Table of Contents
- Introduction
- The Short Answer: How Deep to Plant
- Identifying the Top and Bottom of the Tuber
- Why Soil Choice and Quality Matter
- When to Plant: Timing for Success
- Spacing and Container Selection
- Light Requirements for Tuberous Begonias
- Watering Wisely During the Early Stages
- Fertilizing for Bigger Blooms
- Transitioning Outdoors (Hardening Off)
- Growing Upright vs. Trailing Begonias
- Troubleshooting Common Growth Issues
- Caring for Tubers at the End of the Season
- Conclusion
- FAQ
Introduction
Imagine stepping onto your porch on a warm July morning to find massive, rose-like blooms in shades of apricot, scarlet, and lemon yellow cascading from your favorite hanging baskets. Tuberous begonias are the gems of the shade garden, offering lush foliage and spectacular flowers that last from midsummer right until the first frost. Whether you are a beginner or a seasoned gardener, the secret to these show-stopping displays often comes down to how you begin.
At Longfield Gardens, we believe that gardening should be a relaxing and rewarding experience for everyone. Our Begonia Flower Bulbs for Sale collection is particularly gratifying because it provides so much color with relatively little effort once you get the basics right. This guide will focus on the most important first step: getting your tubers in the ground at the perfect depth and orientation.
We will cover exactly how deep to plant your tubers, how to tell which side is up, and the best way to transition your plants from indoor starts to outdoor beauties. For more growing basics, see our Tips for Growing Tuberous Begonias. By following these simple steps, you can enjoy a season filled with vibrant, healthy begonias that brighten up even the shadiest corners of your yard. Success starts with a well-placed tuber and a little bit of patience.
The Short Answer: How Deep to Plant
When you are ready to tuck your begonia tubers into their growing medium, the most important rule is to keep it shallow. Begonia tubers should be planted about 1/2 inch to 1 inch deep. The goal is to cover the top of the tuber with just enough soil so it is no longer visible, but not so deep that the emerging sprouts have to work hard to find the light.
If you plant a tuber too deep, you increase the risk of the tuber rotting before it has a chance to establish a strong root system. Conversely, if the tuber is left sitting on top of the soil without any coverage, the delicate "eyes" or growth points can dry out, and the plant may lack the stability it needs as the heavy stems and flowers grow.
Finding that middle ground—roughly the thickness of your thumb—ensures the tuber stays moist and protected while allowing the sprouts to reach the surface quickly. This shallow planting depth applies whether you are starting them in small nursery pots indoors or planting them directly into large decorative containers.
Identifying the Top and Bottom of the Tuber
Before you can worry about depth, you need to know which way is up. Unlike many flower bulbs that have a clear "pointed" end, begonia tubers can look a bit like a dusty brown stone or a small, hairy potato. However, once you look closely, the orientation is quite clear.
Most begonia tubers are shaped like a shallow bowl or a saucer. One side will be indented or "concave," and the other side will be rounded or "convex."
- The Indented Side (The Bowl): This side should always face upward toward the sky. The hollow area is where the "eyes" or growth points are located. These eyes will eventually turn into the stems, leaves, and flowers of your plant.
- The Rounded Side (The Bottom): This side should face downward into the soil. While roots will eventually emerge from both the sides and the bottom, the rounded side provides the base for the plant.
If you happen to find a tuber that is exceptionally flat or difficult to read, don't worry. You can simply place it on its side. The plant is smart enough to direct its stems toward the light and its roots into the soil. However, whenever possible, placing the "hollow" side up is the best way to get your begonias off to a fast start. For a quick refresher, see How to Plant Tuberous Begonias: Which End Is Up?.
Key Takeaway: Always plant begonia tubers with the hollow, bowl-shaped side facing up. Cover them with no more than one inch of soil to prevent rot and encourage fast sprouting.
Why Soil Choice and Quality Matter
While planting depth is vital, the environment surrounding the tuber determines how well it will grow at that depth. Begonias are tropical plants that love moisture, but they are very sensitive to "wet feet." This means they need soil that stays damp like a wrung-out sponge but never stays soggy or waterlogged.
Using Potting Mix vs. Garden Soil
For the best results, we recommend using a high-quality, peat-based potting mix rather than standard garden soil. Garden soil is often too heavy and dense for containers. It can pack down tightly, cutting off the air supply to the roots and trapping too much water around the tuber. For more container details, see How to Plant Begonias in Pots: A Guide to Stunning Blooms.
A good potting mix usually contains peat moss or coconut coir for moisture retention and perlite or vermiculite for drainage. This creates a light, fluffy texture that allows the young roots to grow easily and ensures the tuber stays healthy at its shallow planting depth.
Improving Drainage in Garden Beds
If you choose to plant your begonias directly in a garden bed, look for a spot with "well-drained" soil. You can test your drainage by digging a small hole and filling it with water. If the water drains away within an hour, the spot is likely perfect. If it sits for several hours, you may want to amend the area with compost or shredded bark to loosen the soil and improve the air spaces.
When to Plant: Timing for Success
Getting the depth right only works if the timing is also right. Begonias are very tender and cannot tolerate frost. In fact, they aren't even big fans of chilly nights.
Starting Indoors (The Head Start)
Because begonias can take 8 to 12 weeks to go from a dormant tuber to a flowering plant, most gardeners in the US choose to start them indoors. This is usually done in March or April. For a step-by-step overview, see How to Start Tuberous Begonias Indoors.
By starting them inside, you give the tubers a warm, protected environment to "wake up." When the weather finally warms up in late May or June, you will already have a small plant ready to go, rather than just a tuber in the ground. This results in flowers much earlier in the summer season.
Planting Directly Outdoors
If you live in a warm climate or prefer to plant directly into the ground, you must wait until all danger of frost has passed. The soil temperature should be at least 60°F. If the soil is too cold and wet, the tuber may simply sit dormant or, worse, begin to decay before it can sprout. If you want help matching timing to your region, check the Hardiness Zone Map.
What to Do Next: Starting Your Tubers
- Gather your supplies: You’ll need your tubers, some 4-inch to 6-inch nursery pots, and a bag of fresh potting mix.
- Moisten the soil: Add a little water to your potting mix before putting it in the pots so it is damp but not dripping.
- Set the tuber: Place the tuber in the center of the pot with the hollow side facing up.
- Cover lightly: Sprinkle enough mix over the top to cover the tuber by 1/2 to 1 inch.
- Find a warm spot: Place the pots in a room that stays around 65-70°F with bright, indirect light.
Spacing and Container Selection
How deep you plant is just one part of the spatial puzzle; how far apart you plant them is the other. For a fuller upright display, the Upright Double Begonias collection is a good place to start. Tuberous begonias can grow quite large, and they appreciate having room for air to circulate around their stems.
Spacing in the Garden
If you are planting your started begonias into a garden bed, space them about 8 to 12 inches apart. This gives the foliage room to spread out without crowding neighboring plants. Good airflow is one of the best ways to keep the leaves healthy and prevent common issues like powdery mildew.
Choosing the Right Pot
When planting in containers, the size of the pot should match the size of the tuber. If you prefer a cascading look, the Hanging Begonias collection is a good place to start.
- Single Tubers: A single begonia tuber typically thrives in a 6-inch to 8-inch pot.
- Multiple Tubers: If you have a large 12-inch or 14-inch hanging basket, you can plant 2 or 3 tubers together. Just space them evenly around the pot, ensuring they aren't touching each other or the edge of the container.
Regardless of the container size, make sure it has at least one drainage hole in the bottom. If water cannot escape, it will collect at the bottom of the pot, causing the soil to become sour and the tuber to rot.
Light Requirements for Tuberous Begonias
Once your tubers are planted at the correct depth, their success depends heavily on where you place the pot. Tuberous begonias are famous for their ability to bloom in the shade, but "shade" can mean many things in a garden.
The Ideal Light: Dappled or Filtered
Most begonias prefer bright, indirect light or dappled shade—the kind of light you find under a tall tree or on a porch that gets morning sun but is shaded during the heat of the afternoon. For more shade-friendly ideas, see Summer Bulbs for Shady Gardens.
Avoiding Direct Midday Sun
While begonias need light to produce energy for those big flowers, the intense midday sun in most parts of the US is too harsh. Direct, hot sunlight can scorch the leaves and cause the flower buds to drop before they open. If you notice the edges of the leaves turning brown and crispy, your plant might be getting a bit too much sun.
Deep Shade
Begonias will grow in deep shade (areas with no direct sun at all), but they may produce fewer flowers and the stems might become "leggy" as they reach for more light. If your garden is very dark, try to find the brightest spot available within that shade.
Key Takeaway: Light and depth work together. A tuber planted at the right depth in a bright, shaded spot will grow sturdy, compact stems that can support heavy flowers.
Watering Wisely During the Early Stages
The period between planting the tuber and seeing the first green sprouts is the most delicate time for a begonia. During this "waking up" phase, the tuber does not have a large root system or leaves to pull moisture out of the soil.
The "Damp, Not Wet" Rule
When you first plant the tuber, water it just enough to settle the soil. After that, wait until the top inch of soil feels dry to the touch before watering again. It is a common mistake to keep the soil constantly wet while waiting for sprouts. Because the tuber is dormant, it can't use all that water, and sitting in soggy soil is the primary cause of failure.
Watering Once Established
Once you see leaves and the plant is growing vigorously, you can increase the frequency of watering. During the height of summer, begonias in containers may need water every day or every other day, especially if the weather is windy or very warm. Always aim the water at the base of the plant rather than over the leaves to keep the foliage dry.
Fertilizing for Bigger Blooms
Because you are planting the tubers quite shallowly in a limited amount of soil, they will eventually use up the nutrients available in the potting mix. To keep the flowers coming all summer long, a little extra "food" goes a long way.
When to Start
Wait until the plant has several sets of healthy leaves before you start a fertilizing routine. Starting too early can overwhelm the young roots.
What to Use
A balanced, water-soluble fertilizer (such as a 10-10-10 or 20-20-20) works well. You can also use a fertilizer formulated specifically for flowering plants, which often has a slightly higher middle number (phosphorus) to encourage bloom production.
How to Apply
We suggest diluting the fertilizer to half-strength and applying it every two weeks. This "weakly, weekly" approach provides a steady stream of nutrients without the risk of burning the roots. Always make sure the soil is already slightly moist before applying fertilizer; never fertilize a bone-dry plant.
Transitioning Outdoors (Hardening Off)
If you started your tubers indoors at that 1/2-inch depth, you will eventually have a beautiful little plant ready to move outside. However, you cannot move it directly from a 70°F living room to a breezy patio overnight. This process is called "hardening off."
The Slow Introduction
- Start small: On a mild, overcast day, set your plants outside in a protected, shady spot for just two or three hours.
- Increase the time: Every day, leave them out for a few more hours, gradually exposing them to a bit more breeze and light.
- Check the nights: Bring them inside every night for the first week.
- Permanent move: After 7 to 10 days, if the nighttime temperatures stay consistently above 60°F, they can stay outside permanently.
This transition allows the plant's cell structure to toughen up, ensuring the leaves don't wilt or get "sunburned" when they face the elements.
Growing Upright vs. Trailing Begonias
When deciding how deep to plant and where to place your begonias, it helps to know which type you are growing. While the planting depth (1/2 to 1 inch) is the same for both, their growth habits differ.
Upright Begonias
These varieties grow on sturdy, vertical stems. For a classic example, try Begonia Upright Double Roseform Pink. They are perfect for garden borders or the center of a large patio pot. Because the flowers can be very large and heavy, you might occasionally need to provide a small bamboo stake for support.
Trailing (Pendula) Begonias
These are designed to spill over the edges of containers. A beautiful example is Begonia Hanging Golden Balcony. They are the classic choice for hanging baskets. When you plant these, you might notice the stems naturally start to lean outward as they grow. This is exactly what they are supposed to do.
Troubleshooting Common Growth Issues
Even when you follow the rules for planting depth and care, nature can sometimes throw a curveball. Most begonia "problems" are easily solved by making one small change at a time.
Why Are the Buds Falling Off?
If your begonia is dropping its flower buds before they open, it’s usually a sign of stress. The most common culprits are:
- Extreme Heat: Begonias struggle when temperatures stay above 85°F. Moving them to a cooler, more shaded spot can help.
- Uneven Watering: If the soil goes from bone-dry to soaking wet, the plant may drop buds. Try to keep the moisture levels more consistent.
What If My Tubers Haven't Sprouted?
If it has been four weeks and you see no signs of life, don't give up! Some tubers are just slower to wake up than others.
- Check the Temperature: Tubers need warmth to sprout. If they are in a cold basement, move them to a warmer room or on top of a refrigerator (which gives off a small amount of heat).
- Check the Moisture: Gently brush away a little soil to see if the tuber is still firm. If it is firm, it’s just sleeping. If it feels soft or mushy, it likely succumbed to rot from overwatering.
Leggy Stems
If your begonia is growing very long, thin stems with lots of space between the leaves, it is "reaching" for more light. Move the container to a slightly brighter location. You can also "pinch back" the growing tips of the stems to encourage the plant to branch out and become bushier.
Caring for Tubers at the End of the Season
One of the best things about tuberous begonias is that they are not a "one and done" plant. With the right care, you can save the tubers and plant them again next year.
Preparing for Dormancy
As the days get shorter and the temperatures drop in the fall, your begonia will naturally start to turn yellow. This is the plant's way of sending all its energy back down into the tuber for winter storage.
When this happens, stop fertilizing and reduce your watering. Once the foliage has turned yellow or been hit by a very light frost, cut the stems back to about an inch above the tuber.
Storing for Winter
Carefully lift the tubers out of the soil. Since they were only planted an inch deep, this is very easy to do with a small hand trowel or even your fingers.
- Dry them out: Let the tubers sit in a dry, shady spot for a few days until any remaining soil can be easily brushed off.
- The Container: Store them in a cardboard box or a paper bag filled with slightly damp peat moss, sawdust, or vermiculite.
- The Location: Keep them in a cool, dark, dry place that stays between 40°F and 50°F (like a cool closet or an insulated garage). Do not let them freeze!
Next spring, you can pull them out, check for firmness, and start the whole process over again.
Conclusion
Planting begonia tubers is a simple process that yields incredible rewards. By keeping your planting depth shallow—just 1/2 to 1 inch deep—and ensuring the hollow side of the tuber faces the sun, you set the stage for a summer of spectacular color. These plants thrive when given the right balance of dappled shade, well-draining soil, and consistent moisture.
At Longfield Gardens, we take pride in providing high-quality tubers that are ready to perform in your garden. Whether you are planting a single upright begonia in a decorative ceramic pot or creating a wall of color with trailing varieties in hanging baskets, the key is to start with the basics and enjoy the process.
- Plant 1/2" to 1" deep.
- Keep the indented "bowl" side facing up.
- Start indoors 8-12 weeks before the last frost for early blooms.
- Use a well-draining, peat-based potting mix.
- Provide bright, indirect light and avoid harsh midday sun.
"The beauty of tuberous begonias lies in their resilience and their ability to transform a shady corner into a vibrant oasis with just a little bit of care and the right start."
We invite you to explore our selection of begonia tubers and start planning your most beautiful shade garden yet. With these simple rules in hand, you are well on your way to a season of success. Our 100% Quality Guarantee helps make that first step even easier.
FAQ
What happens if I plant my begonia tubers upside down?
If you plant a begonia tuber with the rounded side up, the plant will still try to grow. The sprouts will emerge from the bottom and have to grow around the side of the tuber to reach the surface. This uses up a lot of the tuber's stored energy and can result in a much weaker plant that takes longer to bloom. If you realize you've planted them incorrectly, you can gently dig them up and flip them over as long as the sprouts aren't too long yet.
Do I need to soak begonia tubers before planting?
While some gardeners like to soak their tubers in lukewarm water for an hour or two to "wake them up," it is generally not necessary. As long as you plant them in moist (but not soggy) potting mix, they will absorb the moisture they need to begin growing. If your tubers look exceptionally shriveled, a brief soak can help, but avoid leaving them in water for too long as this can lead to rot.
Can I plant begonia tubers directly in the ground?
Yes, you can plant them directly in the garden once the soil has warmed up to at least 60°F and all danger of frost has passed. However, keep in mind that begonias grow slowly at first. Planting directly outdoors usually means you won't see flowers until much later in the summer compared to starting them indoors a few months earlier.
How many begonia tubers should I put in a 12-inch hanging basket?
For a lush, full look in a 12-inch hanging basket, we recommend planting three tubers. Space them evenly in a triangle pattern, keeping them about 2 inches away from the edge of the pot. This gives each plant enough room to develop a healthy root system while ensuring the basket looks overflowing with blooms by midsummer. For a bulk option, try Begonia Non Stop Mix - Bulk Offer.