Pollination
Every fruit and nut grower should know the simple theory of pollination.
When a tree appears thrifty but fails to produce, nine times in ten the
trouble is with the pollination. The walnut is bi-sexual and
self-fertile; the staminate catkins appear first, at
the end of the
year's growth (see Fig. 1), and the female blossoms, or pistillates,
from one to three weeks later at the end of the new growth (see Fig. 2).
Thus the staminate catkins sometimes fall before the pistillates form,
and naturally there is no pollination and no crop. This should not
discourage the grower or cause him to uproot his trees. Often by waiting
a few seasons--if the tree is of the correct variety--the trouble may
right itself. Many growers have gotten a crop from single trees where
there was trouble with the pollination by artificially fertilizing, that
is, shaking the pollen from fertile trees, even black walnut, over the
barren pistillates. Birds, insects, and the breezes carry pollen from
one tree to another. Therefore, if nuts for seed are desired, keep each
grove of pure strain separate that there may be no deterioration owing
to cross-fertilization. But the mixed orchard may bear best. Some
varieties of walnut trees--notably the Los Angeles--are suitable only
for shade in Oregon and should not be planted with any other thought in
mind. The staminate blossoms of this variety appear six weeks ahead of
the pistillates and, there being no pollination, naturally there are no
nuts.
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