Royal Blue Seedless Grapes
Royal Blue Seedless. This blue grape is a parthenocarpic seedless grape with a checkered history. It seems identical to Seedless Concord, though a private individual claims Royal Blue is a variety he found. I have grown it for over 20 years and the fruit is a typical parthenocarpic seedless with an occasional seeded berry. Well filled clusters are small as are the berries. In the growing season of 2006 it did something unprecedented in that every berry on every cluster had fully developed seeds, with a large percentage of the seed having full, normal endosperm. The seeded fruit did resemble Concord, but it ripened at least two weeks earler, was higher in sugar, and had a milder flavor from true Concord elsewhere in the vineyard. Is Royal Seedless a sport of Concord? It's possible, but genetic testing will be needed to sort out it's identity for certain.
The vine is extremely low in vigor on light soils, and only moderate at best on heavy, fertile soils. Hardiness is unknown, but anecdotal reports suggest it could be hardy to -20 F. Prune to canes, but be sure to limit crop as any overcropping reduces the low vigor even further.