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A: There are those who suspect Wildflower Center volunteers are the culpable and capable culprits. Yet, others think staff members play some, albeit small, role. You can torture us with your plant questions, but we will never reveal the Green Guru's secret identity.

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Ask Mr. Smarty Plants is a free service provided by the staff and volunteers at the Lady Bird Johnson Wildflower Center.

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Thursday - October 04, 2012

From: Lansing, MI
Region: Midwest
Topic: Planting, Trees
Title: Native plants for under a black walnut from Lansing MI
Answered by: Anne Bossart

QUESTION:

What native plants can you recommend that will grow in Michigan under a mature black walnut tree?

ANSWER:

Walnut trees can present a real challenge for gardeners.  Although they are great shade trees, they exude a chemical called juglone which inhibits the growth of other plants near it.  A great adaptation if you are a walnut tree and want lots of room to grow; not so great if you are a gardener with a limited amount of space!

Research indicates that the juglone increases the alkalinity of the soil, creating harsher conditions for plants nearby (the ideal condition for most plants is neutral to slightly acidic soil) so the pH of your soil will impact your success.  Also, if your soil is sandy and well drained, the effect of juglone may be less than if you have clay soil. There are publications which you will find by doing an internet search like this one by Virginia Cooperative Extension service which will be helpful.  Although not Michigan specific, Walnuts behave in a smiliar way across their native range.

Although our Native Plant Database can create lists of plants native to Michigan using the Combination Search it cannot sort according to tolerance to juglone.  However, many of the individual plant entries do indicate if a plant is juglone tolerant.  So in your search for native plants that are tolerant, you will have to check a few lists of plants like this one from Grandville, Michigan which lists non-native plants as well as native and this one from a native plant grower in Ontario (with many native plants in common with Michigan).  You can cross reference those suggestions against our lists of native plants. Many Extension offices do publish fact sheets and sometimes will have one with suggestions so do call or visit yours, but often a gardener is left to trial and error. 

Unfortunately, we can't just give you a list because every situation is different so finding suitable plants is a bit of an arduous process.

 

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