A combination of zinc or zinc sulfate, ammonium nitrate or mixed urea, and composted manure is effective for fertilizing grapes. Grape plants also need a soil pH of 5.5 to 7.0, so planters might need to add dolomitic limestone as a fertilizer to increase it.
Gardeners should create a solution of 1/10 pound of zinc or zinc sulfate with 1 gallon of water and spray this on the leaves of the plant two weeks before the vines begin to bloom. This helps with pollination, hormone production and other plant functions. After the plant blooms or begins to produce grapes, gardeners should mix 3/8 pound of ammonium nitrate or 1/4 pound of mixed urea into the soil near the roots. Composed manure provides nitrogen to grapes when they grow in the spring, so gardeners should apply 5 to 10 pounds of poultry or rabbit manure per vine in January or February.