North Texas falls into zones 6 and 7a/7b of the USDA hardiness map. This means temperatures can reach lows of minus 10 degrees Fahrenheit in the winter in the upper regions of Texas. Temperatures generally do not fall below 0 to 5 degrees F in the lower northern regions. Summers in Texas are hot and humid. Choose annual flowers well-suited to the North Texas climate and group plants with similar light and water requirements.
Firebush (Hameilia patens) is an evergreen shrub or small tree that reaches a height of 15 feet, but is usually seen much smaller--about 2 feet tall grown as an annual. Its green leaves are elliptic-oval shaped, about 6 inches long, with reddish veins and stems. Firebrush produces showy clusters of bright red-orange or scarlet flowers throughout the year. Firebush berries are ornamental as well. Grow firebush in full sun in well-drained soil. Once established, firebush is heat and drought tolerant.
According to Texas A&M extension, pansies are the most popular hardy annual grown in Texas. Viola x wittrockiana is a fancy pansy, growing 4 to 6 inches tall and available in a wide range of colors. All pansies are small, clumping plants with kidney or heart-shaped leaves and colorful, five-lobed flowers. Grow pansies in sun or shade on a wide range of soils, depending on the variety. Pansies prefer moist, well-drained soils.
Moss Rose (Portulaca grandiflora), also known as purslane, is an evergreen perennial often grown as an annual bedding plant. It is a low-growing succulent with a trailing form, growing up to 12 inches tall, but usually seen around 3 to 4 inches tall. Its leaves are light green, thick and fleshy, and its flowers come in shades of white, orange, red, yellow and pink. Moss rose flowers are an inch across and bloom heavily, but only in sunshine. Grow moss rose in full sun, on various, well-drained soils.
Salvia (Salvia splendens), also known as scarlet sage, is a perennial shrubby plant often grown as an annual bedding plant. As an annual, salvia reaches about 30 inches in height, with 4-inch long, bright green leaves, and scarlet-red stalks of showy flowers blooming summer to frost. Grow salvia in full sun to partial shade, on various, well-drained soils.