On the U.S. Department of Agriculture's plant hardiness zone map, Zone 8 runs from coastal North Florida and South Georgia to west, central Texas and also includes small parts of inland California, southern Nevada, northern Arizona and the northern Pacific Northwest. Temperatures may dip to 10 degrees Fahrenheit in the northern part of the zone and 15 degrees in the southern part. Zone 8 has fairly mild winters, but many parts have hot, humid summers. Hydrangeas--which have large clusters of small, showy flowers and large bright-green leaves--are popular in the mid-South. Hydrangeas are deciduous in Zone 8 and, in the southern parts of this zone, should be planted in dappled or partial shade and watered frequently during the height of the summer.
The mophead hydrangea (Hydrangea macrophylla) is also known as the bigleaf, garden or lacecap hydrangea. This variety thrives in Zone 8. Its species is among the most popular and includes the "Blue Wave" with lacecap flowers, the double-floret "Domotoi" and the "Goliath," which has a 15-inch bloom. Mopheads may grow to 12 feet high, though most top out around 8 feet. Flowers are available in white, pink, red or blue--though, as with most hydrangeas, the blues (acidic soil) and pinks (alkaline soil) may be changed by tinkering with the pH level in the soil. Mophead hydrangeas should be planted in full to partial sun in the northern part of Zone 8 and in partial shade in the southern part. These plants will wilt without frequent watering during the warmest summer months.
Oakleaf hydrangea (Hydrangea quercifolia) has leaves shaped like those of an oak tree and flower clusters that are elongated and resemble an upside-down cone. The leaves may be as long as 8 inches and they turn bronze or crimson in the fall before dropping. This species blooms best in hot summers and does well in Zone 8, but is hardy to Zone 4. Among the cultivars are "Snow Queen," which has larger flowers, and "Snowflake," which has additional petals. This plant can grow to 6 feet and prefers some shade in Zone 8. While oakleaf hydrangea needs ample water, the soil should not be constantly wet.
The smooth hydrangea (Hydrangea arborescens) is an open plant with gray-green, oval-shaped leaves that may be up to 8 inches across. This species, which can grow to 10 feet, performs best in the southern part of Zone 8 and above. Native to Missouri and one of the most cold-hardy species, the smooth hydrangea usually has smaller blooms than the mophead or oakleaf species, but it is a more prolific bloomer. The plant itself is looser and more woody. Smooth hydrangea is available in several cultivars, including the giant "Annabelle," which has blooms of up to 12 inches across, and the "Grandiflora," which has 6-inch blooms. In Zone 8, this plant should be in partial shade with ample water.