Origin
Juglans rupestris Engelm. ex Torr. is a species of Walnut tree that is native to North America. Its range extends from Arizona and New Mexico in the Southwest to Texas and Oklahoma in the south-central United States.
Common names
The plant is commonly referred to as the Southwest Native American Walnut, Texas Walnut, or simply, Rock Walnut.
Appearance
Juglans rupestris is a deciduous tree that can grow up to 40 feet tall and 30 feet wide. The tree's bark is gray and smooth when young, but as it matures, it develops deep furrows and ridges. The leaves are pinnately compound, with 9-15 leaflets which are oblong-lanceolate. The leaflets are about 2-4 inches long and 1-2 inches wide with serrated margins and a rounded base. In the fall, the leaves turn yellow before dropping.
The tree produces nuts that are round and about 1 inch in diameter. The nut has a thick, woody shell that is difficult to crack, but inside it, you'll find a delicious nutmeat that is similar in taste to the Black Walnut. The nutmeat is rich in protein and oil, making it a valuable food source for wildlife.
Uses
The wood of Juglans rupestris is prized for its strength and beauty, making it an excellent choice for furniture and cabinetry. The native people of the Southwest used the tree's bark for medicinal purposes, while the nutmeat was an important food source. Today, the tree is cultivated as an ornamental tree and is sometimes used in reforestation projects.
Growth Conditions for Juglans rupestris Engelm. ex Torr.
Juglans rupestris Engelm. ex Torr. is commonly known as the Texas black walnut. The tree has specific requirements for optimal growth, and these conditions vary depending on the region where the tree is planted. In general, it requires ample amounts of sunlight, warm temperatures, and well-draining soil.
Light Requirements
The Texas black walnut grows best in full sunlight. When planted in areas with too much shade, this tree tends to grow poorly with a sparse canopy. Therefore, when selecting a site to plant this tree, it is crucial to choose an area with direct sunlight for most of the day.
Temperature Requirements
The Texas black walnut grows best in warm temperatures. The tree is native to western Texas and northern Mexico, where the climate is typically hot and dry. However, it can still tolerate cold temperatures as low as 15°F, and it is well-suited to survive the winter in colder zones.
Soil Requirements
The Texas black walnut prefers well-draining soils. The ideal soil for its growth is sandy loam, but it can also grow in clay soils as long as they are well-draining. This tree grows poorly in soils with poor drainage, as it is susceptible to root rot. Therefore, when planting this tree, ensure that the soil is well-prepared with adequate drainage.
Cultivation Methods
Juglans rupestris Engelm. ex Torr. is a tree that thrives in full sun and well-draining soil. It can tolerate a wide range of soil types, including sandy, loamy, and rocky soils. Plant the trees in a site that provides good air circulation to prevent disease. The ideal planting time is in the early spring season, which allows the roots to establish well before winter.
Watering Needs
The tree has moderate water requirements and should be watered regularly, especially during drought periods. Water deeply and less frequently than shallow and frequent watering. Young trees require more water than mature ones. Avoid getting water on the leaves when watering the trees to prevent fungal growth. In winter, reduce watering to prevent waterlogging of the soil.
Fertilization
Apply fertilizer to Juglans rupestris Engelm. ex Torr. trees once a year during early spring before new growth appears. Nitrogen-based fertilizers are ideal for young trees, and fertilizers with a balanced ratio of nitrogen, phosphorus, and potassium are suitable for mature trees. Over-fertilization can lead to foliage burn, so apply the recommended amount of fertilizer based on the age of the tree.
Pruning
Prune Juglans rupestris Engelm. ex Torr. trees to maintain their shape, promote strong branch growth, and eliminate diseased branches. Pruning is best done during the dormant season, late winter or early spring. Cut to remove any dead, broken, or diseased branches, and shape the tree to form an open center to allow light and air circulation into the canopy.
Propagation of Juglans rupestris Engelm. ex Torr.
Juglans rupestris Engelm. ex Torr. is commonly propagated by seeds and grafting.
Propagation by seeds
Seeds require stratification to break dormancy. The seeds should be collected in the fall and dried in shade for a few weeks. They should then be placed in a sealed container with moistened peat moss and stored in a refrigerator for 3-4 months. After stratification, the seeds can be sown in a well-draining potting mix and kept moist until germination.
Propagation by grafting
Grafting is the preferred method for propagation of Juglans rupestris Engelm. ex Torr. as it ensures that the selected characteristics, such as nut quality and growth habit, are maintained. Grafting can be done by whip grafting or bark grafting. The scion wood should be collected during the dormant season and stored in moist conditions until grafting can be done. The rootstock can be selected based on desired characteristics such as disease resistance or growth habit.
Disease Management
The plant Juglans rupestris Engelm. ex Torr. can be affected by various diseases, including:
- Phytophthora crown and root rot
- Verticillium wilt
- Thousand cankers disease
- Anthracnose
- Powdery mildew
- Bacterial leaf scorch
To manage these diseases, it is essential to maintain proper cultural practices and adopt preventative measures, such as:
- Planting disease-resistant cultivars of Juglans rupestris Engelm. ex Torr.
- Planting in well-draining soils with a pH level between 6.0 and 7.5.
- Regularly inspecting plants throughout the growing season to identify diseases early.
- Removing and destroying infected plant parts immediately to reduce the spread of the disease.
- Properly sanitizing pruning tools to avoid spreading disease.
- Using fungicides according to instructions provided by the manufacturer.
Pest Management
Juglans rupestris Engelm. ex Torr. can also be affected by various pests, including:
- Walnut husk fly
- Walnut aphid
- Walnut scale
- Walnut twig beetle
- Webworms
To manage these pests, it is vital to regularly inspect plants throughout the growing season and adopt preventative measures, such as:
- Planting disease-resistant cultivars of Juglans rupestris Engelm. ex Torr.
- Removing and destroying infected plant parts immediately to reduce the spread of pests.
- Using horticultural oils and insecticides according to the instructions provided by the manufacturer.
