Tuberous begonias, especially the trailing types, offer a spectacular cascade of color for hanging baskets. Achieving a dense, vibrant display depends on correct planting density, balancing fullness with air circulation. Overcrowding creates a humid microclimate, encouraging fungal diseases like powdery mildew and tuber rot. Knowing the proper quantity of tubers for your basket size is the first step toward a successful, healthy floral show.
Linking Basket Size to Tuber Quantity
The ideal number of begonia tubers is determined by the container’s diameter, aiming for spacing approximately 4 to 6 inches apart. This spacing allows sufficient room for root development and ensures air movement around the foliage. Planting too few tubers results in a sparse display, while planting too many risks the health of the entire basket.
For common basket sizes, specific tuber counts guide achieving a lush, cascading appearance. A smaller 8-inch or 10-inch diameter basket is best suited for one or two medium-sized tubers. A standard 12-inch basket can hold three medium-sized tubers or four smaller tubers, providing the density needed for a full look by mid-summer.
Larger hanging baskets, measuring 14 to 16 inches across, can accommodate four to five medium tubers spaced evenly around the perimeter. This quantity accounts for the expansive growth habit of trailing varieties. Always factor in the mature size of the specific cultivar, as denser planting requires more vigilant watering and feeding.
Essential Pre-Planting Preparation
Preparing the growing medium and the tubers is essential before planting. Tuberous begonias require a light, well-draining potting mix to prevent tuber rot caused by waterlogged conditions. Use a peat-based or specialized container mix enriched with materials like perlite or coir to improve aeration and drainage.
Ensure the hanging basket has adequate drainage holes. If using a wire basket, line it with sphagnum moss or a coco-fiber liner to retain moisture without saturation. Tubers should be “woken up” indoors four to eight weeks before the last expected frost date to give them a head start. This pre-sprouting ensures the tuber is actively growing before moving outdoors.
To pre-sprout, place the tubers shallowly in a tray filled with damp material like peat moss or vermiculite. Keep the tray in a warm location, ideally around 70°F, with bright, indirect light. The tuber must be oriented with its concave, or hollow, side facing upward, as this is where the growth eyes emerge. Once small sprouts appear, the tubers are ready for transplanting.
Step-by-Step Tuber Placement
Planting the pre-sprouted tuber requires careful attention to orientation and depth. The concave side of the tuber contains the growth nodes and must always face upward toward the sky. The convex, or rounded, side is the base where the roots develop, resting flat against the soil.
Partially fill the basket with the potting mix, then position the tubers according to the density guidelines. Set the tuber just below the soil surface, covering the sprouts with no more than one inch of mix. Planting too deeply is a common error that causes water pooling in the tuber’s center, promoting decay.
Water the basket lightly after planting to settle the soil, but avoid spraying water directly into the hollow center. Keep the medium consistently moist but never soggy, especially during early growth. Keep the newly planted basket in a sheltered, frost-free location until the danger of cold temperatures has completely passed and the plant has developed a few true leaves.