The filbert is grown commercially over a large part of Europe and Asia, and the nuts are found for sale in about every grocery and fruit-store. Tons of the nuts are annually shipped to the United States. The varieties from west Europe have not succeeded well in any part of the Union. Over about the whole country, our summers are too hot or the winters too cold. The flower catkins develop in autumn. In the North they are apt to be killed by the cold, and in the South and in California the warm spells of early winter expand the flowers, to be caught usually by winter frosts, and in nearly frostless regions in California the summers are so hot that fungus diseases are developed. Yet we have some seedlings from imported varieties - mostly hybrids it is suspected - which are grown in a small way in the Eastern States and California.
The propagation of special varieties is usually by cuttings of new wood planted in the fall or during winter in mild climates. In Europe, the trees are shaped in nursery prior to selling or planting, with a stem three to four feet high, with an open top and a head with not less than six branches.
The pruning is never neglected by professional growers. The thin, unfruitful twigs are cut out, and the new growth in the dormant period is shortened back nearly to the female buds. But in this cutting, care is taken to leave enough of the male catkins for an ample supply of pollen. The male catkins and female buds are shown in Fig. 82.
Fig. 82. - A, Male catkins of filbert ; B, female flowers of filbert. (After Bailey.)