What Can You Substitute for Grass in a Mulch Pile?

Nitrogen-to-carbon Ratio

• In a mulch or compost pile, materials you add are broken down by microorganisms. These microorganisms require carbon and nitrogen, as well as phosphorus and potassium, in the correct amounts to function efficiently. If carbon or nitrogen is insufficient or present in excessive amounts, it can greatly affect the rate of decomposition. The ideal ratio of carbon to nitrogen for a compost pile is 30 to 1, or 30 parts carbon for every 1 part nitrogen, by weight.

Sources of Nitrogen

• Grass clippings are a widely available source of nitrogen for composting, as freshly cut grass has a carbon-to-nitrogen ratio of 20 to 1. Other sources of nitrogen include vegetable trimmings or table scraps, which have carbon-to-nitrogen ratios around 15 to 1, as well as alfalfa hay, coffee grounds, spent grain from breweries and some manure. Where no relatively nitrogen-rich materials are available, a small amount of nitrogen fertilizer may be incorporated into the pile.

Sources of Carbon

• Leaves that are not fresh have a carbon-to-nitrogen ratio of about 60 to 1, as do corn stalks. Other brown materials include straw and pine needles, which both have carbon-to-nitrogen ratios under about 100 to 1. Woody materials like sawdust and wood chips have very high carbon-to-nitrogen ratios.

Building the Mulch Pile

• Even if materials exist in the pile in the correct amounts to create the appropriate carbon-to-nitrogen ratio, decomposition will not occur rapidly unless the materials are distributed evenly throughout the pile. When building the pile initially, especially if you have a lot of material to work with, make alternating layers of brown and green materials several inches thick and include thin layers no more than about 1 to 2 inches thick of topsoil on top of each pair of layers.

Additional Compost Care

• Regular moisture in the mulch pile is critical for efficient decomposition, as is sufficient oxygen. Every few weeks, use a garden fork to flip the pile and water the material whenever it starts to dry out. The pile is ready to use as compost when the material is uniformly dark and crumbly, with no recognizable parts of original materials.