn into garden, given more time.
Gardeners call it "lasagna" mulching. Famous for its layering technique, it's also called sheet composting.
Patience is the key, according to Cindy Wise, coordinator of the Compost Specialist Volunteer Program at the Oregon State University Extension Service in Lane County.
"There are several advantages to sheet composting and it's an easy way to start or expand a garden with a minimum amount of equipment, material and time," Wise said, "but it is a slow process that can take six months or longer to decompose enough to allow planting."
In other words, plan ahead. Although fall is an excellent time to start, spring and summer are good times to begin using, instead of trashing, organic materials from the yard. The method's alternating layers of nitrogen and carbon materials also can be used to improve soil or add to existing beds and borders, Wise said.
Common nitrogen sources are coffee grounds, kitchen scraps, composted manures, alfalfa pellets, vegetable scraps, fresh grass clippings and cottonseed, soybean and blood meal.
Carbon sources are sawdust, leaves, corn stalks, pine needles, peat moss, newspaper, cardboard, straw and hay.
"Begin by mowing or scalping as low as possible grass or other vegetation in the area you choose and loosen the soil with a spading fork to improve drainage," Wise advised. "Remove persistent weeds such as blackberry, bindweed, morning glory or quackgrass that composting might not smother."
Cover the ground with four to six overlapping layers of cardboard or newspaper (black ink on newsprint only) to keep out light and eliminate vegetation underneath. Wet the newspaper or cardboard thoroughly and cover with a thin, one-inch layer of a nitrogen source such as manure.
Top the nitrogen layer with an inch of leaves, straw, bark or other carbon material.
Add another inch of nitrogen, then another of carbon, another of nitrogen and a top layer of carbon. The final layer can also be covered with an overlapping layer of burlap coffee sacks to keep the materials in place. The burlap will decompose over time.
"If the pile gets too wet, loosely cover it with a sheet of black plastic, weighted down at the sides," Wise said. "This also will help warm the pile, encourage faster decomposing and prevent losing nutrients during heavy rains."
Continue to add layers as materials become available, and always end with a carbon layer on top. "This is the blanket that discourages flies from laying eggs on exposed nitrogen such as kitchen scraps," she said.
A bed is "finished" and ready for planting when the layers have decomposed to the point that the original materials are no longer recognizable and look and smell like fresh earth. "You can dig down through the layers to plant seeds or seedlings, or turn over the new bed, although it's not necessary," Wise said.
"You also can screen a two-to-three-inch layer of good compost over the top of the bed and plant seeds in it."
The composted material will need to be replenished as it is "consumed" by your plants. Leave six inches open around plants so they won't come in contact with fresh, decaying organic matter.
For more information and classes on sheet and other composting, go to the Web site for Home Gardening, written by OSU Extension Service in Lane County, or check out your local OSU Extension Service office.