Grow Mexican Petunias (Ruellia Simplex) For A Heat And Shade Tolerant Perennial

Ruellia Simplex

Ruellia simplex, a perennial herbaceous plant, is an enigma wrapped in controversy. Its sweet purple flowers have won the hearts of many gardeners, but its tendency to spread rapidly has earned it detractors. We’re firmly on the pro-ruellia side, and here’s why: this evergreen plant, suitable for USDA Hardiness Zones 8 to 11, is a must-have for southern gardens. Its forms range from tall, clumping varieties that reach 18 inches across to shorter types that form 12-inch clumps.

The plant itself is erect, often multi-stemmed, with long, droopy leaves that are a deep green color. Its claim to fame lies in its papery, trumpet-shaped flowers that come in every shade of purple, as well as white and pink – although each flower only lasts a day. Fear not, however, as the plant produces a succession of two-inch flowers daily from spring through fall.

While some gardeners may find this spread too aggressive for their liking, we believe its charm is worth considering for your own garden.

What You’ll Learn

If you’re not living in Florida, or if you’re interested in exploring the possibilities of growing turmeric, which incidentally thrives in this region, then you’ve come to the right place. Ruellia simplex is a versatile plant that can be grown in either shady conditions or full sun, making it suitable for various landscaping purposes such as edging or mass plantings.

What’s more intriguing is the effect of light on its stem – when exposed to bright sunlight, the stem takes on a purple hue, whereas it remains greenish in shadier areas. In my experience, I’ve always grown Mexican petunia in shade, but during a visit to Tucson, Arizona, where it was planted in full sun, I was delighted to see the stems display their natural purple color.

Cultivation and History

This botanical has accumulated a variety of names over time. While it may not be closely related to petunias, many refer to it as Britton’s wild Texas petunia or Mexican bluebell. In the scientific community, it’s been labeled R. brittoniana, R. coerulea, R. malacosperma, and R. tweediana, but most taxonomists agree that R. simplex is the correct classification.

Native to Mexico and South America, this plant has naturalized in Hawaii and across parts of the United States, including from South Carolina to Texas where it’s highly regarded by gardeners. Butterflies also appreciate its flowers, which attract species like swallowtail, brush-footed, and monarch butterflies seeking nectar.

However, it’s considered invasive in Florida, where it has thrived freely since its introduction, crowding out native species and prompting local horticulturists to warn against its use. The plant is named after Jean de la Ruelle, a 15th- to early 16th-century French herbalist and physician to King Francois.

Propagation

The Mexican petunia’s ability to spread is a remarkable phenomenon that can be attributed to its unique propagation methods. Not only does it produce small brown seed discs that can travel up to ten feet, but it also grows rhizomes, allowing it to spread through underground stems. This versatility in spreading means you have multiple options for propagating the plant, including purchasing seeds, taking cuttings, or dividing established plants.

From Seed

For successful germination and growth, sow R. simplex seeds in early spring once the risk of frost has dissipated. To ensure a thriving crop, plant one to two seeds per desired plant, leaving about 12 inches of space between each seed for optimal development.

From Cuttings

When you’re ready to expand your plant collection further afield, consider propagating by taking cuttings in the spring. To do so, grab a sharp, clean blade and snip off a healthy stem just below a node, about four to six inches from the tip. Remove any leaves near the base of the stem, as well as the bloom. Next, prepare a clean four-inch pot filled with a mix of perlite and peat moss that’s been moistened to perfection. Create a two-inch-deep hole in the potting mix using a pencil.

Then, dip the cut end of the cutting into powdered rooting hormone before placing it into the hole you just dug. Finally, position your potted cuttings in bright, indirect light and keep them consistently moist until their roots are established. At that point, you can safely transplant them outside to join the rest of your plant family.

Division

To successfully divide a perennial plant, start by loosening the soil around the area you wish to excavate. Next, carefully dig around the clump, taking care not to damage any surrounding roots or foliage. Gently lift out the entire clump and use a shovel to slice through the crown of the plant, separating it into multiple sections. For each new transplant, create a hole that’s the same depth as the original root ball but twice as wide.

Spread the roots out evenly within the hole, ensuring they’re not bunched or tangled. Finally, cover the roots with soil and thoroughly water the area to settle everything in place. It’s essential to continue watering well for several weeks after division, allowing your newly transplanted perennials time to establish a strong root system.

How to Grow

Mexican petunia is often sought after for its shade-tolerant properties, but if your region’s summers are relatively mild, the plant can thrive in full sun as well. This adaptable flowering annual boasts impressive drought tolerance, withstanding Central Texas’s scorching summers without supplemental watering. In contrast, it flourishes in wet conditions, making it an excellent choice for Florida’s humid climate.

As with many plants, Mexican petunia benefits from regular deep waterings immediately after transplanting, typically done in the spring. Following this initial watering schedule, you can gradually reduce watering to suit your plant’s needs. When it comes to soil, you have two options: enrich the native soil with rich compost or leave it as is. The plant will still thrive either way. For optimal growth, fertilize with a balanced 10-10-10 NPK mixture in the spring.

However, if you prefer a more relaxed approach, simply omit fertilization and let nature take its course.

Growing Tips

When planting your garden, consider the lighting conditions. If you reside in an area with intense sunlight, avoid direct exposure for your plants. Instead, opt for a spot that receives partial shade to prevent overheating and potential damage. Additionally, make sure to provide your newly planted seedlings or saplings with adequate hydration, taking extra care during their initial growth stages. For the majority of plants, a balanced blend of sun and shade is ideal.

By striking this equilibrium, you’ll set your garden up for success and encourage healthy development.

Pruning and Maintenance

To maintain a visually appealing arrangement, eliminate any wilted leaves and remove spent flowers from your R. simplex plant. Additionally, consider cutting off seed pods to prevent unwanted spreading. If you’d like to propagate the seeds, you can dry and store them for future planting or share with fellow gardening enthusiasts. Alternatively, if the plant has become too vigorous and is encroaching on surrounding areas, carefully remove any errant stems to maintain control.

Cultivars to Select

While Mexican petunia cultivars primarily differ in flower color, height variations are also notable. One popular cultivar, ‘Katie’s Dwarf’, stands out for its compact growth habit, reaching only 8 to 12 inches tall. This dwarf variety is less aggressive than its taller counterparts, although it can still spread. Another well-known cultivar is ‘Chi Chi’, a pink-flowering variety often found at plant centers.

In contrast, Southern Star cultivars, such as ‘Pink’ and ‘White’, are dwarf varieties that top out at 10 to 12 inches tall. These compact plants make excellent ground covers. If you’re looking for a sterile option, the ‘Purple Showers’ cultivar is sterile but can still spread through rhizomes. For those in Florida, this cultivar is an ideal choice.

Managing Pests and Diseases

While deer might not be interested in R. simplex, it’s possible that these herbivores are browsing on other plants in your garden. If you’re experiencing issues with deer helping themselves to your flora, consider checking out our article on how to protect your plants. In terms of potential problems, R. simplex doesn’t typically come with notable insect pest or disease concerns.

Best Uses

When incorporating Coleus into your garden design, consider mass planting the taller varieties along the edges of your beds to create a striking border. Alternatively, opt for the shorter forms to add a pop of color and texture as an edging plant. Additionally, this versatile plant can also bring vibrancy to shady areas, making it an excellent choice for adding some much-needed brightness to areas that might otherwise lack sunlight.

Quick Reference Growing Guide

The Ruellia simplex, a stunning perennial flower, boasts vibrant purple/violet hues. Native to Mexico and South America, this low-maintenance beauty thrives in USDA Zones 8-11, with some protection allowing it to marginally survive in Zone 7. This drought-tolerant plant blooms throughout spring, summer, and fall, making it an excellent choice for any garden. Its adaptability extends to soil type, exposure, and pH, as long as the ground is well-draining.

With a maturity time of just one to two months, you can quickly enjoy its 8-12 inch (dwarf type) or 18-36 inch (tall type) stature. Spacing at 12 inches allows for effortless companion planting with lantana. Planting depth requires only about 1/4 inch. This versatile flower attracts butterflies like the swallowtail, brush-footed, and milkweed species, as well as hummingbirds. Its spread reaches 24-36 inches, making it perfect for edging or mass plantings in borders.

The Ruellia simplex is a member of the Acanthaceae family, with moderate to low water needs.

Purple Power

While Floridians may have a special affinity for this purple-blooming plant, its benefits extend to gardeners throughout the southern United States. As a statuesque addition to the back of a bed or a charming edging for the front, R. simplex is a versatile species that can be enjoyed in multiple ways. One of its most appealing characteristics is its low-maintenance nature. Requiring minimal attention and being virtually pest-free, this lovely plant is an ideal choice for busy gardeners.

Its beauty is matched only by its ease of care, making it a wonderful addition to any garden. So, are you a fan of R. simplex or do you have reservations about this pretty plant? Share your experiences in the comments section below.

For more information on plants that thrive in shady conditions, be sure to check out our guides on how to grow and care for Salvia, Full-sun Flowering Perennials for Southern Gardens, Learn How to Grow Asparagus Fern, Grow Coneflower, A Native American Favorite, and other informative articles. Follow us on Facebook, Twitter, Pinterest, or explore our website to discover more.