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Monday - September 22, 2014

From: Austin, TX
Region: Southwest
Topic: Plant Lists, Soils
Title: Nitrogen Fixing plants for Austin Texas
Answered by: Larry Larson

QUESTION:

I recently saw a piece on Central Texas Gardener recommending winter covers to fix nitrogen such as elbow rye, hairy vetch, and crimson clover. Can you recommend a native plant that will grow through a central Texas winter such as these?

ANSWER:

  We actually have a fair selection of plants that fit that request, at least as per being nitrogen fixing.  This description of “Nitrogen fixing Crops”  from Wikipedia gives that: “Plants that contribute to nitrogen fixation include the legume family – Fabaceae – with taxa such as clover, soybeans, alfalfa, lupines, peanuts, and rooibos. They contain symbiotic bacteria called Rhizobia within nodules in their root systems, producing nitrogen compounds that help the plant to grow and compete with other plants. When the plant dies, the fixed nitrogen is released, making it available to other plants and this helps to fertilize the soil.”

This brings to mind immediately our famous Lupinus texensis (Texas bluebonnet), which have a symbiotic relationship with rhizobium bacteria which helps them fix nitrogen.  Here is the page from the Wildflower Center “How-to” discussions that describes this.

  In the meantime though, while looking for more suggestions, I found a very powerful search engine on the USDA website that reveals native plants that fix nitrogen and even rates the amount of nitrogen fixing!  Rated as “HIGH” is Dalea candida (White prairie clover), which is native to Bastrop County, so I think it deserves mention.  There are more that are rated as “MEDIUM”,  these include:

Amorpha fruticosa (Indigo bush)
Apios americana (Groundnut),
Chamaecrista fasciculata (Partridge pea)
Desmanthus virgatus (Wild tantan)
Robinia pseudoacacia (Black locust)
Senna marilandica (Maryland senna)
Sophora secundiflora (Texas mountain laurel)

 

From the Image Gallery


Texas bluebonnet
Lupinus texensis

Texas bluebonnet
Lupinus texensis

White prairie clover
Dalea candida

White prairie clover
Dalea candida

Indigo bush
Amorpha fruticosa

Groundnut
Apios americana

Partridge pea
Chamaecrista fasciculata

Texas mountain laurel
Sophora secundiflora

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