Walnut trees (Juglans) are a family of numerous tree species. There are six walnut tree species that are native to the United States according to the Virginia Extension Cooperative. Numerous English/Persian walnut tree varieties, which are native to Asia, are grown commercially and for ornamental purposes across the nation. Walnut trees are both male and female which enables them to be self-fertile and produce an abundance of nuts. The wood of walnut trees is highly valued in the timber industry.
Walnut trees require a distance of 30 feet when being planted. They also require a soil depth of at least 6 feet without reaching bedrock or any other obstruction. The tree normally maintains its highest root system cluster in the first 3 feet of soil. Most English/Persian walnut tree varieties are grown on rootstock that is a mix of Persian and black walnut tree roots. Of all the species the black walnut grows the largest and can easily tower 100 feet
Pollination and Nut Production
The older the walnut tree, the more successful self-pollination becomes. As the tree ages the period of male and female flower production begins to overlap more dramatically which enhances self-pollination. Trees will not begin nut production until the tree is 3 to 5 years old old. A tree grown for commercial nut production will not begin serious production until the tree is more than 10 years of age.
All walnut tree varieties produce a substance known as juglone. The black walnut tree produces an abundance of this toxic substance. Juglone is found in the leaves, roots, nut hulls, buds and flowers of the tree. The substance is toxic to other plants and makes it difficult to grow certain species anywhere near the root system of the tree.
In the month of October, the husk of the nut begins to crack and the nuts will fall to the ground. The trees branches are often shook at this time period to release a rain of nuts. The nuts must be promptly gathered to prevent mold. Hulls occasionally fall with the nuts. The hull contains a substance that can cause skin irritation. The substance will easily stain hands and clothes.
Walnut shells and nuts are dried within 24 hours of harvest. The nut can be removed from the shell for easier drying. The nuts require a drying temperature of between 95 to 105 degrees.
The lumber of the walnut tree is highly valuable. The University of Minnesota states that wood from the black walnut tree is considered to be the most valuable lumber product in the Midwest based on price per board feet. The trees wood produces a pleasing color, durability, good machining qualities and ease of drying. Walnut trees are also used in veneer production.