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Magnificent Black Walnut trees need compatible “neighbors”

“What can I plant near my Black Walnut trees?” That’s a question that I sometimes hear, and it’s a very good question, because not every plant will thrive in close proximity to a Black Walnut. Today, I’ll explain why, and tell you about some trees and shrubs that can cohabit with your Walnuts.

The Black Walnut (officially known as Juglans nigra) is the largest of the twenty species of Juglans native to the United States. It can easily grow to a height of 100 feet; its strong, straight trunk and magnificent canopy enhance any landscape that has an appropriate scale for the tree’s size.

However, it is prized by the high-end furniture market because of its uniformity, durability and the luxurious chocolate-brown color of its heartwood. Many landowners, who have a few acres to spare, are planting Black Walnut trees as an investment, knowing that the value of those trees when harvested in 25 or 30 years could increase dramatically. There are a number of former Plant Man columns and related articles about Black Walnut trees (and their investment value) posted at my Web site. Go to www.landsteward.org and type “black walnut” into the search window.

Horticulturists discovered that certain plants did not do well (and some even withered and died) when planted close to Black Walnut trees. The reason: Black Walnut trees secrete a biochemical substance known as Juglone. These secretions sometimes drip from the leaves in the canopy down onto plants below or leach out from the roots below ground. The process is known as allelopathy and was described by the Roman author Pliny the Elder as early as 77 A.D.

There are several excellent Web sites that provide a lot of information about the effects of Juglone and which plants are most susceptible and most resistant to it. If you wish to learn more, you can find direct links to two of the best when you go to my Web site and find this column under the Plant Man heading. Here are those Web addresses:

http://www.ext.vt.edu/pubs/nursery/430-021/430-021.html

http://ohioline.osu.edu/hyg-fact/1000/1148.html

But let me reassure you that you CAN plant a large number of trees and shrubs near Black Walnuts and be confident that they are resistant to the effects of Juglone!

Firstly, horticultural tests indicate that you should AVOID planting the following near your Black Walnuts:

Apple, white Birch and Mountain Laurel trees, blackberry, blueberry and tomato plants, azalea, chrysanthemum, crocus and rhododendron. (You’ll find much more complete lists at the sites I mention above.)

And now for some plants that you CAN plant near Black Walnut trees:

Tolerant grasses, flowers, vines and ground covers
Tall fescue and Kentucky bluegrass, Aster, Daffodil, Shasta Daisy, Daylilly, hardy Geraniums, Hosta, Morning Glory, Phlox, Virginia creeper, Wisteria.

Tolerant trees and shrubs
American Arborvitae, white Ash, American Beech, Catalpa, black Cherry, Crabapple, flowering Dogwood, Forsythia, Hibiscus, Hydrangea, Red Maple, Japanese Maple, White Oak, Privet, Eastern Redbud, Sumac, Sycamore, Tulip Tree

A word of caution: Many factors, other than the presence of Juglone, will affect the viability of your trees and plants. Soil, moisture, temperature, shade and sunlight all play a role. As they say in TV commercials, “Your results may differ!”

The Black Walnut is one of the world’s most magnificent and beautiful trees. In addition to their breathtaking beauty, an acre or two of Black Walnuts could well provide some significant retirement income when harvested in the years ahead!

All you need to know is which other trees and plants can cohabit as good neighbors with your walnuts. Do a little research at the Web sites I’ve mentioned here and you should avoid disappointment. I always encourage readers to contact their nearest Agricultural Extension agents who are eager to help and really know the local conditions. And of course, I’m always happy to respond personally to any e-mailed questions to care to send to steve@landsteward.org

The Plant Man is here to help. Send your questions about trees, shrubs and landscaping to steve@landsteward.org and for resources and additional information, or to subscribe to Steve’s free e-mailed newsletter, visit www.landsteward.org