Persian Walnut Juglans regia

English Walnut is a broadleaf deciduous tree that usually grows 40 to 60 feet tall and equally as wide and is cultivated for its sweet nuts. It has a spreading, rounded crown. The bark is gray and smooth, but it develops ridges with age. The leaves are pinnately compound with 5 to 11 oblong leaflets and have a citrus fragrance when crushed. Yellow-greenish flowers appear from May to June. The male flowers are catkins, and the female flowers appear in clusters. The female flower produces the edible nut. Each nut is covered in a smooth green husk that turns brown as it matures. The shell of the nut is very thin and wrinkled, ripening in the fall. The tree will begin to produce nuts when it is 4 to 6 years old, but it will generally produce a good crop of fruit after the tree is about 15 to 20 years old. 

This tree is native to Europe and Central Asia. It is grown for commercial purposes on the West Coast of the United States. About 99% of all commercially produced walnuts are grown in California. It is also grown in many areas of the United States as an ornamental tree.

The genus name, Juglans, is derived from two Latin words, jovis, which means Jupiter, and glans meaning an acorn or nut. The specific epithet, regia, is defined as kingly or royal and references the quality of the fruits.

The English Walnut prefers full sun, and moist, rich, loamy, well-drained soils. It is intolerant to shade, and poor or wet soils. It is very difficult to transplant due to its deep tap root. This tree doesn't do well in hot, humid climates; therefore, pecans trees are a better choice in the southern United States.

This ornamental tree is best planted in a large landscape area. It is a host plant for the larvae of the Hickory horndevil (Citheronia regalis) moth.

Seasons of Interest:

Bark:  Winter     Bloom:  Spring      Foliage:  Spring, Summer, and Fall      Fruits:  Fall

Quick ID Hints:

• deciduous tree, 40 to 60 feet tall, spreading, rounded crown
• gray and smooth bark, develops ridges with a diamond pattern
• odd-pinnately compound leaves 12 to 18 inches long with 5 to 11 oblong leaflets with a citrus fragrance when crushed
• male flowers are catkins and female flowers appear in clusters
• fruit is a thin shell nut encased in a green to brown husk, maturing in the fall

Insects, Diseases, and Other Plant Problems: The English Walnut has no serious insect or disease problems. Anthracnose, bacterial blight, root rot, canker, leaf spot, and shoot dieback can occur. Potential insects include webworms and caterpillars that like to chew on the foliage. The roots of this tree produce a chemical known as juglones. This chemical is toxic to other plants including azaleas, rhododendron, blueberries, peonies, tomatoes, peppers, and potatoes. The litter from the nuts can be messy in the fall.

VIDEO created by Ryan Contreras for “Landscape Plant Materials I:  Deciduous Hardwoods and Conifers or Landscape Plant Materials II:  Spring Flowering Trees and Shrubs” a plant identification course offered by the Department of Horticulture at Oregon State University