Hazelnuts, sometimes called filberts, have a long and fascinating history. The name filbert probably derived from the German term vollbart (full beard) in reference to some hazelnut varieties in which the husk entirely covers the nut. However, some people believe the name derives from St. Philibert, whose feast is celebrated on August 20, about the time the earliest hazelnuts ripen in England. In the Pacific Northwest, we grow Corylus avellana, the European hazelnut. The genus name Corylus comes from the Greek word korys (helmet or hood). The word hazelnut is derived from the Anglo-Saxon word haesel (bonnet).

Hazelnut trees thrive in cool, moist climates and require the chill to break dormancy.

Hazelnuts are monoecious, meaning they have separate male and female flowers on the same tree. Male and female flowers may bloom at different times. Hazelnuts are self-incompatible, which means a tree cannot set nuts with its own pollen. Also, cer­tain combinations of varieties are cross-incompatible. That is, pollen of some varieties will not set nuts on certain other varieties. Hazel flowers are wind-pollinated, so no bees or butterflies are needed for pollination.

It is usually recommended to plant three pollinizer varieties (early, mid, and late) in an orchard so pollen is avail­able throughout the extended period of time during which female flowers appear. Stigmas are receptive to pollen from the time they first appear as a tiny red dot at the tip of the bud until they extend to their maximum length. In some seasons, this occurs from late November until early March.

So from all the research, I would recommend you plant both a red zellar and maximus purpurea along with a pollinator such as Eta, York, or Gamma.

Here are some publications you will find useful:

https://catalog.extension.oregonstate.edu/sites/catalog/files/project/pdf/em9073.pdf

https://catalog.extension.oregonstate.edu/sites/catalog/files/project/pdf/em9072.pdf

https://landscapeplants.oregonstate.edu/plants/corylus-avellana-rote-zeller

http://www.growinghazelnuts.com/our-nursery/understanding-compatibility/pollen-compatibility/

Hope this helps!