Compost does some of the same work that fertilizer does, at a reduced cost. In addition, organic matter contains nutrients that are sometimes missing in synthetic fertilizers. Composts release nutrients into the soil more slowly than synthetic mixtures do. The slow release is perfect for grapes because they have low nitrogen needs. Vineyards do need fertilizers from time to time, but even then, adding compost helps the soil use the fertilizer more efficiently and to hold on to the nutrients longer. (See References 1).
Grapes grow best in specific environments. They prefer a lot of sun and protection from prevailing winds. American grape varieties do well in sandy loam that has a pH of 5.0 to 6.5, while European varieties prefer a pH of 5.5 to 6.5 (See References 2). The best way to determine the correct soil conditions for grape plants is to perform a soil test. Soil tests guide growers toward ideal plant growth. A soil test may reveal, for example, that the pH is adequate, but the magnesium level is low. Grapes benefit from many elements contained in compost, such as potassium and zinc (See References 2).
Sandy soil is great for grapes, but it is porous and needs help maintaining moisture and nutrients. Compost remedies that situation. Some grape varieties grow well in clay soils that tend to become compact and drain poorly. Compost aerates the soil and promotes better draining (See References 3). It keeps the soil from clumping up and allows plant roots to spread out easily. Compost inhibits soil erosion from wind and heavy rain. It also keeps the dirt from splashing on to the plants and spreading harmful diseases. Compost is inexpensive because it is made from agricultural waste that is available locally.
Compost contains bacteria that break down organic materials into beneficial nutrients. Some bacteria convert nitrogen from the air and deliver it as plant nutrients. Organic additives contain insects and worms that burrow through soils and keep them aerated. Grapes grow in full sun, so moist soil is crucial. Planting on an elevated site reduces the risk of damage from late spring frosts and low winter temperatures (See References 2).
Pomace is made up of grape skins and seeds that are left over after processing. Although it is useful for other purposes, such as feeding livestock, most of it is used as compost for vineyards, gardens and landscapes. Pomace contains moisture, and nitrogen, potassium and phosphorus, the same nutrients found in commercial fertilizers (See References 4). Pomace, like other composted materials, helps filter environmental pollutants (See References 5). It also helps plants improve their drought tolerance.