How to Grow Mexican Petunia 

The Mexican Petunia (Ruellia brittoniana) is one of the flower gardens’ most attractive members. A member of the Acanthaceae family, these evergreen shrubs are commonly grown for their violet blooms, hence one of their alternative names, Purple Showers. Also known as Mexican Bluebells, some cultivars produce the papery, trumpet shaped flowers in shades of white and pink. While each flower lasts for just a day, the plant’s profuse flowering habit means that the blooms continue to emerge daily from spring until fall. 

Originating in Mexico and South America, the Mexican Petunia is also classified as naturalized in the states of Texas and South Carolina. These resilient hardy perennials are considered a desert plant, making them ideal for warm, dry climates. As well as being drought resistant they are also pleasingly low maintenance. This means that with just a little effort the bright violet blooms of the Mexican Petunia can easily grace your flower garden. 

The quick growth habit of the Mexican Petunia also makes it a great choice if you want to cover a wall or unsightly elements in your garden such as an air conditioning unit. Purple Showers can also be used for ground cover.

Flowering throughout the summer, this is your complete guide to adding the Mexican Petunia to your garden.

Bright, light and easy to grow, the Mexican Petunia is a reliable, low maintenance addition to the flower garden. 

Be warned in Florida the Mexican Petunia is considered an invasive species. This is because the plants quick growth habit can smother slower growing, native plants. If you are unsure of the plant’s status in your area, check with your local extension office before planting. 

Mexican Petunia Varieties 

While Mexican Petunia plants are commonly sold by garden stores, seeds offer a wider range of choice and also provide more value for your money. Seeds can be purchased in garden stores or online. If you are purchasing online make sure that you use a reputable company.
 

When selecting your plants bear in mind the position that they are going to occupy. Larger plants are great for blocking unsightly structures or in mass plantings at the back of flower beds. Smaller varieties work well in container gardens and also as an edging plant. 

Most varieties of Mexican Petunia range in height from 18 to 36 inches. Tall varieties can form clumps 18 inches wide while smaller varieties have a spread of about 12 inches. If space is at a premium try planting small or dwarf cultivars, such as Katie’s Dwarf. This particular variety has a height of 8 to 12 inches.

Popular varieties include Purple Katie. This variety is considered less aggressive than other varieties, however it will still spread through your garden if allowed to. For something a little lighter, Chi Chi is a popular pink variety.

Purple Showers is another attractive variety. It is also sterile meaning that it won’t set seed and spread through your garden. The variety can still spread through rhizomes however so avoid planting in overly moist soil. Likewise the popular Katie Dwarf cultivar is also sterile and therefore not considered invasive. 

Other sterile cultivars include Mayan White and Mayan Purple. These provide all the attractiveness of the Mexican Petunia without any of the invasive growth habits. 

Finally, Alba is also considered non-invasive. Attractive and resilient, Alba is not commonly found. However its attractive white blooms mean that tracking down the seeds is well worth the effort. 

What is the Difference Between Mexican Petunia Plants and Annual Petunias?

Despite the name and similar looking flowers, Mexican Petunia plants are not closely related to petunias. If you look closely you will notice a number of differences between the two plants. 

While they may partly share a name, there are a number of differences between the two plants. 

The main difference is in the foliage. Mexican Petunia plants have long, thin foliage which upon close inspection clearly differs from the full and pointy annual petunia foliage. 

Unlike petunias, which are typically grown as floral bedding plants, Mexican Petunia plants are shrubby plants with woody stems. They grow much taller than annual petunias.

Growing from Seed

Start the seeds undercover in trays in later winter. The trays should be filled with a general purpose potting soil. You can also sow two seeds per biodegradable pot. Following germination pick out the weakest seedling allowing the strongest to grow on. 

Sow the seeds on the top of the moist soil and cover lightly. Place in a warm, light position. The temperature should average 72 to 76 ℉. Keep the soil moist during germination and as the seedlings grow. Germination takes around 10 days in ideal conditions.

Seeds are easily germinated undercover in pots or trays for transplanting outside once the temperatures are warm enough. 

 

Following germination, continue to keep the soil moist, allowing the seedlings to grow on. Once the last frost date has passed begin to harden the seeds off before planting outside.

In warmer climates you can also sow the seeds into their final position. Weed and work the soil before dampening. Sow the seeds on the damp soil and cover lightly. 

Following germination space the plants out. Each variety has a different spacing requirement, this is specified on the seed packet, but most cultivars require a spacing of around 12 inches.  

Where to Plant?

Planting in warm, sunny positions extends the flowering season and also helps to reduce maintenance. 

Full sun positions are ideal, the more direct sunlight the plants receive the more profusely they flower. They can also grow in partial shade and shade positions. But the darker the position the fewer flowers the plant produces. Interestingly in light positions the stems of the flowers turn purple. In shady positions the stems remain green. 

A full sun loving plant, the more light Purple Showers receives, the more flowers it produces. 

While they prefer warm conditions Purple Showers are cold hardy in USDA Zones 7 to 11. A perennial in warm zones, in cooler areas they are best grown as annuals. Typically a desert plant, the Mexican Petunia also does well in humid conditions. 

These are robust plants that tolerate a variety of soil types. However they thrive best in well draining, fertile soil. If planted in marshy soil or close to water Purple Showers quickly grow and spread. While they can cope with alkaline soil, for the best results the soil pH should be neutral to slightly acidic. 

A soil test kit will tell you the pH level of your soil. It is also a good way to check the nutrient content of the soil before planting. Too much nitrogen in the soil can turn the foliage dark green. It can also encourage too much foliage to form and inhibit flower production. Mulching the soil is one way to counteract too much nitrogen in the soil. The mulch works to draw the nitrogen up away from the soil without drying out or damaging the soil further. 

Work in a layer of compost or well rotted organic matter before planting to help improve the soil. A layer of sand can be worked into heavy soils to improve drainage.

Planting Out Mexican Petunia Plants

Once the seedlings have been hardened off, they are ready for planting out. Plants purchased for garden stores are usually ready for immediate planting out.

Dig a hole in the garden large enough to hold the plant. Carefully remove the seedling from the tray or pot. If you have started your seeds in biodegradable pots, such as ANGTUO Seed Starter Pots, they can be planted still in the pots. As the plant grows the pot will break down, allowing the roots to spread.
 

Aim to plant so that the top of the root system sits just below the soil level. When the plant is correctly positioned, firm the soil down and water well. A layer of mulch can also be applied. This helps the soil to retain moisture and keep an even temperature. 

Once established these are drought tolerant plants, until then however you should keep the soil evenly moist. After a couple of weeks you can reduce the frequency with which you water.

Growing in Containers

Mexican Petunia plants are also suitable for growing in pots as part of a container garden. This is particularly useful if you want to control their growth habit. 

Growing in containers is also a useful cultivation method if you are growing in a cooler climate, you can move the plants inside in the colder winter months. Coadura Plant Caddies are a great way to easily move plants around the home and garden. This helps you to ensure that your flowers are warm and happy in their position without too much physical strain. 

Purple Showers also make attractive and resilient indoor houseplants. 

Be warned, these are quick growing shrubs that require repotting more frequently than other plants. To reduce the frequency with which you need to repot, plant in medium to large sized pots. Planters and old barrels can also be used. 

 

Whatever container you choose it should be clean and have lots of drainage holes in the bottom. 

Fill your container with a well draining potting mix and plant as described above. 

Caring for Mexican Petunias

Once established these are surprisingly low maintenance plants.

With just a little care and a lot of sun Purple Showers flower continuously from spring until early fall. 

Watering your Flowers

Once established these plants are considered drought resistant. However they will appreciate, and even do better, if you water them occasionally. Try watering only when the top layer of soil is dry to the touch. 

When watering use a hose to evenly soak the soil around the plant. Try to water as early in the day as possible. This gives the foliage time to dry out during the day, helping to prevent mold and fungal issues. 

During the winter months if there is sufficient rainfall you may not need to water the plants at all. Reducing the amount of water you give is also a useful way to control the spread of the plant. 

Do I Need to Feed my Plants? 

The Mexican Petunia does not require fertilizing. Even in poor nutrient deficient soils the plants continue to flower. However, an occasional dose of balanced fertilizer does not harm, particularly in poor soils. Alternatively, work compost into the soil in early spring. 

Pruning Mexican Petunia Plants

As I have already noted this is a low maintenance plant. The only pruning you truly need to do is removing dead or damaged stems. You can also prune the plant into a specific shape, if you want to keep its sometimes unruly growth looking neat. 

In early spring, cut the stems with garden scissors to encourage more flowers to form. Each stem produces a flower. Pruning encourages the stem to branch out setting several new stems, each of which will produce a flower. 

Finally, if you want to prevent self-seeding deadhead fading or spent flowers. 

How to Propagate Mexican Petunia Plants

There are a number of different ways to propagate Mexican Petunia plants. 

Unless you have planted a sterile variety growing from seed is the easiest way to propagate Mexican Petunia plants. As the spent flowers fade they are replaced by seed pods. Once these have turned brown the pods can be harvested. 

Make sure that you remove the seed pods before they split. These plants are vigorous self-seeders. This habit can be particularly aggressive in moist climates where seeds can set up to 10 ft from the parent plant. 

Open the pods and allow the seeds to dry out. Once they are dry you can store the seeds in a cool, dry place, in a labeled envelope or jar, until you are ready to sow. 

If you have planted a sterile variety you will need to propagate by cuttings or division. 

Tip or Stem Cuttings

This method of propagation is best done during the summer months.

Take cuttings, about 5 inches long, from healthy stems. Try to make the cut just below a node. From the node new roots emerge. 

Remove any buds and flowers as well as the lower foliage. Dip the cut end in a rooting hormone and plant in a pot filled with an even mix of soil and peat moss. Moisten the soil before planting. 

Source: https://www.youtube.com/watch?v=D4vzrKLjN5g 

Place the cutting in a light position. Roots should form within a few weeks. To test for the presence of roots gently pull the cutting. If you feel resistance it means that roots are forming. 

Once roots are present, the plants can be transplanted into the garden. Transplanting is best done in the fall before the plants enter their winter dormancy period. As the temperatures warm up the following spring, your new plants will begin to flourish. 

Dividing the Rhizome

As Mexican Petunia plants grow their rhizome, or crown, also spreads. Once the plants are a few years old they can be lifted and the rhizome divided in order to produce new plants.

 

Carefully loosen the soil around the plant and use a shovel to lift the plant. Use a shovel or sharp knife to slice the crown into several pieces. Each piece should be an even size and have some roots and stems attached. 

Replant the transplants to the same depth, spreading the roots out in the hole as you plant. Backfill the hole and water well for several weeks until established. 

Common Problems and How to Solve Them

Mexican Petunia plants do not suffer from many problems. 

If conditions are not ideal they may suffer from blight. 

Cold weather can cause the foliage to brown. Move the plants indoors or cover with a horticultural fleece, such as a Garden Fleece, if frosts threaten. 

Plants can also fall victim to spider mites. Check the foliage regularly for signs of infestation. Wash any affected leaves with an insecticidal soap.

 

Containing Their Spread

The most difficult problem encountered by many growers is how to contain Purple Showers’ vigorous spread. As we have already explored planting sterile varieties, or deadheading spent flowers to prevent seed pods from forming is an effective form of control. 

You can also plant the flowers in large pots and plant the pots in the garden. This method of planting means that the spread of the root system is contained by the walls of the pot. Planted in this way, plants can flourish for a number of years before they require repotting. 

You can also push wooden planks into the soil, to a depth of about 6 inches deep to slow and control the spread of the root system. 

Attractive and easy to care for, as long as you are prepared to control their spread, these are reliable additions to the flower garden. 

A reliable addition to the garden Mexican Petunia flowers look great if planted in swathes on their own. They are also useful companion plants for lantanas, purple verbenas, pentas, the blue star creeper and dwarf fire bush. Just be careful not to plant them too close to small, slow growing plants that may be smothered by their fast growth habit. 

Ideal in desert or xeriscape planting schemes the Mexican Petunia also works in more traditional flower beds. Why not add one to your garden today?