1. Breath thief.
Walnut trees, by which term I include both black walnuts (Juglans nigra) and white walnuts (Juglans cinera), better known in some circles as butternut trees, are members of the Juglandacea family, which has a peculiar defence mechanism. They (and some of their relatives) produce a chemical called juglone, which interferes with the respiratory system of some plants. While most of this toxic material is contained in the tree's roots, it can also be found in leaves and twigs. The noxious substance extends 50 to 80 feet beyond the drip line of the tree and stays in the earth for some time even after the offending tree has been removed.
2. A home and native tree.
Both black and white walnuts are native to North America, occurring naturally in Eastern Canada; they are hardy to zone 3a. Walnuts of both types are highly prized in more western parts of the country. They have been trialed in Alberta with success although they may not get quite as large there. There is a strain of Black walnut that thrives in Manitoba, especially in the Morden area. In Winnipeg's suburb of St. James, there is a White walnut (butternut) in a front yard that is reported to be over 50 years old. The oldest know walnut is 300 years old in Sered, Slovakia at Castle Park.
3. It's called alleopathy, my dear.
The horrific habit of these trees is well-known. Alleopathy is the ability of a plant to produce bio chemicals that have an impact on the survival of other plants or organisms. The chemicals thus produced are known as allelochemicals. In the case of our walnut friends, the chemicals suppress certain other plants by cutting off their ability to exchange carbon dioxide for oxygen.
4. So why plant walnuts?
If you garden on a small city lot, then walnuts are the last plant I would recommend. Black walnuts grow to massive widths, easily spreading their low, 10-foot-off-the-ground branches 60 to 70 feet and, in most places, grow just as tall. You need a park or an estate for that kind of mass. Having said that, they are pretty with their bright, almost lime-green, feathery pinnate leaves, and they make wonderful shade trees. Their fruits look a little like suspended tennis balls. The trees don't start producing nuts until about 10 years old and don't really produce heavily until they reach 30.
5. Black walnuts are, well, the blackest.
Black walnuts are "blacker", as in more dangerous, in the amount of juglone they produce. The tree also has black, furrowed and ridged bark and 12 to 24 feathery pinnate leaves. The tannins in the husks protecting the nuts make a black mess, staining everything they touch a rich dark brown-black when they are opened up. The tannins were used to dye hair as well as stain wood back in the good old days.
6. I like your nuts.
Also called butternut trees, white walnuts have light gray bark with 11 to 18 downy leaves and lemon-shaped fruits that have a slightly milder taste than their black cousins. White walnuts are grown mostly for their harvest. They are becoming an endangered species in southern Ontario thanks to a fungal disease called butternut canker.
7. Poached walnut.
Black walnuts are highly prized for their wood, which is just a little less dense than that of oak. It is used for gun stocks, for paddles and for coffins. In 2004, DNA evidence was used to convict a walnut poacher who had stolen a tree worth about $2,500.
8. Where's the beef, er, walnut meat?
You have to love walnuts to get at their nuggets of meat. Firstly, the nuggets are protected by a thick husk that should be removed when it is still green to ensure a tastier nut. It's also easier to remove the husk then. Even so, removing the husks is a messy and difficult task; be prepared to have everything you use stained. Next, the inner nuts need to be cured until their hard outer shell dries. Lastly, we all know how hard it is to shell a walnut to get at the two somewhat bitter nuggets inside.
9. Horses and dogs beware.
Horses can get a condition called laminitis, an inflammation of the feet, if their bedding is made from walnut chips or sawdust. And walnuts are lethal to dogs. As for people, don't eat a walnut with a mouldy shell, because poisonous mycotoxins can leak into the meat.
10. What happened to my tomato?
So back to the juglone effect; some plants are very susceptible to juglone and among these are the members of the nightshade or Solanacea family. Tomatoes, peppers, potatoes and eggplant are all part of this family. White birch, apples, and cotoneaster are also sensitive. Cabbages, chrysanthemums, and peonies may wither and die when exposed. Symptoms of exposure include stunted growth and wilting, but if the plants start wilting, it's game over. The next inevitable step is death.