Muscadine grapes have shallow roots that feed upon nutrients within the top 12 inches of the soil. Correct application of nutrients is important. The type and schedule of fertilization depends largely upon the existing conditions of the soil and age of the muscadine grape. Before planting vegetation, perform a soil test, which will inform you of the soil pH and the nutrient status of your site.
First Year Fertilization
Provide 1/4 to 1/2 lb. of a complete fertilizer, such as 10-10-10 or 12-12-12, to each muscadine grape vine during April of the first growing season. Apply in a wide band, 1 to 2 feet in diameter, making sure to encompass all of the plant roots. Repeat this process with reapplications in July and in early August. Allow approximately six weeks to elapse between fertilizer applications.
Fertilization - Second Year and Beyond
Provide the same type of fertilizer to second-year muscadine grape vines, but double the amount to 1/2 to 1 lb. per vine. Provide two applications total in early March and June or July. In future years, continue to fertilize on this time schedule, but increase rates to 2 to 3 lbs. of fertilizer per vine. As the plant matures, increase the broadcast range of fertilization to a 6-foot diameter. Expect muscadine grapes to grow an average of 30 to 36 inches per year. Increase nitrogen if less growth occurs, cut back on nitrogen if more growth takes place.
Muscadine grapes benefit from periodic applications of micronutrients. In particular, muscadine grapes have a high magnesium requirement. Indications of magnesium deficiency include leaf yellowing and premature fruiting. To prevent or fix this problem in one- or two-year-old vines, evenly distribute 2 to 4 oz. of Epson salt over a 3- to 6-foot radius around each vine. Provide 4 to 6 oz. of Epson salt, in the same manner, to mature muscadine vines. If possible, apply to plants in July.
Boron is considered the second most important micronutrient. A shortage of boron, which is fairly common in soils with a high pH, will cause underdeveloped or deformed grapes. Two tablespoons of borax mixed into fertilizer is enough to treat a 400 square foot area. Apply no more frequently than every two to three years just prior to blooming. Avoid excessive application of boron. Too much of this nutrient is toxic to muscadine grapes.