Grow Mexican Petunias (Ruellia Simplex) for a Heat and Shade Tolerant Perennial

Ruellia Simplex

Beloved by many gardeners for its heat tolerance and shade-loving nature, but reviled by others for its eagerness to spread with abandon, R. simplex can be divisive. Largely due to its sweet purple flowers, however, we come down firmly on the pro-ruellia side of the debate.

Close up macro photos of two violet Mexican Petunias (Ruellia Simplex) flowers.

With forms tall and short, this evergreen, herbaceous perennial — hardy in zones 8-11 — deserves consideration for inclusion in southern gardens. The tall version forms clumps 18 inches across, while the short type forms 12-inch clumps.

It’s an erect, often-multi-stemmed plant with dark green, droopy, slender, and long leaves. It’s especially loved for its papery, trumpet-shaped flowers that mimic every shade of the purple rainbow, as well as white and pink.

Each lovely flower, sadly, lasts just a day. But fret not — the plant produces a succession of profuse two-inch flowers daily from spring through fall.

Let’s learn more about this lovely but divisive plant, and why Floridians want nothing to do with it! Here’s what we’ll tackle in this article:

If you live in Florida, you’re certainly excused from reading this article, though you might want to check below for a cultivar that is safe to grow in your region. Or perhaps you’d like to learn about growing turmeric, which also does quite well in the Sunshine State.

The tall variety of Mexican pansies used as an edging bed for a stone pathway.
Ruellia simplex can be grown in either the shade or full sun and is great for edging or mass plantings.

Interestingly, the stem of this plant becomes more purple when it’s in bright light, as opposed to when it’s grown in a shady area, where the stem stays fairly green. I’ve always used my Mexican petunia as a shade plant and was surprised to see purple-stemmed ruellia on a recent visit to Tucson, Arizona, where it was planted in full sun.

Cultivation and History

As with so many of our favorite botanicals, this one comes with a host of aliases. Though not closely related to petunias, many know the plant as Britton’s wild, Texas petunia, or sometimes even Mexican bluebell.

Scientifically, it’s been labeled R. brittoniana, R. coerulea, R. malacosperma and R. tweediana, though today’s taxonomists are in agreement that R. simplex is the correct moniker.

The plant is native to Mexico and South America, and has naturalized in Hawaii and from South Carolina to Texas, where gardeners appreciate it greatly. Butterflies like it too — it attracts swallowtail, brush-footed, and milkweed butterflies eager to enjoy the flowers’ nectar.

However, as alluded to above, it is considered invasive in Florida. There, like a septuagenarian Minnesotan in January, it has populated freely, and the locals RUEllia the day it was introduced. It has a tendency to crowd out native Florida species, and so local horticulturists strongly warn against its use.

The plant is named for Jean de la Ruelle, a late fifteenth- to early sixteenth-century French herbalist and physician to King Francois.

Propagation

Mexican petunia spreads naturally by both seeds — it can spew the small brown discs as far as ten feet — and rhizomes.

Top down vie of the green leaves of Ruellia simplex with no blooms.
Photo by Gretchen Heber.

You can also propagate this plant via purchased seeds, cuttings, or division.

From Seed

Sow R. simplex seeds in early spring, after all danger of frost has passed. Plant one to two seeds for each expected plant, spaced 12 inches apart.

From Cuttings

If you want even more plants — in a different part of the yard, for example — you can propagate by taking cuttings in springtime.

With a sharp, clean blade, cut a healthy-looking stem just below a node, 4-6 inches from the end. Strip off any leaves near the bottom of the stem, and remove the bloom.

Prepare a clean 4-inch pot with a mix of perlite and peat moss and moisten the mixture. Make a 2-inch-deep hole in the potting mix with a pencil.

Dip the cut end of the cutting into a powdered rooting hormone and place the cutting into the hole you made in the potting mix.

Place your potted cuttings in bright, indirect light, and keep them moist. After roots are established, you can transplant them outside.

Division

To divide this plant, loosen the soil around the area, and then dig around the clump you wish to excise.

Lift out the clump and, using a shovel, slice the crown of the plant into several pieces. Place your transplants into holes the same depth as the root balls of your clumps and twice as wide. Spread the roots out in the holes.

Cover the roots with dirt and water thoroughly; continue to water well for several weeks until well-established.

Get more details about dividing perennials here.

How to Grow

Generally, Mexican petunia is highly prized as a shade plant, but if your summers aren’t too brutal, the plant may be able to take full sun.

It is drought tolerant, and in fact, throughout our brutal Central Texas summers, I give mine nary a drop of supplemental water and they do just fine. However, the plant also does even better in wet conditions (hello, Florida!).

Mexican petunia lines a brick wall along a waterfront in a park-like setting.

As with most plants, you’ll want to treat them to regular, deep waterings immediately after transplanting, which you’ll do in springtime, and then you can back off the watering if you like.

You can baby the plant with rich compost or you can stick in the native soil that’s just there, and it will still do fine.

Fertilize with a 10-10-10 mixture in springtime. Or don’t. See a theme here?

Growing Tips

  • Don’t plant in full sun if the heat is brutal where you live
  • Give the plant extra water right after you plant it
  • Plant in sun or shade

Pruning and Maintenance

Trim out any dead leaves and remove dead flowers for aesthetic purposes. Cut off the seed pods if you don’t want the plant to spew its seeds. You can dry and save them for planting elsewhere if you wish, or trade with the neighbors.

A clump of the tall purple variety of Mexican petunia grown as a clumped panting along with orange latana flowers.
Photo by Gretchen Heber.

Of course, if your R. simplex spreads too far and wide, you can excise the metastasizing plants.

Cultivars to Select

Several cultivars of this plant are available, with the distinguishing characteristic typically being flower color.

Ruellia Rooted Live Plants via Amazon

A notable and popular cultivar differs from the straight species in its height. While most standard forms of Mexican petunia range in height from 18 to 36 inches, ‘Katie’s Dwarf’ ranges from eight to 12 inches tall.

‘Purple Katie’ Mexican Petunia

This variety is less aggressive than its taller cousins, though mine definitely spreads. Packages of 50 seeds are available from Amazon.

Pink Mexican Ruellia Petunia ‘Chi Chi’

‘Chi Chi’ is a popular pink cultivar often found at plant centers, or you can purchase a packet of 35 seeds today on Amazon.

Floridians, if you’re still with us, you should choose the cultivar ‘Purple Showers,’ which is sterile and does not produce seed.

Ruellia Simplex ‘Purple Showers’

It can still spread via rhizomes, however.

Established plants in three-gallon pots are available via Amazon.

Managing Pests and Diseases

It’s not on the menu for deer, but if these graceful herbivores are helping themselves to other plants in your garden, check out this article about protecting your plants.
R. simplex doesn’t have any notable insect pest or disease concerns to worry about, either.

Best Uses

Mass plantings of the tall type make a nice border for the back of your beds, whereas the shorter variety makes a lovely edging plant.

You also might want to use ruellia to add some color to shady areas.

Mexican Pansy Quick Reference Chart

Plant Type: Perennial Flower Color Purple/violet
Hardiness (USDA Zone): 8-11 (marginally hardy in Zone 7 with protection) Maintenance Minimal
Bloom Time: Spring, Summer, Fall Soil Type: Any; good drainage
Exposure: Sun or shade Soil PH: Any
Time to Maturity Blooms freely Companion Planting: Lantana
Spacing 12 inches Uses: Tall type - borders and mass plantings
Dwarf type - edging
Planting Depth: 1/4 inch Family: Acanthaceae
Height: 8-12 inches (dwarf type)
18-36 inches (tall type)
Subfamily: Acanthoideae
Spread: 24-36 inches Tribe:
Water: Will tolerate drought; grows more aggressively with additional watering. Genus: Ruellia
Attracts: Butterflies (swallowtail, brush-footed, and milkweed) and hummingbirds
Pests & Diseases: None identified Pests: aphids and thrips. Pests: aphids and thrips.
Edit

Floridians notwithstanding, gardeners in the southern United States would do well to add this purple-blooming beauty to their gardens. A lovely tall plant for the back of a bed, or a pretty edging for the front — one species, two practical uses.

Purple blooms of Ruellia simplex mixed in with other orange blossoms.
Photo by Gretchen Heber.

Virtually maintenance-free and pest-free, and requiring hardly any attention, R. simplex is a lovely addition to any garden.

Are you in the pro- or anti-ruellia camp? Share your experience with this pretty plant in the comments section below.

If you found this guide valuable, you’ll also find some good info here:

Photos by Gretchen Heber © Ask the Experts, LLC. ALL RIGHTS RESERVED. See our TOS for more details. Product photos via liveplantflower, SVI, andlvrgarden. Uncredited photos: Shutterstock. With additional writing and editing by Allison Sidhu.

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About Gretchen Heber

A former garden editor for a daily newspaper in Austin, Texas, Gretchen Heber goes through entirely too many pruners and garden gloves in a year’s time. She’s never met a succulent she didn’t like and gets really irritated every 3-4 years when Austin actually has a freeze cold enough to kill them. To Gretchen, nothing is more rewarding than a quick dash to the garden to pluck herbs to season the evening meal. And it’s definitely time for a happy dance when she’s able to beat the squirrels to the peaches, figs, or loquats.

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