The Density of Sod

Definition of Sod

• Sod, also known as turf, consists of the grass itself, the underlying root system and a layer of soil. Farmers do the soil preparation, the seeding, the fertilizing and the watering. Depending on the soil type and the climate, sod can be ready for harvesting in as little as 18 months. To ensure maximum density, sod farmers mow their crops frequently to stimulate root growth. Usually, the sod is mowed every four or five days, but Kentucky bluegrass sod is one of the exceptions, requiring a cut every two or three days to achieve maximum density.

Fibrous Root System

• Grass has a fibrous root system, which makes sod possible. Rather than one single taproot, such as a carrot, fibrous root systems have clusters of fiber-like roots, all of similar size. This is a characteristic of monocots, which are plants that only have one seed leaf, or cotyledon. These intertwining fibers create a dense root carpet, which, when harvested, hangs on to part of the topsoil. Grass also has the ability to reproduce asexually using rhizomes. These are modified roots that grow out rather than down and are found barely beneath the soil’s surface. New grass shoots sprout along the rhizomes, creating a clone of the original plant. This further strengthens the sod and contributes to its density.

Qualities of Sod

• Sod farmers ultimately want to produce a product that is uniform in color and has sufficient density to make it easier to handle and increase shelf life. It should be as free as possible of weeds, insects and disease. The rhizomes and roots should be dense enough that the sod does not fall apart when handled. Sod must also be mature enough that the plants have enough stored carbohydrates, or food, that they can withstand the shipping and planting process. The denser the root system, the more nutrients are pulled from the soil and stored in the plant cells. Most sod producers are within 50 miles of their market. Sod can dry up in as little as 12 hours in hot, dry conditions.

Density and Cutting Sod

• Sod is cut thin or thick, depending on the density and the species. Sod with good density and root/rhizome structure can be cut thinner. Thin sod, or turf, is easier to handle, often being stored and shipped in long rolls. A thin cut of sod will also take root faster. Sod with a poorer density, or poorer root development, will require a thicker cut. This means more soil will have to be taken to protect the root system. However, thick sod is more drought-resistant. Growers use mechanical cutters for harvesting, removing the sod in pieces between 15 and 36 inches wide. Most cutting is done early in the morning when the soil is cool. This helps it retain moisture and increases its shelf life.