Also referred to as Persian or Carpathian walnut, English walnuts can be grown in USDA plant hardiness map zones 4 through 9. For optimal growth potential, English walnut trees prefer loamy soil. Less fertile soil is tolerated by English walnut, but the tree will grow slower. Plant walnut trees in late fall to early winter before the ground freezes.
Evaluate the landscape for well-drained soil in a full sun location where the English walnut tree can grow unencumbered. The walnut tree can reach a height of 100 feet if not pruned. When planting multiple English walnut trees, space them at least 30 feet apart. Dig the hole about 18 inches wide and 12 inches deep for bare root plants. If planting a container-grown English walnut, dig the hole two to three times the width of the container and as deep as the container is tall. In compacted soil, jab the shovel point into the sides and bottom of the hole to help root penetration.
Examine the walnut tree roots
Examine the root of the English walnut. Cut damaged or dead roots off a bare root tree. If planting from a container, remove the tree from the container and look for roots wrapping around the root ball. Loosen tangled or wrapped roots and use hand pruners to snip them close to the side of the root ball.
Position the English walnut tree in the hole. Hold the bare root with the crown (where the roots meet the stem) about 2 inches below ground level. Add soil to the center of the hole to create a cone-shape to support the roots. Spread the roots around the soil cone and then backfill the hole. Water around the root to settle the soil. Add more soil if needed to level the surface.
The top of the root ball of a container plant should rest at ground level. Add or remove dirt from the bottom of the hole if needed. With the root ball in the center of the hole, backfill the hole halfway. Water around the root ball to settle the soil, and then finish backfilling the hole. Do not fertilize trees at time of planting.
Apply 2 to 4 inches of mulch, like wood chips, to help retain moisture and help block weed growth as the English walnut tree grows. Keep the mulch about 2 inches from the trunk of the tree. Water the walnut tree about every 10 days from spring to fall the first year if there is no rainfall. Saturate the soil deeply.
University of California Ag Issues Center: Commodity Profile, English Walnuts
University of Idaho College of Natural Resources: Carpathian Walnut (pg 2)
Oregon State University Extension Service: Growing Walnuts in Oregon
North Carolina State University Coop Extension Service: Planting Techniques for Trees and Shrubs