What Should I Fertilize My Grape Plants With?

Which Fertilizer to Use

• An all-purpose organic fertilizer is sufficient for many grape varieties, providing that enough water is supplied. A 10-10-10 NPK (10 percent nitrogen, 10 percent phosphorus and 10 percent potassium) is generally preferred for grape plants. Alternatively, 6-6-18 tobacco fertilizer can be used to provide a wider variety of micronutrients, according to the North Carolina State University Horticultural Department.

How to Apply Fertilizer

• Dilute the fertilizer of your choice as described on the packaging, then apply 1/4 lb. in a wide circle around the base of each vine. Aim to apply the fertilizer in a circle under the widest leaves of the vine, no closer than 21 inches from the trunk. Double the amount of fertilizer used each year until your grape plants are fully established (generally at 3 years old). At this point, apply 2 lbs. of fertilizer in a 60- to 120-square foot area around the base of each vine at each fertilization.

When to Fertilize

• In this first year, grape plants should be fertilized every six weeks until early July. In the second year, fertilize every other month from early March to July, and in subsequent years, apply fertilizer once in mid-March and again in mid-June. If your grape plants are growing at a fast rate and not setting much fruit, reduce the amount and rate of fertilization. On the other hand, if your vines are growing slowly, you may need to increase the rate of fertilization.

Special Requirements

• Grape plants require magnesium, calcium and boron, which aren't generally provided in widely available fertilizers. Sprinkle 3 oz. of Epsom salts around the trunks of young vines (5 oz. for mature vines) in early July to provide magnesium. Apply 6 to 7 oz. of calcium nitrate in mid-May each year and 2 tbsp. of Borax mixed in with your chosen fertilizer every two to three years in early spring.