The black walnut is a stately native of the United States east of the Rocky Mountains, with a huge crown and dark, ridged bark. Its nuts have been used for their oil and protein by indigenous people for at least 4,000 years, and its timber – durable and chocolate-brown – has for centuries been over-exploited for veneers and furniture.
Two-thirds of the annual black walnut harvest in the United States comes from Missouri. Their flavor is more intense than that often common, cultivated “English” kind but their tough, deeply corrugated shells are hard work for a casual snack – possibly an adaptation to dissuade rodents from polishing off the next generation of trees.
Walnut trees protect themselves with juglone, a natural herbicide that discourages competing plants, and tannin, an inspect repellent. For humans though, these chemicals work as dye and fixer, handily delivered in one package. During the American Civil War, walnut husks were used to dye homespun uniforms a brownish-grey for Confederate soldiers and to make the ink they used to scratch out letters to loved ones back home.
During World War I, black walnut was specified for aircraft propellers because it could withstand huge forces without fragmenting. By World War II, walnut has been so depleted that the US government ran a campaign to encourage private individuals to donate trees to the war effort. Simultaneously, powdered walnut shells were combined with nitroglycerine to make a form of dynamite. With such associations, it is perhaps appropriate that black walnut wood has also long been popular for upmarket coffins.
Weed Control for the Black Walnut Tree
Weeds that grow in your yard effect black walnut trees in the same way as it does with other plants. Weeds will rob your trees of vital moisture. light, and nutrients that it needs to stay healthy and grow. There are several things you can do to help prevent weeds from impacting the health of your walnut trees:
- Cultivation is the best weed control method. Cultivate a shallow area around your tree and take precautions to not dig too deep, so that you don’t damage the roots.
- Mowing periodically removes the top layer of the weeds. This allows more sunlight to get to your tree.
- Mulching with plastic, sawdust, bark, or wood chips can control weeds. Make sure and do this each year (see our more in depth article on mulching to learn more).
- Several chemicals are effective in controlling weeds in black walnut, particularly one
preemergent herbicide, simazine, and five postemergent herbicides: atrazine, amitrol, dalapon, glyphosate, and 2,4-D. These are tolerated well by black walnut, generally available, inexpensive, and safe when handled and applied properly.
Ground Cover for the Black Walnut Tree
The ideal ground cover for a black walnut plantation would be similar to that in a
dense mature forest. Unfortunately, when a plantation is established, regardless of the type of site preparation, the walnut seedlings will not be tall or dense enough to shade out the vegetation that competes against them.
In general, it’s important to keep in mind that grasses will reduce the growth of a black walnut tree, while legumes will promote it. Here’s a couple of key things to think about when it comes to ground cover:
Here’s a couple of key things to think about when it comes to ground cover:
- The ground cover should not compete with your tree
- The ground cover should help control or prevent weeds
- The ground cover should improve the soil
- The ground cover should either prevent or control pests
- The ground cover should be easy to maintain
Walnut Council Org
Around the World in 80 Trees by Jonathan Drori
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