How to Grow and Care for Mexican Petunias

Mexican petunia flowers with deep purple petals closeup

The Spruce / Adrienne Legault

This Mexico-native evergreen perennial is not a petunia, despite its name. However, it is known for its petunia-like purple flowers that attract bees, butterflies, and hummingbirds. Its leaves are dark green and lance-shaped.

The Mexican petunia (Ruellia brittoniana) is a fast grower, quickly spreading through self-seeding and rhizomes. Because of their fast growth, these plants are considered invasive. 

Common Name Mexican petunia, Mexican bluebell, Britton's petunia 
Botanical Name Ruellia brittoniana  or Ruellia simplex
Family Acanthaceae
Plant Type Perennial, rhizome
Mature Size  1-4 ft. tall, 1-3 ft. long, 1-3 ft. wide
Sun Exposure Full, partial
Soil Type Loamy, sandy, moist but well-drained
Soil pH Acidic, neutral
Bloom Time Summer, fall
Flower Color Purple
Hardiness Zones 8-11, USDA
Native Area North America, South America, Caribbean

Mexican Petunia Care

This hardy plant can be grown almost anywhere, as long as temperatures are warm enough. They are tolerant of heat, humidity, flooding, and droughts, and they can be planted in dry as well as boggy areas. Once established, these plants don’t require much attention beyond the occasional watering and deadheading. Mexican petunias are also disease resistant, though these plants occasionally have problems with spider mites

Warning

Mexican petunias are fast growers and quick spreaders. They easily reseed themselves and can quickly get out of hand, overtaking native flora. According to the University of Florida, they are considered invasive in Florida

Mexican petunia plant with deep purple flowers on stem with long leaf blades

The Spruce / Adrienne Legault

mexican petunia plant with deep purple flowers on stem ends and surrounded by long leaf blades

The Spruce / Adrienne Legault

Mexican petunia flower with deep purple petals closeup

The Spruce / Adrienne Legault

Light

Mexican petunias love sunshine and will thrive in full sun. They also grow quite well in partially shaded areas, but shade reduces flower production. Plants grown in full sun will have purple stems while those grown in the shade will have green stems. 

Soil

These hardy plants can be grown in almost any soil type but do the best in well-draining, rich soil. They prefer neutral to acidic soil pH levels. 

Water

Mexican petunias are resilient when it comes to water intake, as they can survive both droughts and floods. During the growing season, it is best to keep the soil evenly moist, watering only once soil begins to dry out. For the winter months, reduce watering until the soil is dry. 

Temperature and Humidity

These tough plants are heat and drought-tolerant. They thrive in areas with high humidity and high heat. Mexican petunias do not handle the cold well and are not frost-hardy. Be sure to protect these plants if any cold weather comes your way. 

Fertilizer

Fertilizer is unnecessary in most situations.

Propagating Mexican Petunia

These plants can be easily and quickly propagated through stem cuttings and rhizome division. This is best done in the summer.

To propagate by cuttings, you will need sharp, clean garden snips, a small pot, well-draining, and rich potting soil: 

  1. Using sharp garden snips, cut a stem about six inches long just below a node.
  2. Remove the leaves from the bottom half of the cutting. 
  3. Dip the cut end into rooting hormone and shake off the excess powder. 
  4. Fill a small pot with rich, well-draining potting soil and plant the cutting a few inches deep. 
  5. Keep the pot in a warm area with bright, indirect light and water regularly, keeping the soil moist. 
  6. Transplant into the garden once a root system has formed.

To propagate through rhizome division, you will need a shovel: 

  1. Gently dig around the plant to loosen the soil. 
  2. Using the shovel, slice through the rhizomes to create multiple, separate plants.
  3. Lift the divided plants out of the ground and transfer them to their new location. 

How to Grow Mexican Petunias From Seed

Growing Mexican petunias from seed is another easy way of propagating these plants. Here’s how:

  1. In starter pots, plant the seeds in moist, rich potting soil. Gently cover the seed with soil. 
  2. Place the pots in a warm area that receives bright, indirect light. 
  3. Keep the soil moist, checking daily. 
  4. Germination should occur in about ten days. 
  5. When the seedlings are a few inches tall, acclimate them to the outdoors by hardening them off
  6. Move the seedlings outdoors when they are acclimated to full sun. 

Potting and Repotting Mexican Petunias

Mexican petunias can be kept in pots, which is an ideal option for those living in areas with cold winters since the plant can be moved. However, because of its rapid growth rate, Mexican petunias will need to be repotted often. To do this, choose a pot that is at least 2 inches larger than its current pot. Gently dislodge the plant from its pot and set it into the new pot. Fill the pot with well-draining, fertile soil and bury the root system to the same depth it was before. Water thoroughly. 

Overwintering

When grown in warm climates with mild winters, Mexican petunias do not require extra winter care. Simply cut back on watering, only when the soil is dried out. If cold temperatures are threatening your area, it is best to move Mexican petunias indoors because they cannot handle cold temperatures. 

How to Get Mexican Petunias to Bloom

Mexican petunias are known for their petunia-like, purple, trumpet-shaped flowers that last about a day. Though the blooms themselves die off quickly, Mexican petunias continue to prolifically produce their vibrant blooms for quite some time, usually from early summer to fall. They do not have a strong aroma. 

To encourage flower production, prune the plant after blooming. Cut down the flowering stems to encourage new growth. Deadhead the spent blooms to make room for future blooms. And be sure to place the Mexican petunia in an area that receives plenty of sunshine, as this will encourage abundant flowering. 

Common Problems With Mexican Petunias

Mexican petunias are difficult to kill and can withstand droughts, floods, and high temperatures. Though hardy, gardeners have encountered a few issues with these plants. One of the most common issues is brown leaves.

Brown Leaves

If your plant has brown leaves, it has most likely experienced cold weather and has sustained damage as a result. Move the plant to a warmer area and remove the damaged leaves. The plant will regrow full and lush, if it receives the warmer temperatures it requires.  

FAQ
  • Is Ruellia brittoniana a perennial?

    Yes, Ruellia brittoniana is a perennial. In areas with warm winters, this plant is evergreen. For areas with cold winters, it is sometimes used as an annual.

  • Do Mexican petunias like sun or shade?

    Mexican petunias can be grown in both sun and partial shade, but prefer full sun. More sunlight will encourage more flowering.



Article Sources
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  1. Ufl.Edu, https://plants.ifas.ufl.edu/plant-directory/ruellia-simplex/