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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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Friday - February 21, 2014

From: Austin, TX
Region: Southwest
Topic: Soils, Problem Plants, Groundcovers, Herbs/Forbs, Trees
Title: Ecosysystem with pecan at center from Austin
Answered by: Barbara Medford

QUESTION:

Dear Mr. Smarty Plants, I would like to create a native tree guild around a mature pecan. It shares its space with native shrubs and ephemerals but I would like to add a nitrogen fixing plant. I am also looking for native plants that attract beneficial insects for that space. I see a lot of lacewings in the fall and I'd like to encourage their presence. The tricky bit is finding plants that will not only thrive in the bright shade but also tolerate the juglone. I wonder if you know of any reference books that describe which plants used to grow near our native trees? I think what I am trying to do is to re-create a mini-ecosystem so that all the parts help each each. Thanks for all you do.

ANSWER:

We were very interested in your stated purpose of "re-creating a mini-ecosystem so that all the parts help each other." This is a laudable purpose and well in line with our basic precepts of sustainable gardening with native plants. However, centering this arrangement on Carya illinoinensis (Pecan) which, as you pointed out, not only creates a lot of shade but also emits substances (juglones) to eliminate and kill competing plants around it, makes the process somewhat more difficult. However, we will try to find some research information on these subjects and help you come to your own conclusions.

Temperate climate permaculture plants - this discusses nitrogen-fixing plants and how they work, but most of the listed plants are non-native. We will go through and pick some plants native to the Austin area that might work in your situation.

PerennialSolutions.org All Nitrogen Fixers are Not Created Equal

Please note this paragraph in that article, which reinforces our determination to recommend only native and non-invasive plants in every situation.

"It’s interesting to note that many of the most hated naturalized species turn out to be incredibly efficient nitrogen fixers. In fact the “high” nitrogen fixtures category is a rogues gallery of successful dispersive species, like Russian olive (Eleagnus angustifolia), kudzu (Pueraria lobata), and Scotch broom (Cytisus scoparius). I decided to use the database to generate lists of native and non-native nitrogen fixers and categorize them by their efficiency."

Here is a list of the nitrogen fixers we found that are native to Travis County. Notice that all belong to the family Fabiaceae, including our iconic Texas bluebonnet.

Acacia angustissima (Prairie acacia)

Amorpha fruticosa (Indigo bush)

Astragalus crassicarpus (Groundplum milkvetch)

Lupinus texensis (Texas bluebonnet)

Apios americana (Groundnut)

Now, on to the juglone problem. We have 2 previous Mr. Smarty Plants answers on juglones, with links to lists of plants that resist them. Again, these are not all going to be native.

Previous answer from Maryland.

Previous answer from San Antonio

And, although we didn't find a book specifically on the juglone-resistant native plants, we did find this article from SF Gate Home Guides, which included this paragraph:

Juglone-Tolerant Wildflowers

"Native wildflowers typically have longer root structures than their domesticated cousins, which may be one reason they are more tolerant of juglone. These plants may have also adapted the tolerance as understory growth in forests where they had to compete with black walnut for soil resources. The purple coneflower (Echianceae purpurea) is tolerant of USDA zones 3 through 8. It also withstands heat, humidity and poor soils, plus its seeds are a delight for birds. Bee balm (Monarda didyma) is another wildflower tolerant of juglone. It has a sweet scent, attracts butterflies and hummingbirds, and is tolerant of USDA zones 3 through 9. Jack-in-the-pulpit (Arisaema triphyllum) is tolerant of USDA zones 4 through 9, but requires more care, needing rich organic soil in order to thrive."

We will check those listed native wildflowers and give you links to our webpages in our Native Plant Database on each to find some native to Texas, if not to Travis County:

Echinacea angustifolia (Black sampson)

Monarda citriodora (Lemon beebalm)

Arisaema triphyllum (Jack in the pulpit)

We suggest that, after you follow our plant links to our webpages from the Native Plant Database and find out the growing conditions for those plants, that you read all of our research references as well as previous answers in hopes you will be able to formulate a juglone-resistant, nitrogen-fixing garden under your pecan tree.

 

From the Image Gallery


Prairie acacia
Acaciella angustissima

Indigo bush
Amorpha fruticosa

Groundplum milkvetch
Astragalus crassicarpus

Texas bluebonnet
Lupinus texensis

Groundnut
Apios americana

Black samson
Echinacea angustifolia

Lemon beebalm
Monarda citriodora

Jack in the pulpit
Arisaema triphyllum

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