this is the first year my trees has produced nuts, however, they are soft and mushy inside, no solid shell or nut
I am in zone 4b
my soil is well drained loam , clay further down
I have 6 trees, planted at the same time, 3 are now 20 ft high, and only one bore fruit, on the east side of the tree only
One factor might simply be time. Black walnut trees (Juglans nigra) can take years to produce a good crop, and quality of both fruit and production appears to be widely variable. Here is information on growing black walnuts from the University of Minnesota Extension Service.
Walnut trees begin producing nuts when they are about 10 years old, but the best nut production begins when trees are 30 years old. Good nut crops occur in about two out of five years. Open-grown trees with large crowns produce more nuts than woods-grown trees with small crowns, but the number of nuts, frequency of nut crops, and quality of nuts (percentage of kernel to shell, by weight) vary greatly from tree to tree.
According to this second, excellent fact sheet from the Missouri Center for Agroforestry, nut production in black walnuts is also helped by added nitrogen fertilization through the growing season. A useful timetable for nut growers is included:
Wishing you the best of luck with your walnut trees.