The Latin name for the walnut tree genus is Juglans, which translates to "Jupiter's nut." They belong to the Juglandaceae family, which also includes hickories and pecans (Carya spp.). Walnut trees are monoecious, meaning a single tree contains both male (catkin) and female (pistillate) flowers, allowing them to self-pollinate. Nut production is best when walnut trees of different cultivars are planted in groups, as is typically done in walnut groves cultivated for nut production.
When choosing a walnut tree for planting on your property, look closely at the recommended USDA Zones as well as the tree height and normal exposure type. It's important to choose the plants around your walnut trees carefully. This genus produces a toxin called juglone that can be harmful to the plants around it in varying degrees, through an effect known as allelopathy. Make sure any surrounding plants you're considering are not prone to juglone toxicity.
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Andean Walnut
horrabin/Flickr/CC BY 2.0 - Latin Name: Juglans neotropica
- Other Common Names: Tropical walnut, Colombian walnut, nogal, Ecuadorian walnut, nogal Bogotano
- Native to: Colombia, Ecuador, and Peru
- USDA Zones: Likely 10–11
- Height: Up to 100 feet
- Exposure: Full to partial sun; cannot grow in shade
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Arizona Black Walnut
Bruce Marlin/Wikimedia Commons/CC 3.0 - Latin Name: Juglans major
- Other Common Names: Arizona walnut, nogal, New Mexico walnut, mountain walnut, River walnut, nogal silvestre
- Native to: Arizona, New Mexico, Oklahoma, Texas, Utah
- USDA Zones: 6–10
- Height: Up to 50 feet
- Exposure: Full sun to part shade
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Brazilian Walnut
George Slickers/Wikimedia Commons/Creative Commons 2.5 - Latin Name: Juglans australis
- Other Common Names: Nogal criollo, tropical walnut
- Native to: Argentina and Bolivia
- USDA Zones: Unknown
- Height: Up to 82 feet
- Exposure: Likely full sun
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Butternut
Modal jig/Wikimedia Commons/CC 3.0 - Latin Name: Juglans cinerea
- Other Common Names: Oilnut, white walnut, long walnut
- Native to: Eastern North America
- USDA Zones: 3–7
- Height: 40–60 feet
- Exposure: Full sun
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Hinds' Black Walnut
Animalparty/Wikimedia Commons/CC 2.5 - Latin Name: Juglans hindsii. Some put this as a variety of Juglans californica.
- Other Common Names: Northern California walnut
- Native to: California
- USDA Zones: 7–10
- Height: 30–60 feet
- Exposure: Full sun
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Japanese Walnut
Tahirs/Wikimedia Commons/CC 1.0 - Latin Name: Juglans ailantifolia
- Other Common Names: Heartnut, which is specifically Juglans ailantifolia var. cordiformis, though some set it as its own species (Juglans cordiformis). Siebold walnut is another possible common name for the Japanese walnut.
- Native to: Japan
- USDA Zones: 4–7
- Height: Usually 40–65 feet
- Exposure: Full sun
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Manchurian Walnut
Jean-Pol GRANDMONT/Wikimedia Commons/CC BY 2.5 - Latin Name: Juglans mandshurica
- Other Common Names: Chinese walnut
- Native to: China, North Korea, South Korea, and Russian Far East
- Height: Up to 82 feet
- Exposure: Full sun
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Texas Black Walnut
Jerry Friedman/Wikimedia Commons/CC BY 2.0 - Latin Name: Juglans microcarpa. It may also be known as Juglans rupestris or Juglans nana.
- Other Common Names: Texas walnut, little black walnut, nogalito, river walnut, little walnut, dwarf walnut, nogal, Mexican walnut
- Native to: Kansas, New Mexico, Oklahoma, Texas
- USDA Zones: Likely 5–7
- Height: 15–50 feet
- Exposure: Full sun to part shade