How to Grow and Care for Mexican Petunias

Mexican petunia (Ruellia brittoniana)

passion4nature / Getty Images

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 seeds and rhizomes. Because of their fast growth, these plants are considered invasive. 

 Common Name Mexican petunia 
 Botanical Name Ruellia brittoniana 
 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, USA
 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. They can be planted in dry areas 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. 

Light

Mexican petunias love sunshine and will thrive in full sun. They also grow quite well in partially shaded areas, but this will stunt 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 it begins to dry out. For the winter months, hold back on 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

These plants grow abundantly, making fertilizer unnecessary in most situations.

Propagating Mexican Petunia

These plants can easily and quickly be propagated through stem cuttings and rhizome division.

For cutting propagation, you will need sharp, clean garden snips, a small pot, well-draining, and rich soil. Then follow the instructions below: 

  1. Using sharp garden snips, cut a stem around 6 inches long just below a node. This is best done in the summer.  
  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 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 roots have formed.

To propagate through rhizome division, you will need a shovel. Then follow these steps: 

  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 to do it:

  1. In starter pots, plant the seeds in moist, rich potting soil. Gently cover the seed with the 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 10 days. 
  5. Once the seedlings are a few inches tall, begin hardening them off. 
  6. Move the seedlings outdoors once 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 giving water once the soil is dried out. If cold temperatures are threatening your area, it is best to move Mexican petunias indoors as 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. Simply cut down the flowering stems to encourage new growth. Deadhead the spent blooms to make room for upcoming blooms. And be sure to place the Mexican petunia in an area that receives plenty of sunshine, as this will encourage more prolific flowering. 

Common Problems With Mexican Petunias

Mexican petunias are hard to kill and can withstand droughts, floods, and high temperatures. Though hardy, some have still encountered an issue or two with these plants. One of the most common issues is brown leaves.

Brown Leaves

If you find brown leaves, the plant has most likely experienced cold weather and sustained damage as a result. Move the plant to a warmer area and remove the damaged sections. The plant will regrow full and lush, if given 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
The Spruce uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Ufl.Edu, https://plants.ifas.ufl.edu/plant-directory/ruellia-simplex/.