Few simple-to-grow flowering plants can top the begonia (Begonia spp.), which usually thrives and flowers well in a home garden, Common types include the wax begonia (Begonia x semperflorens-cultorum), the Dragon Wing or angel wing begonia (Begonia x argenteoguttata Dragon Wing) and the tuberous begonia (Begonia x tuberhybrida). Wax and Dragon Wing begonias such as Dragon Wing Red (Begonia "Bepared" Dragon Wing Red) survive outdoors year-round in U.S. Department of Agriculture plant hardiness zones 10 through 11 while tuberous begonias are perennial in USDA zones 9 through 11. All can also grow as annuals and bloom dependably when given the right lighting and some basic care.
Enough water during the growing season promotes lots of flowers on any type of begonia. Water wax and Dragon Wing begonias whenever the top 1 or 2 inches of their soil feels dry to the touch. The tuberous begonia is more sensitive to drying out, which can cause its flower buds to drop; so keep that plant's soil consistently moist while the plant grows, never letting the soil become dry.
All begonia types need good drainage and can suffer from constantly wet and soggy conditions, which may promote root rot and slow flowering. Adding some coarse sand to garden soil at planting time improves drainage of clay-rich soil. Begonias also grow well in containers, but use a well-draining potting soil and a pot with at least one bottom drainage hole; never leave the pot in a water-filled saucer.
Light for Blooming
Providing a begonia with the proper light helps promote a full flush of flowers and continued production of new flower buds; a begonia needs bright light to produce flowers, but too much sunlight can burn the foliage and interfere with blooming. Tuberous and Dragon Wing begonias do best in partial to full shade, especially during hot summer afternoons. So protect them from burning by adding shade-producing, taller plants nearby or keeping container-grown begonias on a patio or porch that gets afternoon shade.
The wax begonia differs slightly from the other types -- tolerating partial to full sun, which promotes heavy flowering. Wax begonia cultivars with bronze-colored leaves do especially well in full sun. All wax types can also grow in shade but flower less under that condition.
Applying fertilizer on a regular basis can help keep new begonia flower buds coming throughout the growing season. If your begonia plants are in the ground, then mix a 10-10-10 granular fertilizer into the top 1 or 2 inches of soil around each plant, beginning in spring after new growth starts in the plants and continuing monthly. Use a small trowel, and be careful not to damage the plants' roots. Apply the fertilizer at a rate of 1/4 pound for 25 square feet of planted area. Water the fertilized soil well.
If you grow begonias in containers, then fertilize the plants with a water-soluble, balanced fertilizer such as 10-10-10 once each week beginning when their new growth starts in spring, but dilute the fertilizer to 1/4 strength, or 1/8 teaspoon per 2 gallons of water; check your fertilizer's label for additional directions because instructions for products' uses can differ.
Pinching, Deadheading and Other Tasks
Pinching back a begonia in spring and early summer promotes branching, producing a bushy plant with lots of side branches, each filled with flower buds. As the growing season progresses, it also helps to remove spent flowers -- a task called deadheading; it stops the plant from producing seeds and directs more of its energy into producing flower buds. Trim and deadhead with sharp shears, wiping the blades with rubbing alcohol before each cut to prevent the spread of plant diseases.
Mulching garden-grown begonias can help conserve soil moisture while keeping down weeds, which compete for soil nutrients. In spring, add a 2- to 3-inch thick layer of straw or shredded bark on the soil surface under the plants, but keep the mulch a few inches from each plant's center to prevent excess dampness that can promote fungal problems.
Begonias are usually simple to grow but may develop fungal problems such as stem rot or powdery mildew -- a white, fluffy growth -- when grown in overly wet conditions. Those problems could slow flowering and are best prevented by keeping plants well-spaced for good air circulation and clearing away plant debris regularly.
Some pests might also appear on begonias, and those pests include snails that eat leaves; handpick snails as needed. Mites, microscopic pests that create webs on leaves, and mealybugs, which look like cotton puffs, could cause slow flowering. Control them by spraying the plants until they are wet with insecticidal soap concentrate diluted at a rate of 5 tablespoons per 1 gallon of water; repeat the application every two weeks as needed.