Before moving any begonia outside, it is crucial to identify its type, as this dictates its hardiness and environmental preferences. Broadly, begonias fall into three categories. Fibrous-rooted begonias, like the ubiquitous Wax Begonia (Begonia semperflorens), are typically the most sun-tolerant and resilient to outdoor conditions. Tuberous begonias (Begonia tuberhybrida) produce spectacular flowers but prefer bright, indirect light and are sensitive to both intense sun and cold. Rhizomatous begonias, such as the Rex Begonia, are primarily grown for their stunning foliage and are the most sensitive to direct sunlight and environmental changes. Knowing your plant's type is the first step in ensuring a successful transition.
Begonias grown indoors are not prepared for the harsh realities of the outdoor world. A sudden move from a stable indoor environment to a patio with full sun, wind, and fluctuating temperatures will shock the plant, leading to leaf scorch, wilting, and potentially death. This process must be gradual. Begin by placing your begonia in a completely shaded, sheltered location on your patio for a few hours each day, gradually increasing its time outside over 7-10 days. Slowly introduce it to morning sun if its type can tolerate it, but always avoid the intense afternoon sun. This slow introduction allows the plant to build a tougher cuticle on its leaves and adjust to the new light and temperature levels.
Once acclimatized, most begonias will flourish in an outdoor setting that mimics their natural understory habitat. The universal rule is to provide bright, but filtered, light. Dappled shade beneath a tree or a covered patio that receives plenty of ambient light is ideal. Very few begonias can tolerate direct, hot afternoon sun. They also require protection from strong winds, which can easily tear their succulent stems and leaves. The soil must be exceptionally well-draining; a peat-based potting mix is perfect. Consistent moisture is key, but they will not tolerate soggy, waterlogged roots. Water when the top inch of soil feels dry, and ensure pots have adequate drainage holes.
Begonias are tropical or subtropical plants and are extremely sensitive to cold. Without exception, they should only be moved outside once all danger of spring frost has passed. Nighttime temperatures should be consistently above 50°F (10°C), with daytime temperatures ideally between 65°F and 75°F (18°C - 24°C). Even a single light frost will kill most begonias. As autumn approaches and night temperatures begin to drop, you must be prepared to bring your plants back indoors long before the first frost is forecast. This temperature sensitivity is the primary reason begonias are often treated as annuals in colder climates or moved indoors for the winter.
When done correctly, moving your begonia outside for the summer season is highly beneficial. The increased air circulation helps prevent fungal diseases like powdery mildew, which can be a problem in stagnant indoor air. Higher humidity levels outdoors are welcomed by most begonia varieties, promoting lusher growth. The boost in light levels (without being direct and scorching) often triggers a spectacular display of growth and flowering that is difficult to achieve indoors. Your plant will essentially recharge during its summer vacation, building up energy to better survive the indoor environment when it must return.
