Hydrangeas & Zone 10
Hydrangeas are shrubby perennial plants best known for their showy blooms. The globe shaped, conical or flat panicles appear in spring and continue on and off through the summer and fall. Different hydrangea species thrive in a variety of climates--in extremely cold winters they can die back to the ground. Plants regrow from the roots when temperatures rise, but gardeners might never see a single bloom on the plants.
The United States National Arboretum classifies different regions in the United States according to average low winter temperatures. Zone 10 encompasses the southern tip of Florida, parts of Southern California as well as some areas in the Southwest. Miami, Florida, falls in the zone 10 perimeter. It experiences average winter lows ranging from 35 to 40 degrees Fahrenheit. Zone 10 also includes such western locations as Victorville, California, which also experiences average lows between 30 and 35 degrees. Although both Miami and Victorville fall into the zone 10 categories, their climates differ dramatically. Victorville is arid and receives only approximately 6 inches of rain annually. Miami gets over 50 inches of rain yearly and has high humidity most of the year.
Growing hydrangeas in warm-winter climate areas such as zone 10 means that the plants will not die back to the ground during freezes, as can happen in cold-winter locations. Zone 10 plantings do not suffer from late-season freezes that can kill tender new foliage--as happens in areas such as the Northeast. Milder winters and longer growing seasons allow hydrangea plants to grow larger in a shorter period in zone 10 than in colder regions--given proper care and conditions.
Climbing hydrangeas (Hydrangea anomala) do well in drier and cooler areas of zone 10, as they originate in colder-winter areas that have less humidity. Hydrangea macrophylla, also called mop-top hydrangeas, do well in coastal areas where fog tempers harsh sunlight, such as Southern California coastal areas. Lace-cap hydrangeas need partial to full shade in summer and look good grown under the cover of larger trees.
Most hydrangea species need filtered sun to shade. Hydrangea paniculata takes more sun. All hydrangeas thrive in humus-rich and moist soil. Low rainfall in the West requires gardeners to water the plants often. Positioning the plants against a north-facing wall or at the bottom of a slope can help keep them from drying out. Hydrangeas do not need pruning in zone 10, but deadheading plants to remove dried flowers can help promote repeat blooming.
Hydrangeas need moisture to thrive, so they are not good choices for areas that have water-restriction regulations. Blue-flowering hydrangeas turn pink in alkaline soil--so some gardeners try to make soil more acidic by adding copious amounts of amendments such as aluminum sulfate. Growing a hydrangea in a pot makes it easier and more cost-effective to lower soil pH--turning it acidic to ensure blue blooms.