Azaleas are popular flowering shrubs that can be grown both indoors and outdoors. Whether they are kept inside or outside depends entirely on the specific variety and the local climate. Confusion often arises because plants sold during the winter holidays are cultivated differently from the hardy shrubs intended for the landscape. Understanding this distinction is key to successful cultivation.
Understanding Azalea Varieties
The distinction lies between landscape azaleas and florist azaleas, which are often different species within the Rhododendron genus. Landscape varieties are typically hardy, either deciduous or evergreen, and bred to withstand colder temperatures. These plants are intended for permanent installation in garden beds and grow into large shrubs. Florist azaleas, commonly sold blooming in winter, are significantly less cold-tolerant. They are often forced into bloom early for the houseplant market and are not frost-hardy, making them unsuitable for surviving a northern winter outdoors. Their smaller, tender nature makes them suitable only for temporary indoor display.
Cultivation Requirements for Outdoor Azaleas
Outdoor azaleas require specific soil conditions to thrive, primarily demanding an acidic pH level, ideally between 4.5 and 6.0. In alkaline or neutral soil, they cannot properly absorb nutrients like iron, which leads to yellowing leaves (chlorosis). The soil must be consistently moist yet well-draining, as their shallow root systems are susceptible to root rot in soggy conditions. These shrubs generally perform best in partial shade or dappled sunlight, such as filtered light under tall trees. While they need at least four hours of light daily to produce abundant flowers, intense afternoon sun can scorch the leaves. Protecting the shallow roots from temperature fluctuations is achieved by applying a two-to-three-inch layer of organic mulch, such as pine needles. Most landscape azaleas are reliably hardy in USDA zones 5 through 9, though cold tolerance varies greatly between cultivars.
Managing Azaleas as Indoor Houseplants
Azaleas kept indoors, typically florist varieties, require a cool, bright, and humid environment to sustain their blooms. They thrive in temperatures cooler than most homes, ideally between 60°F and 65°F, as cooler temperatures prolong the flowers’ lifespan. Placement near a bright, indirect light source, like an east-facing window, provides sufficient light without the risk of leaf burn. Maintaining high humidity is a significant challenge indoors, since dry air rapidly causes flower buds to shrivel and drop. A humidity level of 40 to 60 percent is preferred. This can be achieved by placing the pot on a tray filled with pebbles and water, ensuring the pot does not sit directly in the water. The potted soil must never be allowed to dry out completely. A helpful technique is to submerge the entire pot in a basin of room-temperature water until air bubbles stop rising, then allowing it to drain thoroughly.
Moving Azaleas Between Environments
Moving an azalea between environments, such as placing a potted plant outside for the summer, requires a gradual adjustment period called hardening off. Sudden changes in light intensity, temperature, or humidity can shock the plant, causing leaf scorch or leaf drop. The transition should involve moving the plant to a sheltered outdoor location for progressively longer periods each day over one to two weeks. When moving a non-hardy indoor azalea outside, wait until all danger of frost has passed, typically late spring. The initial outdoor location should offer deep shade to protect the plant from direct sun exposure, which is more intense than indoor light. Conversely, if a potted plant is being brought inside for winter protection, the shift should be made before the first frost. Move it from a cool outdoor spot to an unheated porch or garage for a few weeks before bringing it into the home’s warmer air.