Black walnut trees are often grown for their high-quality wood, aesthetic appeal, and the nuts they produce. These trees have specific growth requirements of their own, they thrive in well-drained soil, and full sunlight and require enough space to grow to their full size.
In this article, we have provided a detailed guide on how to plant, grow and care for black walnut trees. By following these guidelines, you can successfully cultivate black walnut trees and enjoy their many benefits for years to come.
Where & When To Plant Black Walnut Trees
Climate
Black walnut trees grow best in USDA hardiness zones 4 to 9. They can tolerate hot summers and cold winters. However, extremely harsh conditions can damage the tree.
Light
These trees need full sunlight for optimal growth and abundant fruit production. While planting them, choose an area that receives at least 6 to 8 hours of sunlight per day.
Spacing
Black walnut trees are very large. Their growth requires ample space. If you are planning to grow multiple black walnut trees, consider planting them 40 to 50 feet apart.
Soil
Due to their deep penetrating roots, extremely well-drained soil is required. Don't plant in areas where soil can get easily wet and waterlogged. A slightly acidic to neutral pH (6.0-7.0) is best for their growth.
Planting time
The best time to plant black walnut trees is in the fall (September to November) or early spring (March to April). During these periods, the tree is dormant, hence plant can focus on establishing roots in the new environment.
If your region has extreme winter, it is better to plant these trees during early spring. Planting on fall may require extra measures to protect the young plant.
How To Grow Black Walnut Trees: Step-By-Step Instructions
Seeds or seedlings both can be used to plant black walnut trees. As planting using seeds is a long process, seedlings available commercially are used as a better choice.
While purchasing, make sure to choose varieties that are suitable for your specific region. As black walnut trees are susceptible to pests and diseases, such as walnut tree canker or thousand cankers disease, make sure the seedlings are resistant to these conditions.
Step 2: Prepare The Soil
The important factor that determines how well the black walnut tree grows is how well-drained the soil is. If your garden soil is too heavy, you can mix it with sand or any other organic matter.
Before planting we also recommend you to amend the soil. Doing so helps to enhance the fertility of the soil, supplying all the nutrients essential for the plant's growth.
Step 3: Planting
Whichever season you are planting in, be it fall or early spring, the tree is dormant during this time. For planting, dig a hole twice as wide as the root ball and of equal depth. Make sure the hole is deep enough to accomodate the roots without crowding.
While planting, place the seedling in the hole so that the root collar is level with the surrounding soil. For areas with poor drainage, consider planting in raised beds or mounds.
Step 4: Backfill
Backfill the hole with the excavated soil after the plantation. Tamp the soil down lightly to remove air pockets.
Step 5: Water Immediately
Water the plantation thoroughly to help the soil settle. Watering immediately also ensures the roots get proper moisture.
How To Care for Black Walnut Trees
Growing Habit
Black walnut trees have impressive size. These deciduous trees exhibit a broad, rounded canopy. The tree has a central leader and a dense, spreading crown.
The annual height of the young tree increases by 1 to 2 feet. As their growth rate slows, they continue to expand in width and height over the decades. Their root system is noteworthy, as a large amount of surface roots are produced.
Watering
Black walnut trees are hardy in nature and don't need much watering. The young growing tree should be supplied with enough water for a couple of years, after which they get drought-tolerant.
Fertilization
Once you have amended the soil before planting, a consistent fertilization schedule won't be required. However, if growth appears slow or the leaves show signs of nutrient deficiency, a balanced fertilizer applied in early spring can be beneficial.
Pruning
As the trees have grown for many years, the older branches start to become brittle or diseased. It is important to remove these branches on time to prevent the spread of the prevalent disease in neighboring ones.
The best time to prune is during late winter or early spring before new growth begins. During this time, you can remove any branches that are crossing or rubbing against each other, as well as any that are dead or damaged.
Maintenance
Besides pruning, it is also important to regularly inspect the tree for any signs of pests and diseases. Common issues include walnut husk fly, which can damage nuts, and walnut blight.
Managing Black Walnut Toxicity
Juglone, a compound produced by the black walnut tree, is toxic to some other plants. This natural herbicide can inhibit the growth of certain plants including tomatoes, peppers, and potatoes.
To manage this toxicity, it is important to maintain a clear zone around the base of the tree. Make sure not to plant these sensitive plants in these areas.
However, you may plant species that are tolerant to juglone, such as ferns and certain grasses.
End of Season Care
Pruning and Shaping
As the growing season ends, the plant benefits the most when pruned in late fall or early winter. During this dormant period, you can assess the tree’s structure and remove any dead, damaged, or crossing branches.
Proper pruning not only helps to maintain the tree's shape but also improves air circulation. Proper air circulation corresponds to the reduced risk of disease.
Overpruning however is not recommended as it can stress the tree. Make clean cuts close to the branch collar to facilitate quicker healing. In cases when the tree is still young and hasn't been established yet, avoid heavy pruning.
Mulching and Soil Care
In cool weather, mulching is very beneficial. Maintain a layer of mulch (3 to 4 inches) throughout the extreme weather. Doing so will protect roots from the frost.
Soil care is associated with applying a layer of compost to the soil around the tree. This will help replenish nutrients and improve soil structure.
While black walnut trees are generally hardy, young trees may benefit from some winter protection. To guard the young ones against extreme cold temperatures, you can wrap the trunk with tree wrap or burlap.
This helps prevent sunscald and mechanical injuries. Additionally, ensure that the area around the base of the tree is clear of any snow or ice accumulation that could cause damage or create unfavorable conditions for the roots.
Preparing For The Spring
As winter ends and spring approaches, prepare for the upcoming growing season by inspecting the tree and making any necessary adjustments. Remove any remaining dead or damaged wood and ensure that the mulch is in good condition.
You may also want to perform a final soil test to check for nutrient levels and pH balance. Additionally, plan for any needed fertilization or pest control measures as new growth begins. Doing all these will ensure that the black walnut tree starts the growing season strong and healthy.
Pests and Diseases
Black Walnut Curculio
The black walnut curculio (Conotrachelus retentus) is a beetle that feeds on nuts. Female beetles lay their eggs inside the developing nuts, and the larvae feed on the nut kernels. They form small holes wherever they feed, and even cause premature nut drop and reduce the overall quality and yield of the nuts.
Controlling Methods: Use insect traps with pheromone lures, remove and destroy infested nuts to prevent larvae from maturing and spreading, regular inspection is the key
Walnut Shoot Moth
The walnut shoot moth (Acrobasis nuxvorella) is a pest that targets the shoots and young branches of black walnut trees. The larvae of this moth feed on the tender growth. This reduces the tree's vigor and decreases overall yield.
Controlling Methods: Use insect traps with pheromone lures to monitor and reduce adult moth populations, prune and remove infested shoots, apply targeted insecticides
Dieback
Dieback in black walnut trees is a condition where parts of the tree start to die off. The cause for this condition can be many, including diseases, pests, or environmental stress. Trees with such conditions show wilting, discoloration, and premature leaf drop.
Controlling Methods: Identify the underlying cause of dieback, manage accordingly
Propagating
Seed Propagation
The most common method for propagating black walnut trees is through seed. Black walnuts produce seeds that, once collected, need to be prepared for planting.
Step 1: Harvest the nuts when they have fallen and their husks have turned brown and soft. After removing the husks, soak the nuts in water for about 24 hours to help with germination.
Step 2: To further prepare the seeds, stratify them by placing them in a moist, sand-filled container and refrigerating them for 2 to 3 months. This mimics the natural winter conditions required for seeds to break dormancy.
Step 3: In spring, plant the seeds about 1-2 inches deep in well-drained soil and water regularly. Germination typically takes 1-3 months.
By Rooting Cuttings
Propagating black walnut trees from cuttings is less common but can be successful with the right techniques. The best time to take cuttings is in late summer or early fall when the tree is actively growing.
Step 1: Select healthy, semi-hardwood cuttings that are about 6-8 inches long and have several leaf nodes.
Step 2: Dip the cut end in rooting hormone to encourage root development, then plant the cuttings in a mix of perlite and peat moss or a similar rooting medium.
Step 3: Keep the cuttings in a humid environment, such as a greenhouse or under a plastic cover, and maintain consistent moisture. Root development can take several months.
Step 4: After successful root development, transplant the cuttings into individual pots or directly into the ground.
Black walnuts are harvested anytime between late summer to early fall. A key indicator that the nuts are ready to be harvested is when the green husks surrounding the nuts start to turn brown and become soft.
The harvesting time however depends on the specific climate and growing conditions of your area. As the nuts begin to drop from the tree themselves, it is the right time to harvest.
Manual Harvesting
The black walnuts when ready to be harvested, can be easily removed by hand. You can also manually gather them from the ground after they have fallen from the tree. It is important to wear gloves while harvesting, as the green husks can stain your hands.
In the cases when the walnuts haven't dropped yet, you can gently shake the branches or use a pole to knock them down. Leaving fallen nuts on the ground for a long time is not recommended as doing so can result in damage or loss due to rot or pests.
Harvesting With Tools
For larger quantities or more efficient harvesting, specialized tools such as nut pickers or large nets can be employed. A nut picker is a device that helps collect nuts quickly by rolling over the ground and picking them up. Nets can be spread under the tree to catch falling nuts and simplify the collection process.
Post-Harvesting Processing
Once collected, the nuts need to be processed to remove the husks. This can be done by hand or using a husking machine. Wear gloves during this process to prevent skin irritation stains. If the husks are stubborn, soak the nuts in water for a few days.
After husking, wash the nuts thoroughly to remove any remaining debris and residue. Allow the nuts to dry properly to prevent fungal growth.
Storage
Fully dried nuts can be stored for future use. Store them in airtight containers or sealed bags in a cool, dry place. If you plan to store them for a longer period, freeze them to prevent insect infestations.
Potting and Repotting of Black Walnut Trees
Potting
Choose a pot that is at least 10-12 inches in diameter for young black walnut trees. Ensure it has adequate drainage holes to prevent waterlogging.
Use a well-draining potting mix rich in organic matter. A good blend includes potting soil, compost, and perlite.
Place a layer of small stones or broken pottery at the bottom of the pot for improved drainage.
Add the prepared potting mix to the pot. Leave adequate space to accommodate the tree’s root ball.
Remove the tree from its original container, gently loosen the roots, and place it in the center of the new pot.
Water the newly potted tree thoroughly to settle the soil.
Apply a layer of mulch on the surface to help retain moisture.
Repotting
Plan to report during the tree’s dormant period, either in late fall or early spring.
Choose a pot that is 2-4 inches larger in diameter than the current pot to accommodate growth.
Add a layer of fresh potting mix to the bottom of the new pot.
Gently remove the black walnut tree from its existing pot. Loosen and inspect the root system, pruning any damaged or dead roots.
Place the tree in the center of the new pot, ensuring the root ball is level with the top of the pot.
Add new potting mix around the root ball, firming it gently to remove air pockets and secure the tree.
Water the tree thoroughly after repotting.
Place it in a sheltered location and avoid fertilizing immediately to reduce transplant shock.
Types of Black Walnut Trees
Carpathian
Carpathian is also known as English Walnut. This cultivar is actually a hybrid between the black walnut and the English walnut. It’s known for its hardiness and higher-quality nuts.
Wesley
Wesley is a selected variety of black walnut that is suitable for timber production. This variety has a straight trunk and is known for high-quality wood.
Thomas
Thomas variety was developed for high-quality nut and disease resistance. These varieties produce high-quality nuts with a thin shell, making them easier to crack.
Harris
Harris variety is valued for its resistance to pests and diseases. It is also known for its heavy nut production and relatively small yet high-quality nuts.
Kigalon
Kigalon is a hybrid variety known for better cold tolerance and high nut yield.
Sheffield
Sheffield is a variety known for its superior nut quality and consistent production.
