Well, something very mild, you don't want to fry them at this point. Maybe 1/4 strength Miracle Grow, or perhaps a tablespoon of Osmocote mixed into the soil around each plant.

Sounds good I have Miracle Grow.

How about blood meal or bone meal?

For what it's worth....Miller provides a pretty detailed information booklet on grape culture in its planting guide. Here is what it says in the section: Fertilizing Grapes. "A Commercial Fertilizer such as 10-10-10 will supply the vine all the nutrients needed. Use 1 pound per vine in a mature vineyard. Use less on young vines and do not fertilize at all the first year. It should be applied as soon as the buds start to swell in the spring. For best results spread the fertilizer away from the base of the vine as grape feeder roots grow 8 to 10 ft. long. If the fertlizer is placed around the base of the vine it will be of little benefit. On vines that make an exceptionally strong growth use fertilizers sparingly."

If you have alkaline soil you might consider some foliar spray.

Thanks for all the info.