South Texas climatic conditions may vary from humid and windy on the coast to semi-arid in inland areas, but all share the heat. It takes a stouthearted plant to tolerate the south Texas sun, especially in July and August, but plants hardy in USDA zones 8b, 9a and 9b flourish in the searing temperatures and paint the landscape with saturated colors that are as intense as the heat.
Verbena bonariensis, or purpletop verbena, has a clumping habit with flowers borne on wiry, erect stems that can grow 3 to 6 feet in height and spread to a width of 1 to 3 feet. Purpletop verbena is useful in beds and borders because its airy, open structure allows views of plants behind it. Light purple flowers are 1/4 inch wide and appear in clusters at the ends of stems; they bloom prolifically through summer until the first frost. Purpletop verbena does best in full sun, which is prevalent in south Texas, but will tolerate a touch of shade. It is fairly drought tolerant. Perennial in USDA zones 7 through 11, it grows as an annual in cooler climates.
Zinnia elegans is the most widely known species of zinnia. It also has the widest range of flower size, color, form and height. Size ranges from a diminutive ½ inch to 5 inches in diameter. Every color in the spectrum is available except true blue, brown and black. Flower forms may be single, double or pompon, and height ranges from 8 to 48 inches. Zinnias require full sun and well-drained soils. They do not require frequent watering and are drought tolerant, which makes them ideal for south Texas gardens. Zinnias are easy to grow in all USDA planting zones and are useful for vase arrangements. The more you cut them, the more they bloom. Good air circulation around plants is a must in coastal areas to avoid problems with powdery mildew.
An asset to the south Texas hummingbird and butterfly garden is Hamelia patens, or firebush. Red-orange tubular blooms contrast with bright green foliage to make this evergreen shrub a standout. Though firebush can grow to a height of 15 feet under optimum conditions, it usually stays smaller. In addition to its showy flowers, firebush also produces berries that ripen in stages and change color from green to yellow and red and finally to black. Firebush usually has both fruit and flowers in some stage of bloom or development. Hardy in USDA zones 8 through 11, firebush does best in full sun with well-drained soil. It is useful as a hedge or as a specimen shrub.