Mexican petunias are a pretty flowering evergreen perennial that can be grown in containers, as shrub-like plants, or as ground cover. They grow rapidly and spread easily, even in conditions that would be less than ideal for many plants.
They can survive drought, flood, heat, and poor soils, which will be a blessing for many gardeners. Unfortunately, these traits can also enable the plant to become invasive, so it will need to be kept in check.
Mexican Petunia Overview
|Origin||South America, Mexico, the Caribbean|
|Scientific Name||Ruellia brittoniana|
|Common Names||Mexican petunia, Mexican bluebell, Florida bluebell, Desert petunia, Britton’s wild petunia, Purple ruellia|
|Height||Up to 6 feet|
|Light||Full sun to partial shade|
|Watering||Medium watering needs|
Caring for Your Mexican Petunia
Mexican petunias are incredibly tolerant of any watering conditions. They will survive both drought and flood, with no noticeable detrimental effects. It is so tolerant of soggy soil that it can be grown in up to 6 inches of water, along with other bog plants in shallow streams and waterlogged riverbanks.
When grown in the garden, the best way to manage their watering is to maintain moist, but not soggy, soil. You can do this by watering the plant as soon as the top layer of the soil starts to dry out. You can test for moisture by touching the top of the soil, or you can simply judge from sight. If the top layer of soil is already moist, then you don’t need to add any further water.
If you have a history of poor watering habits or have experienced plants that die from either overwatering or from lack of water, then the Mexican petunia would be a great feature in your garden, as it will not have a problem with inconsistent watering. The plant grows rapidly, and because of this, it is known as an invasive species in some regions, notably Florida. I
f you want to keep it under control in your garden, then allow the plant a little less water. It is when the plant is growing in very moist soils that it tends to become overgrown more easily. During winter, you shouldn’t need to water the plant so long as there is sufficient rainfall. If you experience a fairly dry winter, then you can continue to water the plant whenever the soil appears visibly dried out.
In terms of frequency of watering, this will depend on lots of variables, including the lighting position that your plant is grown in, the climate, the type of soil, and whether it is growing directly in the ground or in a pot.
As the Mexican petunia will grow in both dry or wet soil, the soil quality isn’t terribly important for this plant. It will grow in almost any condition, including poor quality soil, but for best results, you should use a well-draining and fertile soil.
The only soil a Mexican petunia may have a problem with is very acidic soil, so if your plant is struggling to grow, you should consider checking the pH of your soil in case this is the reason.
Mexican petunias thrive in full sun. When allowed to grow in these conditions, they will produce an abundance of flowers. They will also grow in partial shade, though plants grown in a partly shaded position may experience less flower development than those grown in full sun. As the plant is not sensitive to heat, the time of day when the Mexican petunia gets direct sun is not important, though in general, sun in the morning and shade in the afternoon is preferable when growing a plant in partial shade.
If you grow these plants in containers, you have the option of moving them throughout the year to a full sun position during summertime, then a more protected and potentially shaded position during cooler months. Aside from flower production, the other way Mexican petunias are affected by light is with the color of their stems. In bright light, their stems will be purple, while plants kept in partial shade will have bright green stems (SF Gate).
These plants are hardy through USDA hardiness zones 7 to 11. They enjoy the warmth and can happily grow in a full sun position where they can bask in the heat all day long. They will thrive in warmer climates and have naturalized themselves in parts of Texas, Hawaii, and South Carolina. They have also naturalized in Florida, where they grow so aggressively that they are able to choke out other plants that are native to the state.
Mexican petunias are very heat-tolerant, so don’t feel the need to shade them to protect them from the heat. They are most tolerant of the heat when grown in moist conditions and note that when grown in a hot climate, the plant will like to be watered more frequently. Mexican petunias are a very hardy plant in many aspects, and they will tolerate a wide range of suboptimal growing conditions, but the one area in which they fall down is in very low temperatures.
If you are growing these plants in a cooler climate, they should be protected from cold winters, either by moving them to a protected position out of the cold breeze, by bringing them indoors or by covering them with gardening fleece. When growing in a colder climate, grow your Mexican petunias in containers so that you have the option of portability during the winter.
Mexican petunias will propagate easily from stem cuttings in the summer months, but this is not something that most gardeners have to do, as the plants readily self-seed to supply the garden with an endless supply of new Mexican petunias.
If you want more of this plant growing in your garden, simply allow the flowers to turn to seed; they will drop to the ground and sow themselves where they land. The plant can have a tendency to self-seed quite aggressively, with the seeds dispersing themselves as much as 10 feet away from the plant. If you would rather not have your garden taken over by Mexican petunias, you will need to deadhead the blooms once they fade.
Aside from removing dead or damaged stems, this plant doesn’t necessarily require pruning, but it depends on the type of look you like in your garden. If you prefer a well-manicured style, then prune the plant to your desired shape. If you want to encourage more flowers to appear, cut back the stems in early spring.
Each stem, which would have developed one flower, will respond by branching out several stems, which will each produce a flower. By tactically pruning the plant in this way, you can increase the flower production quite dramatically, but the plant does tend to flower quite prolifically even without this measure. You can also deadhead the plant if you want to prevent self-seeding.
The flowers of the Mexican petunia bloom from the middle of summer through to fall. They typically measure around 2 inches in diameter and have a delicate lilac-blue color. They resemble petunia’s, as you would expect from their common name, but in fact, the Mexican petunia is not a petunia at all. These flowers have a trumpet or bell shape, and rise high above the foliage of the plant, growing from dark purple-hued stems.
They have no scent but are still very attractive to butterflies, hummingbirds, and other pollinators. Each flower only lasts one day, but during the long blooming season, the plant produces so many flowers that you will never be short on the pretty purple blossoms. After the flower fades, it will develop into a pod resembling a bean pod, containing a cluster of seeds.
Upon bursting, the seeds will be dispersed onto the ground, where they will sow themselves. The seeds have been known to travel quite a distance from the plant; this is helped by rainfall or watering hoses, which can carry the seeds further than usual.
Mexican petunias do not require feeding. They will still flower even in nutrient-deficient soils, though if a soil has a nutrient imbalance, then this is where problems can occur. Soil, which is high in nitrogen, will see the Mexican petunia produce lots of dark green foliage in favor of flowers.
If you have a Mexican petunia that is struggling to flower but has lots of lush foliage growth, then you may need to test your soil for nutrient imbalance. You can try to flush out the nitrogen with lots of generous watering to resolve this problem, or you can add a layer of mulch to the surface of the soil, as this can help to draw nitrogen out.
In the most extreme cases, you may need to dig up your plant and transplant it to a different soil. If your soil is nutrient deficient, your Mexican petunia should still produce a good number of flowers, but you can help it along by adding a balanced fertilizer if you wish.