Table of Contents
- Introduction
- Identifying the Top and Bottom of a Begonia Tuber
- Why Orientation Matters for Begonias
- When to Plant Your Begonia Tubers
- Step-by-Step Planting Guide
- Where to Grow Begonias: Light and Soil
- Watering and Feeding for Best Blooms
- Choosing the Right Variety for Your Space
- What to Do If You're Not Sure Which Side is Up
- Caring for Begonias Through the Season
- Preparing for Winter
- Conclusion
- FAQ
Introduction
Tuberous begonias are some of the most rewarding plants you can grow in a shade garden. Their lush, rose-like flowers and vibrant colors bring a tropical feel to porches, patios, and garden beds alike. There is a special kind of excitement that comes with seeing those first thick, waxy leaves emerge from the soil, knowing a season of spectacular blooms is just around the corner.
At Longfield Gardens, we want to make sure your gardening experience is as successful as it is enjoyable. While begonias are quite easy to care for once they get going, the very first step—planting the tuber—is where many gardeners pause. Because begonia tubers have a unique, chunky shape, it isn't always obvious which side should face the sky.
This guide will show you exactly how to identify the top and bottom of a begonia tuber so you can plant with confidence. We will cover the simple physical cues to look for, the best planting depths, and how to get your begonias off to a strong start. Getting the orientation right is the first step toward a summer full of spectacular, non-stop color.
Identifying the Top and Bottom of a Begonia Tuber
Unlike a tulip or a daffodil, which have a clear pointed top and a flat bottom, a begonia tuber looks more like a dark, hairy potato or a small, earthy saucer. These tubers are thickened underground stems that store energy for the plant. Because they don't have a "point," you have to look for a specific shape to tell which way is up.
The most reliable way to identify the top is to look for a "dish" or a "hollow." One side of the tuber will be slightly indented, resembling a shallow bowl or a thumbprint. This concave side is the top. The other side will be rounded and smooth, similar to the bottom of a bowl. This convex side is the bottom.
If you look closely at the indented side, you might also see small, pinkish or reddish bumps. Gardeners often call these "eyes" or "pinkies." These are the growth points where the stems and leaves will eventually emerge. On the rounded bottom side, you might see the remains of old, dried-out roots from the previous year, which often look like thin, brown hairs.
Key Takeaway: The "Bowl" Rule Think of the begonia tuber as a small soup bowl. You want the hollow part of the bowl facing up toward the sun so it could "hold water." The rounded bottom of the bowl sits in the soil.
What to Look for on the Top (Concave Side)
- A hollow or indentation: This is the most obvious sign.
- Growth "eyes": Small, nubby bumps that may be pink, red, or white.
- Scarring: Sometimes you will see a scar where last year’s main stem was attached.
What to Look for on the Bottom (Convex Side)
- A smooth, rounded shape: This side is meant to nestle into the dirt.
- Old root hairs: You may see fine, dried-out fibers.
- No growth points: This side will not have the pink "eyes" seen on the top.
Why Orientation Matters for Begonias
You might wonder if a plant can eventually figure out which way is up on its own. While plants are remarkably resilient, planting a begonia tuber upside down can lead to several unnecessary challenges. When a tuber is planted correctly, the sprouts have a direct path to the surface and the roots can quickly grow downward to find moisture.
If a tuber is planted upside down, the sprouts must grow downward first, then curl around the side of the tuber to reach the light. This extra effort uses up the tuber's stored energy and delays the appearance of leaves by several weeks. In some cases, the sprout might even rot before it manages to break through the soil surface.
By taking a moment to ensure the hollow side is facing up, you ensure the plant spends its energy on growing tall and producing flowers rather than navigating its way out of the dark. It is a simple win that sets the stage for a much healthier plant.
What to do next:
- Unpack your tubers and lay them out on a flat surface.
- Identify the "hollow" side of each tuber.
- Look for any tiny pink sprouts (eyes) to confirm your choice.
- If you find a tuber that is completely flat on both sides, look for the side with the most texture or scarring—that is usually the top.
When to Plant Your Begonia Tubers
Timing is just as important as orientation. Begonias are tropical plants that love warmth and are very sensitive to frost. Because they take a while to "wake up" and begin blooming—often 12 to 15 weeks—many gardeners choose to start them indoors before the weather warms up.
Starting Indoors (Recommended)
In most parts of the United States, starting them indoors in late winter or early spring (March or April) is the best approach. This gives the tubers a head start so they are already leafy and ready to go by the time the weather is safe for outdoor planting. Starting early often results in flowers a full month sooner than if you waited to plant them directly in the garden.
Planting Directly Outdoors
If you live in a warm climate or prefer to plant directly in the ground, wait until all danger of frost has passed. The soil should be warm to the touch, and nighttime temperatures should consistently stay above 60°F. If the soil is too cold and wet, the tubers may sit dormant for a long time or potentially rot before they start growing.
Step-by-Step Planting Guide
Once you know which way is up and the timing is right, the actual planting process is very straightforward. Whether you are starting them in small nursery pots indoors or planting them directly into large decorative containers, the depth and spacing rules remain the same.
1. Choose the Right Container and Soil
Begonias need excellent drainage. Choose a pot with plenty of holes in the bottom. Use a high-quality, lightweight potting mix rather than heavy garden soil. A good potting mix stays fluffy, allowing the delicate roots to spread easily while letting excess water drain away.
2. Prepare the Soil
Fill your container with soil, leaving about two inches of space at the top. Lightly water the soil so it is moist but not soaking wet. It should feel like a wrung-out sponge.
3. Place the Tubers
Set the tuber on the soil surface with the hollow side facing up. If you are planting in a small individual pot, place one tuber in the center. If you are using a larger window box or garden bed, space the tubers about 8 to 12 inches apart to allow room for the bushy foliage to grow.
4. Cover Lightly
Begonias do not like to be buried deep. Cover the tuber with just enough soil so that the top is about 1/2 inch to 1 inch below the surface. Some gardeners even leave the very top of the hollow visible until the first sprouts appear, then add a little more soil later. This prevents water from pooling in the hollow, which can sometimes cause rot.
5. Water Gently
Give the soil a light drink of water to settle it around the tuber. Avoid heavy watering at this stage. Since there are no leaves yet, the plant isn't "drinking" much water. You only want to keep the soil from drying out completely.
Key Takeaway: The Perfect Depth Shallow planting is a secret to success. Aim for 1 inch of soil coverage. Deep planting can lead to slower growth and increases the risk of the tuber staying too wet.
Where to Grow Begonias: Light and Soil
Begonias are the superstars of the shade garden. While many flowering plants struggle without full sun, begonias thrive in areas where other plants might fail. However, "shade" can mean different things, so it helps to find the right balance.
Sunlight Needs
The ideal spot for a begonia is one that receives bright, indirect light or filtered "dappled" sunlight. Early morning sun is usually fine because it is cool. However, you should avoid placing begonias in a spot that gets hot, direct afternoon sun. The intense heat can scorch their succulent leaves and cause the flowers to wilt.
If your begonias are growing in deep shade, they will still grow, but they may become "leggy" (tall and thin) as they stretch for the light, and they may produce fewer flowers. If you notice this, try moving them to a slightly brighter location.
Soil and Drainage
"Well-draining soil" is the most important requirement for begonia health. Drainage refers to how fast water leaves the soil. If water sits in the pot for hours after you water it, the soil is too heavy. You can improve drainage in garden beds by adding organic matter like compost or peat moss. In containers, simply using a professional-grade potting mix is usually enough.
Watering and Feeding for Best Blooms
Once your begonias have sprouted and have a few sets of leaves, their needs will change. They are now actively growing and will require regular attention to stay lush and productive.
How to Water Correctly
The goal is to keep the soil consistently moist but never soggy. A good rule of thumb is to wait until the top inch of soil feels dry to the touch before watering again. When you do water, apply it directly to the soil rather than over the leaves. Wet leaves, especially in shaded areas with low airflow, can sometimes lead to mildew or spotting.
If your begonias are in hanging baskets, they will dry out much faster than those in the ground. During the heat of mid-summer, you may need to check hanging baskets every day.
Feeding Your Plants
Begonias are "heavy feeders," meaning they use a lot of nutrients to produce those massive, beautiful blooms. Start fertilizing once the plant has established its first few leaves. Use a balanced, water-soluble fertilizer formulated for flowering plants. Following the instructions on the label, apply the fertilizer every two to three weeks throughout the growing season. This consistent supply of food will keep the flowers coming until the first frost of autumn.
Choosing the Right Variety for Your Space
When you browse the options at us or your local garden center, you will notice that begonias come in two main growth habits: upright and trailing (sometimes called pendula). Choosing the right one depends on where you plan to plant them.
Upright Begonias
These varieties grow into sturdy, bushy mounds. They are perfect for garden borders, flower beds, and standard patio pots. They produce large, heavy flowers that sit on top of thick stems. Popular types include Double Begonias, which have rose-like centers, and Fimbriata Begonias, which have ruffled, fringed edges.
Trailing (Pendula) Begonias
As the name suggests, these varieties have stems that gracefully arch downward. They are the best choice for hanging baskets, window boxes, or the edges of tall containers. As the season progresses, the stems will cascade over the sides, creating a waterfall of color.
Fragrant and Specialty Types
Some newer varieties have been bred specifically for their scent, which is a rare treat in the begonia world. Others, like the Non-Stop series, are prized for their ability to bloom continuously even during the hottest parts of the summer. No matter which you choose, the planting process remains the same: hollow side up!
What to Do If You're Not Sure Which Side is Up
Sometimes you might encounter a tuber that is unusually shaped, or perhaps it’s very young and doesn't have a clear hollow yet. If you have studied the tuber and honestly cannot tell which side is which, do not worry.
The best solution is to plant the tuber on its side.
When a tuber is on its side, the sprouts can easily reach the surface by growing horizontally for a very short distance and then turning upward. Similarly, the roots can easily find their way down. This is a much safer "insurance policy" than accidentally planting it completely upside down.
Another trick is to pre-sprout the tubers. Place them in a shallow tray of moist peat moss or potting soil in a warm room, but do not bury them. Leave them exposed to the air. Within a week or two, the "eyes" will begin to swell and turn pink or green. Once you see these sprouts, you will know exactly which side is the top. You can then move them into their permanent pots and cover them with soil.
Caring for Begonias Through the Season
As the summer progresses, your begonias will become more impressive. To keep them looking their best, a little "grooming" goes a long way.
Deadheading
Deadheading is the process of removing faded or spent flowers. This not only keeps the plant looking tidy but also encourages it to put its energy into creating new buds rather than making seeds. Simply pinch off the flower stem where it meets the main branch.
Handling Tall Stems
Some upright begonias produce flowers so large and heavy that the stems may begin to lean. If this happens, you can use a small bamboo stake and a piece of soft garden twine to give the plant some extra support. This is common with "Dinnerplate" varieties that have massive blooms.
Avoiding Common Issues
The most common mistake gardeners make is overwatering. If you notice the leaves turning yellow or the stems feeling mushy at the base, the plant is likely getting too much water. Scale back your watering and ensure the drainage holes aren't blocked.
If you see a white, dusty coating on the leaves, this may be powdery mildew. This usually happens when there isn't enough airflow around the plant. To help, make sure your pots aren't crowded too closely together and try to water early in the day so the foliage can dry out before evening.
Preparing for Winter
Tuberous begonias are perennials, but they are not hardy in most of the United States (typically only in zones 9-11). In most regions, the tubers must be dug up and stored indoors for the winter.
Wait until the first light frost turns the foliage yellow or black. Cut the stems back to about an inch above the tuber. Gently lift the tubers from the soil, shake off the excess dirt, and let them dry in a cool, shaded spot for a few days. Once they are dry, store them in a box filled with peat moss or sawdust in a cool, dark place (like a basement) that stays above freezing.
In the spring, you can pull them out, find that hollow side again, and start the cycle all over. It’s a wonderful way to enjoy your favorite varieties year after year.
Key Takeaway: A Rewarding Cycle Begonias are an investment. Because the tubers can be saved and replanted, you can grow your collection over time and enjoy bigger, more impressive displays each summer.
Conclusion
Planting begonia tubers doesn't have to be a guessing game. By looking for the tell-tale "bowl" shape and ensuring the hollow side faces up, you have already cleared the biggest hurdle in begonia care. Remember that these plants prize drainage and warmth above all else. With a shallow planting depth, a bit of shade, and consistent moisture, you will be rewarded with a stunning display of color that lasts from early summer right through the first frost.
- Identify the hollow side (top) and the rounded side (bottom).
- Start tubers indoors 8-12 weeks before the last frost for early color.
- Plant shallowly, with only 1 inch of soil covering the top.
- Choose a spot with bright, indirect light and well-draining soil.
Our goal at Longfield Gardens is to help you feel confident in every step of your gardening journey. Whether you are filling a single hanging basket or a whole shaded border, tuberous begonias are a fantastic choice for any skill level.
Success with begonias starts with one simple rule: keep the hollow side up and the soil moist but not wet. Once you master the basics of orientation and timing, these plants will do the rest of the work for you.
FAQ
How deep should I plant begonia tubers?
Begonia tubers should be planted shallowly. For a deeper walkthrough, see How Deep Do You Plant Begonias? Aim to have the top of the tuber (the hollow side) covered by about 1/2 inch to 1 inch of potting soil. Planting them too deep can delay sprouting and may lead to rot if the soil stays too wet.
What happens if I plant my begonia bulb upside down?
If planted upside down, the sprouts will have to grow downward and then curl around the tuber to reach the surface. This delays the plant's growth by several weeks and uses up valuable energy. While the plant may eventually emerge, it will be much slower and weaker than a correctly oriented tuber.
Should I soak begonia tubers before planting?
It is generally not necessary to soak begonia tubers. While some gardeners do it to "wake them up," simply placing them in moist (not soggy) potting soil is enough to trigger growth. Soaking for too long can actually increase the risk of fungal issues or rot before the tuber even starts to grow.
Can I grow begonias in full sun?
Tuberous begonias prefer partial shade or filtered light. While they can handle some early morning sun, direct afternoon sun is usually too intense and can scorch their leaves and flowers. If you have a very sunny spot, look for specific varieties bred for sun tolerance, but most will perform best in the shade.