Answer: You don't need two varieties of grapes for fruit set, but you do need to have the right varieties for your growing region. The wrong varieties may flower, but they won't set fruit - or the fruit will not ripen. Overfertilization will encourage lots of green growth at the expense of fruit; inadequate sunshine will also affect fruiting, as will immaturity of the plant.
So, make sure your grapevines get plenty of sunshine and plenty of water. Hold off on fertilizer, and be patient for another year or two. When the vines are mature enough, they'll flower and begin to set small quantities of fruit.
Just FYI, the top green varieties for your area are Perlette, Sugraone, Thompson Seedless, and Calmeria. The top red varieties are Red Globe, ChristmasRose, Rouge, Emperor, Flame Seed-less, Ruby Seedless, and Crimson Seedless. The leading blue-black varieties are Autumn Royal, Niabell, Ribier, Fantasy Seedless, Beauty Seedless, and Marroo Seedless.
Hope this information is helpful!
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