Mexican petunias, also known as desert petunias, produce more flowers the more sunlight they have, so choose a sunny spot in your yard.Once established, Mexican petunias are very hardy, and can survive for long spells without water. However, young plants need regular watering. You can also grow these plants indoors in pots, provided they have a sunny location. Indoor plants must be watered regularly as well during hot weather. Keep them away from any heat vents and electrical equipment. In the winter, indoor Mexican petunias must only be watered when the soil shows signs of drying. These plants are highly resistant to most pests and diseases. In warmer climates, Mexican petunias can grow rapidly and propagate themselves by way of seeds. In some areas, this plant is considered an invasive species because they can spread very fast, taking over the yard if not controlled. If you feel that these pretty plants are taking over your yard, you can easily pull out the required number of stems. These shrubs also need their woody and tough stems regularly pruned to maintain their shape and appearance. If you want more of these beautiful flowers in your backyard, cutting stems halfway after flowering will result in the growth of several more stems and flowers. In colder climates, the foliage will be damaged by frost, in which case the damaged parts must be removed and disposed of promptly to avoid infection.