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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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Monday - May 14, 2012

From: San Antonio, TX
Region: Southwest
Topic: Invasive Plants, Herbs/Forbs
Title: Invasive American Germander from San Antonio
Answered by: Barbara Medford

QUESTION:

I brought home some American Germander (Teucruim canadense) - page 259 In Wildflowers of Texas by Geyata Ajilvsgi - from a railroad right-of-way. Since it is a member of the mint family it has become super invasive in my wildflower garden. I have tried solarization, Roundup, tilling and mulching to kill it but none of these methods have been successful. Do you have any suggestions? Maybe Ornamec?

ANSWER:

We have probably mentioned this before, but the best way to control invasives is to never plant them. Because Teucrium canadense (Canada germander) is a member of the Lamiaceae (mint) family it is unusually invasive. You can see from this USDA Plant Profile map that it is indeed native to Bexar County and to a whole lot of the surrounding area.

We did some research on the herbicide Ornamec, and discovered that it is a grass killing herbicide. In other words, it will kill monocot plants, grasses, and not touch dicots, or broad-leaved plants. So you would add a toxic material to your garden soil that would not faze the germander at all. Always research the specific purposes of a herbicide before you purchase or apply it.

We learned that the Teucrium canadense spreads by underground rhizomes, so that even an appropriate herbicide would probably not be able to get to those rhizomes. We also learned that it appears to be a wetland plant. If you have wildflowers native to the Bexar county area, you could probably water them less and at least discourage the germander. However, you also need to get down and root out those rhizomes, getting the tubers that store food for the plant and ensure its safety from the herbicides. There is no quick solution to a plant that can protect itself this easily. Of course, you should always cut down the plant before it has a chance to bloom and seed, as that is another way it spreads.

If worse comes to worse, you can try the paintbrush and herbicide method. Get a small amount of undiluted herbicide, the kind for dicots or broad leaf plants and some small disposable sponge paintbrushes. Full disclosure: This is hands and knees work and not easy. One at a time, clip the stem of the germander as close to the earth as possible. Then, within 5 minutes, paint the cut edge with the herbicide. You need to do it quickly because the plant will try to heal the cut over to protect the very rhizomes you are trying to kill. And keep pulling them out, digging out the rhizomes.

Next time you see some wildflowers in a wild situation, step away from the plant.

 

From the Image Gallery


Canada germander
Teucrium canadense

Canada germander
Teucrium canadense

Canada germander
Teucrium canadense

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