Table of Contents
- Introduction
- Understanding Begonia Corms
- When to Start Your Begonias
- Preparing for Indoor Planting
- Step-by-Step Guide to Planting Corms
- Caring for New Sprouts
- Moving Begonias Outdoors
- Summer Care and Maintenance
- Overwintering Begonia Corms
- Growing Different Begonia Varieties
- Troubleshooting Common Issues
- Summary of Success
- FAQ
Introduction
Shady areas of the garden often feel like hidden retreats, and nothing brightens these quiet corners quite like the lush foliage and brilliant colors of begonias. Whether you have a covered patio, a north-facing porch, or a garden bed tucked under a canopy of trees, these plants offer a spectacular show of color that lasts from early summer all the way through the first frost. At Longfield Gardens, we enjoy helping gardeners discover how simple it is to transform these low-light spaces into vibrant displays using our Begonia Flower Bulbs for Sale.
Growing begonias from corms is an accessible project for gardeners of all experience levels. While the wait for the first sprout requires a bit of patience, the result is a plant that produces dozens of showy, rose-like blooms. For a broader overview, see our How to Plant and Care for Begonias. This guide will walk you through every step of the process, from starting your corms indoors to maintaining healthy plants throughout the season.
By following a few basic principles, you can ensure your begonias thrive and return year after year. Successfully growing begonias from corms is a straightforward process that rewards you with continuous, high-impact color in the most difficult parts of your yard.
Understanding Begonia Corms
Before you start planting, it helps to understand what a begonia corm actually is. A corm is a thickened, underground stem that stores energy for the plant during its dormant period. In the gardening world, you may hear these referred to as tubers. While there are botanical differences, both terms describe the sturdy, brown, puck-like structures that will eventually grow into your favorite flowers.
When you look at a begonia corm, you will notice it has two distinct sides. One side is rounded, and the other side has a noticeable hollow or indentation. This indentation is where the new growth will emerge. Identifying this early on is important because it determines which way you place the corm in the soil.
Corms come in various sizes, but a larger corm generally translates to a more robust plant with more stems and flowers. They are incredibly resilient and packed with all the nutrients the plant needs to get a strong start in the spring.
Key Takeaway: Always look for the hollow, indented side of the corm before planting. This is the top of the plant where the stems and leaves will emerge.
When to Start Your Begonias
Begonias are tropical plants that love warmth and are very sensitive to cold temperatures. Because they have a relatively long growing cycle, most gardeners in the United States benefit from starting their corms indoors. If you need help matching timing to your area, the Hardiness Zone Map is a helpful reference.
Starting Indoors
For the best results, start your begonia corms indoors about 8 to 12 weeks before the average last frost date in your area. This usually falls sometime in March or April for most northern and central zones. By starting indoors, you bypass the slow initial growth phase and move established plants outside once the soil is warm.
Planting Outdoors
In warm climates like USDA zones 9 through 11, you can plant corms directly into the ground or outdoor containers once the soil temperature reaches at least 60°F. In cooler zones, do not move your begonias outside until the danger of frost has completely passed and overnight temperatures consistently stay above 60°F.
Recommended Timing by Zone
- Zones 3–5: Start indoors in late March or early April. Move outdoors in early June.
- Zones 6–7: Start indoors in late February or March. Move outdoors in mid-to-late May.
- Zones 8–9: Start indoors in early February. Move outdoors in April.
- Zone 10: Start indoors in late December or January. Move outdoors in February or March.
If you are planning your order, our Shipping Information page explains how Longfield times shipments by zone.
Preparing for Indoor Planting
Starting begonias indoors is a great way to enjoy gardening while it is still chilly outside. You do not need a greenhouse to be successful. A warm room with a bright window or a simple grow light setup works perfectly. For more container tips, see our How to Plant Begonias in Pots.
Choosing the Right Containers
You can start corms in individual 3-inch or 4-inch pots. If you are growing several at once, a shallow nursery tray or a seed-starting flat also works well. Ensure that whatever container you choose has plenty of drainage holes. Begonias do not like to sit in water, so "drainage" (how fast water leaves the soil) is your top priority.
The Best Soil Mix
Use a high-quality, lightweight potting mix. Avoid using heavy garden soil from the yard, as it can be too dense and may harbor pests or diseases. A mix containing peat moss, perlite, or vermiculite provides the airy texture begonia roots love. Moisten the soil before you fill your containers so it feels like a wrung-out sponge.
What to Do Next
- Check your local frost dates to determine your start date.
- Purchase a high-quality potting mix designed for containers.
- Ensure your pots or trays have functional drainage holes.
- Find a warm spot in your home that stays consistently above 60°F.
Step-by-Step Guide to Planting Corms
Now that you have your supplies ready, it is time to get the corms into the soil. This part of the process is quick and sets the foundation for the entire growing season. For another step-by-step reference, see our How Do You Plant Begonia Tubers?.
1. Position the Corm
Fill your container with 2 to 3 inches of moistened potting mix. Place the corm on the soil surface with the hollow, indented side facing up. If you cannot tell which side is the top, look for tiny pink or white buds, often called "eyes." If the corm is completely smooth and you are unsure, you can plant it on its side, and the plant will naturally find its way up.
2. Set the Depth
For indoor starting, you do not need to bury the corm deeply. Gently press it into the soil so the top is just barely visible or covered by a very thin layer (no more than 1/2 inch) of soil. Tucking them in lightly allows the sprouts to reach the light quickly.
3. Spacing
If you are planting multiple corms in one tray, space them about 2 to 3 inches apart. If you are planting directly into a large outdoor container, space them 8 to 12 inches apart to allow for their mature width.
4. Initial Watering
Water the soil lightly to settle it around the corm. Be careful not to overwater at this stage. Since the corm has no roots or leaves yet, it cannot process much water. Excessive moisture can lead to the corm rotting before it ever gets a chance to grow.
Key Takeaway: Begonias prefer a "warm and cozy" start. Covering your trays loosely with plastic wrap can help retain humidity and warmth, which speeds up the sprouting process.
Caring for New Sprouts
Begonias are not known for being fast starters. It can take anywhere from three to six weeks to see the first signs of green. Do not worry if nothing seems to be happening at first; the corm is busy establishing a root system beneath the surface.
Light and Warmth
Once you see sprouts emerging, move the containers to a bright location. A south-facing window is ideal, but make sure the sunlight isn't so intense that it heats the pots excessively. If you are using grow lights, keep them a few inches above the foliage and run them for 12 to 14 hours a day.
Humidity and Moisture
Begonias thrive in humid environments. If your home is dry during the spring, you can mist the area around the plants or use a pebble tray. Continue to water sparingly. The goal is to keep the soil damp, like a damp cloth, but never saturated. Always feel the soil with your finger before adding water. If the top inch is dry, it is time for a drink.
Transplanting Indoors
If you started your corms in small 3-inch pots or trays, they will eventually need more room. Once the plants have two or three leaves, move them into their final containers. For more potted-care tips, see our How to Care for a Potted Begonia Plant.
- Use a 6-inch pot for one corm.
- Use an 8-inch to 10-inch pot for two corms.
- Use a 12-inch or larger pot for three corms.
Moving Begonias Outdoors
Transitioning your plants from the controlled environment of your home to the great outdoors is a process called "hardening off." Doing this gradually prevents the leaves from being scorched by the sun or shocked by the wind. For a fuller outdoor transition guide, see our Can I Plant Begonias Outside?.
The Hardening Off Process
Start by placing your begonias in a sheltered, shady spot outside for a few hours during the day. Bring them back inside at night. Over the course of 7 to 10 days, gradually increase the amount of time they spend outside. Avoid placing them in direct, midday sun during this time, as indoor-grown leaves are very tender.
Choosing the Final Spot
When you are ready to plant them in the ground or place your containers permanently, look for a spot that receives partial shade to full shade.
- Morning Sun: A few hours of gentle morning sun is fine.
- Midday Shade: Protection from the harsh sun between 11:00 AM and 4:00 PM is essential.
- Wind Protection: Begonia stems can be brittle. Choose a location sheltered from strong gusts of wind to prevent the stems from snapping.
Soil and Drainage Outdoors
If you are planting in garden beds, ensure the soil is rich in organic matter. Adding compost or well-rotted manure improves the soil structure. If you notice water puddles in your chosen spot hours after a rain, it is better to plant your begonias in raised beds or containers to ensure proper drainage.
Summer Care and Maintenance
Once your begonias are established in their summer home, they are relatively low-maintenance. A little bit of regular attention will keep them blooming vigorously until autumn.
Watering Correctly
The most common mistake with begonias is overwatering. Instead of watering on a strict schedule, water based on the moisture level of the soil.
- Check the soil: Stick your finger into the soil. If it feels dry to the first knuckle, water deeply.
- Water at the base: Avoid getting water on the leaves and flowers, as this can encourage fungal issues.
- Container needs: Remember that pots and hanging baskets dry out much faster than garden beds. In the heat of mid-summer, they may need water every day.
Feeding for Flowers
Begonias are "heavy feeders," meaning they use a lot of energy to produce those big blooms. Start fertilizing about four to six weeks after you have moved them outdoors. Use a balanced, water-soluble fertilizer or one with a slightly higher middle number (phosphorus) to encourage flowering. Applying a diluted fertilizer every two weeks is usually sufficient.
Deadheading and Grooming
"Deadheading" means removing flowers that have finished blooming. This keeps the plant looking tidy and encourages it to put its energy into creating new buds rather than seeds. For more on this, see our How to Deadhead a Begonia Plant for More Vibrant Blooms. Simply pinch off the faded flower at the base of its stem. You should also remove any yellowed or damaged leaves to maintain good air circulation around the plant.
What to Do Next
- Establish a bi-weekly fertilizing routine once flowers appear.
- Check moisture levels daily, especially for hanging baskets.
- Pinch off spent blooms to keep the plant productive.
- Monitor for any signs of powdery mildew, which looks like white flour on the leaves, and improve air circulation if you see it.
Overwintering Begonia Corms
Begonias are perennials, but they are not hardy in most of the United States. If you live in a zone with freezing winters, you will need to bring the corms indoors to save them for next year. For a full storage guide, see our How to Overwinter Begonia Plants. This is a rewarding way to build a larger collection over time, as corms often grow bigger each year.
Preparing for Dormancy
As autumn approaches and temperatures drop, your begonias will naturally begin to slow down. The leaves may start to turn yellow. This is the plant's way of sending energy back into the corm for the winter. Reduce your watering at this stage.
Lifting and Cleaning
After the first light frost kills the top growth, or before a hard freeze occurs:
- Cut back: Use clean garden shears to cut the stems back to about an inch above the soil.
- Dig gently: Carefully lift the corm out of the soil. Be mindful not to bruise or nick the surface of the corm.
- Clean: Shake off excess soil. You do not need to wash them; a little bit of dry soil left behind is fine.
- Cure: Place the corms in a dry, shady spot for a few days to "cure." This allows the outer skin to toughen up.
Storing for Winter
Once the corms are dry to the touch, store them in a cool, dark, and dry place. A basement or a cool closet is usually perfect.
- Medium: Place them in a paper bag or a cardboard box filled with peat moss, sawdust, or vermiculite. This prevents the corms from touching each other and helps regulate moisture.
- Temperature: Aim for a storage temperature between 40°F and 50°F.
- Check-ins: Every month or so, peek at your stored corm. If they look shriveled, a very light mist of water can help. If you see any soft or mushy spots, remove those corms immediately to protect the rest.
Growing Different Begonia Varieties
When you shop with us, you will find several different types of begonias, including Upright Double Begonias. Each has a slightly different growth habit, and knowing which one you have helps you choose the right spot for it.
Upright Begonias
These varieties grow vertically and produce large, rose-like flowers. They are excellent for the center of a container or as a colorful border in a garden bed. Because the flowers can become quite heavy, these plants sometimes benefit from a small bamboo stake for support. A classic example is Begonia Upright Double Roseform Pink.
Trailing or Cascading Begonias
Also known as Pendula types, these begonias have a relaxed habit. The stems drape over the sides of the pot, making them the perfect choice for hanging baskets or window boxes. They produce a profusion of smaller flowers that create a waterfall effect of color. For a ready-made option, try Begonia Hanging Golden Balcony.
Non-Stop and Multiflora Begonias
These varieties are bred to be exceptionally floriferous. They tend to be a bit more compact and are known for blooming "non-stop" throughout the heat of the summer. Begonia Non Stop Mix - Bulk Offer is a great choice for mass plantings in shady garden beds where you want a carpet of color.
Key Takeaway: Match the variety to your container. Use upright types for floor pots and trailing types for baskets to get the most dramatic visual impact. For larger displays, Begonia Upright Double Superba Mix - Bulk Offer is a convenient bulk option.
Troubleshooting Common Issues
Even though begonias are easy to grow, you might encounter a few minor hurdles. Most issues are easily solved by adjusting your care routine.
Why Are My Flowers Dropping?
If you see healthy-looking flower buds falling off the plant, it is usually a sign of stress. The most common causes are the soil being too dry or a sudden spike in temperature. Ensure you are watering consistently and that the plant is not sitting in a spot that gets too much direct afternoon heat.
What Causes Yellow Leaves?
While yellow leaves at the end of the season are a natural sign of dormancy, yellow leaves in mid-summer often mean the plant is getting too much water. Check the drainage holes in your pot and wait for the soil to dry out a bit more between waterings. If the leaves are yellow and the stems feel mushy, the corm may be staying too wet.
Why Isn't My Begonia Blooming?
Begonias need a certain amount of light to produce flowers. If your plant is in deep, dark shade, it may produce beautiful green leaves but very few buds. Try moving the container to a spot with "bright shade"—somewhere that gets plenty of indirect light or a little bit of morning sun. Additionally, make sure you are using a fertilizer designed for flowering plants.
Leggy Growth
If your begonias are growing very tall and thin with lots of space between the leaves, they are "reaching" for more light. Providing a bit more indirect light will help the plant grow more compactly. You can also pinch back the growing tips early in the season to encourage the plant to branch out and become bushier.
Summary of Success
Growing begonias from corms is a rewarding journey that takes you from a simple brown bulb to a lush, flowering masterpiece. By starting your corms indoors, paying attention to the orientation during planting, and providing the right balance of shade and moisture, you can enjoy a spectacular display all summer long.
At Longfield Gardens, we take pride in providing high-quality corms, and our 100% Quality Guarantee backs that up. Whether you are planting a single hanging basket or a whole row of shade-loving borders, begonias are a reliable and beautiful choice. With the right start and a little bit of summer care, these plants will quickly become a favorite part of your gardening routine.
Next Steps for Your Begonias:
- Select your favorite colors and habits (upright or trailing).
- Start your corms indoors 8–12 weeks before the last frost.
- Wait for warm weather before moving plants outdoors.
- Fertilize every two weeks once the first blooms appear.
"The secret to beautiful begonias lies in the balance. Give them enough light to bloom but enough shade to stay cool, and keep the soil moist but never soggy. Getting these basics right ensures a season full of color."
FAQ
Which side of the begonia corm should face up when planting?
You should always plant the begonia corm with the hollow, indented side facing up. This scooped-out area is where the new stems and leaves will emerge. The rounded side, which often has a few old, dry roots attached, should face down into the soil.
Do I have to start my begonia corms indoors?
While you can plant them directly outdoors once the weather is warm, starting them indoors is highly recommended for most regions. Begonias grow slowly at first and require a long season to reach their full flowering potential. Starting them inside 8 to 12 weeks before the last frost ensures you get flowers in early summer rather than late autumn.
How often should I water my begonias in containers?
The frequency of watering depends on the weather and the size of the container, but you should generally water whenever the top inch of soil feels dry. For most containers, this might be every 2 to 3 days, while hanging baskets in hot weather may need daily watering. Always check the soil moisture with your finger before adding water to prevent overwatering.
Can I save my begonia corms to plant again next year?
Yes, begonia corms can be saved and replanted year after year. In the fall, after the foliage has turned yellow or a light frost has occurred, dig up the corms and cut off the stems. Let them dry for a few days, then store them in a cool, dry place in a box of peat moss or sawdust until the following spring.