From our perspective as begonias, the single most important factor determining our ability to thrive outdoors is the complete absence of frost. Our tissues are succulent and water-rich, making us extremely vulnerable to ice crystal formation. A single freezing night can cause irreversible damage, collapsing our cell walls and turning our vibrant leaves and stems to mush. Therefore, our outdoor growing season is strictly confined to the period after the last spring frost and before the first autumn frost. Our survival outdoors is not about enduring winter, but about flourishing during the warm, gentle months.
Gardeners use the USDA Plant Hardiness Zone Map as a guide, which is essentially a measure of average annual extreme minimum winter temperatures. For most begonia species, we are tender perennials only truly hardy in Zones 10-11, where winters are very mild (30°F / -1°C and above). A notable exception is the hardy begonia (Begonia grandis subsp. evansiana), which can survive winters down to Zone 6. For the vast majority of us—like showy tuberous begonias or delicate wax begonias—we are treated as annuals in zones below 10. You plant us for a single glorious season of growth, knowing the cold will claim us in the end.
To truly thrive outdoors, we require specific conditions that mimic our native understory habitats. Light is crucial; most of us prefer bright, filtered light or partial shade. Direct, intense afternoon sun can scorch our leaves, causing brown, crispy edges and faded colour. However, deep shade will result in leggy growth and few flowers. Well-draining soil is non-negotiable. Our fine, fibrous roots are highly susceptible to rot if left sitting in waterlogged soil. A rich, organic, and airy potting mix or garden bed amendment provides the perfect foundation. While we appreciate consistent moisture, we insist on perfect drainage.
The process of moving us from a sheltered indoor environment to the great outdoors must be gradual. This process, known as "hardening off," is critical to avoid shock. Suddenly placing us in full sun and wind will cause severe stress, stunting our growth and scorching our leaves. Instead, please place us in a sheltered, shaded location for a few hours each day, gradually increasing our exposure to outdoor conditions over 7-10 days. This allows our leaves to thicken and adapt to the increased light and air movement, ensuring we establish ourselves strongly for the season ahead.
Once acclimated, we will reward you with a spectacular display of foliage and flowers throughout the summer and into autumn. For those of you in climates with cold winters, our fate depends on our type. Fibrous-rooted begonias (like wax begonias) are typically treated as annuals and composted after the first frost. Tuberous begonias, however, have a survival mechanism: our energy retreats into an underground tuber. After the first frost blackens our foliage, you can lift these tubers, dry them, and store them in a cool, dark place over winter to be replanted the following spring, allowing us to live another season.
