Black Walnut Tree – Facts, Identification, Grow and Care
November 1, 2019
The Black Walnut Tree is a large deciduous tree native to Eastern North America that produces edible nuts in the fall. Growing to heights of 120′ (40 m) by 50′ wide (~15 m) in optimum conditions, the Black Walnut can make an excellent shade tree. The main drawback for the Black Walnut is a chemical its roots produce and secrete called Juglone, which kills many different species of plants should their root come into contact with it. So, one must be aware of that fact, and chose companion plants accordingly.
It is hardy from USDA zones 4-10. Check your USDA zone here.
Black Walnut Trees grow between 12-30 inches per year (30-70 cm), depending on conditions
Can start producing nuts as early as 5 years old, with significant production once it reaches 10 years old
Nuts attract a wide variety of wildlife (squirrels, chipmunks, etc)
A true favorite of woodworkers (and the author), the dark closed-grain heartwood has a beautiful dark brown color
The scientific name of Black Walnut is Juglans nigra
All parts of the tree, but particularly the roots produce Juglone, which can prevent growth or kill certain plants growing under or near them
Want to see full list of plants that should not be grown under Black Walnut Trees? Click HERE
Black Walnut Identification and Physical Description
Black Walnut Trees grow tall! Over 100′ for a mature tree, and they can branch to 50′ diameter. The rough bark can be mistaken for Ash or Tulip Poplar trees, with its rough vertical ridges. But the leaves are more unique, being ‘compound’. A true confirmation of a Black Walnut Tree can always be done in the Fall (September/October), by looking for the many 2-4″ diameter nuts that will be in the tree, and all over the ground. And should you see the cross section of the log, you will have no problem identifying it by the dark-brown heartwood surrounded by white/yellow sapwood.
Typically the trunk will be quite long and not have branches, making it excellent for lumber. The bark is rough ridges that run vertical. Significant branching can/does occur in the upper 2/3 of the tree. At full maturity, the trunk of the Black Walnut can be up to 6′ diameter (2 m).
The limbs will have more immature bark, which will be much smoother. You often see the limbs having bark that is smoother than the mother trunk in various species, such as Redbud or Shagbark Hickory.
The leaves of Black Walnut are compound, with alternate leaves. The total compound size is around 18″ (30-60 cm) long, give or take 6″, and approximately 6″ wide (15 cm). The size of the individual leaf is approximately 1″ (25 mm) wide by 3″ (~75 mm) long. The leaves on the tip of the compound are shaped differently than the others, being smaller or misshapen. Individual leaves are shaped like a spear-tip, and have serrated edges like a saw.
Small florets appear in late spring. Since Black Walnut trees are monoecious, it will have both male/female flowers and will self-pollinate. The male flowers are attached to stems that hang down cylindrically, and are about 5″ long (12 cm). Female florets are in small groups on a small spike, and will have 3-6 florets. The size of both male and female florets are about 1/8″ (3 mm).
The female florets will eventually turn into large, golf ball sized nuts. These nuts will have an outer green husk that eventually turns yellow to black. A mature nut will be the size of a ping-pong ball, with a black/shriveled and rough texture.
Black Walnut Trees have a deep taproot. The root produces a chemical called Juglone, that inhibits or prevents growth of certain plants. This mechanism helps reduce competition, raising the chances of the individual tree to survive and collect nutrients.
Black Walnut Trees poisoning other plants
Black walnut trees produce a chemical in their roots called Juglone, which is chemically known as C10H6O3 or 5 hydroxy-1, 4- napthoquinone. This chemical will slowly kill susceptible plants. Head over here to get the full list of known plants that will die from Juglone ==>HERE
But some common species that are grown include the following;
Blue False Indigo, or any other Baptisia species
Trees and Shrubs
Yes – even your vegetable garden could be at risk. In fact some of the most commonly grown vegetables will likely die if their roots reach Black Walnut Tree roots. Some of the common species of vegetables that will die include;
Black Walnut Growing Conditions
This tree likes moist soil that is moist. It will grow in a variety of conditions and almost any soil, from sandy to clay – the main thing is that it needs moist, well-draining soil to thrive. It can tolerate occasional flooding, as evidenced by its propensity to grow near streams, creeks, ponds. If you provide it the necessary space, moisture and good soil, then you can expect significant year over year growth.
How to care for
Not much care is required. Just provide this tree with conditions that it prefers, and you will have a thriving tree to be enjoyed by future generations.
The biggest maintenance job for this tree is cleaning up the nuts. If you plant this near a sidewalk or street, it will be littered with the nuts. When crushed, there is a black husk that stains skin, clothes, and pavement. It is difficult to remove the color. Eventually the squirrels will likely get all the nuts and bury them, but not before they start to break down naturally and stain areas.
How to Establish Black Walnut from seed
If you collect some black walnuts and wish to grow them from seed, you first need to do a test to make sure the nut is a viable seed. To do this, wear rubber gloves and remove the husk, so that you get to the hard nut inside. Then, place the nut into water. If the nut sinks, it is viable. If the nut floats, it is not viable and should be discarded as it will not germinate.
Viable nuts can be direct sown in the fall, about 1-2″ (25-50 mm) deep, and will germinate in the following Spring. This is the easiest way to germinate them, as they require cold moist stratification for about 2 months. You can simulate this ‘wintering’ by placing it in moist sand in a zip-lock bag and storing in the refrigerator until Spring. But I prefer to let mother nature do it for me!
Uses for Black Walnut Trees
Black Walnut Trees are valuable in that they produce reliable food, by way of the nuts. It requires a bit of effort to crack the nuts and remove the meat, but specialty nutcrackers are available. The wood of black walnut is quite valuable. Mature trees with long, straight trunks produce many boards that are commonly used in furniture making, cutting boards, and other decorative means.
Fauna Associations of Black Walnut Tree
More than 20 different species of moth larvae feed on black walnut trees, making it a valuable part of the ecosystem. Additionally, there are another 20 or so insects whose larva bore into the bark to feed. Chipmunks and squirrels will collect and bury nearly all the nuts, to use as food throughout the winter. In that regard they are valuable for our ecosystem. Also, by way of burying them they help propagate the species.
Black Walnut Reference Table
Small florets, 1/8” wide (3 mm)
Florets will be hang down, arrayed on a stem. Female florets are several to a group and the same size as male.
80-130’ (24-40 m)
12’ (4 m) (for nut production)
25′ (8 m) for general landscaping
Full sun – Full Shade
Moist to Medium
Pick up the walnuts each year! Or let the squirrels do it
Woodlands, border, planting for nut production, timber
~ 40 species of moths and insects feed on Black Walnut. Squirrels, chipmunks, eat nuts.
Over 20 different moths
Plant in fall, direct sown
USDA Zones 4-9
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Hi - I grew up outdoors in nature - hiking, fishing, hunting. In high school I got my first job at a garden center where I learned to garden and landscape. I've been growing plants from seed and designing native plant gardens for over six years. I hope to share some of my knowledge with you!
Additionally I am a wood worker / DIY enthusiast. I enjoy designing/building projects (with hand tools when I can!). I hope to give you some tips and useful information!