Mexican petunia is almost as beautiful as it is invasive


I have a thick stand of Mexican petunia (Ruellia brittoniana or Ruellia simplex) next to a couple of the greenhouses at school. The plants have been established for close to 20 years. This past week we replaced the plastic covering on one of the houses, and I didn’t realize the job it would be.

I’ve replaced plastic dozens of times, but never had I been forced to deal with this invasive perennial to get the job done. Roots and rhizomes had really built up over the years.  There was such an overgrowth of plant material that the easiest fix was to put new baseboards above the existing ones and install new locking rails.

Mexican petunia is not really a petunia at all. It’s an upright perennial plant highly adaptable to the southeastern US. It gets covered with purple, pink or white petunia-like flowers in summer, and they hang on well into the fall.

Each flower lasts only a day, but you would never know it. When plants are in bloom they’re loaded. A thunderstorm can strip plants of every flower and the next day these guys are a sea of color again.

Mexican petunia tolerates wet soils. It will even grow in ponds. Plants can be maintained at less than waist height but left unpruned they can grow six feet tall in rich wet soil. For best flowering, plants should be in full sun. They make a great screen and they’re easy to grow.

Propagation is easy. Stem cuttings root well without the need for rooting hormone. Division is another productive method. They also naturally spread from seed. Butterflies and hummingbirds are attracted to the tubular flowers.

The problem is that Mexican petunias don’t play nice. If used in the landscape, they must be planted alone and a place where they can’t spread.

Purple types are the most aggressive. White and pink flowered types are usually somewhat shorter and don’t spread as quickly.

Recently, plant breeders have developed shorter less aggressive cultivars in all three colors. The drawback is that most of them are also less winter hardy. Last winter killed all my dwarfs but none of the full-size types.

This exotic perennial has few insect or disease problems. Mine get covered with mealybugs, but they don’t seem to be bothered by them. Deer generally save their foliage for last.

Chemical control is usually successful. Most broadleaf herbicide mixtures will control Mexican petunia as will glyphosate. The problem is that they will also kill or injure most other ornamental plants in your perennial garden.

Fortunately, we are near the edge of the hardiness zone for Mexican petunia. When planted in open areas, winter will spank them every few years. Those planted in sheltered places are rarely killed or even injured.

We don’t propagate very much Mexican petunia for our school plant sales anymore. We used to sell a lot and some people still ask for it. Its bloom can be spectacular. However, its invasiveness is a turnoff, and I can’t bring myself to promote it.

Plants beginning to emerge in mid-March.

 

Purple Ruellia making its way under the greenhouse walls

Mexican petunia covered with mealybugs

Ted Manzer teaches agriculture at Northeastern High School.

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About tedmanzer

I grew up in Old Town Maine and got a B.S. at the University of Maine in Plant Sciences/ minor in Botany. From there I moved to West Virginia and earned a M.S. in Agronomy at WVU. I also met my wife there. She grew up in rural WV as the daughter of tenant farmers who raised cattle and hogs. Their lifestyle at times was one of subsistence and I learned a lot from them. I've always been a foraging buff, but combining my formal botanical knowledge with their practical 'Foxfire-type' background opened up my eyes a little more. I now teach agriculture to high school students at Northeastern High School in Elizabeth City, NC. My wife teaches with me and we make a great team. I also write a weekly nature/foraging column for the local paper (dailyadvance.com). I also have written several Christian nature/adventure novels that I plan to publish eventually. One is a five book family saga I call the 'Forgotten Virtues' series. In the first book, Never Alone, a young boy comes of age after his father dies in a plane crash, and he has to make it alone. Never Alone is now available in paperback, Kindle and Nook. The second book, Strange Courage, takes Carl from his High School graduation to his recovery from a nasty divorce. The third book, Second Chances, takes Carl from his ex-wife's death and the custody of his son to his heroic death at age 59. The fourth book, Promises Kept, depicts how his grandchildren react and adjust to his death. In the final book, Grandfather's Way, his youngest and most timid granddaughter emerges from the shadow of her overachieving family and accomplishes more in four months than most do in a lifetime. I use many foraging references with a lot of the plants I profile in these articles in those books.
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5 Responses to Mexican petunia is almost as beautiful as it is invasive

  1. tonytomeo says:

    You know, that does not look at all familiar. Perhaps that is a good thing.

    • tedmanzer says:

      It started out in Florida. Maybe it hasn’t made its way west yet, or maybe the California Department of Agriculture was smart and denied its entry.

      • tonytomeo says:

        There is not much ‘smart’ in the California Department of Agriculture. Those who work at the border station on Highway 5, the main highway from Oregon, can not distinguish between blue spruce and roses . . . . seriously! They kept asking me if my spruce seedlings were roses! I kept repeating that they were spruce. After I got back, I learned that spruce were quarantined too!

      • tedmanzer says:

        That’s a howl! Bureaucracy at its worst.

      • tonytomeo says:

        That is how all these weird pathogens get in, and why San Jose now has those nasty fat mosquitoes that are out during the day.

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