Table of Contents
- Introduction
- The Strategic Head Start: Why We Start Indoors
- Understanding Temperature and Timing
- Planting Timing by USDA Hardiness Zone
- Reading the Signs: Is Your Corm Ready?
- The Process of Hardening Off
- Can You Plant Too Late?
- Creating the Perfect Environment
- Waking Up Dormant Corms: A Step-by-Step
- Managing Expectations: Weather and Growth
- Timing the End of the Season
- Summary of Success
- FAQ
Introduction
There is a unique kind of excitement that comes with the arrival of spring gardening season. While many gardeners focus on the first green shoots of tulips or the cheerful faces of daffodils, those in the know are already looking ahead to the lush, tropical beauty of begonias. These plants are beloved for their oversized, rose-like blooms and their ability to bring vibrant color to the shadiest corners of the yard. Whether you are tucking them into hanging baskets or lining a garden path, begonias offer a spectacular reward for a very small amount of effort.
At Longfield Gardens, we want every gardener to experience the joy of a successful growing season. Begonias are one of the most versatile plants you can choose, but because they are tropical by nature, getting the timing right is essential. If you plant them too early, the cold might set them back; if you wait too long, you might miss out on weeks of beautiful flowers. This guide is designed to help you navigate the calendar and understand exactly when to plant begonia corms for the best possible results.
We will cover the benefits of starting your corms indoors, the temperature triggers you need to watch for, and how to adjust your schedule based on your specific USDA hardiness zone. By the end of this article, you will have a clear timeline that takes the guesswork out of planting and sets you up for a summer filled with brilliant blooms. Our goal is to make the process simple and enjoyable, so you can spend less time worrying and more time enjoying your garden.
Timing is the foundation of gardening success, and for begonias, it is the secret to a long and lush flowering season.
The Strategic Head Start: Why We Start Indoors
One of the most important things to understand about begonias is that they are not in a hurry. While some bulbs sprout and bloom within a few weeks, begonia corms prefer a slower, more deliberate pace. Because they thrive in warm weather and have a long growing cycle, most gardeners in the United States find that starting their corms indoors is the best way to maximize their bloom time.
Starting indoors essentially "wakes up" the corms while the ground outside is still cold or frozen. This gives the plants a 6-to-8-week head start, allowing them to develop a strong root system and their first few sets of leaves before they ever touch outdoor soil. When you finally move them outside in late spring, they are already established and ready to begin their summer show.
The ideal window for starting begonia corms indoors is roughly 8 to 12 weeks before the average last frost date in your area. For most of the country, this falls somewhere between February and April. This timing ensures that by the time the weather is consistently warm, your begonias will be healthy, sturdy, and perhaps even showing their first flower buds.
Key Takeaway: Starting begonia corms indoors in late winter or early spring provides a "head start" that leads to earlier flowers and a longer blooming season.
What to Do Next
- Check your local frost dates to determine your 8-to-12-week window.
- Gather your supplies, including shallow trays or small pots and a high-quality potting mix.
- Find a warm, bright spot in your home (away from drafts) to serve as your "nursery."
Understanding Temperature and Timing
Begonias are tropical plants, which means they are very sensitive to temperature. They don’t just dislike frost; they are also not particularly fond of chilly nights. To get the timing right, you have to look at two different sets of numbers: the temperature of your home (for starting) and the temperature of the air and soil outside (for moving).
Indoor "Waking" Temperatures
When you first bring your corms home, they are likely in a state of dormancy. To encourage them to sprout, they need to feel like spring has arrived. We recommend keeping your indoor starting area at a consistent temperature of 60°F to 70°F. If your house is on the cooler side, the corms will still grow, but they will take much longer to break dormancy.
Some gardeners use a seedling heat mat to provide gentle bottom heat, which can speed up the process. However, a sunny windowsill or a spot near a warm (but not hot) radiator usually works just as well. The goal is to provide a "cozy" environment that mimics a tropical spring.
Outdoor Transition Temperatures
The biggest mistake a gardener can make is rushing begonias outdoors too early. Even if the sun is shining, cold soil and chilly night air can cause the plants to stall or, in some cases, rot.
Wait to move your begonias outside until the following conditions are met:
- The danger of frost has completely passed.
- Nighttime temperatures are consistently above 50°F (ideally 60°F).
- The soil has warmed up and is no longer cold to the touch.
In many regions, this doesn't happen until late May or even early June. It might feel late, but your begonias will grow much faster in the warmth of June than they would in the damp chill of April.
Planting Timing by USDA Hardiness Zone
Because the United States has such a wide range of climates, a "one size fits all" date for planting simply doesn't exist. Your USDA hardiness zone is the best tool for fine-tuning your schedule. If you aren't sure which zone you are in, a quick search of your zip code on a hardiness zone map will give you the answer.
Zones 3 through 6
In these cooler northern climates, the growing season is relatively short. To get the most out of your begonias, starting indoors is almost a necessity.
- When to start indoors: Mid-March to early April.
- When to move outdoors: Late May to mid-June. Since the first frost in autumn can arrive as early as September, that indoor head start ensures you get at least three full months of flowers.
Zones 7 and 8
These regions have a more moderate climate and a longer growing season. You have a bit more flexibility here, but an indoor start is still highly recommended for the best display.
- When to start indoors: February to early March.
- When to move outdoors: Late April to early May. Gardeners in these zones can often enjoy begonia blooms well into October if the weather stays mild.
Zones 9 through 11
In these warm, southern climates, begonias can often be grown as perennials or started directly outdoors much earlier in the year.
- When to start indoors (optional): January.
- When to plant outdoors: March. In these zones, the primary concern isn't the cold, but the heat. Planting early allows the begonias to establish themselves before the intense humidity and sun of mid-summer arrive.
Key Takeaway: Match your planting schedule to your USDA zone to ensure your begonias have enough time to mature before the summer heat or autumn frost.
Reading the Signs: Is Your Corm Ready?
While the calendar is a great guide, the plants themselves will often tell you when they are ready for the next step. If you are starting your corms indoors, you should watch for specific developmental milestones.
The first sign of life is usually a tiny pink or green "eye" or bud appearing in the hollow, indented side of the corm. This is the signal that dormancy is over. Once you see these sprouts, you can plant the corm in soil.
Over the next several weeks, you will see stems elongate and the first leaves unfurl. A begonia is generally ready to be moved to its "forever home"—whether that is a large patio pot or a garden bed—when it meets these criteria:
- It is roughly 4 to 5 inches tall.
- It has at least two or three fully expanded leaves.
- The root system has filled out its small starter container.
If your plant reaches this stage but the weather outside is still too cold, don't worry. You can simply keep it in its indoor spot a little longer. It is much better to have a slightly larger plant indoors than a struggling plant outdoors in the cold.
The Process of Hardening Off
Timing your move outdoors involves more than just picking a date on the calendar. It also involves a process called "hardening off." This is a gradual transition that helps the plant adjust from the controlled environment of your home to the variable conditions of the outdoors.
If you take a begonia that has spent its whole life in a 68°F living room and put it directly into a breezy, 80°F garden, it may experience shock. Its leaves might wilt or "sunburn." To avoid this, we recommend a one-week transition period.
A Sample Hardening Off Schedule
- Days 1-2: Place your begonias outside in a protected, fully shaded spot for 2 to 3 hours during the warmest part of the day, then bring them back inside.
- Days 3-4: Increase the time to 5 or 6 hours. You can move them to a spot with very dappled sunlight, but avoid direct, harsh afternoon sun.
- Days 5-6: Leave them out all day. Bring them in only if the nighttime temperature is forecasted to drop below 50°F.
- Day 7: If the weather is stable, they are ready to stay out for good.
This gradual introduction ensures that the plant’s cellular structure toughens up, making it much more resilient to wind and temperature swings.
What to Do Next
- Monitor the 10-day weather forecast before starting the hardening off process.
- Identify a "transition spot" on your porch or patio that is sheltered from heavy wind.
- Keep a close eye on soil moisture during this week, as outdoor air dries out pots faster than indoor air.
Can You Plant Too Late?
We often get questions from gardeners who didn't get around to planting their corms in March or April. If it's already May or June, is it too late to start?
The short answer is no! Begonias are incredibly resilient. If you plant begonia corms later in the season, they will still grow and bloom; they will simply start their show later in the summer. Because begonias bloom continuously until the first frost, even a late-start plant can provide months of enjoyment.
If you are planting late (for example, in June), you may want to skip the indoor starting phase and plant them directly into their outdoor containers or garden beds. Since the soil and air are already warm, the corms will sprout much faster than they would have in February. Just be sure to keep the soil consistently moist, as young sprouts are more vulnerable to drying out in the summer heat.
Key Takeaway: It is almost never "too late" to plant begonias in the spring and summer. While an early start is ideal, these plants are happy to grow whenever the weather is warm.
Creating the Perfect Environment
While timing is the primary focus of this guide, the "where" and "how" of planting are closely tied to the "when." To ensure your timing pays off, you need to provide the right conditions from day one.
Choosing the Spot
Begonias are famous for their love of shade plants. In the wild, they grow on forest floors where they receive filtered light. In your garden, this means a spot that gets morning sun and afternoon shade is perfect. If you live in a very hot climate, they might prefer almost total shade during the hottest part of the day.
Soil and Drainage
Regardless of when you plant, drainage is non-negotiable. Begonia corms are like sponges; they hold a lot of moisture. If they sit in soggy, waterlogged soil, they can easily rot. Always use a light, peat-based potting mix for containers. If planting in the ground, ensure the area doesn't collect standing water after a rain. Well-draining soil is essential.
The "Hollow Side Up" Rule
When you are ready to plant, take a close look at the corm. One side is usually rounded, while the other has a slight indentation or "bowl" shape. Always plant the corm with the hollow side up. This is where the sprouts will emerge. If you can't tell which side is which, you can plant the corm on its side, and the plant will naturally figure out which way to grow.
Waking Up Dormant Corms: A Step-by-Step
If you have purchased your corms early in the season, they might look a bit like shriveled brown puckers. This is perfectly normal! They are simply resting. Here is a simple way to wake them up and get your timing off to a great start.
- Inspect the corms: They should feel firm and heavy for their size. If they feel light and "dusty," they may have dried out too much, but most will plump back up once they touch moist soil.
- Prepare a tray: Use a shallow nursery tray or individual small pots filled with 2-3 inches of moist potting mix.
- Position the corms: Place them on top of the soil, hollow side up. You don't need to bury them deeply yet; just press them gently into the surface so they have good contact with the soil.
- Cover lightly: Sprinkle just enough soil over them so they are barely covered (about half an inch).
- Water sparingly: Give them a light drink to settle the soil. From this point on, only water when the soil feels dry to the touch. Overwatering at this stage is the most common cause of failure.
- Provide light and heat: Place the tray in a warm room with indirect light.
Within two to four weeks, you should see the first signs of life. Once the sprouts are an inch or two tall, you can move them into larger pots if they were started in a tray.
Managing Expectations: Weather and Growth
Even with perfect timing, nature sometimes has its own plans. A particularly cloudy spring might slow down growth, while a sudden early heatwave might cause your begonias to grow faster than expected.
It is important to remember that begonias are a marathon plant, not a sprint plant. They spend the first part of their life building a strong root system. If you don't see massive top growth in the first few weeks, don't worry. Once the roots are established and the weather turns warm, they will suddenly take off.
Also, keep in mind that different upright begonias have slightly different "vines." Upright begonias, which produce large, rose-like flowers on sturdy stems, tend to grow a bit slower than trailing or "cascading" varieties. If you have both types, you might notice the trailing ones reaching the transplant stage a week or two earlier. This is perfectly normal and a great reason to enjoy a variety of types in your garden.
Timing the End of the Season
Just as it is important to know when to start, it is helpful to know when the season ends. For most of the United States, begonias are treated as annuals, meaning they finish their life cycle when the first frost hits.
However, because these plants grow from corms, you can actually save them and replant them next year! This is a wonderful way to grow your garden without extra cost.
When to Dig Them Up
When the weather begins to turn cold in autumn, you will notice the leaves on your begonias starting to yellow. This is a sign the plant is entering dormancy. You should aim to dig up your corms (or bring the pots inside) before the first hard freeze. A light frost might blacken the leaves, but as long as the corm in the soil doesn't freeze, it will be fine.
Once you have removed the stems and cleaned off the soil, you can store the corms in a cool, dry place (like a basement or garage) in a paper bag with some peat moss or shredded paper. They will sleep through the winter, ready for you to start the whole timing process over again next spring!
Key Takeaway: The "when" of begonias comes full circle in the fall. Protecting the corms from the first hard freeze allows you to enjoy the same plants year after year.
Summary of Success
Getting the timing right for begonia corms is one of the most rewarding skills a shade gardener can learn. It turns a simple plant into a season-long masterpiece.
To recap the most important points:
- Start corms indoors 8-12 weeks before your last frost for the earliest blooms.
- Wait for nighttime temperatures to stay consistently above 50-60°F before moving plants outdoors.
- Always plant with the hollow side up in well-draining soil.
- Use your USDA zone as a roadmap for your specific region.
- Be patient during the first few weeks of growth; the summer reward is worth the wait.
At Longfield Gardens, we take great pride in providing high-quality corms that are ready to perform. We ship our orders based on your planting zone, ensuring that your begonias arrive at the ideal time for you to get started. See our Shipping Information.
Gardening is a journey of observation and joy. By paying attention to the needs of your begonia corms and the rhythm of the seasons, you are setting yourself up for a summer of spectacular color and a garden you can truly be proud of, backed by our 100% Guarantee.
FAQ
Can I plant begonia corms directly in the garden without starting them indoors?
Yes, you can certainly plant them directly outdoors once the soil is warm and the danger of frost has passed. However, because begonia corms grow relatively slowly, direct-planted begonias will likely not start blooming until late summer. Starting them indoors is the best way to get flowers in June or July.
What should I do if my begonia corms haven't sprouted after four weeks?
First, check the temperature of the room; if it is below 60°F, they may just be taking their time. You can also gently check the corm to ensure it isn't mushy (a sign of rot). If the corm is firm, simply be patient. Some varieties take longer to "wake up" than others, and as long as they stay firm and the soil is barely moist, they will eventually sprout.
Is it okay to move my begonias outside if it's still 45°F at night?
It is generally best to wait. While a single night at 45°F likely won't kill a begonia, consistent cold nights will cause the plant to stop growing and can make it more susceptible to disease and rot. For the best growth, wait until nighttime temperatures are reliably 50°F or higher.
Do I need to soak begonia corms before planting them?
Soaking is not usually necessary for begonia corms, and in some cases, it can actually increase the risk of rot if the corm absorbs too much water too quickly. Simply planting them in moist (but not soggy) soil is the safest and most effective way to encourage them to break dormancy.
What about other spring bulbs?
If you want to compare begonias with other spring favorites, tulips and other spring-flowering bulbs are also worth a look.