Table of Contents
- Introduction
- Understanding the Begonia Tuber
- What to Do If You Can't Tell Which Side Is Up
- When to Start Your Begonia Tubers
- Step-by-Step Guide to Planting Indoors
- Planting Directly in the Garden
- Watering Your New Tubers
- Caring for Begonias Throughout the Season
- Upright vs. Trailing Begonias
- Transitioning to the Outdoors (Hardening Off)
- Managing Pests and Common Issues
- What to Do at the End of the Season
- Conclusion
- FAQ
Introduction
Finding a splash of bright, cheerful color for the shady corners of your yard is one of the most rewarding parts of spring planning. Tuberous begonias are the perfect solution, offering lush foliage and rose-like blooms that last from midsummer right through the first frost. At Longfield Gardens, we love how these versatile plants transform porches and garden beds with very little effort.
If you are holding a begonia tuber for the first time, you might notice it looks a bit different from a typical tulip or daffodil bulb. Instead of a clear "pointy end," it has a unique, bowl-like shape that can leave many gardeners wondering which way is up. This guide is designed for home gardeners who want to get their begonias off to the best possible start.
We will cover exactly how to identify the top and bottom of your tuber, the best planting techniques for containers and garden beds, and how to care for your plants as they grow. Getting the orientation right is the first simple step toward a season full of spectacular flowers.
Understanding the Begonia Tuber
To understand which way to plant a begonia, it helps to know what you are looking at. Technically, begonias grow from tubers rather than true bulbs. A tuber is a thickened underground stem that stores nutrients and energy for the plant. While a tulip bulb has a clear top and bottom, a begonia tuber looks more like a dark, hairy, or textured potato.
If you look closely at a tuber, you will see it has two distinct sides. One side is indented, looking like a shallow bowl or a saucer. This is the concave side. The other side is rounded or domed, which is the convex side.
The indentation is where the magic happens. This "bowl" contains the growth points, often called "eyes," where the stems and leaves will eventually emerge. The rounded, domed side is where the root system develops to anchor the plant and draw in moisture.
Identifying the Top
The easiest way to remember which way is up is to look for the hollow. The indented, hollow side of the tuber should always face up toward the sky. This allows the new sprouts to grow directly toward the light without having to navigate around the body of the tuber.
Sometimes, you might even see tiny pink or white nubs inside that hollow area. These are the early sprouts, sometimes called "pinkies." If you see these, you have a 100% guarantee that the hollow side is the top.
Identifying the Bottom
The rounded, domed side is the bottom. This side should rest on the soil surface or be tucked into the planting medium. Because it is smooth and lacks a hollow, it provides a stable base for the plant as it establishes its roots.
Key Takeaway: Always plant begonia tubers with the "bowl" (indented side) facing up and the "dome" (rounded side) facing down.
What to Do If You Can't Tell Which Side Is Up
Nature can be irregular, and occasionally you might find a tuber that is exceptionally flat or unusually lumpy. If you are staring at a begonia tuber and truly cannot distinguish the hollow side from the rounded side, don't worry.
The best approach in this situation is to plant the tuber on its side. Begonias are resilient plants. If planted on its side, the sprouts will naturally grow upward toward the light, and the roots will grow downward into the soil. This is a much better "safety" move than accidentally planting it upside down, which can delay growth or cause the sprouts to struggle.
You can also look for "eyes" or small bumps that look like the eyes on a potato. These points of new growth are almost always located on the side that should face up. If you see old, dried-up root hairs from the previous season, those are a clear sign of the bottom.
When to Start Your Begonia Tubers
Timing is everything when it comes to begonias. Because they are tropical plants, they are very sensitive to cold temperatures. In most parts of the United States, we recommend starting begonia tubers indoors about 8 to 12 weeks before the last expected frost date in your area. If you are ordering online, our Shipping Information page explains how Longfield Gardens schedules shipments by zone.
Starting them indoors gives the plants a significant head start. Begonias are slow starters and can take several weeks to "wake up" and show their first leaves. By starting them early, you ensure you get the maximum amount of bloom time once the weather warms up.
Indoor Starting Timeline
If you live in a northern climate, March or early April is usually the ideal time to start your tubers in pots. If you live in a warmer southern zone, you may be able to plant them directly outdoors once the soil is warm and all danger of frost has passed.
A good rule of thumb is to wait until nighttime temperatures consistently stay above 50°F to 60°F before moving your begonias outside. Cold, damp soil can cause dormant tubers to rot, so patience is rewarded with healthier plants. To check your zone, use the USDA Hardiness Zone Map.
Step-by-Step Guide to Planting Indoors
Many gardeners prefer to start their begonias in shallow trays or small "starter" pots before moving them to their final containers or garden beds. This makes it easier to monitor their moisture levels and keep them in a warm spot.
1. Choose the Right Container
For starting tubers, you don't need a deep pot. A shallow tray with drainage holes or a 4-inch pot is perfect. Ensure the container is clean to prevent any fungal issues.
2. Use Quality Potting Soil
Begonias need a light, airy growing medium. A standard high-quality potting mix works well. Avoid using heavy garden soil, as it doesn't drain fast enough and can pack down too tightly around the tuber.
3. Position the Tuber
Fill your container with moist soil, leaving about an inch of space at the top. Place the tuber on the surface with the hollow side facing up.
4. Set the Depth
This is a "simple gardening rule" that makes a big difference: don't bury the tuber too deep. In fact, many successful gardeners leave the top of the tuber just barely visible or covered with only a light dusting of soil (about half an inch). For more detail, see our How Deep to Plant Tuberous Begonias for Best Blooms guide. This prevents water from sitting in the hollow "bowl" of the tuber, which could lead to rot.
5. Provide Warmth and Light
Place your pots in a warm spot, ideally around 65°F to 70°F. Indirect light is best at this stage. You don't need bright, direct sun until the leaves begin to unfurl.
Pro Tip for Success: If you are starting multiple tubers in one tray, space them about 2 to 3 inches apart so their roots don't get tangled before you are ready to transplant them.
Planting Directly in the Garden
If you prefer to plant your begonias directly in the landscape, wait until the soil is warm to the touch. This usually happens a few weeks after the last frost. For more ground-planting advice, see our Can I Plant Begonias in the Ground? guide.
Site Selection
Begonias are famous for their love of shade. Choose a spot that receives dappled sunlight or morning sun with protection from the harsh afternoon heat. Too much direct sun can scorch the leaves, while too much deep shade might result in fewer flowers.
Soil Preparation
The soil should be "well-draining," which simply means water leaves the area quickly instead of forming puddles. If your garden soil is heavy clay, you can improve it by mixing in some compost or peat moss. This creates the loose, crumbly texture that begonias love.
Spacing and Depth
Dig a shallow hole and place the tuber hollow-side up. Space upright begonia varieties about 10 to 12 inches apart to allow for good air circulation. Just like with indoor planting, cover the tuber with only about an inch of soil. Water the area gently to settle the soil around the tuber.
Watering Your New Tubers
Watering is the area where most new begonia gardeners feel a bit of uncertainty. The goal is to keep the soil "moist but not soggy."
When you first plant a dormant tuber, it doesn't have a root system yet to drink up water. Because of this, you should water very sparingly at the start. Just a light misting or a small drink to keep the soil from drying out completely is enough.
Once you see green sprouts and the first leaves appearing, you can begin to water more regularly. At this stage, the plant is building roots and needs more hydration to support its new growth. Always water at the base of the plant rather than over the top of the leaves to keep the foliage dry.
Caring for Begonias Throughout the Season
Once your begonias are established and growing, they are relatively low-maintenance. However, a little bit of attention will help them produce the most flowers.
Lighting Needs
As the plants grow, they will tell you if they are getting the right amount of light. If the leaves look pale or the stems are getting very long and "leggy," they might need a bit more light. If you see brown, crispy edges on the leaves, they probably need more shade. For more light guidance, see our Are Begonias Shade Plants? article.
Fertilizing for Blooms
Begonias are "heavy feeders," meaning they use a lot of energy to produce those big, beautiful blooms. Once the plant has several sets of leaves, you can begin using a balanced, water-soluble fertilizer every two weeks. Follow the instructions on the label for the best results. This steady supply of nutrients keeps the flower production going all summer long.
Deadheading
To keep your plants looking tidy and encourage more flowers, you can "deadhead" them. This just means removing the flowers as they begin to fade. Simply pinch off the spent bloom and its small stem. This prevents the plant from putting energy into making seeds and keeps it focused on making more petals.
Upright vs. Trailing Begonias
When you are deciding where to plant your tubers, consider the growth habit of the variety you have chosen.
- Upright Begonias: These grow on sturdy stems and are perfect for garden borders or the center of a container. They produce large, showy flowers that face outward or slightly upward.
- Trailing (Pendula) Begonias: These varieties have stems that naturally arch and cascade downward. They are the best choice for hanging baskets or the edges of window boxes. When planting trailing begonias, follow the same "hollow side up" rule.
Action Plan for Containers:
- Choose a pot with a drainage hole.
- Use fresh potting mix (not garden soil).
- Plant 1-3 tubers per 12-inch pot, depending on the variety's size.
- Keep the soil damp, but let the top inch dry out between waterings.
If you want a ready-made trailing option, Begonia Hanging Golden Balcony is a natural fit.
Transitioning to the Outdoors (Hardening Off)
If you started your begonias indoors, you cannot move them straight into the garden all at once. They need a transition period called "hardening off." For a step-by-step transition plan, see When to Plant Begonias Outside for the Best Blooms. This allows them to get used to the wind, fluctuating temperatures, and brighter light of the outdoors.
Start by placing your pots in a sheltered, shady spot outside for just an hour or two during the warmest part of 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 and slowly expose them to a bit more light. This gentle process prevents "transplant shock" and ensures your plants continue to thrive.
Managing Pests and Common Issues
While begonias are generally healthy, they can occasionally run into small issues. Most of these are easily solved with a few simple changes.
Powdery Mildew
If you see a white, dusty coating on the leaves, it is likely powdery mildew. This usually happens when the air is still and humid. You can prevent this by making sure your plants aren't crowded. Good air circulation is the best defense. If you notice it starting, try moving the plant to a spot with better air movement.
Stem or Tuber Rot
If a stem feels mushy or the plant tips over easily, it may be a sign of rot. This is usually caused by overwatering or planting the tuber too deep. If this happens, let the soil dry out significantly before watering again. For future plantings, remember to keep the top of the tuber very close to the surface.
What to Do at the End of the Season
In hardiness zones 9 through 11, begonias can often stay in the ground year-round. However, for most gardeners in the United States, begonias are treated as "tender perennials." This means they will not survive a freezing winter outdoors, but you can save the tubers to plant again next year.
When the leaves begin to turn yellow in the autumn, stop watering the plant. This signals to the tuber that it is time to go dormant. After the first light frost kills the top growth, or if a hard freeze is predicted, lift the tubers out of the soil.
Cut the stems back to about an inch above the tuber and gently brush off any excess soil. Let the tubers dry in a cool, dark, well-ventilated spot for a few days. Once they are dry to the touch, store them in a box filled with peat moss, sawdust, or shredded paper. Keep the box in a cool, dry place (like a basement) where temperatures stay between 40°F and 50°F.
Conclusion
Planting a begonia bulb—or tuber—is a simple task once you know the secret of the "bowl." By placing the indented side facing up and the rounded side down, you give the plant the perfect foundation for growth. Whether you are planting them in a colorful container for your front porch or tucked into a shady garden bed, these stunning flowers will reward your small effort with months of elegance.
At Longfield Gardens, we take pride in providing high-quality tubers that are ready to perform in your garden. We stand behind the 100% Quality Guarantee and want every gardener to feel confident in their success. Remember that gardening is a journey of observation; by getting the basics like planting depth and orientation right, you are setting yourself up for a season of beauty.
Success with begonias starts with the right orientation and a little bit of patience. By starting your tubers indoors and keeping them warm, you’ll enjoy a spectacular show of color all summer long.
If you prefer a classic upright choice, Begonia Upright Double Roseform Pink is a reliable option.
Ready to add some shade-loving color to your yard? Start by selecting your favorite varieties and gathering your pots. For a larger planting, Begonia Upright Double Superba Mix - Bulk Offer is a convenient way to fill a space. With the hollow side up and a little bit of water, you’ll be on your way to a beautiful garden in no time.
FAQ
Can I plant begonia tubers directly in the ground?
Yes, you can plant them directly in the ground, but only after the soil has warmed up and all danger of frost has passed. Because begonias take a long time to bloom, gardeners in northern climates usually prefer starting them indoors to get a longer season of flowers.
How deep should I bury a begonia tuber?
Begonia tubers should be planted very shallowly. The top of the tuber should be covered by no more than half an inch to one inch of soil. Planting them too deep can cause the new sprouts to struggle to reach the surface and may increase the risk of the tuber rotting.
What happens if I plant my begonia bulb upside down?
If a begonia tuber is planted upside down, the sprouts will have to grow around the body of the tuber to reach the light. This takes a lot of energy and can significantly delay the appearance of leaves. In some cases, the sprout may not make it to the surface at all, so it is always best to double-check for that "bowl" shape before planting.
How much water do begonia tubers need right after planting?
Immediately after planting a dormant tuber, you should water very lightly. The tuber does not have roots yet, so it cannot absorb much moisture. Keeping the soil slightly damp but not wet is the key to waking the tuber up without causing it to rot. Once you see green growth, you can gradually increase watering. For more detailed tips, see our How to Plant and Care for Begonias guide.