How to Grow Begonias From Tubers for Shady Gardens

Table of Contents

1. Introduction
2. Understanding Tuberous Begonias
3. When to Start Your Begonia Tubers
4. Getting Started: Waking Up the Tubers
5. How to Plant Begonia Tubers Indoors
6. Caring for Begonias During the Indoor Phase
7. Moving Begonias Outdoors: The Hardening Off Process
8. Choosing the Best Outdoor Location
9. Summer Care and Maintenance
10. Specific Begonia Varieties to Try
11. Troubleshooting Common Issues
12. How to Overwinter Begonia Tubers
13. Growing Begonias in Different US Regions
14. Summary of Success
15. FAQ

Introduction

Shade gardens are often celebrated for their soothing greenery, but they can also be home to some of the most spectacular, rose-like blooms in the plant world. Tuberous begonias are the undisputed stars of the summer shade, offering brilliant colors and lush textures that thrive where many other flowers struggle. Whether you are looking to fill a hanging basket with cascading petals or brighten a patio with upright, dinnerplate-sized blossoms, these plants are a rewarding choice for any gardener. For a quick shopping path, see our Hanging Begonias.

At Longfield Gardens, we enjoy helping people transform their outdoor spaces with high-quality bulbs and perennials that perform reliably season after season. Learning to grow begonias from tubers is a cost-effective way to fill your yard with color, and it is a simple process once you understand the basic needs of these tropical beauties. This guide will walk you through everything from starting your tubers indoors to enjoying a full season of vibrant blooms.

Growing tuberous begonias is an achievable and enjoyable project that allows you to witness a remarkable transformation from a rough, brown tuber to a lush, flowering masterpiece.

Understanding Tuberous Begonias

Before you get your hands in the soil, it is helpful to know what makes these plants unique. Tuberous begonias are different from the common wax begonias often found in six-packs at local nurseries. While wax begonias are typically grown as annuals for their foliage and small flowers, tuberous begonias grow from a thick, potato-like underground stem called a tuber.

This tuber acts as a storage unit, holding the energy the plant needs to produce large, showy flowers throughout the summer. These begonias are native to tropical regions, which means they love warmth and humidity but cannot tolerate frost. In most parts of the United States, we treat them as tender perennials—starting them indoors in the spring and bringing the tubers inside to rest during the winter.

There are two primary forms of tuberous begonias you might encounter:

• Upright Begonias: These grow on sturdy stems and are perfect for garden beds, borders, and traditional pots. They produce large, often double flowers that resemble roses or camellias. Browse our Upright Double Begonias for this classic look.
• Trailing or Pendula Begonias: These varieties have a cascading habit, making them the ideal choice for hanging baskets and window boxes where the stems can drape elegantly over the edges.

Key Takeaway: Tuberous begonias offer larger, more dramatic flowers than standard bedding begonias and can be saved from year to year by storing the tubers during the winter.

When to Start Your Begonia Tubers

Timing is one of the most important factors when you grow begonias from tubers. Because they have a relatively long growing cycle, starting them indoors gives you a significant head start on the blooming season. If you wait to plant them directly outside, you might not see flowers until late summer.

The 8-to-12-Week Rule

As a general rule, we recommend starting your begonia tubers indoors about 8 to 12 weeks before the average last frost date in your area. This typically falls in February or March for most gardeners. Starting them early allows the tubers to develop a strong root system and several sets of leaves before they ever face the outdoor elements.

Understanding Your Zone and Weather

While your USDA hardiness zone provides a helpful guideline for when frost typically ends, pay close attention to your local weather forecast. Begonias are tropical plants that thrive when temperatures are consistently warm. They should not go outside until nighttime temperatures are reliably above 60°F. If you start them indoors in March, they will be well-established and ready to bloom shortly after they are moved to their summer home in May or June.

Getting Started: Waking Up the Tubers

When you first receive your tubers from us at Longfield Gardens, they will likely be dormant. They look like small, brown, slightly fuzzy discs or bowls. Before planting, it is helpful to "wake them up" by bringing them into a warm environment. For a broader overview, see All About Begonias.

Place your tubers in a bright room with indirect light. A temperature of around 70°F is perfect. You do not need to do anything else at this stage; simply giving them a bit of warmth for a week or two can encourage the first tiny pink or green "eyes" (buds) to appear in the hollow center of the tuber. Once you see these signs of life, you are ready to plant.

How to Plant Begonia Tubers Indoors

Starting begonias indoors is a straightforward process. You can plant them in individual small pots or together in a shallow tray. The goal is to provide a cozy environment where they can sprout without being overwhelmed by too much wet soil. For a step-by-step primer, see How to Start Tuberous Begonias Indoors.

Step 1: Choose the Right Container and Soil

Use a container with plenty of drainage holes at the bottom. A light, well-draining potting mix is essential. Avoid using heavy garden soil, which can pack down too tightly and hold too much water. A mix specifically designed for containers or a blend of peat moss and perlite works beautifully.

Step 2: Identify the "Top" of the Tuber

This is the most common question beginners have: which side is up? Begonia tubers have a distinct shape. One side is rounded, and the other side has a depression or a hollow, bowl-like shape.

• The hollow side faces UP. This is where the stems and leaves will emerge.
• The rounded side faces DOWN. This is where the roots will grow.

If you cannot tell which side is which, look for tiny pink buds or the remnants of last year’s stems. If you are still unsure, you can plant the tuber on its side, and the plant will naturally figure out which way to grow.

Step 3: Planting Depth and Spacing

Fill your container with 2 to 3 inches of moistened potting mix. Place the tuber on the surface with the hollow side up. You have two options for covering them:

1. Partial Covering: Some gardeners prefer to leave the very top of the tuber exposed until the sprouts are an inch tall.
2. Full Covering: We recommend covering the tuber with about 1 inch of soil. This encourages roots to grow from the top and sides of the tuber, resulting in a more stable and vigorous plant. For more detail, see How Deep to Plant Tuberous Begonias for Best Blooms.

Step 4: Initial Watering

Water the soil gently after planting to settle it around the tuber. Be careful not to pour water directly into the hollow "bowl" of the tuber, as standing water in that depression can cause rot. Instead, water the soil around the edges.

What to do next:

• Find a warm spot (70°F) with indirect light.
• Check the soil every few days; keep it moist like a wrung-out sponge, but never soggy.
• Wait patiently—it can take 3 to 6 weeks for the first green leaves to break through the soil.

Caring for Begonias During the Indoor Phase

As your begonias begin to grow, they will need a bit more attention to ensure they become strong, sturdy plants rather than tall and "leggy."

Light Requirements

Once the first leaves appear, move the pots to a very bright window or place them under grow lights. While begonias love shade outdoors, they need plenty of indirect light indoors to grow compact stems. If they aren't getting enough light, the stems will stretch toward the window and become weak.

Humidity and Airflow

Begonias love humidity. If your home is very dry in the late winter, you can loosely cover the pots with a clear plastic bag to create a mini-greenhouse effect. Just be sure to leave a small opening for air to circulate. Good airflow is important to prevent any fungal issues on the young leaves. For more growing advice, read Tips for Growing Tuberous Begonias.

When to Repot

If you started your tubers in small 3-inch pots or a communal tray, you will eventually need to move them to their permanent summer containers. You can do this once the plants have two or three sets of true leaves.

• Use a 6-inch pot for one tuber.
• Use an 8- to 10-inch pot for two tubers.
• Use a 12-inch or larger pot (or a standard hanging basket) for three tubers.

Moving Begonias Outdoors: The Hardening Off Process

Moving a plant from a climate-controlled home to the great outdoors is a big transition. To ensure your begonias stay healthy, you must "harden them off" gradually. This process acclimates the tender leaves to wind, fluctuating temperatures, and brighter light.

1. Start on a warm, calm day: Place your pots in a fully shaded, protected spot for just 2 to 3 hours, then bring them back inside.
2. Increase time daily: Over the next 7 to 10 days, gradually increase the amount of time they spend outside.
3. Monitor the temperature: If a late spring cold snap is predicted, keep them indoors. Do not leave them out overnight until you are certain the temperature will stay above 60°F.
4. Final Planting: Once they are hardened off and the soil is warm, you can move them to their final spot in the garden or leave them in their decorative patio pots.

Choosing the Best Outdoor Location

To grow begonias from tubers successfully, you must match the plant to the right environment. Begonias are the queens of the shade, but "shade" can mean different things.

Sun and Shade Balance

The ideal location for most tuberous begonias is a spot that receives dappled sunlight or morning sun followed by afternoon shade. The hot, intense midday sun in the US can scorch their succulent leaves and cause the flowers to wilt.

• In cooler climates: They can handle a bit more morning sun.
• In hot, humid climates: Deep shade or filtered light during the heat of the day is essential.

Protection from the Elements

Because tuberous begonias have thick, water-filled stems and heavy flowers, they can be somewhat brittle. Choose a location that is sheltered from strong winds, which can snap the stems. If you are growing tall, upright varieties in a garden bed, you might find it helpful to provide a small bamboo stake for support as the plants reach their full height.

Soil and Drainage

Whether in the ground or a container, drainage is the most critical factor for soil. Begonia tubers will rot if they sit in waterlogged earth. If your garden has heavy clay soil, we recommend growing your begonias in raised beds or containers where you can control the drainage.

Summer Care and Maintenance

Once your begonias are established outdoors, they are relatively low-maintenance. Following a few simple rules will keep them blooming beautifully from mid-summer until the first frost.

Watering Correctly

Begonias prefer "consistent moisture." This means the soil should stay damp, but you should allow the top inch of soil to dry out slightly before watering again.

• Check daily: Containers and hanging baskets dry out much faster than garden beds, especially in the summer heat.
• Water at the base: Try to keep the foliage and flowers dry by watering at the soil level. This helps prevent powdery mildew and other fungal spots on the leaves.

Feeding for Better Blooms

Begonias are "heavy feeders," meaning they need a steady supply of nutrients to produce those massive flowers. Use a balanced, water-soluble fertilizer every two weeks during the growing season. A standard 10-10-10 or 20-20-20 formula works well. Once the plants start blooming heavily, some gardeners switch to a fertilizer higher in phosphorus to encourage even more flower production.

Deadheading and Grooming

To keep your plants looking their best, remove any wilted flowers or yellowing leaves. This practice, called deadheading, prevents the plant from putting energy into seed production and instead encourages it to keep producing new buds. It also keeps the plant tidy and reduces the risk of mold or disease.

Key Takeaway: Consistent moisture, regular feeding, and protection from the midday sun are the three pillars of summer begonia care.

Specific Begonia Varieties to Try

We offer a wide range of begonias at Longfield Gardens, each with its own personality. Here are a few popular types to consider for your garden:

• Scentiment Begonias: These are a rare treat in the begonia world because they offer a lovely, delicate fragrance. Most begonias are grown only for their looks, but these provide a wonderful scent for a porch or entryway.
• Begonia Hanging Golden Balcony: These varieties are bred to have flexible stems that drape downward. They are loaded with medium-sized flowers that create a "waterfall" effect.
• Begonia Upright Double Roseform Pink: These are the classic upright types with layers upon layers of petals. They come in vibrant primary colors like scarlet, yellow, and orange, as well as soft pastels.
• Types of Begonias: These unique flowers have fringed edges that look like carnations, adding a different texture to your shade containers.

Troubleshooting Common Issues

While begonias are generally easy to grow, you might encounter a few minor hurdles. Most issues are related to water or light and are easy to fix.

Why Are the Buds Dropping?

If your begonia is producing buds but they fall off before opening, it is usually a sign of stress. The most common causes are:

1. Extreme Heat: If temperatures soar above 85-90°F, the plant may drop buds to conserve energy. Move containers to a cooler, shadier spot.
2. Uneven Watering: If the soil goes from bone-dry to soaking wet, the plant can get "shocked." Try to keep the moisture levels more consistent.

Leggy Stems

If your plants look tall, thin, and sparse, they are likely searching for more light. Move them to a spot that gets more bright, indirect light or dappled sun. You can also "pinch back" the growing tips early in the season to encourage the plant to branch out and become bushier.

Powdery Mildew

This looks like a dusting of white flour on the leaves. It usually happens when there is high humidity and poor airflow. To fix it:

• Ensure your plants have enough space between them for air to move.
• Avoid watering the leaves late in the evening.
• Remove any heavily affected leaves to stop the spread.

How to Overwinter Begonia Tubers

One of the best things about tuberous begonias is that they can live for many years. Since they are not hardy in cold climates, you will need to bring them indoors for the winter. This process is called "overwintering."

Step 1: Let the Plant Go Dormant

In late summer (late August or September), stop fertilizing your begonias. As the weather cools, you can reduce watering. The leaves will eventually start to turn yellow. You can dig the tubers after the first light frost, which will blacken the foliage but won't hurt the tuber underground.

Step 2: Dig and Cure

Carefully lift the tubers from the ground or pot with a garden fork or trowel. Cut the stems back to about 1 inch above the tuber. Don't worry about cleaning them perfectly yet.

Place the tubers in a warm, dry, indoor spot (like a garage or basement) for about two weeks. This is called "curing." During this time, the remaining stem will dry up and eventually fall off easily, and the outer "skin" of the tuber will toughen up.

Step 3: Cleaning and Storage

Once cured, gently brush off any excess soil. Do not wash them with water, as moisture can lead to rot during storage.

• Place the tubers in a cardboard box or a paper bag.
• Cover them with dry peat moss, sawdust, or vermiculite. This keeps them from drying out completely while still allowing them to "breathe."
• Store the box in a cool, dark, dry place that stays between 40°F and 50°F. A cool basement or an insulated crawl space is often ideal.

Step 4: Monthly Check-ins

Check your tubers once a month during the winter. If any feel soft or look moldy, remove them immediately so they don't infect the others. If they look extremely shriveled, you can give the storage medium a very light mist of water, but be careful not to overdo it.

Growing Begonias in Different US Regions

Because the US has such varied climates, your approach to growing begonias might change slightly depending on where you live.

• The Pacific Northwest: This is begonia heaven. The cool, humid summers and mild temperatures allow begonias to thrive with very little effort. You may even be able to provide them with more sun than in other regions.
• The South and Southeast: High heat and humidity are the biggest challenges. Focus on providing deep shade during the afternoon and ensure your potting mix is very well-draining to handle heavy summer rains.
• The Midwest and Northeast: Your main focus will be the timing of the seasons. Starting tubers indoors is essential to get a good bloom season before the autumn frost arrives.
• The Southwest: Low humidity can be tough on begonias. You may need to mist the area around your plants or use a pebble tray to increase local humidity, and they must be kept out of the intense desert sun.

Summary of Success

Growing begonias from tubers is a journey that begins in the late winter and rewards you with months of spectacular color. By getting the basics right—timing, planting depth, and water management—you can enjoy these tropical treasures regardless of your experience level.

What to do next:

• Order your favorite Begonia Upright Double Superba Mix from us at Longfield Gardens in late winter.
• Prepare your indoor starting area with fresh potting mix and clean containers.
• Plan your shade garden layout with our Summer Flowers for Shade.

We stand behind the quality of our tubers with a 100% guarantee. When your order arrives from our facility in New Jersey, you can be confident that you are starting with healthy, true-to-variety tubers that are ready to perform. Gardening is a rewarding way to connect with nature, and there is nothing quite like the satisfaction of seeing your first begonia bloom open in the shade.

FAQ

Which side of the begonia tuber should face up when planting?

The hollow or indented side of the tuber should always face up. This is the top of the tuber where the new stems and leaves will emerge. The rounded side, which often has small root remnants, should face down into the soil.

How long does it take for begonia tubers to sprout?

Begonia tubers are notoriously slow starters and can take anywhere from 3 to 6 weeks to show signs of growth. Maintaining a consistent temperature of around 70°F and keeping the soil lightly moist (but not wet) will help speed up the process.

Can I grow tuberous begonias in full sun?

Most tuberous begonias prefer partial shade to full shade. While they can handle some gentle morning sun, the intense afternoon sun in most parts of the US will scorch their leaves and cause the flowers to drop. If you have a very sunny yard, look for varieties specifically bred for sun tolerance, or keep them in the shade of a porch or large tree.

Why are my begonia tubers rotting in the pots?

Rot is almost always caused by too much water or poor drainage. Ensure your pots have drainage holes and that you are using a light potting mix. When watering, avoid pouring water directly into the hollow center of the tuber, as standing water there can quickly lead to decay. Wait until the top inch of soil feels dry before watering again.