If you have a shady space where you want to add color, begonias are the perfect choice! Begonias will add effortless color in shade gardens, under trees and in containers. In general, you'll find a warm color palette of yellow, red, orange, pink, and white flowers. Begonia plants are typically under 1 foot tall, with loads of colorful flowers up to 4 inches wide. Begonias are generally considered annuals in most zones (1-7), but with proper overwintering, they can be perennial.
Light Requirements: Begonias are classic shade-lovers that are only reliable perennials in zones 9 and 10. Most are grown as annuals in all other zones. Some newer varieties can tolerate direct sun, especially if it's morning sun. In cooler areas, begonias can tolerate more sun than in hot climates. Most like bright, dappled light to grow their best.
Soil Conditions: Begonias grow best in sandy, loamy soil that is light and fertile. Average moisture and proper drainage is essential - Begonias are very susceptible to root and stem rot when exposed to cold, wet soils.
Spacing: You can plant 3 tubers per square foot.
Planting: We recommend starting begonia tubors indoors in late winter, to give them the head start they need. Then, you can move them outside when the weather warms up. Plant begonias for the garden in spring, after any danger of frost has passed. Begonias are very sensitive to frost and cold, wet weather, so don't hurry to plant them outdoors. Even temperatures below 50F can damage young begonias depending on the type you're growing.
The photo above shows a begonia tuber. One side of the tuber has a hollow dip, and the other is round. Plant with the round side down. The hollow dip is the top, and sometimes it will already be sprouting buds. If the buds are coming up, try not to bump or break them, and carefully place the tuber in the ground.
Growth Habit: Tuberous begonias can be upright or trailing, depending on the variety. Tuberous begonias can be grown in the ground under trees or in shady parts of your garden, or in containers placed in shady areas of your porch, patio, or yard.
Staking: Trailing varieties of tuberous begonias are meant to creep, so they do not need staking. Upright tuberous begonias, however, can benefit from staking so the flower stems stand tall to make it easier to viewing the beautiful flowers. When upright varieties are 4 to 6 inches tall, place a narrow bamboo or metal stake in the soil near the main stem. Fasten the stem to the stake with plant ties or garden twine, being careful not to damage the stem. Add more ties to provide ongoing support as the plant grows.
Watering: Begonias need moist soil, but are very susceptible to rotting under wet conditions. Water slightly every few days, or when the soil dries out. Water less frequently if you have regular rain. Water containers of begonias more frequently, but always be cautious to not over water, or their stems might rot. Always water around the tuber, not directly on it.
Fertilizing: Amend your soil with compost before planting begonias in the ground. Begonias are heavy feeders, so fertilize plants in the ground and in containers monthly with an organic balanced fertilizer (Look for 20-20-20 fertilizer mixes). For container begonias, use a liquid fertilizer, so the nutrients are more readily available.
Mulching: Since begonias are susceptible to rot due to wet conditions, mulching should be done cautiously. Use bark mulch around plants to preserve soil moisture and prevent weeds from growing. Keep mulch a few inches away from the succulent begonia stems to prevent them from rot. Begonias in containers don't need mulching.
Trimming & Pruning: Pinch back the growth tips of tuberous begonias in Spring, when new growth is about 3 to 6 inches long. Pinch back to the second healthy bud from the tip. Repeat this process monthly until mid-summer to encourage bushiness and more flowers. Deadhead regularly to clean up the tuberous begonia's look, and to remove rotting old flowers that might infect the plants.
Dividing & Transplanting: All begonias can be propagated by stem and leaf cuttings. This is an easy way to produce more plants quickly. In the spring, remove begonias from the soil and carefully separate the newer side plants from the mother plant. Replant in with fresh soil. We recommend planting into a container so that you can give young plants the support they need for a long life.
Overwintering: In zones 1-7, begonia tubers can be overwintered - meaning you can move these annuals indoors to allow them to regrow next year! Here's how to do it:
- You can dig up plants and their tubers from the ground after the first frost has killed off the tops.
- Cut back foliage, but leave some soil on the roots.
- Cure your tubers by letting them dry in a warm, dry location out of direct sun, for one week.
- Store tubers between layers of paper or dry sand in a room with temperatures between 40F-50F. It's important to make sure they stay dry, since they're susceptible to rot.
- Then, in late winter or early spring, you can repot your tubers inside to give them a healthy start for the new season!
Pests/Disease: The biggest problems with begonias is their propensity to rot if exposed to poor drainage or wet conditions.
- Botrytis rot is one of the more common fungal diseases that attacks begonias. Use light potting soil with extra perlite to promote proper drainage. In the garden, grow begonias in sandy loam soil. If you have heavy clay soil, grow begonias in raised beds filled with compost and topsoil.
- Powdery mildew is another fungus that can attack begonias, forming stubborn white splotches on leaves and flowers and causing them to yellow and drop prematurely. Look for disease resistant varieties if mildew is a common problem in your areas. Otherwise, space plants further apart to increase air flow. Try spraying Serenade (Bacillus subtilis) organic fungicide on the plants to prevent mildew growth. Or, use the natural homemade recipe of 1 tablespoon baking soda mixed with 1 tablespoon horticultural oil in 1 gallon of water. Both of these sprays work best if used as a preventive.
- White flies and mealybugs sometimes will attack begonias -- especially those grown indoors. Spray insecticidal soap to kill white flies, and dab mealybugs with a cotton swab drenched in rubbing alcohol.