The Black Walnut tree (Juglans nigra)

Today I'm going to talk about the Black Walnut tree.  This tree is not common to Canada.  However, it grows extensively to the south of the border, and will likely soon find much more of southern Canada to be a hospitable environment due to climate change, even this "early" in predicted climate changes models.  In fact, black walnut trees already grow quite commonly in southwestern Ontario, especially in moisture-rich lowlands.

 

Here's a range map for this species, courtesy of Wikipedia:

 

Black walnut is a pioneer species, similar to red maple.  This means that it grows well in wide-open spaces with plenty of sunlight, and is not a shade tolerant tree.  When a forest is cut, it will grow back quickly, but eventually (after several decades) other successional species will take over.  This is why you'll commonly see black walnut along roadsides and forest edges, but not deep in the forest.  It is important to note that full sunlight is also important to maximize nut production.

Speaking of the nuts, this tree has nuts which are quite edible.  In fact, they are grown and harvested commercially in the United States.  Missouri is the main state for black walnut production, accounting for around two-thirds of the US total.  For anyone who is a bit rusty on their geography, Missouri is very central to the US, just to the west of Illinois.  So it isn't that far from Canada.  However, if you're someone who likes to eat walnuts, it's more likely that you're eating English walnuts.  That's because the shell of the black walnut is thicker and much harder to crack than the English walnut.  Seriously, you'll need a hammer to crack the shell, not a traditional nut cracker.

Walnuts are very healthy to eat, although some people have allergies.  Walnut is one of the most common allergies to tree nuts, and can be severe.  Anaphylaxis can be fatal.  And unfortunately, unlike other food allergies, a lot of people don't "grow out" of these allergies as they age.

Here are some black walnuts in shell:

 

The leaves of the black walnut are similar to the white walnut, but generally have more leaflets on them.  But the interesting fact here is that a black walnut leaf is typically almost a foot and a half long on a mature tree!  That's huge.  But the definition of the "leaf" is tricky.  A lot of people confuse the "leaflets" on a black walnut leaf, thinking that those are the individual leaves.  But they aren't, they're part of the single larger leaf.  So this photo shows one single leaf, which has almost twenty leaflets on it:

 

One drawback with this species is that its roots emit a chemical known as juglone.  Juglone is a natural herbicide, which tends to kill off a number of other species that might want to grow near a black walnut.  This is in the best interests of the black walnut, as the tree rids itself of nearby competition, thus keeping more soil moisture and nutrients to itself.  But it does mean that you have to be careful of nearby plants and other trees when you plant it.  If you keep your other plants and vegetables out of the drip-line of the black walnut, you should be ok.

As always, here are some Fun Facts about the black walnut:

1.  The leaves of the black walnut have a distinct smell.  It's hard to describe, but think of an earthy medicine odor with hints of citrus lime soda.

2.  Black walnut is prized for its wood by furniture makers and cabinet makers.  The wood is is dense and durable, with a fine colour.

3.  The heartwood of the black walnut is extremely decay-resistant (similar to cedar).  Lots of people use it for outdoor applications, such as fence-posts.

We'll leave you with a photo of a black walnut seedling, growing in the spring:

 

Thanks for reading!

- Jonathan Clark

www.replant-environmental.ca

Replant.ca Environmental is a Canadian company that plants trees for carbon capture and builds community forests.  We also plant trees in national, provincial, and municipal public parks to mitigate damage from wildfires, storms, insects, and forest diseases.  We operate thanks to numerous small contributions from the general public, in addition to larger project sponsorships from businesses and corporations around the world.  If you'd like to learn how to show your support, visit our donations page.  Even if you aren't able to make a contribution, we very much appreciate when people are able to share our posts or our website link on social media, to help spread the word about the work that we're doing!

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