How and When to Plant Begonia Corms for a Beautiful Garden

Table of Contents

1. Introduction
2. When to Plant Begonia Corms
3. Choosing the Right Spot for Your Begonias
4. How to Plant Begonia Corms: Step-by-Step
5. Caring for Your Begonias as They Grow
6. Transitioning Begonias to the Garden
7. Understanding Different Begonia Types
8. End of Season Care and Overwintering
9. Conclusion
10. FAQ

Introduction

Finding bright, colorful flowers for the shady parts of your yard can sometimes feel like a challenge. While many popular summer flowers crave intense sunshine, tuberous begonias thrive in filtered light and partial shade. These plants are famous for their oversized, rose-like blooms and lush foliage. At Longfield Gardens, we enjoy helping gardeners discover how these versatile plants can transform porches, patios, and garden beds into vibrant retreats.

This guide is designed for home gardeners who want to learn the best techniques for growing begonias from corms. We will cover exactly when to get your plants started and how to ensure they grow strong and healthy. Whether you are a beginner or a seasoned gardener, you will find the practical steps needed to achieve a season of stunning color. For a broader overview, see our All About Begonias.

By understanding the simple needs of these tropical plants, you can enjoy a continuous show of flowers from midsummer all the way until the first frost. Success starts with a few basic rules about timing, placement, and care.

When to Plant Begonia Corms

Timing is the most important factor when planting begonias. Because these plants are tropical by nature, they have no tolerance for frost. They also prefer warm soil and consistent temperatures. There are two ways to approach the timing of your planting: starting them early indoors or waiting to plant them directly in the ground.

Starting Begonias Indoors

Most gardeners choose to start their begonia corms indoors about 8 to 12 weeks before the last expected frost date in their area. Starting early gives the plants a significant head start. Begonias can be slow to wake up from their winter dormancy, often taking several weeks just to show the first signs of green growth. For step-by-step help, see our How to Start Tuberous Begonias Indoors.

By starting indoors in late February or March, you allow the plant to develop a strong root system and several inches of foliage before the outdoor weather is warm enough for them. This usually results in flowers that appear much earlier in the summer compared to those planted directly outside.

Planting Begonias Directly Outdoors

If you prefer to plant directly into the garden or outdoor containers, you must wait until the threat of frost is completely gone. In most regions, this means waiting until late May or early June. The soil should be warm to the touch, and nighttime temperatures should consistently stay above 50°F. If you need a planting window by region, check the Hardiness Zone Map.

If the ground is too cold or wet, the corms may sit idle and are more likely to struggle. Waiting for the right weather ensures the plant can begin growing immediately without the stress of cold snaps.

Key Takeaway: For the earliest possible blooms, start your begonia corms indoors 2 to 3 months before your local frost-free date.

Choosing the Right Spot for Your Begonias

Begonias are quite particular about where they live. To get the best results, you need to match begonias to the conditions in your yard. The two most important factors are light and drainage.

Light and Shade Requirements

Begonias are the stars of the shade garden. They prefer "dappled" or "filtered" sunlight. This is the kind of light you find under a leafy tree or beneath a covered porch. In many climates, begonias appreciate a little bit of gentle morning sun followed by shade during the hottest part of the afternoon. For more ideas on placement, see our How to Plant Begonias for a Stunning Shade Garden.

If begonias get too much direct, intense sunlight, their leaves and delicate flower petals can scorch. On the other hand, if they are in total, deep shade where no light reaches them, they may produce beautiful leaves but fewer flowers. A spot with bright, indirect light is usually the "sweet spot" for maximum blooming.

Soil and Drainage

Drainage refers to how fast water leaves the soil. Begonias need soil that stays moist but never stays soggy or "wet." If the corms sit in water that cannot drain away, they are likely to rot.

If you are planting in the ground, look for a spot where water doesn't puddle after a rainstorm. You can improve your garden soil by adding organic matter like compost or finely ground bark. This creates a fluffier soil structure that allows roots to breathe and water to move through freely. For more detailed spacing help, see our How Far Apart Should Begonias Be Planted?.

For container gardening, always use a high-quality potting mix rather than garden soil. Potting mixes are specifically designed to provide the airy, well-draining environment that begonias love. Ensure your pots have plenty of drainage holes at the bottom.

How to Plant Begonia Corms: Step-by-Step

Once you have your corms and your site is ready, it is time to plant. Begonia corms have a unique shape that tells you exactly how they should be positioned in the soil.

Identifying the Top and Bottom

When you look at a begonia corm, you will notice that one side is indented or "dished," similar to a small bowl or a saucer. The other side is rounded or "domed."

The indented side is the top. This is where the "eyes" or growth points are located. These eyes will eventually sprout into the stems and leaves. The rounded side is the bottom, where the roots will emerge.

Planting in Trays or Small Pots

If you are starting indoors, follow these steps:

1. Fill a shallow tray or small pots with a light, damp potting mix.
2. Place the corm on the surface of the soil with the indented (hollow) side facing up.
3. Press the corm gently into the soil so it is mostly nestled in, but do not bury it deeply yet.
4. Many gardeners leave the very top of the corm visible or cover it with just a dusting (about 1/2 inch) of soil.
5. Place the tray in a warm spot with bright, indirect light.

Spacing and Depth in the Garden

If you are planting directly into the garden or a large outdoor planter:

• Spacing: Give each plant enough room to grow. Most begonias should be spaced 8 to 12 inches apart. This allows for good air circulation, which helps keep the foliage healthy.
• Depth: Dig a shallow hole and place the corm indented-side up. Cover the top with no more than 1/2 inch to 1 inch of soil. Planting too deep can slow down the sprouting process.

What to Do Next:

• Check your corms to find the hollow side before planting.
• Use a light potting mix for indoor starts.
• Space plants at least 8 inches apart to allow for airflow.
• Ensure the top of the corm is only lightly covered with soil.

Caring for Your Begonias as They Grow

After planting, begonias require a bit of regular attention to look their best. They are not high-maintenance plants, but they do appreciate consistency.

Water and Moisture Management

At Longfield Gardens, we suggest the "touch test" for watering. Stick your finger into the soil about an inch deep. If it feels dry, it is time to water. If it still feels damp, wait a day or two.

When you water, try to apply the water directly to the soil rather than over the leaves. Wet leaves in a shady environment can sometimes lead to mildew or other foliage issues. Begonias prefer to be consistently moist, but they should never be kept "swampy." In the heat of mid-summer, containers may need water every day, while garden beds might only need it once or twice a week.

Feeding Your Plants

Begonias are "heavy feeders," meaning they use a lot of nutrients to produce those giant, showy flowers. Once you see a few inches of green growth, you can begin a regular fertilizing schedule.

Use a balanced, water-soluble fertilizer designed for flowering plants. Applying a diluted dose every two to three weeks is usually sufficient. This provides a steady supply of energy for the plant to keep creating new buds throughout the season. Always follow the instructions on the fertilizer label for the correct amount.

Encouraging More Blooms

One of the easiest ways to keep your begonias looking fresh is "deadheading." This simply means removing flowers that have started to fade or wilt.

When a flower begins to look brown or shriveled, snap or snip it off just below the flower head. This prevents the plant from putting energy into producing seeds and encourages it to put that energy back into making new flowers. It also keeps the plant looking tidy and prevents old petals from dropping and sticking to the leaves.

Transitioning Begonias to the Garden

If you started your begonias indoors, you cannot move them directly into the full outdoor environment all at once. They need a transition period called "hardening off." This process helps the tender indoor leaves get used to the wind, temperature changes, and brighter light of the outdoors. For a full timing guide, see our When to Plant Begonias Outdoors for Best Results.

About a week before you plan to plant them outside, start by placing the pots in a sheltered, shady spot outdoors for just a few hours during the day. Bring them back inside at night. Gradually increase the amount of time they spend outside each day.

After 7 to 10 days of this gradual introduction, your plants will be much tougher and ready to stay outside permanently. Remember, even a hardened-off begonia will be damaged by frost, so keep an eye on the weather forecast and bring them in if a surprise cold night is predicted.

Understanding Different Begonia Types

When you are planning your garden, it helps to know that tuberous begonias come in two main growth habits: upright and trailing.

Upright begonias grow on sturdy stems and usually reach a height of 12 to 18 inches. These are perfect for garden borders or the center of a patio pot where they can stand tall and show off their blooms.

Trailing begonias (often labeled as "hanging basket" begonias) have stems that naturally arch and cascade downward. These are the ideal choice for window boxes and hanging containers. As they grow, they will spill over the edges, creating a beautiful "waterfall" of flowers.

Regardless of the type you choose, the planting method for the corms remains the same. You just need to decide where you want that splash of color to be—at eye level in a basket or down low in a garden bed.

End of Season Care and Overwintering

In most parts of the United States, begonias are treated as annuals because they cannot survive freezing winters. However, because they grow from a corm, you can actually save them and replant them next year. This is a rewarding way to keep your favorite begonias going season after season.

Saving the Corms

When the weather begins to turn cool in the fall, you will notice the foliage starting to yellow. This is a sign the plant is going dormant. After the first light frost kills the top of the foliage, or when temperatures regularly dip into the 40s, follow these steps:

1. Carefully dig up the corm, being careful not to bruise or cut it.
2. Cut the stems back to about an inch or two above the corm.
3. Let the corms sit in a warm, dry place for a few days to "cure" and dry out.
4. Once dry, gently brush off any excess soil.
5. Store the corms in a cool, dark, and dry location. A cardboard box filled with peat moss, sawdust, or even just wrapped in newspaper works well.
6. The ideal storage temperature is between 40°F and 50°F—usually a cool basement or a dark closet works perfectly.

In the spring, you can pull them out of storage, check for any that might have shriveled or softened, and start the planting process all over again.

Key Takeaway: Begonia corms can be saved for multiple years if they are kept dry and cool during the winter months.

Conclusion

Growing begonias from corms is a wonderful way to bring professional-quality blooms into your own backyard. By starting your corms indoors in early spring and waiting for warm weather to move them outside, you ensure a long and successful growing season. Remember to focus on the basics: indented side up, well-draining soil, and a spot with plenty of shade.

At Longfield Gardens, we believe that gardening should be a source of joy and relaxation. Begonias are the perfect partner for this goal because they offer so much beauty for such a simple routine. With a little water, some regular fertilizer, and the right amount of shade, your garden will be the highlight of the neighborhood.

• Start corms indoors 8-12 weeks before the last frost.
• Always plant with the hollow side facing upward.
• Keep the soil moist but ensure the pot has great drainage.
• Transition plants slowly to the outdoors to prevent shock.

"A well-placed begonia can turn a dark corner of the yard into a vibrant focal point. The key to success is simply respecting their tropical roots and providing a bit of shelter from the midday sun."

We invite you to explore our Begonia Flower Bulbs for Sale and start planning your most colorful shade garden yet.

FAQ

How deep should I plant begonia corms?

Begonia corms should be planted very shallowly. Whether you are planting in a tray or the ground, the top of the corm should be level with the soil surface or covered by no more than half an inch of soil. Planting them too deep can cause the corms to rot or significantly delay the time it takes for sprouts to reach the surface. For a more detailed walkthrough, see our How Deep to Plant Tuberous Begonia for Best Growth.

Which way is up on a begonia corm?

The top of the begonia corm is the side that is indented or hollowed out, resembling a small bowl. This is where the stems will grow from. The rounded, smooth side should face downward into the soil, as this is where the roots will develop. For photos and orientation tips, see our How to Plant Tuberous Begonias: Which End Is Up?.

When should I move my begonias outside?

You should only move begonias outside when the danger of frost has completely passed and nighttime temperatures are consistently above 50°F to 60°F. Since begonias are tropical plants, they are very sensitive to cold. It is also important to spend about a week "hardening them off" by giving them short periods of outdoor time before moving them out permanently. For more timing guidance, see When to Plant Begonias Outdoors for Best Results.

Why are my begonia leaves turning yellow or falling off?

Yellowing leaves are often a sign of overwatering or poor drainage. If the soil stays too wet, the roots cannot "breathe," which causes the plant to struggle. Check the soil moisture with your finger; if it feels soggy, allow it to dry out more between waterings. Ensure your containers have open drainage holes and that you are using a light, airy potting mix. For more watering and drainage tips, see Tips for Growing Tuberous Begonias.