When Can Begonias Be Planted Outside

Table of Contents

1. Introduction
2. The Best Time for Planting Begonias Outside
3. Understanding Your USDA Hardiness Zone
4. Starting Begonias Indoors for an Earlier Start
5. Selecting the Right Location
6. Planting Steps for Success
7. Popular Begonia Varieties for Your Garden
8. Caring for Begonias Through the Season
9. Preparing for the End of the Season
10. Conclusion
11. FAQ

Introduction

There is nothing quite like the sight of a begonia in full bloom to signal that summer has truly arrived. These versatile plants are beloved for their ability to transform shaded corners into vibrant displays of color, whether they are cascading in hanging begonias or lining a garden path. At Longfield Gardens, we enjoy helping gardeners find the perfect varieties to match their style, from the massive, rose-like blooms of tuberous begonias to the striking, patterned foliage of Rex varieties.

This guide is designed for home gardeners who want to know exactly when to move these tropical beauties into the landscape. We will cover the specific temperature triggers to watch for, how to transition plants from indoors to outdoors, and how to ensure your soil is ready for planting. Understanding the timing of your local climate is the most important step in growing healthy, vigorous begonias.

By focusing on soil temperature and frost dates, you can ensure your begonias thrive from the moment they touch the ground until the first hint of autumn.

The Best Time for Planting Begonias Outside

Begonias are tropical and semi-tropical plants, which means they have no tolerance for frost or cold soil. If you plant them too early, the cool air can stunt their growth or cause the stems to become brittle. For the best results, you should wait until the danger of frost has completely passed in your area.

In most parts of the United States, this window opens in late spring or early summer. A good rule of thumb is to wait until your local lilacs have finished blooming or when you are comfortably wearing short sleeves in the evening. While the calendar date is a helpful guide, the biological cues of the plants and the actual temperature of the soil are much more reliable indicators.

Monitoring Nighttime Temperatures

Nighttime temperatures are often more important than daytime highs when deciding when to plant. Begonias prefer nights that stay consistently above 50°F, though 60°F is even better for most varieties. If the nights are still dipping into the 40s, it is best to keep your plants in a protected area like a garage or a bright windowsill.

When temperatures stay warm throughout the night, the plant can continue to process nutrients and grow without the "shock" of a sudden cold snap. This consistency leads to faster leaf development and earlier flowering. If you are ever in doubt, waiting an extra week is always safer than rushing the season.

Checking Soil Temperatures

The temperature of the soil is just as critical as the air temperature. Begonias grow from tubers or fibrous roots that need warmth to activate. If the soil is cold and wet, the roots may struggle to establish or, in some cases, remain dormant for much longer than expected.

A soil temperature of 60°F is the ideal target for planting begonias. You can check this easily with a basic soil thermometer inserted about four inches deep. If you do not have a thermometer, a simple test is to touch the soil with your bare hand; if it feels uncomfortably cold, it is too early for begonias. Warm soil ensures that the roots can begin absorbing water and nutrients immediately, giving the plant a strong start.

Key Takeaway: The ideal window for planting begonias outside is when all danger of frost has passed, nighttime temperatures stay above 50°F, and the soil has warmed to at least 60°F.

Understanding Your USDA Hardiness Zone

Knowing your Hardiness Zone Map helps you understand the general timeline for your region. At Longfield Gardens, we use these zones to help determine the best time to ship plants so they arrive right when it is nearly time to plant.

• Zones 9-11: In these warm, frost-free regions, begonias can often be grown as perennials. You can plant them much earlier in the spring, as soon as the soil is warm.
• Zones 3-8: In these cooler climates, begonias are typically grown as annuals. They must be planted after the spring frost and often need to be lifted and stored indoors before the first autumn freeze.

Because weather varies every year, your specific frost date is a "best guess" based on historical data. Always check your local 10-day forecast before heading out to the garden. If a surprise late frost is predicted, be prepared to cover outdoor plantings with a light cloth or bring containers back inside temporarily.

Starting Begonias Indoors for an Earlier Start

One of the best ways to enjoy blooms sooner is to start your begonia tubers indoors before the weather warms up. For a closer look at tuber orientation, see How to Plant Tuberous Begonias: Which End Is Up?. This gives the plants a head start, so they are already leafy and robust by the time they are ready to go outside.

When to Start Tubers Indoors

You should ideally start your begonia tubers about 8 to 12 weeks before your average last frost date. For many gardeners in the northern half of the country, this means starting them in late February or March. This timing allows the tubers to sprout and develop a healthy root system in a controlled environment.

By the time the outdoor soil reaches that magic 60°F mark, your indoor plants might already be showing their first flower buds. This "jump start" can result in a blooming season that lasts weeks longer than if you had planted the tubers directly in the ground.

How to Wake Up Tubers

To start them indoors, use a shallow tray or individual small pots with drainage holes. Fill them with a high-quality, moist potting mix. Place the tubers with the indented (hollow) side facing up. Do not bury them deeply; just tuck them into the soil so the tops are barely covered or even slightly exposed. For more step-by-step growing advice, see Tips for Growing Tuberous Begonias.

Place the containers in a warm spot with indirect light. A room temperature of 70°F is perfect for encouraging growth. Avoid overwatering at this stage; keep the soil lightly moist, like a wrung-out sponge, but never soggy. You should see small pink or green sprouts appearing within a few weeks.

Moving Started Plants to the Garden

Once your indoor plants are established and the outdoor weather is warm enough, they are ready to be moved. However, you cannot move them directly from a cozy indoor room to the garden all at once. They need a transition period known as "hardening off." For container-specific planting advice, see How to Plant Tuberous Begonias in Containers.

1. Start by placing the pots in a shaded, protected spot outside for 2-3 hours during the day.
2. Bring them back inside for the night.
3. Gradually increase their time outdoors over 7 to 10 days.
4. Slowly introduce them to the level of light they will receive in their permanent garden home.

Action Plan for Starting Indoors:

• Check your local frost date and count back 8–12 weeks.
• Plant tubers hollow-side up in moist potting mix.
• Keep in a warm, bright room (around 70°F).
• Hardening off is required before final outdoor planting.

Selecting the Right Location

When the time is right to plant, choosing the correct spot is just as important as the date. Begonias are famous for their love of shade, but "shade" can mean many things. Getting the light and soil right will ensure your plants bloom continuously until the first frost.

Light Requirements

Most begonias prefer filtered light or partial shade. This mimics their native environment under the canopy of tropical trees. In the garden, this translates to spots under tall trees, on the north side of a house, or tucked into a porch or patio.

• Morning Sun: Many varieties enjoy a few hours of gentle morning sun, but the harsh rays of the mid-afternoon can scorch their succulent leaves.
• Deep Shade: While begonias tolerate shade better than most flowers, "deep shade" (where no sunlight ever reaches) may lead to fewer flowers and leggy stems. Aim for a spot with bright, indirect light.
• Darker Foliage: Generally, begonias with darker or bronze-colored leaves can handle a bit more sun than those with bright green leaves. For more on the exceptions, see Can You Plant Begonias in Full Sun?.

Soil and Drainage

Begonias have fleshy stems and roots that store water. This makes them somewhat drought-tolerant, but it also means they are very sensitive to "wet feet." If the soil stays saturated, the roots cannot breathe, which can lead to health issues for the plant.

The best soil for begonias is rich in organic matter and very well-draining. "Drainage" simply means how fast water leaves the soil after a rain or watering. If you have heavy clay soil that stays muddy, consider planting in raised beds or containers. Adding compost or finely ground bark to your garden soil can also help improve its texture and drainage.

Wind Protection

Because begonia stems are often thick and full of water, they can be somewhat brittle. Tall upright varieties or heavy cascading types can be damaged by strong, gusty winds. When choosing a location, look for a spot that is sheltered by a fence, a hedge, or the wall of your home. This protection helps keep the foliage looking pristine and prevents stems from snapping under the weight of their own blooms.

Planting Steps for Success

Once the weather is warm and you have picked the perfect spot, it is time to get your begonias into the ground or into their summer containers. Following a few simple steps during planting will help the plants settle in quickly.

Spacing and Depth

Getting the depth and spacing right is one of the "quiet winners" of successful gardening. It allows for plenty of air circulation and gives each plant enough room to reach its full size. For more detail on placement, see How Deep to Plant Tuberous Begonias for Best Blooms.

• Planting Depth: If you are planting tubers directly, cover them with about one inch of soil. If you are transplanting a begonia already growing in a pot, plant it so the top of the root ball is level with the surrounding soil surface.
• Spacing: Most wax begonias and smaller varieties should be spaced about 6 to 8 inches apart. Larger tuberous varieties or Rex begonias usually need 10 to 12 inches of space to spread out.
• Containers: In pots, you can plant them a bit closer together for a full, lush look, but ensure the pot is large enough to hold the moisture they will need as they grow.

Watering After Planting

After you set your plants in their new home, give them a good soak to settle the soil around the roots. This eliminates air pockets and helps the plant establish a connection with the garden soil.

After that initial watering, let the top inch of soil dry out before watering again. For the rest of the season, the goal is to keep the soil consistently moist but never waterlogged. Using a watering can to apply water directly to the soil rather than over the leaves can help keep the foliage healthy and clean.

Quick Checklist for Planting Day:

• Confirm soil temperature is 60°F+.
• Amend soil with compost for better drainage.
• Space plants 8–12 inches apart depending on variety.
• Water deeply once to settle the soil.

Popular Begonia Varieties for Your Garden

At Longfield Gardens, we offer a wide selection of begonias to suit different garden roles. Knowing which type you have can help you understand its specific needs for sun and space, and the Upright Double Begonias collection is a good place to start.

Tuberous Begonias

These are the stars of the shade garden. They grow from a single tuber and produce some of the largest and most spectacular flowers in the begonia world.

• Upright Varieties: These grow into sturdy, mounded plants that look beautiful in garden borders or window boxes. Begonia Upright Double Roseform Pink is a classic example.
• Trailing Varieties: Often called "pendula" begonias, these have stems that cascade gracefully over the edges of hanging baskets and elevated planters. Begonia Upright Double Odorata White adds fragrance to that look.
• Double Delight®: These are known for their high petal count and rose-like appearance, often featuring a light, pleasant fragrance. Begonia Upright Double Superba White offers a similar full, elegant flower form.

Wax Begonias (Begonia semperflorens)

These are incredibly reliable bedding plants. They are called "wax" begonias because of their shiny, waxy leaves. They are very heat-tolerant and bloom continuously from spring until frost. Varieties like the Surefire® series grow much larger than traditional wax begonias and can even handle a fair amount of sun in northern climates.

Rex and Foliage Begonias

If you love interesting patterns and textures, Rex begonias are the perfect choice. They are grown primarily for their stunning leaves, which can feature swirls of silver, purple, pink, and deep green. These are excellent choices for containers or as indoor-outdoor plants that spend the summer on a shaded patio.

Caring for Begonias Through the Season

Once your begonias are planted and the summer heat sets in, they are relatively low-maintenance. For a broader look at seasonal maintenance, see How to Care for a Begonia Plant for Beautiful Results. However, a little bit of consistent care will keep them blooming at their peak.

Fertilizing for Constant Color

Begonias are "heavy feeders," meaning they use a lot of energy to produce those constant blooms. To keep them going, use a balanced, water-soluble fertilizer every two to three weeks during the growing season. If you prefer a more hands-off approach, you can mix a slow-release granular fertilizer into the soil at planting time.

If your plants start to look a bit tired in mid-summer, a fresh dose of fertilizer can often give them the boost they need to produce a new flush of flowers. Always follow the instructions on the fertilizer label for the best results.

Grooming Your Plants

Many modern begonia varieties are "self-cleaning," meaning the old flowers fall off on their own. However, if you see spent blooms or yellowing leaves, it is a good idea to pinch them off. This keeps the plant looking tidy and prevents any old petals from resting on the leaves, which can sometimes cause spotting.

If your begonias start to look "leggy" (with long, thin stems and few leaves), you can pinch back the tips of the stems. This encourages the plant to branch out and become bushier and fuller.

Managing Pests and Weather

One of the great things about begonias is that they are rarely bothered by major pests. Insects like mealybugs or aphids are occasionally seen, but they are usually easy to manage with a gentle spray of water or an insecticidal soap. If you need a vigorous option, Begonia Upright Double Bertini tolerates a wider range of conditions.

If you live in an area with very heavy summer rains, keep an eye on your plants. Extended periods of wet weather can sometimes cause the soil to stay too soggy. If your begonias are in pots, make sure they aren't sitting in saucers full of water after a storm. Simply tipping the excess water out can prevent root issues.

Preparing for the End of the Season

As the days grow shorter and the temperatures begin to drop in the fall, it is time to think about the next steps. Begonias will continue to bloom until the first frost, but they cannot survive a freeze.

Lifting and Storing Tubers

If you are growing tuberous begonias in zones 3-8 and want to save them for next year, you need to "lift" them.

1. When the leaves start to turn yellow in late autumn, or immediately after the first light frost, dig up the tubers.
2. Cut the stems back to about an inch or two above the tuber.
3. Let the tubers dry in a warm, shady spot for a few days until the remaining soil is easy to brush off.
4. Store them in a cool, dark, dry place (about 50°F). Many gardeners find that placing them in a box of peat moss or sawdust works perfectly.

In the spring, you can bring them back out, start them indoors, and begin the cycle all over again!

Overwintering Wax and Rex Begonias

Wax begonias and Rex begonias can often be brought inside and kept as houseplants during the winter. Before the first frost, move them into pots if they are in the ground, and bring them into a bright room. They may lose a few leaves as they adjust to the lower humidity and light of your home, but they will often reward you with greenery all winter long.

Key Takeaway: While begonias are treated as annuals in most regions, their tubers can be easily stored in a cool, dark place to be replanted next spring, making them a wonderful long-term investment for your garden.

Conclusion

Planting begonias is a rewarding way to add dependable color and texture to the shaded parts of your yard. By waiting for the soil to warm to 60°F and ensuring nighttime temperatures stay above 50°F, you set your plants up for a successful, vibrant season. Whether you choose the dramatic blooms of tuberous varieties or the reliable charm of wax begonias, these plants are sure to become a favorite part of your summer landscape.

At Longfield Gardens, we take pride in providing high-quality tubers and plants that help you garden with confidence. For details on timing, see our Shipping Information. Remember that every garden is a little different, and paying attention to your local weather is the best tool you have. If you want to learn more about our promise of quality, see our About Us page. With the right timing and a little bit of care, your begonias will provide beauty from the first warm days of summer all the way to the first frost of autumn.

"Gardening is a journey of timing and patience. When you wait for the right conditions to plant your begonias, the reward is a garden that glows with color all season long."

We invite you to explore our selection of begonias and start planning your most beautiful shade garden yet.

FAQ

Can I plant begonias outside if it is still 40 degrees at night?

It is best to wait. While a single night at 40°F might not kill the plant, consistent cold temperatures will stunt its growth and may cause the stems to become brittle. For the healthiest growth and best flower production, wait until nighttime temperatures are consistently 50°F or higher.

How deep should I plant begonia tubers?

Begonia tubers should be planted quite shallowly. Place them in the soil with the hollow, indented side facing upward and cover them with only about one inch of soil. Planting them too deep can make it difficult for the young sprouts to reach the surface and may increase the risk of the tuber staying too wet.

Do begonias need full sun to bloom?

No, most begonias actually prefer shade or partial shade. While they need bright, indirect light to produce flowers, the direct midday sun in many regions is too intense and can burn their leaves. A spot that receives gentle morning sun and afternoon shade is usually the perfect balance for most varieties.

What should I do if a frost is predicted after I have planted my begonias?

If a late-season frost is in the forecast, you should protect your begonias. For plants in the ground, cover them with a light frost cloth, an old bedsheet, or even an upside-down bucket overnight. For plants in containers, the easiest solution is to move them into a garage, shed, or porch until the temperatures rise the next morning.