Table of Contents
- Introduction
- Understanding Begonia Corms
- Timing Your Planting for Success
- Preparing the Best Environment
- How to Start Begonia Corms Indoors
- Transitioning to the Garden
- Summer Care and Maintenance
- Troubleshooting Common Issues
- Overwintering Your Begonia Corms
- Conclusion
- FAQ
Introduction
There is a special kind of excitement that comes with transforming a quiet, shady corner of the yard into a lush oasis of color. While many gardens rely on the bright sun for their biggest blooms, tuberous begonias offer a spectacular alternative for those dappled and shaded spaces. These plants produce some of the most stunning, rose-like flowers in the gardening world, ranging from soft pastels to electric oranges and reds. (longfield-gardens.com)
At Longfield Gardens, we want to help you experience the joy of watching these unique plants develop from humble-looking corms into overflowing baskets of foliage and flowers. Whether you are looking for an upright variety like Begonia Upright Double Roseform Pink to anchor a garden bed or a trailing type like Begonia Hanging Pink Balcony to drape over the sides of a container, growing from corms is an affordable and rewarding way to garden. We provide high-quality plants and practical support to ensure your gardening journey is as smooth as possible. (longfield-gardens.com)
This guide is designed for any gardener who wants to master the art of growing tuberous begonias. We will walk you through the essential steps of starting your corms indoors, transitioning them to the garden, and keeping them healthy throughout the summer. By following a few simple steps, you can enjoy a season full of high-impact color with very little stress. (longfield-gardens.com)
Understanding Begonia Corms
Before you get your hands in the dirt, it helps to understand what you are working with. In the gardening world, the terms "corm," "tuber," and "bulb" are often used interchangeably by home gardeners. Tuberous begonias technically grow from tubers—fleshy, thickened underground stems that store nutrients and water. However, many people refer to them as corms because of their rounded, disk-like shape.
These corms are the powerhouse of the plant. They contain all the energy needed to kickstart growth in the spring. Because begonias are tropical plants, they have a specific growth cycle that responds to warmth and moisture. They are not hardy in most of the United States, meaning they cannot stay in the ground during a freezing winter. Instead, we treat them as tender perennials that need a bit of indoor care before the summer heat arrives.
When you receive your begonia corms, you will notice they have a very distinct shape. One side is usually rounded or slightly pointed, while the other side has a noticeable hollow or indentation. This indentation is where the new stems and leaves will emerge. Knowing which way is up is the first "easy win" in begonia gardening.
Key Takeaway: Begonia corms (tubers) are storage organs that hold the plant's energy. Always look for the hollow, indented side—this is the top where the growth will happen.
Timing Your Planting for Success
One of the most important rules for growing begonias is that timing matters more than almost any other "trick." Because begonias have a relatively long lead time from planting to blooming (often 8 to 12 weeks), starting them early is the best way to ensure a full summer of flowers.
Starting Indoors
Most gardeners in the US should start their begonia corms indoors about two to three months before the average last frost date in their area. If you wait until it is warm enough to plant them directly outside, you might not see flowers until very late in the summer. By starting them in the late winter or early spring, you give the plants a "head start" so they are already leafy and vigorous by the time the weather warms up.
Following the Zones
Your local climate dictates your schedule. Here is a general timeline to help you plan:
- Zones 3-5: Start indoors in early to mid-April.
- Zones 6-7: Start indoors in mid-March.
- Zones 8-9: Start indoors in February.
If you aren't sure of your zone, a quick check of a USDA plant hardiness map will give you the answer. Remember, weather varies every year. It is always better to wait for consistent warmth before moving plants outside than to rush and risk a late-season frost. (longfield-gardens.com)
What to Do Next
- Check your local frost dates online or with a local extension office.
- Count back 8 to 12 weeks from that date to find your ideal indoor start day.
- Gather your pots and potting mix a week before you plan to plant.
Preparing the Best Environment
Begonias are not overly picky, but they do have a few "non-negotiables" when it comes to their environment. Getting the site and soil right from the beginning saves you a lot of troubleshooting later in the season.
Right Soil, Right Drainage
"Drainage" is simply a measure of how fast water leaves the soil. Begonias have fleshy stems and tubers that store a lot of water, which makes them prone to rotting if they sit in soggy earth. Whether you are planting in a pot or a garden bed, the soil must be light and airy.
For containers, use a high-quality, peat-based potting mix. Avoid heavy "garden soil" or "topsoil" in pots, as these compress and trap too much moisture. If your garden bed has heavy clay, consider growing your begonias in raised beds or containers where you can control the soil quality more easily.
Selecting the Spot
Tuberous begonias are the stars of the shade garden. They grow best in dappled light or partial shade. Direct, hot afternoon sun can scorch their leaves and cause the flowers to wilt prematurely. A spot under a leafy tree, a covered porch, or the east side of a house where they get gentle morning sun is perfect.
Key Takeaway: Begonias need excellent drainage and protection from the hot afternoon sun. If water puddles in your chosen spot for hours after a rain, it is too wet for begonia corms.
How to Start Begonia Corms Indoors
Starting your corms indoors is a rewarding process. It feels like bringing a little bit of summer into the house while there might still be snow on the ground.
Step 1: Choose Your Containers
You don't need fancy equipment to start begonias. Shallow trays or small 3-inch individual pots work well. Ensure every container has drainage holes at the bottom. If you are starting many corms at once, a seed tray is an efficient use of space.
Step 2: Waking Up the Corms
Before planting, some gardeners like to "wake up" the corms by placing them in a warm room (about 70°F) in bright, indirect light for a week or two. You may begin to see tiny pink or white "eyes" or buds forming in the hollow of the corm. This is a great sign that the plant is ready to grow.
Step 3: Planting Depth and Position
Fill your container with moistened (but not dripping wet) potting mix. Place the corm on the surface with the hollow side facing up.
- Depth: Push the corm gently into the soil so it is just barely covered or so the top is level with the soil surface. Covering them with about half an inch of soil is usually sufficient.
- Spacing: If using a tray, space the corms about 2 inches apart.
Step 4: Warmth and Humidity
Begonia corms love a "warm and cozy" start. They will sprout much faster if the soil temperature is around 65–70°F. You can loosely cover the pots with clear plastic wrap to create a mini-greenhouse effect, which keeps the humidity high.
What to Do Next
- Check the soil daily to ensure it is moist but not soggy.
- Watch for the first tiny leaves to emerge (this can take 3 to 6 weeks).
- Once leaves appear, remove any plastic covering and move the plants to a bright window.
Transitioning to the Garden
The process of moving indoor plants to the outdoors is called "hardening off." This is a vital step because it allows the plants to get used to the wind, temperature swings, and stronger light of the outside world.
The Hardening Off Schedule
Don't move your begonias outside until nighttime temperatures stay consistently above 50°F and the threat of frost is completely gone.
- Days 1–3: Place your pots in a sheltered, fully shaded spot for 2–3 hours, then bring them back inside.
- Days 4–7: Gradually increase the time outside and allow them to experience a small amount of morning sunlight.
- Day 8 and Beyond: If the weather is warm, you can leave them outside overnight.
Planting in the Permanent Spot
Once your begonias are toughened up, you can move them to their final home.
- In Containers: If you started them in small pots, you can now move them into large decorative planters or hanging baskets. A 12-inch basket can comfortably hold 2 or 3 begonia plants for a full, lush look.
- In Garden Beds: Space the plants about 8 to 12 inches apart. Dig a hole just large enough for the root ball and set the plant at the same depth it was growing in its pot.
Key Takeaway: Never rush begonias into the cold. A week of gradual acclimation (hardening off) ensures your plants don't suffer from "transplant shock."
Summer Care and Maintenance
Once your begonias are established in the garden, they are relatively low-maintenance. However, a little bit of regular attention will keep them blooming at their peak until the first frost of autumn.
Watering Correctly
The rule for begonias is: "water deeply, then let the top of the soil dry out." Stick your finger into the soil; if the top inch feels dry, it is time to water. Always try to water at the base of the plant rather than over the leaves. Wet foliage in a shady, stagnant area can lead to mildew issues.
Feeding Your Flowers
Begonias are "heavy feeders," meaning they use a lot of energy to produce those big, beautiful blooms. Start fertilizing about a month after you have moved them outside. Use a balanced, water-soluble fertilizer or one designed specifically for flowering plants (high in potassium/potash). Applying fertilizer every two weeks is usually enough to keep the engine running.
Deadheading and Tidying
To keep your plants looking fresh, remove wilted flowers as they fade. This process, called deadheading, prevents the plant from putting energy into seed production and encourages it to keep making new buds. Tuberous begonias can also have somewhat brittle stems, so if your variety is a tall, upright type, you might want to provide a small bamboo stake for support in windy areas.
What to Do Next
- Set a bi-weekly reminder on your phone to fertilize your begonias.
- Check your hanging baskets more often than ground plants, as they dry out faster.
- Snip off any yellowing leaves to keep the plant's airflow high.
Troubleshooting Common Issues
Even the most careful gardeners run into a few hiccups now and then. The good news is that most begonia problems have very simple fixes.
Why Won't My Corms Sprout?
If you've been waiting for weeks and see no green, the most likely cause is temperature. Begonias are tropical and won't "wake up" if they are too cold. Ensure they are in a room that stays consistently above 65°F. Another possibility is that the corm was planted upside down. If you aren't sure, you can gently brush away the soil to check for sprouts. If it's upside down, simply flip it over.
Why Are the Leaves Turning Yellow?
Yellow leaves usually point to one of two things: too much water or not enough food. If the soil feels like a wet sponge, stop watering and let it dry out. If the soil moisture is correct but the plant looks pale and yellow, it likely needs a dose of fertilizer to replenish its nutrients.
Dropping Flower Buds
If your begonia is dropping its buds before they even open, the plant is likely stressed. This often happens during extreme heat waves or if the soil has been allowed to dry out completely. Move the container to a deeper shade during heat spikes and keep the moisture levels consistent.
Key Takeaway: Most begonia issues are related to water and temperature. Adjusting these two factors usually solves the problem within a week.
Overwintering Your Begonia Corms
One of the best things about tuberous begonias is that the corms get larger and better every year. Instead of buying new ones every spring, you can save your corms and grow them again next season.
When to Lift
In the fall, when the leaves start to turn yellow and the temperatures begin to drop toward freezing, it is time to bring the begonias in. A light frost may blacken the foliage, which is actually a signal to the plant to go dormant. Do not wait for a hard freeze, as this can damage the tuber itself.
The Drying Process
- Dig them up: Carefully lift the corm from the soil, being careful not to bruise it.
- Trim the stems: Cut the stems back to about 1 inch above the corm.
- Dry out: Lay the corms in a cool, dry, shaded area (like a garage or basement) for a few days until the remaining stem stub dries up and falls off naturally.
- Clean: Shake off any loose soil, but do not wash them with water.
Storage
Store the dry corms in a breathable container. A paper bag or a cardboard box filled with slightly damp peat moss, sawdust, or vermiculite works perfectly. Keep the box in a cool, dark, frost-free place (around 40–50°F) until next spring.
What to Do Next
- Check your stored corms once a month during winter.
- If they look shriveled, lightly mist the storage medium with water.
- If you see any soft or mushy spots, remove those corms so they don't affect the healthy ones.
Conclusion
Growing begonias from corms is a wonderful way to bring professional-level beauty into your home garden. By focusing on the basics—starting them early indoors, providing excellent drainage, and keeping them in the shade—you can enjoy a spectacular display that lasts for months. These plants remind us that gardening is not about perfection, but about the simple joy of watching a small corm turn into a flourishing plant.
We are proud to be part of your gardening journey. At Longfield Gardens, we stand behind the quality of our corms with a 100% guarantee, ensuring that you start your season with healthy, true-to-variety plants. Whether you are a beginner or a seasoned pro, begonias offer a rewarding experience every time.
- Order early: Get your corms in late winter so you are ready to plant indoors on schedule.
- Watch the weather: Use the "50-degree rule" for overnight temperatures before moving plants outside.
- Feed the blooms: Use a liquid fertilizer every two weeks for the best flower show. (longfield-gardens.com)
Every garden has a shady spot waiting for a splash of color. Tuberous begonias are the perfect, easy-to-grow solution for a more beautiful summer yard.
FAQ
How long does it take for begonia corms to sprout?
Typically, it takes between 3 and 6 weeks for the first green shoots to appear. This timeline depends heavily on the temperature; corms in a warm room (70°F) will sprout much faster than those in a cool basement. Patience is key during this initial phase, as the plant is busy establishing roots underground before the leaves emerge.
Can I plant begonia corms directly in the ground?
Yes, but only after the soil has warmed up and all danger of frost has passed. However, because begonias grow slowly at first, planting them directly outside often results in a very short blooming season. For the most flowers, we recommend starting them indoors in pots about 8 to 12 weeks before your last frost date.
Which side of the begonia corm faces up?
The "hollow" or indented side of the corm should always face up. This side often looks like a small bowl or a saucer. The rounded side, which may have some old, hair-like dried roots, should face down into the soil. If the corm is very flat and you cannot tell, you can plant it on its side, and the plant will naturally grow toward the light.
Why are my begonias tall and "leggy" instead of bushy?
Leggy growth usually happens when the plant is not getting enough light. While begonias love shade, they still need bright, indirect light to grow strong stems. If your indoor plants are stretching toward the window, try moving them to a brighter spot or using a grow light. You can also pinch off the very tip of the main stem to encourage the plant to branch out and become bushier.