Filbert (Hazelnut) (Corylus sp.) Little research has been done
on the Filbert in California. Thus, we know little about its
specific adaptability or productive capacity. Filberts are
monoecious (separate female and male flowers are borne on one
plant—like walnuts) and some cultivars are self-unfruitful;
thus, two different varieties should be grown for cross-
pollination to produce consistent crops. Trees reach a height of
18 ft. under ideal conditions. Filberts are almost pest free in
California. Seedling is the only known rootstock. - [PDF]
Filbert Varieties for Planting in the Home Garden , Paul Vossen,
Sonoma and Marin Co. UCCE