Great vines start in the vineyard…Great vineyards start with the soil.

Good vineyard managers know that soil characteristics interact with irrigation management when producing high quality wine grapes. Soil moisture and other soil characteristics are managed throughout the year to produce the best grape quality, reduce excessive canopy formation, and regulate crop levels.

Good vineyard soils typically have several common characteristics including good drainage with accessible rooting depths. In Eastern Washington, vineyards are on landscapes that are naturally graced with quick draining soils yet may be extremely low in soil organic matter.

Low organic matter may compromise other soil characteristics important to good grape production, such as soil structure, the activities of beneficial microorganisms, and the ability to supply needed nutrients to the vine.

With ample organic matter, the rooting zones wets up more effectively under irrigation and then retain this moisture longer. When soil moisture changes more slowly, vine roots are less likely to experience the most extreme wilting points or drowned by excess water.

Because organic matter is the energy source that supports a healthy soil food chain, additions of compost generally increase populations of beneficial microorganisms. Healthy soil populations produce vines better able to resist pests and disease outbreaks.

The formation of good soil structure is dependent on the activity of many soil organisms. The advantage of having good soil structure is that it fights soil compaction and reduces wind erosion, keeping the soil where it belongs in the vineyard and allowing roots to more easily penetrate and breathe. Without organic matter, good soil structure may deteriorate or never form.

Soil amendments are one way to increase organic matter and there are several common types of amendments that can be used. However, not all amendments are suitable for vineyards. For example, organic amendments made from manure may be high in salts and soluble nitrogen, resulting in excessive canopy formation and salt affected soils.

Yard debris compost is a soil amendment suitable for winegrape vineyards. Yard debris compost generally does not have high amounts of readily available nitrogen. The nitrogen present is generally in the slow release form. In most yard debris composts, less than 1 percent of the nitrogen and phosphorus is in the available form, and the remainder is in a complex organic form that releases slowly over time.

Yard debris compost is made from the decomposition of plant materials such as leaves, grass, and tree and shrub trimmings. Commercial composting is a process that includes a heating cycle that kills pathogens and weed seeds that may be in the original feedstocks.

The compost is usually applied and incorporated into the soil using mechanical equipment. Compost complements other soil additives and management practices, such as fertilizers, pesticides, herbicides, and cover crops.

An early spring application of yard debris compost approximately 3 inches thick as a top mulch in spring can be used for weed control. This same material can be tilled in the fall as preparation for the following season. Application rates from 40 to 50 tons per acre (60 to 70 cubic yards per acre) are recommended to realize the benefits of using yard debris compost. 65 cubic yards spread over one acre is about 1/2 inch deep.