Hazelnut Help

Hi, I have five hazelnut trees that I planted from saplings about 8 years ago. This is the second year that four of the trees have put on a good number of flowers, but last year I didn’t get a single nut. Is there something I should do – some type of fertilizer they need? My soil is mostly red clay. Mid Atlantic region weather. The five trees include York, Theta, and Jefferson varieties.