Answer: Grapes grow and produce best when planted in full sunshine, not in part shade. Are your plants receiving at least 8 hours of sun daily? Note that new vines take some time to become established and produce well. They also need to be pruned. The best time to prune grapes is in late winter, very early spring. They should be pruned back hard to only a few buds. Here's a website with grape pruning info:
Another consideration is that grapevines will develop lush growth but few fruits if overfertilized with nitrogen.
Here's some basic information on fertilizer and nutrients that plants require. The 3 numbers on a fertilizer bag refer to the percentage of N (nitrogen), P (phosphorous), and K (potassium) in the bag. There are different formulations for different purposes. In general terms, nitrogen produces lush green growth, phosphorous helps strengthen stems and produce flowers, and potassium keeps the root system healthy. If you're applying fertilizer to fruiting (e.g., tomatoes) or flowering plants, you're not as interested in the plant developing leaves as you are in it flowers and fruit, so you'd use a formulation lower in nitrogen and higher in phosphorous, such as Miracle-Gro's Plant Food at 15-30-15. Bone meal is an organic source of phosphorous. Good luck!
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