Table of Contents
- Introduction
- Choosing the Right Tuberous Begonias
- Timing Your Planting
- How to Start Begonia Tubers Indoors
- Selecting the Best Outdoor Location
- Planting Begonia Tubers in the Garden
- Summer Care and Maintenance
- Handling Common Challenges
- Overwintering Your Begonia Tubers
- Conclusion
- FAQ
Introduction
Finding the perfect plant for a shady corner is one of the most rewarding parts of gardening. While many shade-loving plants focus primarily on foliage, tuberous begonias offer something truly special: huge, rose-like blooms in a dazzling array of colors. These tropical beauties can transform a quiet patio or a dim garden bed into a vibrant sanctuary. At Longfield Gardens, we believe that everyone should experience the joy of watching these spectacular flowers unfold throughout the summer.
Growing begonias from tubers is an accessible project for gardeners of all experience levels. Because the tubers act as a built-in energy source, the plants are remarkably resilient once they get started. This guide will walk you through the entire process, from selecting the right varieties and starting them indoors to keeping them healthy all summer long. By focusing on a few simple steps, you can enjoy professional-quality results in your own backyard. For a deeper look at plant basics, see our All About Begonias guide.
Whether you want to fill hanging baskets with cascading flowers or edge a walkway with upright blooms, tuberous begonias are the answer. We will cover how to time your planting, how to care for them during the heat of summer, and how to save your tubers for next year. If you’re building a broader shade display, our Summer Bulbs for Shady Gardens article can help you plan companion plantings.
Choosing the Right Tuberous Begonias
Before you get your hands in the soil, it helps to understand the different types of tuberous begonias available. Not all begonias grow from tubers, so making sure you have the right type is the first step toward success. Tuberous begonias are prized for their large, ornate flowers and their ability to thrive in low-light conditions where other flowering plants might struggle. If you want to shop a ready-made option, the Begonia Non Stop Mix is a great place to start.
Upright Begonias
Upright varieties are the traditional choice for garden beds and borders. These plants grow on sturdy stems that reach about 12 to 18 inches in height. They produce large, often double blooms that look like roses or camellias. Because the flowers can become quite heavy, these begonias are excellent for window boxes or large patio containers where they can be enjoyed at eye level. Some popular types include the "Non-Stop" series, which is known for its ability to produce a steady stream of flowers all season long.
Cascading or Hanging Basket Begonias
If you want flowers that spill over the edges of a container, look for cascading varieties, often called Pendula begonias. These plants have a more relaxed growth habit. Their stems naturally arch downward, making them the perfect choice for hanging baskets or elevated planters. The flowers on cascading types are often slightly smaller than upright varieties, but they make up for it in sheer volume. A single basket can produce hundreds of blooms that create a waterfall of color.
Specialty Flower Forms
You can also choose begonias based on the specific shape of their petals. Fimbriata begonias have fringed edges that give the flowers a ruffled, carnation-like appearance. Picotee varieties feature petals with a contrasting color on the edges, adding a sophisticated look to your shade garden. For step-by-step care, Longfield Gardens’ Tips for Growing Tuberous Begonias article is a helpful reference.
Key Takeaway: Choose upright varieties for beds and window boxes, and cascading varieties for hanging baskets and tall planters.
Timing Your Planting
Tuberous begonias are tropical plants by nature. They love warmth and humidity, but they have zero tolerance for frost. Getting the timing right is more important than any special fertilizer or "trick" you might find online. If you plant them too early, the cold soil can cause the tubers to sit dormant or even rot. If you plant them too late, you miss out on weeks of beautiful blooms.
Starting Indoors for an Early Show
Most gardeners prefer to start their begonia tubers indoors about 6 to 8 weeks before the last expected frost in their area. Because begonias can be slow to "wake up" from their winter slumber, this head start is very beneficial. It allows the plant to develop a strong root system and several inches of leafy growth before it ever touches the outdoor soil. By the time the weather is warm enough for them to go outside, they are often already forming their first flower buds.
Moving Outdoors Safely
The biggest mistake a gardener can make with begonias is moving them outside too soon. Even if the days are warm, cool nights can stress the plants. Wait until the nighttime temperatures stay consistently above 60°F. If you live in a northern climate, this might not happen until late May or early June. For regional guidance, check the Hardiness Zone Map. Begonias grow very quickly once the weather warms up, so waiting for the right temperature is always worth the delay.
How to Start Begonia Tubers Indoors
Starting your tubers indoors is a simple process that requires just a few supplies. You will need some shallow pots or trays, a high-quality potting mix, and a warm, bright spot in your home.
Inspecting Your Tubers
When your tubers arrive, take a moment to look them over. A healthy tuber will feel firm and heavy for its size. You will notice that one side of the tuber is indented or "hollowed out" like a small bowl. This is the top. The other side is rounded or "domed." The top side is where the new growth will emerge, while the rounded side is where the roots will grow.
The Planting Process
- Prepare the Soil: Use a light, well-draining potting mix. Begonias do not like heavy soil that stays too wet.
- Position the Tuber: Place the tuber in the soil with the hollow side facing up.
- Depth is Key: Do not bury the tuber deeply. It should be just barely covered with soil, or the top edge can even stay slightly exposed. Planting too deep can lead to rot before the sprouts reach the surface.
- Add Moisture: Water the soil lightly after planting. The goal is to make it feel like a wrung-out sponge, not a muddy puddle.
- Provide Warmth: Place the pots in a warm spot, ideally around 70°F. You don’t need bright light until you see the first green sprouts, but warmth is essential to wake the tuber up.
Caring for Sprouts
Once you see small pink or green "eyes" emerging from the hollow of the tuber, move the pots to a bright window with indirect sunlight. Avoid placing them in a window that gets hot, direct afternoon sun, as this can scorch the tender new leaves. As the stems grow, you will see the root system fill the pot. If you started them in a very small tray, you might need to move them into a slightly larger pot (about 5 or 6 inches wide) once they have two or three sets of leaves.
What to do next:
- Identify the hollow side of the tuber.
- Plant in well-draining mix with the top just barely covered.
- Keep the soil damp but never soggy.
- Move to indirect light once sprouts appear.
Selecting the Best Outdoor Location
Right plant, right place is the most important rule in gardening. For tuberous begonias, this means finding a spot that mimics their natural forest-floor environment.
Light Requirements
Begonias are famous for their shade tolerance, but they still need light to produce flowers. The ideal location provides "filtered" or "dappled" sunlight. This is the kind of light you find under a leafy tree or beneath a porch overhang.
Direct morning sun is usually fine because it is cool. However, direct afternoon sun in the heat of the day can be too intense. If the leaves of your begonia start to look brown and crispy on the edges, they are likely getting too much sun. If the plant looks "leggy" with long stems and very few flowers, it may be too dark.
Soil and Drainage
Drainage simply refers to how fast water leaves the soil. Begonias have a very sensitive root system that will rot if it sits in water for too long. If you are planting in the ground, make sure the soil is rich in organic matter. You can improve heavy clay soil by mixing in some compost or finely ground bark.
For container gardening, always use a pot with drainage holes. If you have a decorative pot that doesn't have holes, keep the begonia in a plain plastic nursery pot and set that inside the decorative one. This allows you to lift the plant out to drain any excess water after a heavy rain.
Air Circulation
Begonias love humidity, but they also need fresh air. If you crowd too many plants together in a corner with no breeze, they can develop powdery mildew, which looks like a dusting of white flour on the leaves. Give each plant about 10 to 12 inches of space to ensure air can move freely around the foliage.
Planting Begonia Tubers in the Garden
Once the threat of frost has passed and your indoor starts are ready, it is time to move them to their summer home. Whether you are transplanting a started plant or planting a dormant tuber directly into the ground, the process is very similar.
Transplanting Started Plants
If you started your tubers indoors, they will need a few days to get used to the outside air. This is called "hardening off." Set your pots outside in a shady, protected spot for a few hours a day, gradually increasing the time over a week. This prevents the leaves from going into shock when they are permanently moved.
When you are ready to plant, dig a hole that is slightly larger than the root ball. Set the plant in the hole so the top of the root ball is level with the surrounding soil. Firm the soil gently with your hands and water the area well.
Planting Dormant Tubers Outdoors
In warmer climates (Zones 9-11), you can plant dormant tubers directly into the garden once the soil is warm. Loosen the soil to a depth of about 6 inches. Place the tuber hollow-side up and cover it with no more than one inch of soil. Space the tubers 8 to 12 inches apart to allow room for the mature foliage.
Key Takeaway: Always wait for warm soil and nights before planting outdoors, and ensure your site has excellent drainage.
Summer Care and Maintenance
Tuberous begonias are relatively low-maintenance, but a little bit of regular attention will keep them looking their best from July until the first frost.
Watering Correctly
Watering is the most frequent task, but it shouldn't be a chore. The rule for begonias is "deep, then dry." Instead of giving them a little bit of water every day, give them a thorough soaking until water runs out of the bottom of the pot. Then, wait until the top inch of soil feels dry to the touch before watering again.
Avoid watering the leaves directly. Wet foliage, especially in the evening, can encourage fungal issues. Aim your watering can or hose at the base of the plant near the soil. If you have begonias in hanging baskets, remember that they dry out much faster than plants in the ground because they are exposed to the wind on all sides.
Feeding Your Plants
Because begonias bloom so prolifically, they are "hungry" plants. They need nutrients to keep producing those large flowers. Start fertilizing about a month after you see active growth.
A balanced, water-soluble fertilizer works well. Many gardeners find success using a fertilizer high in potassium (often sold as "tomato food" or "bloom booster") once the flower buds appear. Apply the fertilizer at half the strength recommended on the label every two weeks. This steady, gentle supply of nutrients is better than one heavy dose that might burn the roots.
Grooming and Deadheading
Begonias are mostly self-cleaning, meaning they will drop their old flowers on their own. However, picking up those dropped flowers from the soil or the leaves is a good habit. Rotting flower petals left on the foliage can cause spots or mold.
If your upright begonias become too tall and start to lean, you can use a small bamboo stake to support the main stem. For cascading types, you can "pinch" the tips of the stems early in the season to encourage the plant to grow more side branches, which leads to a fuller look.
Handling Common Challenges
While growing begonias is usually a smooth process, you might run into a few common issues. Most of these are easily fixed by adjusting your care routine.
Flower Drop
If your begonia is dropping its flower buds before they even open, it is usually a sign of stress. The most common cause is the soil becoming too dry. If the plant feels it doesn't have enough water to support a bloom, it will shed the bud to save energy. High heat (consistently above 85°F) can also cause bud drop. Moving a container to a cooler, more shaded spot during a heatwave can help.
Powdery Mildew
If you see white, chalky spots on the leaves, you are likely dealing with powdery mildew. This is common in late summer when the air is humid and still. To prevent this, lead with the correct approach: ensure your plants have plenty of space for air circulation and always water at the soil level rather than over the leaves. If it appears, you can find simple organic sprays at your local garden center, but improving airflow is the best long-term fix.
Yellow Leaves
Yellow leaves can be a sign of two opposite things: overwatering or a lack of nutrients. Check the soil first. If the soil is soaking wet and the leaves are yellowing, let it dry out completely. If the soil is fine but the plant looks pale and yellow, it might be time for a dose of fertilizer.
Overwintering Your Begonia Tubers
In most of the United States, tuberous begonias are treated as annuals because they cannot survive the winter. However, the tubers can be saved and replanted year after year. This is a wonderful way to grow your garden without having to buy new plants every spring.
When to Dig Them Up
As the summer ends and the nights get cool, your begonias will naturally start to slow down. The leaves may turn yellow, and the plant will stop producing new flowers. This is the plant's way of getting ready for dormancy.
You should lift the tubers before the first hard frost. A light frost that nips the leaves is usually fine and serves as a signal to the plant to move its energy down into the tuber. Once the foliage has died back, cut the stems off about an inch above the tuber.
Curing and Storage
- Dry Them Out: Lift the tubers gently from the soil. Let them sit in a dry, shaded spot (like a garage or porch) for a few days until the remaining soil dries and can be brushed away.
- Pack Them Up: Store the tubers in a breathable container. A cardboard box or a paper bag filled with peat moss, sawdust, or vermiculite is ideal. This keeps them dry but prevents them from shriveling up completely.
- Choose a Cool Spot: Keep the box in a cool, dark, frost-free place. A basement or a cool closet that stays between 40°F and 50°F is perfect.
- Check Periodically: Once a month, take a quick peek at your tubers. If any feel soft or mushy, remove them so they don't affect the others.
By following this simple storage routine, you can keep your favorite begonia varieties for many years. Some gardeners have begonia tubers that have grown to the size of a dinner plate over several decades! If you want shipping details before you order, see Longfield Gardens’ Shipping Information page.
What to do next:
- Wait for the foliage to yellow in the fall.
- Lift tubers before a hard freeze.
- Cure in a dry spot for several days.
- Store in peat moss in a cool, dark room.
Conclusion
Growing begonia tubers is a rewarding way to bring elegance and vibrant color to the shaded parts of your landscape. By starting your tubers indoors, choosing a site with excellent drainage, and providing consistent moisture and food, you can create a professional-looking display with very little stress. Gardening should be an enjoyable journey, and the bold blooms of the begonia are a magnificent reward for your efforts.
- Start tubers indoors 6–8 weeks before the last frost.
- Plant in filtered light with the hollow side of the tuber facing up.
- Water deeply when the top of the soil feels dry.
- Lift and store tubers in a cool, dry place for the winter.
At Longfield Gardens, we are here to help you succeed with high-quality tubers and practical advice. The next step is to choose your favorite colors and get ready for a summer filled with beautiful blooms. We stand behind our plants and look forward to hearing about your garden's success!
"The secret to a beautiful shade garden isn't about working harder; it's about choosing the right plants and giving them the simple care they need to thrive."
FAQ
Which side of the begonia tuber faces up when planting?
The tuber has a hollowed-out or indented side and a rounded side. The hollowed-out side should always face up, as this is where the stems and leaves will emerge. The rounded side should be placed against the soil so the roots can grow downward.
Why are the flower buds falling off my begonias?
Bud drop is usually caused by environmental stress, most often dry soil or extreme heat. To help your plant, ensure you are watering deeply whenever the top inch of soil feels dry and move containers to a cooler, shadier spot if temperatures rise above 85°F.
Do I need to remove the dead flowers from my begonias?
Tuberous begonias are generally "self-cleaning" and will drop their old flowers on their own. However, it is a good idea to pick up the fallen petals from the leaves and soil surface. This helps prevent fungal issues and keeps the plant looking tidy.
Can I grow tuberous begonias in full sun?
In most climates, tuberous begonias prefer partial shade or filtered sunlight. While they can handle cool morning sun, the intense heat of the afternoon sun can scorch their leaves and wilt the flowers. If you live in a very cool northern climate, they may tolerate more sun, but filtered light is always the safest choice.