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Growing Walnut: Juglans regia

Botanical Overview

The Walnut family (Juglandaceae) contains 12 genera, including Hickory (Carya) and Walnut (Juglans). The Walnut genus contains 21 species of deciduous nut trees, including Black Walnut (Juglans nigra).

Description

Form: Tree.
Lifespan: Over 200 years.
Leaf retention: Deciduous.
Growth rate: Slow to moderate.
Mature Size: 25-60' high and as wide.
Flowers: Separate yellow-green male catkins and female flowers in clusters on the same tree.
Bloom: Spring.
Self-fruitful: Depends on cultivar. Two trees produce a larger crop. The flowers are wind-pollinated.
Years before fruiting: 8-12 from seed, 4-6 grafted. The tree must be in the ground 20 years before it produces a full crop of nuts.
Fruit: A fleshy green husk covers a woody, wrinkled shell containing an edible seed commonly called a nut.
Months for fruit to ripen: 6.
Storage after harvest: After the fleshy outer husk is removed, the nuts should be stored in a low humidity environment. Temperatures at or just below freezing provide the longest storage, but 77 °F or below is acceptable. A humid environment will lead to mold infestation producing aflatoxin, a potent carcinogen. Any moldy batch of walnuts must be discarded.
Leaves: Green, ovate leaflets with a lemon or lime aroma when crushed.
Stems: The bark is olive brown when young, silver grey when older. Trunks develop fissured, grey bark and may grow up to eight feet in diameter.
Roots: A walnut tree is usually grown on a rootstock such as Paradox. A deep taproot develops on trees grown from seed. This tree will develop large, widespread, deep roots over time and needs soil at least 5' deep and well drained to avoid root rot.
Cultivars of Note:
'Pedro' A small tree, 27-40' tall, adaptable, having a popular flavored nut, self-fruitful, 400 chill hours.
'Placentia' A tree for mild climates, self-fruitful, 300 chill hours.
Wildlife: This tree is not known to attract wildlife.
Toxic / Danger: Nuts which are not ripe contain cyanide and must not be eaten. Walnut husks can irritate skin and stain clothing. The pollen is a problem for some people. Horses may contact laminitis from wood chips or sawdust.
This tree produces a substance known as Juglone from its leaves, bark and roots that infuses into the ground inside the drip line and can remain in the soil for years. Many plant species are inhibited or killed by this chemical. Because of this, edible food plants and gardens should be located away from a walnut tree to avoid reduced crop size.
Origin: Central Asia to the Balkans.

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Cultivation and Uses

USDA hardiness zones: 5-9.
Chill hours: 300-700 for residential cultivars.
Heat tolerant: At temperatures of 100°F and above, most cultivars are greatly stressed and the nut kernels will shrivel and darken.
Drought tolerant: No.
Sun: Full sun. This tree is shade intolerant.
Planting: Plant in early spring after the last predicted frost. Dig a hole twice as wide as the seedling's root ball or pot. Avoid areas prone to flooding or that will have standing water after a rain.
Spacing: Plant seedlings 12-17' apart from other trees.
Soil: Plant in well drained, moist, high organic content soil at least 5' deep. Walnuts tolerate a soil pH of 5.1-8.3 (strongly acidic to somewhat alkaline), but prefer pH 6.6-7.5 (neutral).
Fertilize: Add organic fertilizer monthly under the drip line during the growing season.
Water after becoming established: Deep water weekly, but allow the soil to dry out before watering again.
Mulch: Use organic mulch under the drip line.
First Year Care: Remove all weeds within 3' of the trunk a seedling by hand. Do not use tools that cut into the soil because that may harm roots of the new seedling.
Prune: Prune in winter to establish a strong, single, trunk. Each year remove the lowest branches until a desired height is reached. Remove crossing branches.
Litter: Male catkins in spring, leaves in the fall, nuts if not harvested.
Propagation: Cuttings grafted onto a fungus resistant rootstock such as Paradox. Seed does not breed true.
Uses: Culinary, shade, ornamental. The seed, its oil, and sap are edible. A sugar can be made from sap tapped in the spring. Even the powder of finely ground shells is used to stuff a certain pasta dish.

Comments

Other common names are English Walnut, Persian Walnut, Carpathian Walnut, and common Walnut.
Walnuts, being large trees that are native to moderate rainfall climates with loamy soil, are not well suited to hot, dry climates. They suffer in high heat and are best grown in mountain regions with deep soil and lower summer temperatures. The poor soil quality of most desert regions is a deterrent to their growth and production.


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By Dontworry - Own work, CC BY-SA 3.0, httpscommons.wikimedia.orgwindex.phpcurid-6500504
Male flowers

By H. Zell - Own work, CC BY-SA 3.0, httpscommons.wikimedia.orgwindex.phpcurid-10528080
Female flowers

By Böhringer Friedrich - Own work, CC BY-SA 2.5, httpscommons.wikimedia.orgwindex.phpcurid-4889779

CC BY-SA 3.0, httpscommons.wikimedia.orgwindex.phpcurid-41129



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Latest update: February, 2020