The Black Walnut

Many people probably do not know that there are quite a few black walnut and butternuts (also known as white walnut) growing in yards in Fort Frances and properties along the Rainy River. It is not intentionally being kept a secret, but many gardeners just don’t know or realize what tree species it is. When I still lived in Fort Frances, I would receive many calls every year asking for me to come and identify the tree or the nuts, or a problem with plants dying the garden (see below for details). It was always exciting to see the butternut or black walnut surviving and growing into a fairly large shade tree and even sometimes producing nuts, in our area.
The black walnut is native to what is known as the Carolinian forest in southern Ontario, along the shore of Lake Erie and extending into the southern United States. The butternut has a similar range in the States but its Canadian range does cover most of southern Ontario and can be found in Quebec and the Maritimes. For the Zone 4 area, these species will grow into a nice shade tree eventually reaching around fifteen metres and may eventually produce nuts which the squirrels love.
Practically everyone recognizes a black walnut tree when the nuts are on it. The leaves are large compound leaves (made up of 15-23 leaflets for black walnut and 11-17 for butternut) and when they fall off large, horse-faced leaf scars on the twigs are left. The pith is chambered, like a honeycomb, which shows in the end-grain cuts of its wood and a tell-tale clue when identifying walnut wood furniture. the butternut or black walnut like fertile soils in mixed hardwood forests but will grow well in pastures, meadows, and on slopes. For the yard, they like full sun and fertile soils so make sure to add lots of compost to the hole. Ensure to plant a distance from the house as the roots will become large like those of the maple species. These trees may suffer some winter damage in this area as they are out of their zone, so it is not unusual.
The walnut nut has a double value, as there is a multi-million market for its nuts. The richly flavoured nut of the black walnut, are those used by bakers, candy and ice cream makers and available in the grocery stores. In addition, the hard shells are used as ornaments, and pulverized and then used to drill oil wells, clean jet engines and to make activated carbon (a type of industrial charcoal used in a variety of ways). During World War II, gas mask filters were made from this activated carbon. Wildlife loves the walnut, too. The nut is enclosed in a solid, non-splitting husk, and is borne on the tree singly or in pairs and a note of warning to humans: be careful handling the nuts of the black walnut as this husk will emit a brown stain that will stain your hands and for some people create a rash. Use gloves when handling. This is where authentic walnut stain (pigment and artist products) comes from. Be patient if you plant one in your garden as they do not produce nuts until they are over ten years old, maybe older in our zone. But when the first nuts appear it will be really exciting.
Most members of the walnut family produce a chemical called “juglone” which occurs naturally in all parts of these plants. Black walnut, pecan, hickory shellbark/shagbark/
bitternut hickory, black walnut and butternut produce the largest quantity of juglone and can cause toxic reactions with a number of other plant species that grow in their vicinity. Symptoms of walnut toxicity range from stunting of growth, to partial or total wilting, to death of the affected plant. The toxic reaction often occurs quickly where sensitive plants can go from healthy to dead within one or two days. Many alarmed gardeners often believe the cause of wilting is due to fungal or bacterial disease and once wilting begins, the effect cannot be reversed. This is why I would often receive calls from distressed gardeners.

You can still enjoy a black walnut or butternut in your yard but gardens, including flower garden, should be located away from black walnut and butternut trees to prevent damage to susceptible plants. Where close proximity is unavoidable (i.e. a neighbour’s yard) then raised garden beds can provide some protection from juglone toxicity. Care must be taken to minimize or prevent walnut tree roots from growing upwards into the raised beds. Underlying a garden with plastic or fabric weed barrier during construction can prevent tree roots from growing into raised beds.
I really encourage you to try and find a black walnut or butternut seedling at your favourite nursery. If you like to experiment and push the zone then this is a perfect choice.