Also called the Persian walnut, this deciduous tree is native to the area from southeastern Europe to China. It was introduced to the Americas by the English colonists by the 1600s and now is cultivated in the United States with a commercially important presence in California especially in the central valley. Although the nuts of the tree are economically important, the tree itself is a beautiful ornamental with handsome bark, long chartreuse catkins, and an elegant canopy of pinnately compound leaves. The roots of the tree produce juglone, a chemical that inhibits the growth of many other plants. The fallen leaves are also toxic to other plants and should not be added to compost piles. English walnut is usually grafted onto Black walnut rootstock to improve disease resistance. Many cultivars have been developed providing a variety of characteristics including thickness of shell, taste of meat, bearing time, and size of tree and nut.
Fruit Description: Nuts are borne in bright green husks that mature to brown and wither away.
Fruit Availability: Fall
Plant Size: 30-50’ H x 30’ W
Light: Full sun
Soil: Fertile, moist, well-drained. Will not tolerate prolonged drought. Soak tree for a half day two weeks before harvest.
Fertilizer: Fertilize once in the spring as buds form and again in the fall just before harvest with a complete fertilizer high in nitrogen such as 18-4-8. Since the roots of the tree extend l½ the size of the canopy be sure to spread the fertilizer through out the area and water in well.
Hardiness: Zones 5-9
Care: Prune older trees during winter dormancy to thin out crowded or crossing branches or to remove damaged or dead wood. Harvest after the green husks have fallen off the nuts, wash, and dry in trays in the sun.
Pests and Diseases: Susceptible to crown rot water mold fungi, aphids, and walnut husk fly.