When to Plant Begonia Bulbs for a Summer of Color

Table of Contents

1. Introduction
2. The Short Answer: When to Plant Begonia Bulbs
3. Why Timing Matters for Tuberous Begonias
4. Starting Begonias Indoors: The 8-12 Week Window
5. Transitioning Outdoors: The 60°F Rule
6. Regional Timing and USDA Zones
7. Timing Your Care Throughout the Season
8. End-of-Season Timing: Preparing for Winter
9. Creating a Successful Planting Schedule
10. Conclusion
11. FAQ

Introduction

Imagine turning a quiet, shaded corner of your yard into a lush gallery of vibrant, rose-like blooms. Tuberous begonias make this transformation possible, offering some of the most spectacular colors and textures available for low-light spaces. Whether you want to brighten a north-facing porch with cascading flowers or add elegance to a garden border, these plants are a gardener’s best friend. At Longfield Gardens, we love helping home gardeners discover how easy it is to grow these tropical treasures starting from a simple tuber.

Timing is the absolute key to success with these plants. Because they are native to warm, tropical climates, begonias have specific needs regarding temperature and light. This guide will help you understand exactly when to plant your begonia bulbs to ensure they thrive from the first sprout to the final frost. By getting the timing right, you set the stage for a season of effortless beauty.

Our goal is to make your gardening experience as rewarding and straightforward as possible. This article is designed for everyone, from busy beginners to seasoned backyard enthusiasts who want a reliable bloom schedule. Following a few simple timing rules will ensure your begonias reach their full potential this year.

The Short Answer: When to Plant Begonia Bulbs

If you are looking for the quickest rule of thumb, the best time to start begonia tubers is in the spring-planted bulbs season. Specifically, you should start them indoors about 8 to 12 weeks before the average last frost date in your area. This early start gives the plants enough time to develop strong roots and foliage before they face the outdoor elements.

If you prefer to plant them directly into the ground or outdoor containers, you must wait until the risk of frost has completely passed. Begonias are very sensitive to cold. Outdoor planting should only happen when nighttime temperatures consistently stay above 60°F. If the soil is still cold or the nights are chilly, the tubers will sit dormant or, in wet conditions, may not perform as expected.

For most gardeners in the United States, the indoor starting window falls between late February and early April. If you want a more local guide, check our hardiness zone map. This schedule allows the begonias to "wake up" in a controlled environment. By the time the summer heat arrives, your plants will be well-established and ready to produce their signature showy flowers.

Key Takeaway: Start begonia tubers indoors 8–12 weeks before your last spring frost, and only move them outside once nighttime temperatures are reliably above 60°F.

Why Timing Matters for Tuberous Begonias

Understanding the "why" behind the timing helps you make better decisions for your specific climate. Tuberous begonias are not like hardy spring bulbs (such as tulips or daffodils) that require a period of winter cold. Instead, they are tropical perennials that enter a period of dormancy during the winter months to survive dry or cool conditions.

When you receive your tubers in the spring, they are in a deep sleep. Waking them up requires a combination of warmth and moisture. If you plant them too early in cold, outdoor soil, the tuber cannot begin its metabolic processes. Conversely, if you wait too long to start them, they may not have enough time to reach their peak blooming size before the end of the summer season.

Begonias also have a relatively long "lead time." It typically takes about 12 to 14 weeks from the initial planting for the first flowers to appear. By starting them indoors while the ground is still frozen, you are essentially "borrowing" time from the spring to ensure a longer blooming season in the summer.

The Role of Soil Temperature

While air temperature is what we usually check on our phones, soil temperature is what the tuber actually feels. For a begonia bulb to begin growing, it needs the soil to be around 70°F. In the early spring, garden soil is often much colder than the air. This is why starting them in small pots inside your warm home is so effective. It mimics the tropical environment they love, signaling to the tuber that it is safe to start sending out roots.

What to do next:

• Find your local "average last frost date" using an online gardening calendar.
• Count back 10 weeks from that date on your calendar.
• Mark that week as your official "Begonia Start Day."

Starting Begonias Indoors: The 8-12 Week Window

Most successful begonia growers choose the indoor start method. This is especially true for gardeners in northern regions (Zones 3-7), where the growing season is shorter. Starting indoors gives you a head start of nearly three months.

When to Buy and When to Plant

We typically ship begonia tubers in late winter and early spring, timed to arrive just as the indoor planting window opens. Once your tubers arrive, you can store them in a cool, dry place for a short time, but it is best to get them into soil within a few weeks. For a deeper overview, see All About Begonias.

The most common mistake is starting too late. If you wait until May to plant your tubers indoors, you might not see significant blooming until late August or September. By starting in March, you can enjoy flowers starting in June and continuing all the way through the first frost of autumn.

The Indoor Process

When you are ready to plant, choose a shallow tray or small individual pots with excellent drainage. Use a high-quality, lightweight potting mix. The timing of your watering during this phase is crucial. After the initial planting, water the soil sparingly. You want it to feel like a wrung-out sponge—damp but never saturated.

During this indoor phase, keep the pots in a warm spot. A room that stays around 70°F is perfect. You do not need bright light until the first green sprouts appear. Once you see those small pink or green "eyes" emerging from the hollow side of the tuber, move the pots to a bright window or under grow lights. This transition to light is the next step in your timing journey.

Monitoring Growth Progress

• Weeks 1-3: The tuber is developing roots beneath the surface. You may not see much action above ground.
• Weeks 4-6: Small sprouts will emerge. This is when the plant begins to grow rapidly.
• Weeks 8-10: Foliage begins to fill out. The plant will start looking like a small bush or a trailing vine.
• Week 12: Small flower buds may begin to form if the plant has had consistent warmth and light.

Transitioning Outdoors: The 60°F Rule

The most critical timing decision you will make is when to move your begonias outside. Because begonias are tropical, they have no defense against frost. Even a light frost can turn the lush leaves to mush overnight.

A common rule among experienced gardeners is to wait until you are comfortable wearing a light t-shirt outside at night. If you still need a heavy jacket after the sun goes down, it is likely too cold for your begonias.

The Danger of Cold Soil

Even if the air feels warm during the day, the ground can remain chilly. If you plant your begonias in the ground too early, the cold soil can shock the root system. This shock often leads to "stunting," where the plant stops growing for several weeks as it tries to recover. In some cases, the plant may never fully regain its vigor for the rest of the season.

How to Acclimate (Hardening Off)

Moving plants directly from a cozy indoor windowsill to the outdoor garden is a big change. You should plan for a 7-to-10-day transition period known as "hardening off."

1. Days 1-3: Place your pots outside in a fully shaded, protected spot for just 2–3 hours during the warmest part of the day. Bring them back inside before the evening.
2. Days 4-6: Increase the outdoor time to 5–6 hours. Ensure they are protected from strong winds, which can snap the brittle stems of young begonias.
3. Days 7-10: If the nights are staying above 60°F, you can leave them out all day and eventually overnight.

Once this transition is complete, you can safely transplant them into their permanent garden beds or container combinations.

Key Takeaway: Never rush the move outdoors. A few extra days inside is always better than one night of unexpected cold.

Regional Timing and USDA Zones

Your location in the United States determines your specific begonia schedule. While the 8-12 week rule applies everywhere, the actual months on the calendar will shift.

Northern Climates (Zones 3-6)

In states like Minnesota, Maine, or Washington, the last frost may not occur until mid-May or even early June. Gardeners here should start their tubers indoors in March. Because the summer season is relatively short, starting indoors is almost a requirement if you want to see a full display of flowers before the cold returns in September.

Central and Southern Climates (Zones 7-8)

In these regions, the last frost usually happens in March or April. You can start your tubers indoors in February to get a very early start. In Zone 8, you may even be able to plant tubers directly outdoors in late April, provided the soil has warmed up sufficiently.

Tropical Climates (Zones 9-11)

In frost-free zones like parts of Florida, Arizona, or California, begonias can be treated as short-lived perennials. In these areas, timing is less about avoiding frost and more about avoiding the most intense heat of the summer. Planting in the early spring allows the plants to establish themselves before the scorching mid-summer sun arrives.

What about shipping?

We time our shipments based on these USDA zones. You can find more details on our shipping information page. We want to ensure that your begonia tubers arrive when it is the right time to start them indoors in your specific area. This takes the guesswork out of ordering and ensures the tubers aren't sitting in a cold warehouse or a hot delivery truck for too long.

Timing Your Care Throughout the Season

Once your begonias are planted and growing, timing continues to play a role in how they perform. Proper maintenance at the right intervals will keep the blooms coming until autumn.

When to Fertilize

Begonias are "heavy feeders," meaning they need plenty of nutrients to produce those large, complex flowers. However, you shouldn't start fertilizing the moment you plant the tuber. Wait until the plant has at least two or three fully expanded leaves.

• Initial Growth: Use a balanced, water-soluble fertilizer every two weeks.
• Peak Summer: Continue this routine to support the heavy blooming period in July and August.
• Late Summer: As the days grow shorter in September, you can stop fertilizing. This signals to the plant that it is time to start storing energy in the tuber for next year's dormancy.

When to Water

The best time of day to water begonias is in the early morning. This allows any water that splashes onto the leaves to dry in the sun. Begonias are susceptible to mildew if their leaves stay wet overnight.

As for frequency, check the soil daily during the heat of summer. Tuberous begonias like "consistent moisture." This means the soil should feel like a damp sponge. If the top inch of soil feels dry, it is time to water. In containers, this may happen every day; in garden beds, it may be every few days depending on your local rain.

When to Deadhead

"Deadheading" is the process of removing old, faded flowers. For begonias, this is mostly an aesthetic choice, as many modern varieties are "self-cleaning" (meaning the flowers fall off on their own). However, removing spent blooms and any yellowing leaves every week keeps the plant looking fresh and prevents any mold or fungus from growing on decaying plant matter.

End-of-Season Timing: Preparing for Winter

As summer winds down, the timing of your "takedown" is just as important as your planting schedule. Tuberous begonias can be saved and replanted year after year, which is one of their most rewarding features.

Watching the Foliage

In the late summer or early fall, you will notice the plant's growth slowing down. The leaves may begin to look a bit tired. This is normal. When the overnight temperatures start to dip toward 40°F, it is time to prepare the tubers for storage.

Do not wait for a hard freeze to kill the plant. Instead, you want to bring the plants into a garage or shed before the first frost hits. If your begonias are in pots, simply stop watering them. Let the soil dry out completely. This dry-down period tells the tuber to enter dormancy.

Digging and Storing

Once the stems have turned yellow and can be easily pulled away from the tuber, it is time to dig them up (if they were in the ground) or remove them from their pots.

• Curing: Let the cleaned tubers sit in a dry, room-temperature spot for about a week. This "cures" the outer skin.
• Storage: Place them in a box with peat moss or sawdust.
• Wintering: Keep the box in a cool, dark, and dry place (like a basement or crawlspace) that stays between 40°F and 50°F.

By following this end-of-season timing, you ensure that your tubers stay healthy and ready to be started again next spring.

Creating a Successful Planting Schedule

To summarize everything we’ve covered, here is a simple timeline you can follow for the best results with your begonia bulbs.

• Late Winter (Feb/March): Order your tubers from our spring-planted bulb bulk buys and prepare your indoor pots and soil.
• Early Spring (March/April): Plant tubers indoors 8-12 weeks before your last frost. Keep them warm and barely damp.
• Mid-Spring: Move sprouted begonias to a bright window. Start a regular fertilizing routine once leaves appear.
• Late Spring (May/June): Monitor outdoor night temperatures. Begin the "hardening off" process once nights are above 60°F.
• Summer (July/August): Enjoy the peak bloom period! Water regularly and enjoy the color in your shady garden spaces.
• Early Fall (Sept/Oct): Stop fertilizing. Monitor for the first signs of cold weather.
• Late Fall: Dry out the tubers and move them into winter storage before the first hard frost.

By sticking to this schedule, you work with the plant’s natural rhythm rather than against it. Gardening is much more enjoyable when you follow these simple cues from nature.

Conclusion

Tuberous begonias are one of the most rewarding additions to any home garden. Their ability to turn shade into a vibrant landscape is unmatched, and their long blooming season provides value for months on end. While they have a few specific needs regarding temperature and timing, these are easy to manage once you know what to look for.

At Longfield Gardens, we want you to feel confident every time you put a bulb or tuber into the ground, supported by our 100% Quality Guarantee. By starting your begonias indoors in the early spring and waiting for warm summer nights before moving them outside, you are following the most reliable path to success. These simple steps ensure that your garden remains a source of joy and relaxation all season long.

• Start tubers indoors 8–12 weeks before the last frost for the earliest blooms.
• Only move begonias outside when night temperatures stay above 60°F.
• Transition plants slowly to the outdoors to avoid shock.
• Save your tubers in the fall to enjoy them again next year.

"The secret to beautiful begonias isn't a green thumb—it's simply knowing when to start. By giving these tropical plants the warmth they crave, you'll be rewarded with a spectacular show that lasts until the first frost."

We invite you to explore our spring-planted bulb collections and start planning your most colorful shade garden yet. With the right timing and a little bit of patience, your backyard will be the talk of the neighborhood.

FAQ

Can I plant begonia bulbs directly in the ground in May?

You can plant begonia bulbs directly in the ground in May as long as the soil has warmed up and there is no longer any danger of frost. However, keep in mind that begonias started directly in the ground will bloom much later in the summer compared to those started indoors. In northern climates, this may mean you only get a few weeks of flowers before the fall weather arrives.

How do I know which side of the begonia tuber is the top?

Begonia tubers have a distinct shape that helps you identify the top. One side is rounded (the bottom), and the other side has a slight hollow or indentation (the top). You should plant the tuber with the hollow side facing up. This is where the new stems and leaves will emerge. If you are unsure, you can also look for small pink "eyes" or dried bits of last year's stems, which will be on the top side.

What happens if I move my begonias outside too early?

If begonias are moved outside when temperatures are too cold (especially below 50°F), they can suffer from cold shock. This usually results in the leaves turning yellow or transparent, and the plant may stop growing entirely for several weeks. If a frost occurs, the plant will likely be killed. If you accidentally move them out too early, bring them back inside immediately and keep them in a warm, bright spot until the weather improves.

Why are my begonia tubers taking so long to sprout indoors?

Begonia tubers can be slow to wake up, sometimes taking 3 to 6 weeks to show the first signs of green growth. This is usually due to the temperature. If your room is cool (below 60°F), the tuber will stay dormant. To speed up the process, ensure the pots are in a warm area, ideally around 70°F. Avoid overwatering during this stage, as too much moisture before the roots have formed can cause the tuber to rot.