September 13, 2007 at 7:19 a.m.
The home of the black walnut is in the deep rich soil of bottom-lands and fertile hillsides. It grew abundantly throughout the heartland of the hardwood forests of the United States. In their glory days it would reach heights of 150 feet, with the first 50 feet clear of branches. This made it a splendid saw log sometimes six feet in diameter.
Except for the pecan tree, it is the most valuable tree in North America. Black walnut provides the finest cabinet and furniture wood in North America due to its beautiful grain. As with so many other natural resources, by the time we realized how valuable the wood was, we had already misused it, so now it is rare. We have friends in southern Minnesota who have 40 acres of Virgin Black Walnut. Needless to say, they are planning their retirement upon its harvest.
In pioneer times, black walnut trees were used for snake-rail fences, railroad ties, cradles, gunstocks, etc., as well as furniture. Slow-growing 100-year-old trees produced very dark heartwood. Present day trees are lighter in color with a beautiful grain. With skillful cutting this veneer can saw out 1/8th inch thick and can produce up to 90,000 square feet of veneer valued sometimes at $20,000 wholesale. That's the good news.
The bad news is that the black walnut produces a substance called juglone that is toxic to many plants. This substance emitted from the roots of black walnut trees can kill many plants. It includes tomatoes, potatoes, cabbage, peppers, rhubarb, blackberries, blueberries, azaleas, mountain laurel, hydrangea, and rhododendron. It also affects apple, silver maple and Norway spruce trees.
Since black walnut roots can stretch 60 to 80 feet from the trunk, a single tree can contaminate a large area.
Compost that contains black walnut leaves, bark or sawdust can be toxic to sensitive plants unless the toxins have had a chance to break down. If exposed to air, this takes a month or two for leaves and about six months for bark. A simple test for compost with black walnut components is to plant a tomato seedling on the compost. If it survives, your compost is safe.
Some plants are found to be growing naturally within range of the black walnut roots, and seem to have no ill affect. They include Japanese maples, Canadian hemlocks, clematis, black-raspberry, weeping forsythia, multiflora rose, pansies, pot-marigold, squash, melons, beans, carrots, hollyhocks, astilbe, hostas, lungwort, summer phlox, and common hyacinth.
PLANT CLINICS: The Monday night plant clinics at the office are done for this year, but you can still talk to a Volunteer Master Gardener at the Lindstrom Farmer's Market, Saturdays, from 8 a.m.-noon, on Highway 8 in the St. Bridget's Catholic Church parking lot.
Please note: there is no longer staff at the North Branch Office who can answer gardening questions.
VOICE MAIL: You can leave a question for a volunteer Master Gardener at 651-674-4417. Depending on the volume of calls, they try to respond within a couple of days. During office hours ask for the Master Gardener voicemail, after hours, select ext. 18. You can also get your question answered on the web at: www.extension.umn. edu/askmg.
UPCOMING CLASSES: Join the Master Gardeners Tuesday, Sept. 25, at 6:30 p.m. for a class on fall lawn care, presented by Master Gardener Donna Tatting. This class will give an overview of basic lawn care practices for all seasons with an emphasis on fall lawn care. We will also discuss lawn care practices that help protect and insure the water quality of our nearby lakes and rivers. The class will be held at the Senior Center in North Branch. You can call 651-674-4417 for more info. This would also be a good opportunity for anyone thinking about becoming a Master Gardener to see what we do and get more information about the program.
A cutback in staffing has made it necessary for the Extension Office to limit hours of operation. We would suggest that you call ahead to verify that the office is open if you plan to stop by.