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When looking to include plants in a landscape bed, why not consider one of our native wildflowers, Carolina wild petunia? The plant enjoys sun to part shade and is drought tolerant once established. And its savory nectar is certain to attract a variety of butterflies, native bees, hummingbirds and other nectar loving visitors. The wild petunia proves much more welcoming in the landscape than its non-native counterpart, Ruellia simplex.
Let's begin with the not-so-good associated with the Category I invasive R. simplex, or Britton Mexican Petunia. As a Cat I, the Mexican petunia can and has escaped cultivation, meaning it has spread well beyond home gardens and into natural terrains, where it has crowded out and replaced native species and, in some cases, hybridized with natives.
Growing to an erect height of 3 feet, the plant tolerates most soil types, pH and drainage conditions. Mexican petunia was a big seller in years past and, to this date, can be found in many a landscape. And, if you have ever had these plants in your garden, you know they are extremely difficult to eradicate. Just when you think you have been successful, the plants sprout again in defiance of your efforts.
The plant reproduces in two ways: through above/below ground horizontal roots known as rhizomes, and, the setting of seeds. The plant flowers prolifically, producing numerous seed pods throughout the year. These burst open, spreading the easily germinated seeds far and wide. So, the chances are good that not only will you see numerous “volunteers” in your landscape over a short time, your neighbors may as well. And, as stated previously, the mayhem doesn't end there. Self-seeding + rhizomes = a recipe for ecological distress. If you see them for sale at a nursery or elsewhere, you are encouraged to steer clear.
It is likely you have seen multiples of non-native Mexican petunia cultivars in big box stores, examples of which include R. simplex “Purple Showers,” R. simplex “Mayan White” and other such sterile varieties in the Mayan series. What differentiates these cultivars from the Category I invasive R. simplex is that they do not set seeds but, rather, multiply solely by rhizomes. Although not considered invasive, these, too, have the ability to dominate the local area if left unchecked.
Now for the good part. The long-lived perennial Carolina wild petunia provides a welcome alternative to non-native species. Being herbaceous, the plant possesses a non-wood stem, attains its full height, flowers and forms seed pods, which then release their seeds, within one season. Each seed pod contains five seeds, unlike the 30 seeds each of the invasive R. simplex. Following a less active period in winter here in Southwest Florida, the wild petunia becomes revitalized in spring and the cycle of life continues on.
Also known as Ruellia caroliniensis, the plant is low growing with an average height and spread to 2 feet. It has a preference for sandy, alkaline soil, and exhibits lovely, delicate blue/lavender blooms spring through fall. Although each bloom lasts but a day, you'll hardly notice because of the proliferation of blooms throughout the growing season.
Attracting a number of nectar-loving visitors, the wild petunia also serves as host to the Common Buckeye, Junonia coenia, and White Peacock, Anartia jatrophe, butterflies.
Interesting fact about the Ruellia genus: The plants are not true petunias. So, to answer the question: When is a petunia not a petunia? When it comes under the Ruellia umbrella.
Join me next time when we will explore another of my favorite wildflowers, the native blue porterweed (Stachytarpheta jamaicensis), not to be confused with its non-native Category II invasive counterpart, S. cayennensis. Until then...
Happy gardening!
Janetta Fox is a Lee County Master Gardener volunteer and a member of the Garden Club of Cape Coral. Visit us at gardenclubofcapecoral.com.