The best thing you can do if a wisteria has attached itself to one of your trees is to cut it off at the base. A wisteria that climbs a tree can strangle it. Don’t worry, the wisteria will grow back.
In the Garden
Q: The vines on my wisteria have grown to the top of a 60-foot conifer. It’s beautiful when they bloom all the way up to the top, but do I have to worry about them harming the tree?
A: It’s probably not a good idea to allow wisteria to climb up into a tree. Unlike climbing vines such as hydrangea, which tend to grow straight up the tree without encircling the trunk and branches, wisteria vines tend to wrap around whatever they climb.
If the tree has a diameter of more than 10 inches, the circling vines probably won’t kill the trunk, but over time the vines will wrap around smaller side branches, thereby strangling them as they grow.
Friday through Sunday Nov. 4-6. Many local artists display their works at this free celebration held throughout the La Conner area. Christianson’s Nursery (15806 Best Road, Mount Vernon) takes part Saturday and Sunday (from 10 a.m. to 4 p.m.), showcasing work from many artists, plus live Cajun music (Saturday noon to 3) and apple cider served from its antique cider press.
Northwest Orchid Society Fall Show & Sale:
9 a.m. to 5 p.m. Saturday, Nov. 5; 10 a.m. to 4 p.m. Sunday, Nov. 6. The show will feature a variety of flowers and displays. Orchid vendors will have plants and supplies for sale. Educational talks on orchids, repotting services and growing advice. Door prizes both days. Free. Address: Swanson’s Nursery, 9701 15th Ave. N.W., Seattle.
“Botanical Centerpieces for the Holidays” lecture at Molbak’s:
Noon to 1 p.m. Saturday, Nov. 5. Riz Reyes, RHR Horticulture, teaches you how to create stunning holiday centerpieces with fresh ingredients from your garden or farmers market. Free. Address: Molbak's, 13625 N.E. 175th St., Woodinville.
There are other problems associated with allowing wisteria vines to climb up into a tree. The vines produce thick foliage that can shade out the tree, causing it to drop needles prematurely, weakening the tree. The weight of all of those ever-thickening vines high up in the tree, along with the wisteria’s summer foliage, greatly increases the chance of the tree coming down in a windstorm.
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I recommend you cut the wisteria off at the base. The thick foliage on most conifer trees will hide the dead vines, and cutting it back to a foot or so tall won’t harm your wisteria. It will grow back like a gangbuster.
To keep it from growing back into the tree, consider pruning your wisteria into a single-trunked specimen that can be maintained at a desired height. Even then, you’ll have to keep a close eye on it. Wisterias have a mind of their own, and undoubtedly, its goal in life will be to climb back up to the top of your tree.
Q: We’re cutting down a black walnut tree in our backyard. I know that black walnuts give off something that prevents plants from growing under them. Do I have to worry about using wood chips from the tree’s branches as mulch around my plants?
A: The black walnut (Juglans nigra) tree produces a substance called juglone. Juglone is a natural substance that inhibits growth, thus making it impossible to grow a wide variety of plants within the root zone of the tree.
The highest concentrations accumulate and seep out of the roots, but all parts of the tree, including the bark, wood and leaves, contain juglone. Because juglone is found in all parts of the tree, most garden experts warn against using wood chips from black walnut as mulch. However, according to WSU Extension associate professor and extension specialist Linda Chalker-Scott, research has not shown that using the wood chips as mulch has any negative effect on established plants.
If you do decide to use the chips as mulch, I would avoid using them in a bed filled with new plants. Also, don’t use them as pathways in your vegetable garden. Plants in the tomato family, along with other kinds of vegetables, are highly sensitive to the effects of juglone.
Also, after the tree is cut down, you should have the stump dug out, if possible. Walnuts don’t give up easily. The roots will send up suckers in an attempt to grow back. Even if you manage to kill the roots, they’ll continue to seep juglone into the soil, making it impossible to grow a wide variety of plants in the area around the stump for years.