Hazel trees are wind-pollinated and there must be a compatible pollinating variety for effective pollination. In addition, the flowering time of male and female flowers is important because the receptivity of female flowers must overlap with the time of pollen release. Hazelnuts are monoecious, meaning they have separate male and female flowers on the same tree. Male and female flowers can bloom at different times.
Hazelnuts are self-incompatible, meaning that a tree cannot produce nuts with its own pollen. In addition, certain combinations of varieties are incompatible with each other. In other words, pollen in some varieties does not produce nuts in other varieties. Since an American hazelnut (Corylus americana) has male and female flowers that can be cross-pollinated, it doesn't need another variety for pollination.
Male growths develop in autumn, persist on the tree during winter and bloom in spring at the same time as female flowers. The wind carries pollen from male flowers to female flowers and the fertilized flowers become nuts that ripen in autumn. Nuts are good to eat fresh or to add to baked goods. Pollen can spread up to 15 meters, but it rarely has to travel that far.
Each hazel tree has male and female flowers, so all you have to do is get to the tree next to the tree it came from. In case you were wondering, hazel trees can't pollinate themselves. The pollen must come from another tree in the garden. If an allele expressed in pollen matches one of the alleles of the female flower, the crossing is incompatible.
Although hazelnuts are monoecious (they have male and female flowers on the same tree), they are incompatible with each other, meaning that a tree cannot produce nuts with its own pollen. First, male growths begin to form in mid-May, appear in June, but don't actually reach maturity until December or January. Male growths (figure) begin to form in mid-May and begin to appear in June, but do not reach maturity until December or January.
