Most of us know begonias as staples of summertime hanging baskets and planting beds and as popular windowsill plants year-round. But there are thousands of varieties and hybrids of this tropical and subtropical plant. Some begonias, for instance, have leaves as blades of grass, while others grow as tall as fifteen feet. Some begonias flower irregularly, while others flower year-round. Today, Beth Castellon, of the New York Botanical Garden, discusses different begonias.
The four basic categories of begonias are classified by their root type. Rhizomatous begonias have thick, fleshy stems that creep across the surface of the soil, sending shallow roots downward and simultaneously shooting leaves upward. The rhizomes hold moisture, which means they require less care as houseplants. Because rhizomatous begonias hold water so well, however, they are particularly prone to damage from overwatering.
Fibrous-rooted begonias are a large group and include angel-wing types, distinguished by their graceful, wing-shaped leaves and erect bearing. The compact wax-leaf types branch freely and are among the best known of the fibrous begonias; they are among the semperflorens, or ever-blooming, begonias. Fuzzy-leafed begonias are also usually fibrous.
Tuberous begonias are grown primarily for their flowers, which bloom in spring and summer. Although a semi-tuberous variety is available in winter, tuberous begonias are not available year-round, and they comprise perhaps the fussiest of the basic categories.
The appeal of rex begonias is their colorful, richly patterned foliage. They are mostly rhizomatous but are considered a different class because of their unique leaves.
All begonias should be kept warm but not hot, ideally between 58& and 72&F. Place them in bright light such as strong, indirect sunlight or under a pair of 4-foot fluorescent grow lights. Plant them in very well drained, light, well aerated, potting soil with a nearly neutral or just slightly acidic pH (6 to 7). You can make an excellent soil by mixing 2 parts garden loam with 1 part sphagnum peat and 1 part perlite, then adding 2 tablespoons of dolomitic limestone to every 10 quarts of potting soil. Of the commercial potting soils, pick one labeled for ferns.