Hydrangea (Hydrangea spp.) is a genus of the Saxifrage family that can add some color to a garden or home. The shrubs and vines develop large leaves and flowers that are either snowball-shaped or flat-topped. Hydrangea hardiness is zone-dependent -- many varieties are suited to Sunset's Climate Zones 3b, 4 to 19, 14 to 24, 26, 28 to 33 and 39. Varieties such as smooth hydrangea (H. arborescens) and climbing hydrangea (H. anomala petiolaris) can grow in the cooler climates of zones A2 and A3, while garden hydrangea (H. macrophylla) can tolerate the warm climate of zone H1.
Hydrangeas can thrive in a sunny area of the garden, but it's best to plant them where they will receive sufficient shade to protect the plants from the hot afternoon sun. Some varieties wilt if they're not protected from the sun's heat, and when placed in deep-shaded areas, the plants may not flower. Hydrangea buds are prone to cold damage. Placing a cardboard box over the plants can help prevent this. Growing hydrangeas in containers is ideal, because you can move the plants inside during extreme temperatures.
Soil and Water Requirements
Grow the hydrangeas in well-drained, loose, fertile soil. A 2-inch layer of compost worked into the soil can add nutrients and help promote drainage. Till the soil to a depth of at least 8 inches. Plant the hydrangeas in a hole deep enough to fit the entire root ball. Aim to level the top of the root ball with the soil surface. Tamp the soil after planting and water immediately. Hydrangeas don't tolerant drought very well -- they prefer moist soil at all times. Provide them with 1 inch of water per week and about 2 inches per week during hot weather.
Fertilizing and Mulching
Placing mulch on the soil around the hydrangeas protects the roots from cold temperatures, suppresses weeds and helps the soil preserve moisture. Apply a 3-inch layer of organic mulch, such as pine bark, on the soil around the plants. Maintain a one-inch distance between the mulch and the stems of the plants. Early in spring, about four weeks after planting the hydrangeas, use a 10-10-10 fertilizer to feed the plants. Fertilize the plants again after they bloom. Always water the soil after fertilizing so the feed dissolves and gets to the roots of the plants.
Color of Flowers
By adjusting the aluminum levels in the soil you can change the color of the blooms of H. macrophylla cultivars. A soil pH of 5.5 and lower is high in aluminum, which results in blue-colored blooms. A soil pH of 6.5 and higher has less aluminum available, which results in red or pink flowers. For blue flowers, wet the soil around the plants with a solution of 1 tablespoon of aluminum sulfate to 1 gallon of water. For pink flowers, use 1 tablespoon of hydrated lime instead. Apply the solution once a month for three months before the buds start blooming.
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