Black Walnut Juglans nigra, is not common and borderline hardy in Calgary but well worth the effort. The arm length pinnate leaves lend a tropical feel to our northern gardens in the summer. These trees emit the chemical juglone which is toxic to some plants including tomato, potato, apple, pine and birch so plan accordingly, do not plant near vegetable gardens or other trees! These trees need plenty of space and direct sun as in their native range they are massive, over 100 feet (30 -40m) tall and almost as wide too. I highly doubt this tree would grow this tall as no trees in Calgary are even this tall. I have also read that they will not set fruit in our zone, not below zone 4, and certainly mine has not in over 15 years.
I have been growing this Black Walnut in my Calgary backyard since 2002. I ordered it through the mail and it came bare root in a box about 2 feet tall, I had to plant it in a pot when it arrived as it was still snowing that spring and wait until about June to plant outside. Although these trees grow massively, several feet a year, they also winterkill to a huge degree so it's a lot like two steps forward one step back. In one of the first five or so years this tree winterkilled right to the ground emerging as a new sprout from the roots, in many years it winterkilled to the snowline. Since growing above the snowline many of the branches winterkill and if you see it in the spring it looks dead, however, the 10 to 20% of the buds that survive grow into what you see in the picture above and grow around 5 feet every summer. This is the latest leafing out of any tree in our area sometimes well into June, the buds are almost microscopic compared to what they grow into. Every few years I thin out the very dead of the deadwood to give a tidy appearance. This tree is currently around 15 feet (5m) tall after 16 years.
These two walnut trees grow a few blocks down my street and seem to do very well, very little winterkill and not bothered by jack rabbits! They have probably been there just under 10 years, if memory serves me. So I would say that these trees are definitely worth a try in Calgary if planted in a responsible way like in a large open space away from gardens and in a warm microclimate like the inner city or established area with mature trees.
Black walnut leaves have a curious medicinal smell and slight stickiness if handled. Because of their immense growth in the growing season, the branches at several feet a year and the leaves 3 feet long, I often tie wayward branches to a stronger branch lifting it out of the way and sometimes snip a branch off which I hate doing. Occasionally the leaves will turn a pale yellow given a long enough fall but in our area often a frosty night freezes the leaves to a crisp and the long pinnate leaf will fall off over the next few days, usually I have to remove the fallen leaves as they get stuck in the branches and look really messy. I do not compost these leaves because of the juglone but dispose of in regular garbage.
Other Walnuts To Grow
Manchurian Walnut Juglans mandshurica,
Above, a large Manchurian walnut grows in the Dorthy Harvie Gardens in the Calgary Zoo, left of gazebo above. It is actually listed as a heritage tree of Alberta, I remember it as a boy over 30 some years ago and it has been happily growing since. This specimen is at least 30 or 40 feet tall (over 10m) and also has a wide spreading canopy. These trees come from China, Russia, North and South Korea and are rated exceptionally hardy down to -45C! This walnut exudes much less juglone than other species of walnut making it ideal as a landscape tree. My only question is why haven't we been growing this tree in Calgary ages ago!?!? Exceptionally hardy, non toxic and absolutely gorgeous, why hasn't the zoo been propagating seedlings and the city planting them all over? Please, a moratorium on Shubert Cherry and more Manchurian Walnut please!
Butternut Juglans cinerea,
Butternut walnut is a much smaller and hardier tree than Black walnut, native to Eastern North America into Wisconsin it is rated as zone 2 and said to bear nuts in zone 3! Many describe the nut as delicious and less astringent tasting than Black walnut. All walnuts need plenty of room for their wide spreading canopies and full sun. Walnuts are self fertile only one is needed to bear fruit. I cannot find any literature or photographs on this tree actually growing in Alberta except that it is rated for our zone which sounds very promising. These trees are also called White walnut and grow to half the size of Black, about 50 feet tall and wide so probably a little smaller in Calgary as most trees grow.
Look online for availability some local nurseries will special order walnut trees, some smaller nurseries will also order trees for you just ask! I got my Black walnut thru mail order and there are some companies online that specialize in nut and fruit trees but I would check locally first.
In the spirit of our pioneering gardeners like William Reader we must always be stretching the boundaries of what can be grown in our challenging climate, try everything see what happens, this city can always use one more species of tree. There are already some examples of walnuts in our climate and there is always room for more!