Unlike other fruiting trees, the hazelnut tree blooms and pollinates in the middle of winter. Wind carries the pollen from catkins (male flowers) to small red female flowers, where pollination occurs. The flowers remain inactive until spring, when fertilisation occurs and the nuts begin to develop.
The natural growth habit of the hazelnut is a bush, or multi-stemmed small tree as found in Turkey and Southern Europe. In the US, hazelnut trees are grown as single trunk trees that can grow to 5 meters or more.
All varieties of hazelnuts require cross-pollination in order to produce nuts, so every planting requires two or more varieties. In the US, where cultivation and automation exceeds that of Europe, the principal varieties grown are Barcelona (originally derived from Spain in the 19th century), Ennis, Lewis and Casina.
Ennis, a later and heavier yielder to Barcelona, produces a larger nut suitable for both in shell and out of shell production. Lewis produces a medium nut whilst Casina produces a small nut.
Research in Australia is being carried out by the Faculty of Rural Management, The University of Sydney, in collaboration with NSW Agriculture and hazelnut growers. The research is funded by the Rural Industries Research and Development Corporation (RIRDC).
Hazelnut trees should be in commercial production when they are about 6 years old, and a well managed orchard should remain active for 40 years or more.
The nuts mature during the summer months (turning in color from green to hazel) and are harvested in late summer and early autumn when the nuts fall to the ground within a short period. The nuts are picked up by hand or harvested mechanically, washed, dried and sorted by size.
There is very little disease in Australia that harm Hazelnuts due to strict quarantine laws. EFB (Eastern Filbert Blight) is not present in Australia.