By Julie Boudreau
Nut trees are a catch-all category that includes just about anything that grows in a hard shell: almonds, pecans, chestnuts, hazels and many others. But there are species that produces what we call the real walnuts: they are the trees of the Juglans genus.
With its 21 species distributed throughout the world, walnuts are trees with several economic interests. They provide edible nuts, the most popular of which is that of the common walnut (Juglans regia). We also use the outer shell of the nuts, what we call the husk, to make dye. Finally, the wood is very popular for making furniture. Gardeners, on their side, are particularly interested in this tree for its majestic appearance, which provides beneficial shade. And of course, we love those edible fruits too!
Tasting the nuts of the black walnut or butternut tree is quite a revelation. Their flavor has nothing to do with that of common walnuts! The flavor is more pronounced. And in the case of black walnut, I would even say that they almost taste like goat cheese! They are perfect to sprinkle on salads or to enjoy as is. They’re not quite as suitable for desserts. Last year, my black walnut cookies left the whole family a little perplexed… (That’s because I am renowned for my industrial (and tasty) production of Christmas cookies)
Walnut trees are recognizable at first glance because of their immense leaves made up of several slender leaflets, up to 25. This gives the tree a little exotic look. We also easily recognize the fruits, green, elongated or globular, the size of a golf ball, gathered in clusters. Finally, where there are walnut trees, we will notice a significant increase in the population of squirrels, who love these fruits.
In spring, walnut trees produce two types of flowers on the same plant. First, long male catkins, with a drooping shape. Then the female flowers, gathered in clusters, which will become the nuts!
Majestic Black Walnuts
Black walnuts (Juglans nigra) are an imposing tree that can live more than 100 years. In my opinion, it is the most beautiful of the walnut trees, with its leaves having up to 23 leaflets (generally between 15 and 19). Its fruits are perfectly round and the nut inside has a very pronounced flavor. Moreover, one of the oldest black walnut plantations in North America is located in the province of Quebec, in the Domaine Joly-De Lotbinière. It was planted in 1882 by Sir Henri-Gustave Joly de Lotbinière himself, lord of his lands and also 4th primeminister of Quebec! He demonstrated that the black walnut is hardier than we think and that it grows well in zone 4. This species is native to the eastern United States.
Since, the black walnut has experienced a great wave of genetic improvement and there are now more than 400 cultivars that can be found all over the world. The ‘Ottawa’ variety produces larger nuts and in greater quantities.
Coveted Heartnut
Another walnut that turns heads is the heartnut (Juglans ailantifolia var. cordiformis). Its name comes from the shape of its nuts which have the advantage of being easier to open than that of other cultivated walnuts. Also, the kernels are easier to extract from the nut. This is the one I grow in the garden! From a seedling and offered by a friend 15 years ago, my heartnut began producing fruits 4 years ago. But with suburban squirrels in overpopulation, I haven’t yet had the pleasure of enjoying its fruits. Abundance will come. I am patient!
These fruits are produced on large clusters of 10 to 20 nuts. It also has the particularity of having a faster growth than its close cousins.
A More Exotic Walnut for the Nordic Gardener
Lovers of rarer species may be interested in the Manchurian walnut (Juglans mandshurica). Originally from eastern Asia, this one looks promising in zone 4 and probably zone 3. It produces a nut with fewer cavities, which makes kernel extraction easier. This species also has good resistance to diseases.
Our Quebec Walnut
Our beautiful forests in the south and southwest of Quebec hide another walnut tree whose fruits are edible. The butternut (Juglans cinerea) mainly occupies the edges of swamps and roadsides. It has also been planted in several parks and gardens, as an ornamental plant. It is a fabulous tree with leaves numbering between 11 and 17 leaflets.
Unfortunately, in recent years, they have been affected by a disease, butternut canker. This disease arrived in Quebec in the 1990s and the butternut tree was predicted to have the same fate as the American elms. Faced with this issue, we can either completely avoid planting butternut trees or encourage planting by seed, which increases biodiversity and gives us the chance of discovering more resistant specimens. Black walnuts and heartnuts are not affected by this disease.
The Hodgepodge of Hybrid Walnuts
Since walnut trees cross easily with each other, this has given rise to some interesting hybrids for gardeners. The buartnut is a crossing between heartnut and butternut. It produces large nuts that are easy to open. It is also a variety that is very resistant to diseases. Specialist nurseries have selected and grafted interesting cultivars, such as ‘Mitchell’, ‘Morgan’, ‘Fioka’ or ‘Corsan’. There is also the ‘Dooley’ walnut which comes from a cross between the black walnut and a common walnut.
Sowing Walnut Trees
The easiest way to grow a walnut tree at home is to start a seedling. It’s very simple, you just have to follow the natural process: observe a squirrel! The squirrel finds a nut in the fall. He buries it in beautiful soil rich in humus and the following spring, the nut germinates! Of course, we will be smarter than the squirrel by placing a fence over our seedlings to protect them from the said rodent. Not all nuts will germinate. A germination rate of 65% is excellent with this technique. It is better to sow several nuts in the same place and then select the plant that seems the most promising.
Planting Walnut Trees
It is also possible to plant walnut trees, but be prepared for a quest for the Holy Grail. Walnut trees are rarely sold by large nurseries. You should take a look at nurseries specializing in fruit trees. Opt for small plants, as most walnut trees develop a taproot, which makes transplanting difficult. Planting is done early in spring or very late in fall. Many specialty growers sell bare root trees in the spring and some can even deliver them to you by mail!
Walnut trees like rich, deep soils with moderate drainage. Full sun is essential to these trees.
Nothing Grows Under a Walnut Trees?
We often hear that you should not plant anything under walnut trees because they release a toxic substance into the soil. Indeed, all walnut trees, especially black walnut and butternut, produce a substance called juglone. Very practical for preventing the growth of competing species, this substance acts the same in the garden. Some plants are very sensitive to juglone, others not. Here you will find a beautiful selection of plants that grow under a walnut tree.
It is also good to remember the importance of judicious positioning of a walnut tree on a plot of land. In addition to respecting the soil and sunlight conditions mentioned above, we will choose a location far from the parking lot or the edge of a road. Yes, the weight of nuts multiplied by the square force of gravity (my math is way off…) can equal a bump on the body of a vehicle! Aside from these predictable and avoidable incidents, walnut trees will provide you with intense satisfaction and years of feasting and competitive wrestling with squirrels!
Thanks for sharing this delightful insight into the world of walnuts.
Juglans is a genus rather than a species. Juglans hindsii is a native Californian black walnut (which is not the Juglans nigra that is more common elsewhere) that was used for understock for the English walnuts, Juglans regia, that inhabited many of the orchards that filled the Santa Clara Valley decades ago. Although uncommon now that the orchards are gone, it is still supposedly not as rare as it was naturally. It is the only species that we know as native. It is sometimes mistaken for Juglans californica, which is native south and east of Santa Barbara County, but looks nothing like it. Juglans californica is a scrawny short tree with multiple trunks.