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The sun gleams through the foxtail-like blooms of the purple fountain grass, whose leaf color works in monochromatic harmony the Mexican petunia. The planting also includes Marguerite sweet potato vines with bright chartreuse foliage, making a great complementary marriage with the petunias' iridescent blue flowers. Enlarged photo
The sun gleams through the foxtail-like blooms of the purple fountain grass, whose leaf color works in monochromatic harmony with the Mexican petunia. The planting also includes Marguerite sweet potato vines with bright chartreuse foliage, making a great complementary marriage with the petunias' iridescent blue flowers.

Mexican petunia dazzles
with radiant blue flowers

By Norman Winter

MSU Horticulturist
Central Mississippi Research & Extension Center

The Mexican petunia, or ruellia, is getting more popular with each growing season, and I give a hearty “amen.” One thing that surprised me is how it has crossed from home to commercial landscapes. Most of the time, commercial landscape plants create a frenzy with homeowners.

As you pace the aisles of your garden center this spring, wondering what to plant for color and what to choose as a partner, think about the iridescent blue from the Mexican petunia.

Not only does it endure high heat and humidity, but it is also a performer in drought-like conditions. I suppose that stands to reason why I saw so many incredible beds last summer.

Although called the Mexican petunia, ruellia is not related to petunias. Petunias are in the family solanaceae, making them related to tomatoes, peppers and eggplant. Ruellia is in the acanthaceae family with members like the shrimp plant or black-eyed Susan vine.

Ruellia has bluish-purple flowers that radiate color from the plant. It's still mostly sold generically, but Purple Showers is starting to be seen more and more. There are also pink-flowered varieties available like the Chi-Chi Pink that reaches 36 to 48 inches in height and has a spread of 18 inches. I am partial to the taller varieties that are well suited to the back of the perennial border. Shorter varieties, like Katie, are available. They only reach 8 to 12 inches and spread 12 to 24 inches.

This garden provides a colorful combination of tough plants including the blue Mexican petunia, New Gold lantana and Knock Out rose. Links to larger image.
This garden provides a colorful combination of tough plants including the blue Mexican petunia, New Gold lantana and Knock Out rose.

Ruellia grows best in full sun, but I have seen some remarkable plantings in part shade. The Mexican petunia thrives in moist, well-drained, organic-rich soils and performs well in poorer soils, too.

The deep green foliage with hints of burgundy is attractive and works well in combination plantings. The leaves are narrow, pointed and reach almost a foot in length on large varieties. The flowers are borne in clusters on forked branches. The flowers are tubular or funnel-shaped and may reach 2 inches in length. The long bloom period is usually early summer through fall.

One planting I saw last year was absolutely stunning. Foxtail-like blooms of the purple fountain grass glowed from being backlit and contrasted with the iridescent blue flowers of the Mexican petunia. The leaf color of the purple fountain grass worked in monochromatic harmony with the Mexican petunia. The planting also had Marguerite sweet potato vines with bright chartreuse foliage, making a great complementary marriage with the petunias' blue flowers.

Another garden that caught my eye partnered the blue Mexican petunia with New Gold lantana and Knock Out rose. You could not ask for a more colorful combination of tough plants.

The ruellias that will be for sale at your nursery until this spring are definitely perennial in zone 8, and people have told me they return in zone 7. The good news for colder areas is they make good annuals like a real petunia.

They are also easy to propagate. You can divide clumps, take root cuttings and plant by seed. Stems are easy to root in moist soil or sand. Another big plus is that they are disease- and pest-free, making them environmentally friendly.

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Released: January 24, 2008
Contact: Norman Winter, (601) 857-2284

Editor's Note: Ideal publication dates of Southern Gardening columns are within one month of their release. Editors should examine older columns carefully for any information that could be time sensitive.

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