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An assortment of petunias: "Purple showers," Mexican petunia (Ruellia simplex), and wild petunia (Ruellia caroliniensis)

Master Gardener Volunteers on… Mexican petunias

By Renee Stevens
Master Gardener Volunteer Program team member

Mexican petunia (Ruellia simplex, syn. Ruellia brittoniana) has a lot going for it.

This native of Mexico, the Caribbean and South America is a colorful blue-to-purple flowering perennial planted in Florida yards since the 1940s. It can grow 3 to 4 feet tall, and has been often used to add height and color to perennial borders. It produces many flowers, is adaptable to different light, temperature, and moisture conditions, and is easy to grow.

Wild petunia (Ruellia caroliniensis). [CREDIT: UF/IFAS Extension Sarasota County, Wilma Holley] Mexican petunia (Ruellia simplex). [CREDIT:] "Purple showers" petunia. [CREDIT: UF/IFAS Extension Sarasota County, Wilma Holley]
(L-R) Wild petunia (Ruellia caroliniensis) [CREDIT: UF/IFAS Extension Sarasota County, Wilma Holley]; Mexican petunia (Ruellia simplex) [CREDIT:]; and “Purple showers” petunia. [CREDIT: UF/IFAS Extension Sarasota County, Wilma Holley]

But, wait. There’s more

Mexican petunia also, unfortunately, produces large quantities of seed. And it can easily grow from bits of plant stem and underground rhizomes (a rhizome is an underground stem, like ginger, used to store food for the plant). That, coupled with its adaptability to various growing conditions, allows it to escape the bounds of the garden and form dense stands of vegetation that can crowd out native plants.

In Florida, Mexican petunia stands have been found in natural areas, often along stream edges and other wet areas. They crowd out native species and change the structure and functions of habitats.

That damage led the UF/IFAS Assessment of Non-Native Plants in Florida’s Natural Areas to list the Mexican petunia in 2013 as “invasive, not recommended” for all climate zones throughout Florida. Earlier, the Florida Exotic Pest Plant Council (FLEPPC) had declared Mexican petunia a category 1 invasive.

Dealing with a petunia problem

An invasive species is defined as one that (a) is non-native; (b) was introduced, intentionally or unintentionally; and (c) causes, or is likely to cause, environmental and/or economic harm, and/or harm to humans.

Research is addressing how best to remove existing Mexican petunia stands in natural areas and to limit re-invasion. At the same time, homeowners are encouraged to manage their own gardens. This is particularly important if your garden is close to Florida natural areas.

If you have Mexican petunia cultivars that set large quantities of seeds, you are encouraged to:

  • Remove them, being sure to get the whole plant. Mexican petunia can easily regrow from bits of plant stem and underground rhizomes.
  • Avoid disposing plants or clippings where they can take root or be carried into waterways.
  • Be vigilant to remove seedlings.
  • Plant something new in the bare ground to reduce the chances of Mexican petunia returning to your garden beds.

We recommend that you do not plant new Mexican petunia unless you can verify that it is a proven sterile cultivar. And please do not accept plants or cuttings from generous friends and neighbors. These are likely to be invasive.

Proxy petunias

Gardeners who like the look of Mexican petunia and want long-lasting color can plant proven sterile cultivars. While these cultivars do not set seeds and are non-invasive by seed dispersal, they can—and do—multiply by rhizomes.

“Purple showers,” a sterile cultivar of Mexican petunia, has been available for some time now and can be found in nurseries, including big box stores.

More recently, the University of Florida has produced a series of sterile cultivars in different colors. These are known as the Mayan™ series, and are available through licensed nurseries in pink, white, purple and a compact purple. Note that these are on the UF/IFAS Assessment caution list, referenced above.

Another option is a Florida native wildflower, the wild petunia. Also known as Carolina wild petunia (Ruellia caroliniensis), it has sparse flowers but a long bloom season, attracts butterflies and is a larval host plant for buckeye and white peacock butterflies.

About the Author
Renee Stevens is a UF/IFAS Extension Master Gardener Volunteer in Sarasota County, a graduating member of the Class of 2018.

One Comment on “Master Gardener Volunteers on… Mexican petunias

  1. Great article; love the fact that there is indeed a sterile variety for folks to utilize! Where is Renee’s lovely visage….Kevin is not the author!