If you have a shady space where you want to add color, begonias are the perfect choice! Begonias add effortless color in shade gardens, under trees, and in containers on porches and patios. 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 hardy in zones 9 & 10, and in colder zones (2 - 8), they can be grown as annuals and overwintered indoors to grow year after year.
Start Indoors For Best Blooms
In zones 2-8, Begonias do best when given a head start indoors so they can develop before being transplanted or moved outside. Start Begonias 8-12 weeks before the last frost in your area.
To help Begonia tubers warm up from their winter dormancy, place in a warm location (about 70°F) with indirect sunlight, preferably an east, west, or south facing window. If you don’t have good natural light, grow lamps can provide the necessary light for growth. Water slightly every few days, or when the soil has dried out. Water around the edges of your tuber, but not directly on it: avoid overwatering or soggy soil, as water can pool in the tuber’s hollow dip and cause rot.
To increase humidity, you can cover pots loosely with a clear plastic bag. Expect to see growth in 3-6 weeks’ time, depending upon your overall growing conditions. (Note: In zones 2-8, if you do not start Begonia tubers ahead of time indoors, you may only see minimal blooms late in the season.)
The photo shows a sprouted begonia tuber. The top side of the tuber has a hollow dip, and the bottom is rounded with roots. 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.
When & Where to Plant Begonias
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 light, fertile, well-drained soil. Begonias are very susceptible to root and stem rot when exposed to cold, wet soils, so proper drainage is essential. Choose a light potting soil with extra perlite if available, or create your own mix using equal parts of potting soil, perlite, and peat moss.
Spacing: Begonia tubers should be spaced about 1 foot apart in the garden, but can be planted closer together in hanging baskets and window boxes. For one begonia plant, a 6 inch pot is the smallest recommended size. (See your Begonia bulb package for specific details.)
Planting: In zones 9 and 10, Begonias can be planted immediately outdoors. In colder zones, Starting begonia tubers indoors to give them the head start they need (see above). Then, you can move them outside when the weather warms up, after any danger of frost has passed and nighttime temperatures have stabilized to 45°F or more.
Begonias are very sensitive to frost, cold, and wet weather, so don't hurry to plant them outdoors; they can't survive temperatures below 45°F. Begonias can be planted directly in the garden, or in hanging baskets or window boxes. Move them carefully -- their stems can break easily.
How to Grow Begonias Throughout the Season
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, to repvent water from pooling in the tuber.
Tuberous and fancy begonia leaves can be stained and discolored by water. Avoid watering with cold water or tap water that is high in minerals, and when possible, use distilled water instead.
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: To encourage fuller, bushier growth, pinch back newly-formed growth tips when they are about 3-6 inches long. Repeat monthly until mid-summer. For fewer, larger flowers, pinch off new young stem growth while leaving new buds to grow into flowers. Pinch back to the second healthy bud from the tip. Deadhead regularly to clean up the tuberous begonia's look, and to remove rotting old flowers that might infect the plants.
How to Care for Begonias at the End of the Season
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 2-8, begonia tubers can be overwintered - meaning you can move them indoors to allow them to regrow next year! In zones 2-8, in fall, after leaves turn yellow and/or temperatures reach below 45°F at night, bring your Begonias inside and grow as house plants. They may benefit from being placed near a humidifier when exposed to central heat indoors. For begonias that you're growing indoors as houseplants in winter, set up a pebble tray under the pots and fill it with water periodically to keep the humidity high.
Or, save tubers for next spring. 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 and foliage has yellowed.
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.