Bruce Marlin / CC BY 3.0
Walnut
Juglans
Overview
A majestic, long-lived tree that produces one of the most nutritionally valuable nuts in the world. Walnuts are uniquely rich in ALA omega-3 fatty acids — the only tree nut with significant omega-3 content. The tree exudes juglone from its roots, a chemical that inhibits the growth of many other plants, so careful planning is needed when integrating walnuts into a food forest.
Walnut trees are deciduous trees that belong to the Juglans genus, which is part of the family Juglandaceae. These trees can grow up to 10-40 meters tall and have pinnate leaves measuring 200-900 millimeters in length, with 5-25 leaflets each. The shoots of walnut trees have chambered pith, a characteristic they share with wingnuts (Pterocarya) but not hickories (Carya).
The 21 species within the Juglans genus are found across the north temperate Old World, ranging from southeast Europe to Japan. In the New World, these species can be found in various regions, including southeast Canada, California, and Argentina.
Edible walnuts, which are consumed worldwide, are typically harvested from cultivated varieties of the species Juglans regia. China is the leading producer of walnuts, accounting for half of the world's total production.
In 2017, global walnut production (in shell) amounted to 3.8 million tonnes, with China leading the production at 50%, followed by the United States (15%) and Iran (9%).
Both Juglans regia and J. nigra are commercially important species, valued for their timber and nuts. These two species have similar cultivation requirements and are widely grown in temperate zones. Walnut trees require full sun exposure and can tolerate drought conditions well.
When cultivated for nuts, it is essential to select compatible cultivars for pollination purposes. Many different cultivars are available for growers, offering various traits such as growth habits, flowering and leafing, kernel flavors, and shell thicknesses. Some cultivars have been developed specifically for novel "hedge" production systems in Europe.
Appearance
The leaves and blossoms of walnut trees typically appear in spring. The male flowers emerge before the female flowers and are catkins that hang from the branches. Female flowers are small and green, appearing in clusters.
Growing Conditions
Habitat & Range
- Habitat
- Forests & Woodlands
- Native Range
- Native to Alabama, Arizona, Arkansas, California, Delaware and 28 more US states; native to New Brunswick, Ontario, Quebec in Canada; also native to Afghanistan, Algeria, Amur and 52 more regions; introduced in Alberta, Oregon
- Native Region
- Canada, Continental US, Puerto Rico
- Cultivation Region
- Temperate regions
Botanical data via projectGAIA.
Companion Planting & Soil
Good Companions
Avoid Planting Near
Sowing & Propagation
Propagation Methods
Planting Calendar
When to sow, transplant, and harvest by growing zone.
| Zone | Action | Months | Notes |
|---|---|---|---|
| Cold (1-2) | Transplant | Apr — May | Plant bare-root in spring; Carpathian walnut hardy to zone 4; needs 50+ foot spacing |
| Cold (1-2) | Harvest | Sep — Oct | Harvest when green hulls split and nuts fall; remove hulls and cure 2-4 weeks |
| Cold (1-2) | Prune | Aug — Sep | Prune in late summer to avoid bleeding; minimal pruning needed once established |
| Cool (3-4) | Transplant | Mar — Apr | Plant bare-root in spring while dormant; deep taproot — choose site permanently |
| Cool (3-4) | Harvest | Sep — Oct | Gather fallen nuts promptly; remove husks and dry |
| Cool (3-4) | Prune | Jul — Aug | Summer prune; avoid winter/spring — sap bleeds heavily |
| Moderate (5-7) | Transplant | Nov — Dec | Plant in late fall; English walnut (zone 5+) or black walnut (zone 4+) |
| Moderate (5-7) | Transplant | Feb — Mar | Spring planting alternative; first nuts in 5-7 years |
| Moderate (5-7) | Harvest | Sep — Nov | Harvest when hulls crack; cure in shade with good ventilation |
| Moderate (5-7) | Prune | Jul — Aug | Prune in summer only; remove dead and crossing branches |
| Warm (8-9) | Transplant | Nov — Dec | Plant during dormancy; needs 400-1500 chill hours by variety |
| Warm (8-9) | Harvest | Sep — Oct | Harvest when hulls split |
| Warm (8-9) | Prune | Jul — Aug | Summer prune; juglone from roots inhibits nearby plants |
| Hot (10+) | Transplant | Dec — Jan (wraps) | Plant in winter; choose low-chill varieties |
| Hot (10+) | Harvest | Aug — Oct | Harvest in late summer/early fall |
Uses
Culinary
- Eaten raw or toasted in baking, salads, and pestos
- Cold-pressed walnut oil for finishing dishes
- Green walnuts pickled or made into nocino liqueur
Medicinal
- Richest tree nut source of ALA omega-3 fatty acids
- Polyphenols support brain health and cognitive function
- Anti-inflammatory properties studied for cardiovascular benefits
Other Uses
- Prized hardwood for fine furniture and woodworking
- Hull used as a natural brown-black dye
- Juglone-aware planting design required
