Rhododendrons come in many colors, sizes and shapes. Many people think the flowering shrubs only grow in humid climates, but the evergreen plants grow all over the world. Most rhododendrons that grow in North America prefer mild temperatures and plenty of moisture. Large-leafed rhododendrons grow well in other parts of the country where they survive warm summers and cold winters amazingly well.
More than 1,000 different species of rhododendrons exist in the wild. Twice that number grow as hybrids, according to Washington State University. The evergreen plants offer showy flowers varying in color from white, peach, and red to pink, purple and other colors. Bloom size ranges from small, delicate flowers to huge clusters of flowers that reach more than 1 foot in height. Depending on the species, the plants bloom anywhere from early spring through the summer.
Rhododendrons thrive in mild climates as well as the tropics and arctic regions. The beautiful flowering plants grow well in humid climates such as those found along the Pacific Coast in Northern California, Oregon and Washington. Some rhododendrons, such as the maddenil types, grow well in warmer climates like those found in Southern California, Hawaii and Florida.
Rhododendrons grow best in slightly acidic soil. To make soil more acidic, gardeners often add organic matter such as pine bark mulch, composted, aged leaves or sphagnum moss. The material is mixed into a depth of about 12 inches. Adding organic matter also helps aerate the soil, another factor rhododendrons appreciate.
Most rhododendrons come in containers or burlap bags, ready for planting in partial to fully shady areas of the garden where they receive shelter from the wind. The hole for the plant should be deep enough so that 1 1/2 inches of the root ball sits above the soil line. After planting, a 2-inch layer of mulch placed around the plant helps conserve moisture.
The plants require frequent watering of about 1 inch per week because their roots grow right below the surface and dry out easily. In late fall or in late spring, the plants benefit from an application of high-nitrogen fertilizer formulated for acid-loving rhododendrons. Once the plants bloom, careful removal of the withered flowers helps direct the plant’s energy into producing more flower buds the following year.
Rhododendrons make attractive specimen plants, especially when planted in a small group. They thrive under taller trees and vegetation that provide natural shade, especially in the summer. The plants work well to form borders because they stay green year-round. Rhododendrons also offer wildlife and birds temporary shelter year-round thanks to their evergreen characteristics.