The most common walnut tree grown in the U.S., aside from the native Black Walnut, is the English (also called Persian) walnut. English walnuts are often preferred for their milder taste and easier shelling, and they will not stain your hands like the husk of black walnuts can.
Where Can Walnut Trees Grow?
Often grown on the West Coast, these trees can be grown in most environments of the United States that are not subject to deep freeze and have a relatively long growing season. They have a slow dormancy attainment, so areas subject to flash freezes and fast-approach fall frosts are not well-suited to growing walnuts. Spring frosts can also be detrimental to walnut production.
Walnut Tree Site Selection
The planting site should be at least thirty feet from any obstruction to allow wide root growth and branches to match. Soil should be well-drained and at least five feet deep to allow root expansion. Spots on a small rise or slope are best to allow for drainage. Prolonged flooding will destroy walnut trees faster than most other problems.
Planting Walnut Trees
Dig the hole approximately to match the width and depth of the seedling’s root system. Prune off broken roots and place the tree into the hole. Fill it in so that the uppermost root is at least three inches below the surface. Tamp down the dirt after filling in the hole and moisten well. Do not fertilize, but water daily to keep the soil moist, until the seedling is well-established.
Management and Pruning of Walnut Trees
New trees will need to be staked to withstand the wind and promote straight trunk growth. Cloth ties should be used to avoid harming the young bark with the stake 6 to 8 inches from the tree on the windward side. Recheck ties regularly to be sure they aren’t getting too tight as the tree grows or the stake moves.
Pruning is usually only to keep the trees well-shaped and remove dead or dying branches. Once the trees are trained, pruning every second or third year (the production year) is done by simply nipping buds to prevent new limb growth and promote more nut production that year.
When the husk can be easily cut free from the nut with a knife, they are ready for harvest. Most growers wait until late fall rains have caused the husks to split, as then the nuts will easily fall from the tree, allowing for the use of shakers. Home growers often spread blankets or bedsheets beneath the tree and use poles or other means to shake tree branches and cause the nuts to fall.
The most common pest for walnut trees is the walnut husk fly. The larvae of the fly reside in the husk of the walnut, eating the inside layers of husk and staining the shell and nut. They are most often noticed after they’ve burrowed in, when the green husk begins showing dark spots from their burrowing. Walnut aphids are another problem, destroying the leaves of the walnut tree and thus negatively affecting nut production. Deer can damage walnut trees and are the most common physical threat to the trees in most areas. Fencing and other barriers are the best protection.
Other Resources for How to Grow Walnuts:
Oregon State University – Growing Walnuts in Oregon [PDF]
University of Minnesota – Growling Black Walnuts