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Monday - March 12, 2012

From: Mandeville, LA
Region: Southeast
Topic: General Botany, Problem Plants, Trees
Title: Black Walnut tree in LA
Answered by: Anne Bossart

QUESTION:

I was just given a black walnut tree and am trying to determine where to place it. I�ve read on your site that �Certain plants will not grow under Black Walnut trees because of the juglones that the tree puts in the soil� I�m considering one of two sites for planting. The understory of the first site will consist of azaleas and an oriental magnolia, and very nearby are gardenias, purple coneflower and American beautyberry. The second site has several Elliot�s blueberry bushes, Virginia sweetspire and a bed containing La. iris and Stoke�s aster. Also nearby are a cypress, turk�s cap, flame azalea and cardinal flowers. We have numerous squirrel and deer, so I�m sure the husks will be spread all over. Will I kill everything in sight by planting this walnut? Is there a list of the types of plants to which the walnut is toxic?

ANSWER:

Although Juglans nigra (Black walnut) is an important native tree that would thrive in your area, it is probably not a good idea to plant it in your garden setting.

You will find a very good article explaining the science of juglone here in an article from the Virginia Cooperative Extension service. There are also lists of plants that have some tolerance to juglone, but I have heard of (and seen) plants that are supposed to be tolerant that just don't survive. Much like lists of plants that are deer tolerant, there are actually no guarantees. You will also notice that the list of plants that are tolerant is much shorter than the list of plants that are susceptible.

Your garden sounds lovely and you don't mention how much property you have, but it would have to be very large before I would recommend including a black walnut tree in it. You might not notice the effects for a few years as a newly planted tree does not produce all that many leaves and has a limited root zone but keep in mind that this is an adaptation the tree has developed in order to outcompete other plants in its quest to reach it's ultimate size, usually between 50-75 ft, but the champions can reach up to 150 feet. Besides the issue of alleopathy with juglone, black walnut is useful for its stain. Even the lime green outside coating of the nut leaves a dark brown (walnut) stain on whatever it comes in contact with: umbrella and patio furniture cushions, patio stones and concrete, painted wood, the list goes on. A squirrel eating a nut high up in a walnut tree can spread the debris far and wide. I speak from experience when I tell you that a mature tree can produce a thousand nuts in a good year. Leaves must be raked up quickly in the fall or they will stain your patio as well and if you have a pond (I am not sure about a swimming pool) they will turn the pond water black in a matter of days.

So ... the short answer is don't plant it. Return it to the gift giver with the explanation that you just don't have enough space or report that it didn't survive the transplanting process (which is a real possibility as they are quite tap rooted as seedlings).

From the Image Gallery

Black walnut
Juglans nigra