Answer: What you describe has a term - blank hazelnuts. Blank nuts are in-shell hazelnuts devoid of normal kernels which result from defective embryo sacs, unviable eggs, failure of fertilization or embryo abortion at varying stages of development. Owing to the alternate bearing cycles for hazelnuts, poorly filled nuts may also result during an overproduction year, and poor kernel fill appears to be a heritable trait. Without knowing what variety you are growing, the condition is hard to diagnose. Hazelnut trees are wind pollinated so a second hazelnut tree needs to be in the vicinity. Without cross-pollination, no nuts will form. If you have more than one tree, the problem might be associated with an alternate year bearing cycle (you'll find out next year when you examine the crop). It could also be weather related.
I'd give the trees one more year to produce. If there are still no edible nuts, you may need a second tree on your property, which will mean you'll need to have your tree identified to you can find a second variety.
Let's hope your tree bears next year!
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