Many different cultivars of walnut trees are grown in the United States. The two main types are English (also known as Persian) and black walnuts, both of which produce edible fruits and provide shade. The trees do grow very tall, often more than 50 feet, making them difficult to harvest for a backyard grower. Pruning is required to keep their growth in check. Read on to learn more about how to care for a walnut tree.
What You'll Learn Today
What Conditions Do Walnut Trees Like?
The conditions that walnuts trees like best are:
- Soil – Deep, rich, fertile, well-drained, loamy, and moist
- pH – The best pH is between 6.5 and 7.2
- Location – where spring is early, and fall is late
- Temperature – Moderate summer and cool winter
- Low wind
- Full sun
Key Site Requirements
Although the walnut tree tolerates a variety of soil types and locations, it thrives and grows larger, producing better wood and more nuts when the conditions are optimum.
Soil Profile
Due to the tree’s large taproots, the soil should be an absolute minimum of three feet in depth. This means things such as iron pans will need to be broken up prior to planting.
Shallow soil cannot hold sufficient water to fully support the tree as it grows, so the deeper the soil, the better.
Both very fast draining soils such as those containing a high percentage of sand, and slow draining soils such as clay, are unsuitable for walnut trees.
Sandy soil doesn’t retain sufficient water or nutrients to support proper growth, while heavy clay soil inhibits root development and suffocates them due to the lack of air movement.
Any soil which is regularly saturated will drown the roots and cause them to die.
To test your soil, dig a small amount up, soak it with water and then take a handful of it and squeeze.
If it stays very wet and forms a tight, compact ball that doesn’t fall apart when you open your hand and push your finger into it, then it’s clay soil. If you can squeeze water from it and it breaks apart when you open your hand and push your finger into it, then it is good loamy soil. If it breaks apart as soon as you open your hand, then it’s sandy soil.
It can take more than five years before hidden problems below the surface of your upper ground level become apparent. This could be a stratum of gravel, rock, or some other type of pan, for example.
These issues are tough to overcome. Typically your tree will not reach its full height, and nut production may also be affected.
Soil Nutrients
The size of soil particles affects their nutrient-holding capacity. Generally, the smaller and finer the soil texture, the easier it is for the nutrients it holds to be released.
The top few inches of soil should ideally be between 6.5 and 7.2 on the pH table with an organic matter content of around 3.5 percent or more. This is why mulching can be advantageous as it increases organic matter and naturally feeds the tree as it breaks down into the soil.
When planting a new walnut tree, don’t worry about feeding it. Instead, work on getting the soil pH as neutral as possible. This can be done by adding appropriate amendments such as limestone.
Also, remove all grass and competing weeds within a three-meter radius from around the tree and keep this area clear. Again mulching is beneficial for helping with this.
Climate, Weather, and Location
When choosing a site, look for areas that stay warm and are protected from the wind, such as southern slopes. Avoid places in dips where cold air pockets get trapped at night and will prolong frosts.
If you live in a more northern part of the United States, ensure you choose a cold hardy variety or at least one that has been grafted onto cold hardy rootstock.
Avoid windy locations, as this results in angled growth patterns and reduced fruit set due to flowers and fruit being blown from the tree. It may also affect pollination.
Types of Walnuts
The United States is the second largest producer of commercially grown walnuts in the world. These come from California and a lesser amount from Illinois, Indiana, Iowa, Minnesota, and Missouri.
They are also largely cultivated in China, Mexico, Iran, and Turkey and in parts of Europe.
English walnuts are hardier than black walnuts and can cope with winter temperatures dropping to between -10° and -20°f.
In areas where late spring and early fall frosts occur, although the trees themselves will be unaffected, nut production will be.
Given the right conditions, you can expect between 50 to 80 lbs of nuts to be harvested from a single mature tree.
Other types of walnut
These include the Butternut, which is native to both Eastern and Midwestern U.S. and likes warmer conditions like the black walnut. It isn’t so widely grown commercially, as it is highly susceptible to a fungal disease – butternut canker. This disease is almost always fatal to the tree.
A walnut type native to Japan, called Heartnut, is quite cold hardy and shorter than the other types. It reaches heights of 35 to 40 feet but produces smaller nuts.
In this video, you can see how to grow and care for walnut trees:
How Much Water Does A Walnut Tree Need?
Newly planted walnut trees require irrigation for the first two to three years of growth.
You want to keep the soil around the root zone of your walnut tree moist but not wet.
Less frequent, deep watering is preferable to light daily watering. This is because you want to encourage the roots to search for moisture deep in the soil and not just grow shallowly on the surface.
Deep watering
This will help moisture to remain available further down in the soil, while shallow watering won’t achieve this and evaporates far faster.
Frequency of watering
This depends on a variety of factors. The temperature, as the hotter it is, the faster water will evaporate. If there is heavy rainfall, less water may be required, while if you are in a drought situation, you’ll have to water more frequently, if permitted.
Once the tree is well established and has grown deep roots, you can reduce the amount of watering you do to around once every 10 or 14 days, depending on soil type and weather conditions.
Deep watering involves allowing a trickle feed to run continually around the root zone area for at least 40 minutes.
Drought hardiness
Walnuts are not particularly drought hardy and will die without sufficient water. Even mature trees in a severe drought situation may die if not given water.
Avoid planting your walnut trees in turf. This is because the grass steals a lot of the water and nutrients intended for the tree.
Remove turf from around the periphery of the tree, at least 3 feet from the trunk, and place a thick layer of mulch there instead.
Mulching
Having around three inches of organic mulch around the root zone will help with retaining moisture, suppressing weeds, and feeding the plant.
Eliminating weeds from around the root zone should be done throughout the tree’s life. This can be achieved with hand cultivation using a hoe or by employing shallow mechanical techniques. Care must be taken not to damage the roots of the tree.
Herbicides
These are another option but they should really be a last resort as they contaminate the environment, are harmful to people as well as weeds and can damage or kill the tree. Only use approved herbicides meant for use around trees, and ensure you protect the trunk prior to application.
How Much Sun Does A Walnut Tree Need?
Walnut trees need a position in full sun to produce a good crop of nuts. When they are young, some light shade, particularly in locations when the afternoon sun is fierce, can be beneficial to prevent leaf burn. This can be provided by a sail or sun shade.
To fruit well, your walnut tree requires between six to eight hours of sunshine a day during the growing period.
What Is The Lifespan Of A Walnut Tree?
Walnut trees can live to be very old. Their exact longevity depends on factors including location, space, climate, soil, water, nutrients, and disease.
It would not be unexpected for a healthy tree to live for 150 to 400 years or sometimes even more.
How Long Does A Walnut Tree Produce?
Young walnut trees put their energy into growing for the first several years of life. Once black walnuts reach six to seven years of age, they start to produce nuts, while English walnuts may take as long as 10 years. The fastest are Butternuts which start fruiting after only two to three years.
All varieties need to be between 10 and 15 years before they become really productive.
You can expect a mature tree to produce 50 to 80 pounds of nuts a year, although some cultivars do tend to have a bi-annual cropping habit. Meaning they only produce a heavy crop every other year.
What Is The Best Fertilizer For Walnut Trees?
You can find out what nutrients are in your soil by doing a soil test. This will help you decide where supplementation is required.
Only add fertilizer in the spring, when the tree is actively growing. Doing so later can cause too much leaf development or stimulate late growth that may be damaged by frost.
The appearance of your tree will also tell you if it is healthy. If there is any yellowing of leaves for example.
Most healthy walnut trees don’t require additional fertilizer, and regular mulching should provide all the nutrients they require.
Other natural feeds include dried poultry mature which can be applied in late March.
What Pests And Disease Affect Walnut Trees?
There are a few pests and diseases which affect walnut trees.
Pests
Gray Squirrels
These seemingly cute furry little critters are capable of wiping out a crop of walnuts. A squirrels gotta eat too, right?
To deter these insanely clever animals, you can place a plastic squirrel guard around the trunk, which means they can’t climb any further. Be aware, however, that they are very capable of accessing the tree by jumping from one tree to another or using buildings or even electricity lines, etc.
Insects
One particularly adapted insect is the Walnut Husk Fly. These lay eggs which develop into maggots on the nut hull, the fleshy, green, protective coating that surrounds the nut.
Although they don’t make the nuts inedible, the maggots cause black staining that affects both the hard shell and the nut.
The flies spend the winter in the soil as pupae and emerge as flies in mid to late summer and early fall.
The eggs are laid on the nut husk, and once hatched, the maggots use the husk as food for several weeks before falling off to the ground below, where they pupate over winter, and so the cycle continues.
The application of ethephon can help reduce the number of walnut husk flies. Whole populations can be dealt with by placing landscaping fabric around the tree the size of the canopy, to stop the maggots from burrowing into the soil.
Traps can also be used to attract adult flies. These are ammonium carbonate and are sticky and yellow.
You can also purchase sprays that contain permethrin, malathion, and Spinosad, but keep in mind that these are chemicals that will affect a larger range of insects, including beneficial ones, and they are toxic.
Disease
The black walnut is particularly prone to Thousand Cankers Disease, which is more often than not fatal to the tree.
It is caused by a fungus spread by the Walnut Twig Beetle and can quickly expand within the tree, cutting off nutrients and causing the death of limbs, the upper crown, and eventually the entire tree.
Once symptoms become visible, it generally takes three to four years before full tree death occurs and will be preceded by yellowing leaves and wilting foliage.
Unfortunately, there is no effective preventive or curative treatment for this disease as even the beetle is impossible to control.
English walnut varieties appear to be less susceptible than black.
Conclusion
Walnuts can be found in most parts of the United States. Different varieties of the English and black types are the most common.
Walnut trees thrive best in an open, sheltered position with long warm summers and short cool winters. Excessive heat or cold is not well-tolerated, particularly by the black walnut varieties.
North America is the second largest producer of walnuts in the world. Showing that the walnut tree can thrive in the appropriate locations within the U.S.
Good soil, plenty of water, and sunlight are all a tree really needs to grow big and strong.
Depending on the type, a walnut tree will usually grow to a height of between 30 and 100 feet without restrictive trimming.
Gray squirrels, walnut husk fly, and thousand cankers disease, which almost always kills the tree, are the biggest concerns.
Overall the walnut tree is easy to care for, with few needs once it has become established.
To learn more about growing walnut trees and their value, visit our site to read more articles.
