Introduction
Starting begonia tubers is one of the most rewarding spring projects for any gardener. If you are shopping for Begonia Flower Bulbs for Sale, these tropical beauties are famous for their ability to transform shaded corners into a lush, colorful paradise. Whether you are looking for massive "dinnerplate" blooms or trailing flowers that spill over the edges of a hanging basket, getting the planting depth right is the first step toward a spectacular summer show.
We enjoy helping home gardeners at Longfield Gardens find success with these versatile plants, and our All About Begonias guide is a helpful place to start. Begonias are remarkably reliable once they get going, and they offer a long season of color that lasts from midsummer right up until the first frost. Because they are tropical in nature, they appreciate a little extra attention during the planting process to ensure they stay warm and healthy.
This guide is designed to help you understand exactly how to handle your tubers, from identifying which side is the top to determining the perfect planting depth for containers and garden beds. By following a few simple steps, you can look forward to sturdy stems and an abundance of beautiful flowers. Proper planting depth ensures your begonias have the support they need to grow tall and the protection they need to stay hydrated.
The Short Answer: How Deep to Plant
When it comes to planting begonia tubers, the most important rule is to keep them near the surface. In most cases, you should plant begonia tubers about 1/2 inch to 1 inch deep. Unlike spring-flowering bulbs like tulips or daffodils that prefer to be buried several inches down, begonias thrive when they are just barely tucked into the soil. For more growing detail, see Tips for Growing Tuberous Begonias.
The goal of this shallow planting is to protect the tuber from drying out while making it easy for the new sprouts to reach the light. If a tuber is buried too deep, the young stems may struggle to push through the soil, which can lead to delayed blooming or even rot. By keeping them close to the surface, you provide a warm, airy environment that encourages the "eyes" or growth points to wake up and start growing.
Key Takeaway: For both indoor starts and outdoor beds, aim for a planting depth of 1/2 inch to 1 inch. The tuber should be covered by a thin layer of soil to stay moist, but not buried so deep that the sprouts cannot easily find the sun.
Identifying the Top and Bottom of the Tuber
Before you dig your holes, you need to know which way the tuber should face. Begonia tubers have a unique shape that makes them look a bit like a small, hairy brown bowl or a rough-textured potato. One side is indented or cupped (concave), while the other side is rounded or domed (convex). For a closer look, read How to Plant Tuberous Begonias: Which End Is Up?.
The indented, bowl-shaped side is the top. This is where the "eyes" or growth points are located. These eyes will eventually sprout into the stems, leaves, and flowers of your plant. The rounded side is the bottom, where the roots will primarily emerge. Always plant your begonia tubers with the hollow "bowl" facing up toward the sky and the rounded side resting on the soil.
If you ever feel unsure, look closely at the indented side. You may see small, pinkish or white bumps—these are the beginning of the sprouts. Positioning these growth points upward ensures the plant doesn't waste energy trying to grow around the tuber to reach the surface.
Why Planting Depth Matters
Getting the depth right is more than just a tradition; it directly affects the health and vigor of your begonias. Because these plants are native to tropical regions, they are adapted to growing in loose, leaf-filled forest floors where they sit near the top of the soil.
Preventing Rot
Begonia tubers are susceptible to rot if they stay too wet for too long. When a tuber is buried deep in heavy soil, it is surrounded by more moisture and less oxygen. This can cause the tuber to soften and decay before it ever has a chance to sprout. A shallow planting depth allows the top of the tuber to stay relatively dry and well-ventilated.
Supporting Stem Growth
Tuberous begonias often produce large, heavy flowers. If the tuber is planted at the correct depth, the base of the stems will be strong and well-supported by the root system. If the tuber is too shallow (sitting on top of the soil), the plant may become top-heavy and tip over. If it is too deep, the stems may be thin and weak by the time they reach the surface.
Temperature Control
Soil warms up from the top down. By planting your begonias just an inch below the surface, you are placing them in the warmest part of the soil. This heat acts as a signal to the tuber that it is time to break dormancy and start the growing season.
Starting Tubers Indoors for an Early Start
Because begonias are tropical and slow-growing at first, they often take about three months from the time they are planted until they produce their first flowers. To get the most out of the growing season, we recommend starting your tubers indoors about 8 to 12 weeks before the last expected frost in your area. If you want a step-by-step refresher, our How to Start Tuberous Begonias Indoors guide is a great companion.
Step-by-Step Indoor Planting
If you are timing an order, our Shipping Information page explains shipping windows by zone.
- Choose your container: Use a shallow tray with drainage holes or individual small pots.
- Select your soil: Use a high-quality, lightweight potting mix. "Drainage" is a term gardeners use to describe how fast water leaves the soil. A good mix should feel light and fluffy, allowing water to pass through easily while staying damp.
- Position the tubers: Place the tubers on the soil surface about 1 to 2 inches apart with the hollow side facing up.
- Cover lightly: Sprinkle just enough potting mix over the tubers so they are covered by about 1/2 inch of soil.
- Water carefully: Use a spray bottle or a small watering can to moisten the soil. Avoid pouring water directly into the hollow "bowl" of the tuber, as standing water there can cause rot.
What to do next:
- Place your tray in a warm spot (around 70°F).
- Keep the soil moist but never soggy.
- Wait for sprouts to appear, which can take 2 to 4 weeks.
- Once sprouts are visible, move the tray to a bright window or under grow lights.
Planting Directly into the Garden
If you live in a warm climate or prefer to wait and plant directly into your garden beds, timing is everything. Begonias are very sensitive to cold. You should only plant them outside once the soil has warmed to at least 60°F and there is no longer any danger of frost. The Hardiness Zone Map can help you check your zone.
Site Selection
Begonias love shade or partial shade. In the garden, look for a spot that receives dappled sunlight or morning sun with afternoon shade. Harsh, direct afternoon sun can scorch the delicate leaves and wilt the flowers.
Soil Preparation
Before planting, loosen the soil in your garden bed to a depth of about 6 inches. If your soil is heavy clay, we suggest mixing in some compost or peat moss to improve the texture and drainage. This ensures that the water moves away from the tubers quickly, keeping them healthy.
Spacing and Depth
Dig a shallow hole and place the tuber inside, hollow side up. Cover it with about 1 inch of garden soil. Space your tubers about 8 to 12 inches apart to give the plants plenty of room to branch out and allow for good air circulation. Once planted, water the area gently to help settle the soil around the tuber.
Planting Begonias in Containers and Hanging Baskets
Begonias are perhaps most famous for their performance in pots and hanging baskets. Because these containers can be moved to the perfect shady spot on a porch or patio, they are a favorite for many home gardeners. For a step-by-step walkthrough, see How to Plant Begonias in Hanging Baskets.
Choosing the Right Pot
A standard 10-inch or 12-inch pot is perfect for planting three Begonia Upright Double Roseform Pink tubers. If you are using a hanging basket, you can space them a little closer—about 4 to 6 inches apart—to create a full, lush look that spills over the sides. Ensure your container has at least one drainage hole at the bottom.
Depth and Technique
Fill your container with potting mix, leaving about 2 inches of space at the top. Place your tubers on the soil, hollow side up. Add enough potting mix to cover the tubers by 1/2 to 1 inch. This leaves a small "lip" at the top of the pot, which makes it easier to water without the soil washing over the edge. For a clean white-and-pink look, Begonia Upright Double Picotee White is another popular choice.
The Benefits of Containers
One advantage of container planting is that the soil in a pot warms up much faster than the ground. This can lead to faster sprouting and earlier blooms. Additionally, because potting soil is designed to be well-draining, the risk of tuber rot is significantly lower in a container than in the ground. If you are still deciding between a pot or a basket, Can Begonias Be Planted in Pots? offers more container guidance.
Water and Aftercare After Planting
Once your begonias are tucked into the soil at the right depth, the way you water them will determine how well they grow. The "Simple Gardening Rule" for watering begonias is: water deeply, then let the soil dry out slightly before watering again.
Avoiding the "Tuber Bowl"
As mentioned earlier, the top of the begonia tuber has a natural indentation. When the tuber is first planted and hasn't yet grown leaves to cover itself, water can pool in this hollow spot. To keep the tuber healthy, try to water the soil around the tuber rather than directly on top of it. Once the plant has several leaves, they act like an umbrella, naturally shedding water away from the center of the plant.
Soil Moisture
Check the soil daily by sticking your finger about an inch into the surface. If it feels dry, it is time to water. If it still feels damp, wait another day. Begonias in containers, especially those in hanging baskets, will dry out much faster than those in the ground, so they may need more frequent attention during the heat of summer.
Fertilizing for Success
Begonias are heavy feeders because they produce so many flowers over a long period. Once your plants are about 4 to 6 inches tall and have several sets of leaves, you can begin using a balanced, water-soluble fertilizer every two weeks. This provides the nutrients they need to keep those big blooms coming all the way through autumn.
Managing Growth Habits
Different types of begonias have different growth habits, which can slightly change how you think about their placement and care. For a different look, the Non Stop Begonias collection is another shade-garden option.
Upright Begonias
Varieties like "Dinnerplate" or "Double" begonias grow upright on sturdy stems. These are excellent for garden borders or the center of large pots. For more upright selections, browse Upright Double Begonias. Because these stems can get quite heavy with flowers, the 1-inch planting depth is critical for providing a solid foundation. If a plant seems to be leaning as it grows tall, you can gently insert a small bamboo stake into the soil near the tuber and tie the stem to it for support.
Trailing Begonias (Pendula)
Trailing begonias, often called Begonia pendula, are designed to cascade downward. These are the stars of hanging baskets and window boxes. If you want a classic cascading variety, Begonia Hanging Golden Balcony is a strong choice. When planting these, you still follow the 1-inch depth rule, but you might tilt the tuber slightly toward the edge of the pot to encourage the stems to spill over more gracefully.
Key Takeaway: Regardless of the variety, the 1/2 to 1-inch planting depth remains the standard for success. Upright varieties gain stability, and trailing varieties get a healthy start for their cascading stems.
Moving Your Plants Outdoors
If you started your tubers indoors, you must be patient before moving them to their permanent summer home. Begonias are tropical plants and can be damaged by temperatures below 50°F.
Hardening Off
When the weather is consistently warm, you should "harden off" your plants. This means gradually introducing them to the outdoor environment. Start by placing them in a sheltered, shady spot for a few hours each day, then bring them back inside at night. Over the course of a week, increase their time outside until they are ready to stay out full-time.
Final Placement
When you are ready for the final move, ensure the spot matches what the plant needs:
- Shade to partial shade: Very few begonias can handle direct, all-day sun.
- Protection from wind: The stems of begonias are somewhat brittle and can snap in high winds. A protected porch or a spot nestled near other garden plants is ideal.
- Good drainage: Ensure the outdoor soil or the pot is ready to let excess water escape.
Seasonal Care and Expectations
Gardening is a journey, and every season brings different weather. Your begonias will respond to the environment around them. In a very hot summer, they may grow more slowly or require more water. In a mild, humid summer, they will likely thrive and grow quite large.
Deadheading
To keep your plants looking their best, you can "deadhead" the flowers. This simply means pinching off the old, faded blooms. This prevents the plant from spending energy on seed production and encourages it to keep producing new flower buds. It also keeps the foliage looking clean and prevents old petals from rotting on the leaves.
Troubleshooting Growth
If you find that your tubers are taking a long time to sprout, check the temperature. Begonias love warmth. If your house or garden soil is cool, they will simply wait until things warm up. As long as the tuber feels firm and not mushy, it is healthy and just needs a bit more time and warmth to wake up.
Preparing for Winter
In most parts of the United States, begonias are treated as annuals or are "lifted" and stored for the winter. They are only hardy in USDA zones 9–11. For those of us in colder zones, the first light frost will turn the foliage black. This is your signal to dig up the tubers if you wish to save them for next year.
- Lift the tubers: Carefully dig them up, leaving a bit of soil around the roots.
- Dry them out: Place the tubers in a cool, dry, frost-free spot (like a garage or basement) for a few weeks until the stems fall off naturally.
- Clean and store: Shake off the excess soil and store the tubers in a paper bag with some peat moss or vermiculite. Keep them in a cool, dark place (around 45–50°F) until next spring.
At Longfield Gardens, we see many gardeners successfully keep their favorite begonia tubers for many years, and our 100% Quality Guarantee helps give them peace of mind. It is a wonderful feeling to replant a tuber that has grown larger over time, knowing it will provide even more flowers than the year before.
Conclusion
Planting begonia tubers at the correct depth is a simple yet vital step in creating a beautiful shade garden. By keeping your tubers about 1 inch deep with the hollow side facing up, you provide the perfect environment for healthy sprouts and strong stems. Whether you are starting them early indoors or waiting for the warm summer sun, these plants will reward your efforts with a stunning display of color.
Remember these key steps for success:
- Identify the top (indented) and bottom (rounded) of the tuber.
- Plant 1/2 inch to 1 inch deep in well-draining soil.
- Keep the soil moist but avoid standing water in the tuber's "bowl."
- Wait for warm weather before moving plants outdoors.
We invite you to explore the many colors and shapes available to find the perfect match for your home. With a little bit of patience and the right planting technique, you can enjoy these tropical treasures all season long.
"The secret to beautiful begonias starts just an inch below the surface. Give them warmth, a shallow bed, and a little room to grow, and they will transform your garden."
FAQ
Can I plant begonia tubers upside down?
If you accidentally plant a tuber upside down, the stems will usually still find their way to the surface, but it takes much longer and uses up the plant's stored energy. To avoid this, always look for the indented or hollow side of the tuber and make sure it is facing upward toward the sky.
What happens if I plant my begonias too deep?
Planting begonias deeper than 1 or 2 inches can cause the tuber to rot before it sprouts. The extra soil holds too much moisture and prevents oxygen from reaching the tuber. If they do manage to sprout, the stems may be weak and the flowering will likely be delayed because the plant had to work harder to reach the surface.
Do I need to soak begonia tubers before planting?
You do not need to soak begonia tubers. In fact, soaking them can sometimes lead to rot if the water stays trapped in the hollow part of the tuber. It is better to plant them in moist potting mix and allow them to absorb water naturally as they wake up from dormancy.
How far apart should I space my begonia tubers?
In garden beds, space begonias about 8 to 12 inches apart to allow for growth and air circulation. In containers, you can plant them more closely together—about 4 to 6 inches apart—to create a fuller look. Just make sure the pot is large enough to hold the root systems of all the plants. For more spacing advice, see How Far Apart Should Begonias Be Planted?.
