Afternoon shade is extremely important if you wish to grow hydrangeas in zone 9. Hydrangeas are hardy from zones 4 through 9, and the heat in zone 9 means hydrangeas need extra protection. Because hydrangeas prefer moist, well-draining soil, they need a shady spot to keep the soil from drying out too quickly. While it is possible to grow many of the most popular hydrangea varieties in zone 9, consider growing the native oakleaf hydrangea (Hydrangea quercifolia), an understory, shade-loving shrub.
Choose a planting site on the north side of a building, as the U.S. National Arboretum recommends. Such a site will offer protection from the heat of the afternoon sun. If your yard borders a woodland area, that is an excellent location for any variety of bigleaf, oakleaf or smooth hydrangea, all of which do well as understory shrubs in zone 9.
Prepare a large site, as the University of Georgia Extension recommends. The Extension recommends adding 50 pounds of compost per 10 square feet of planting space and incorporating it with a rototiller or shovel to a depth of 8 to 12 inches. Hydrangeas love deep, fertile, well-drained soil.
Space hydrangea plants 36 to 60 inches apart. Hydrangeas do especially well in mass plantings, but be sure you have the space and the plants aren't crowded; hydrangea plants can grow to a substantial size, at least 5 to 6 feet tall.
Plant the hydrangea so the top of the root ball is level with the soil, as the University of Georgia Extension recommends.
Water the newly planted hydrangeas thoroughly. The soil for hydrangeas should never be allowed to dry out or the plants will abort their blooms and they are only mildly drought tolerant. Provide extra irrigation during dry spells; otherwise, keep soil moist.
Lay 3 to 5 inches of organic mulch. The University of Georgia Extension recommends pine straw, pine bark or dried leaves.