Table of Contents
- Introduction
- Why Choose Seeds Over Tubers?
- Timing Your Begonia Sowing
- Essential Supplies for Success
- The Sowing Process: Step-by-Step
- Managing the Germination Phase
- Caring for Young Seedlings
- Potting Up: Moving to Larger Quarters
- Transitioning to the Great Outdoors
- Summer Care for Maximum Blooms
- Understanding the Life Cycle: From Seed to Tuber
- Preparing for Winter Dormancy
- Achieving the Best Results
- Conclusion
- FAQ
Introduction
There is a unique kind of magic in watching a plant as spectacular as a tuberous begonia grow from a seed no larger than a speck of dust. These garden favorites are famous for their lush, rose-like blooms and dramatic foliage, often serving as the crown jewels of shady porches and garden beds. While many gardeners start with dormant tubers, growing from seed offers a rewarding sense of accomplishment and a cost-effective way to fill your landscape with color.
At Longfield Gardens, we want to make sure your gardening journey is as successful as it is enjoyable. begonias are incredibly generous plants, blooming reliably from early summer all the way through the first frost. Because they thrive in areas where other flowers might struggle—like dappled shade or north-facing patios—they are essential for creating a vibrant, multi-layered garden.
This guide is designed for any gardener ready to take on the exciting project of begonia seeds from scratch. We will walk you through every step, from the first tiny sprout to the moment you move your lush, flowering plants into their permanent summer homes. With a little patience and the right environment, you can grow a professional-quality display right in your own home.
Why Choose Seeds Over Tubers?
Most home gardeners are familiar with planting begonia tubers in the spring. Tubers are wonderful because they contain stored energy, which leads to fast growth and large flowers in the first year. However, starting from seed has its own distinct advantages that make the extra time and effort worthwhile.
First, growing from seed is highly economical. A single packet of seeds can produce dozens of plants for the price of one or two mature tubers. If you have a large area to fill, such as a long border or several dozen hanging baskets, starting from seed is the most budget-friendly way to achieve a high-impact look.
Second, the variety available in seed form is often much broader. You can find specific flower shapes, such as the ruffled petals of Picotee types or the cascading habit of 'Pendula' varieties, which may not always be available as tubers at your local garden center. Finally, there is the simple joy of the process. Seeing a tiny green leaf emerge from the soil is a reminder of how resilient and powerful nature can be.
Timing Your Begonia Sowing
One of the most important things to understand about tuberous begonias is that they are slow starters. They take their time to develop a strong root system and a sturdy stem before they begin to bloom. To have flowers by the time summer arrives, you must start your seeds early.
In most parts of the United States, the best time to sow begonia seeds is between mid-January and early March. This gives the plants four to five months of indoor growth before they are ready to be moved outside. While this might feel like a long wait, the progress is steady and exciting to watch.
Because begonias are sensitive to cold, you should not move them outdoors until all danger of frost has passed and the night temperatures are consistently above 50°F. If you start your seeds too late, you may find that your plants are only just beginning to flower as the growing season comes to an end. Starting early ensures you get the longest possible window of beauty, and our Shipping Information page can help you plan the timing.
Key Takeaway: Tuberous begonias require a long lead time. Start your seeds indoors at least 16 to 20 weeks before your last expected spring frost to ensure a full season of summer blooms.
Essential Supplies for Success
Growing begonias from seed requires a few specific tools to create the right environment, and How to Start Flower Seeds Indoors covers the basics.
Quality Begonia Seeds
Always start with fresh seeds from a reputable source. Begonia seeds are often "pelleted," which means they are coated in a thin layer of dissolvable clay. This makes them much easier to handle and see against the soil. If you are using raw seeds, be prepared for them to look like fine powder or orange dust.
Seed Starting Mix
Do not use standard garden soil or even regular potting soil for starting seeds. These are too heavy and may contain pathogens that can harm delicate seedlings. Instead, use a "soilless" seed starting mix. These mixes are usually made of peat moss, perlite, and vermiculite. They are sterile, lightweight, and hold onto moisture while allowing air to reach the developing roots.
Trays and Humidity Domes
You don't need deep containers for the initial sowing. Shallow plastic trays or even recycled clear plastic food containers with holes poked in the bottom work well. A clear lid or a piece of plastic wrap is essential for maintaining the high humidity these seeds need to germinate.
A Reliable Light Source
Begonia seeds need light to germinate, so they cannot be buried under the soil. While a very bright windowsill might work, a simple LED or fluorescent shop light is much better. This provides consistent, direct light that prevents the seedlings from becoming "leggy"—a term gardeners use for plants that grow tall and weak while searching for sun.
What to do next:
- Clear a small space in your home that stays warm and has access to an electrical outlet for lights.
- Purchase a high-quality seed starting mix and ensure it is fresh.
- Gather shallow trays and clear covers to create a mini-greenhouse environment.
- Order your seeds early to ensure you have your favorite varieties, like Non-Stop Begonias, ready for January planting.
The Sowing Process: Step-by-Step
Sowing begonia seeds is a delicate task, but it is not difficult if you follow a few simple rules. The most common reason for failure is planting the seeds too deep. Unlike a bean or a sunflower seed, a begonia seed does not have enough stored energy to push through a layer of soil.
Step 1: Prepare the Mix
Start by moistening your seed starting mix in a bucket before putting it into the trays. It should feel like a wrung-out sponge—damp but not dripping wet. Fill your trays to within half an inch of the rim and press the surface down gently to create a flat, even bed.
Step 2: Sowing the Seed
If your seeds are pelleted, place them on the surface of the mix about an inch apart. If they are raw, you can mix them with a small amount of fine, dry sand to help distribute them more evenly as you sprinkle them. Do not cover the seeds with soil. They must be exposed to light to wake up and begin the germination process.
Step 3: Watering In
Instead of using a watering can, which can wash the tiny seeds away or bury them, use a fine misting bottle. Lightly spray the surface to settle the seeds. If the seeds are pelleted, the misting will help dissolve the coating so the seed can make contact with the moist soil.
Step 4: Cover and Heat
Place the clear lid or plastic wrap over the tray to trap moisture. Begonias germinate best when the soil temperature is between 70°F and 75°F. If your home is cool, placing the tray on a seedling heat mat can make a significant difference. Place your lights directly over the tray, leaving about two to three inches of space between the light and the top of the cover.
"The golden rule for begonia seeds is 'light and air.' Never bury the seeds, and always ensure they stay moist but never waterlogged."
Managing the Germination Phase
Patience is your best friend during this stage. Begonia seeds can take anywhere from 10 to 21 days to germinate, and sometimes even longer if the conditions are slightly cool. During this time, your main job is to monitor the moisture levels.
Check the trays daily. If you see heavy droplets of water dripping from the lid onto the soil, the environment might be too wet. You can prop the lid open for an hour to let some fresh air in. If the surface of the soil looks light brown or dry, give it a gentle misting.
Once you see the first tiny green dots appearing, you have succeeded in the hardest part! These are the cotyledons, or "seed leaves." As soon as the majority of the seeds have sprouted, you can remove the humidity dome or plastic wrap. This allows for better airflow and helps prevent a common fungal issue called "damping off," which can cause young seedlings to collapse at the soil line.
Caring for Young Seedlings
After germination, the plants will enter a slow growth phase. They may look the same for several weeks as they focus on building roots. Keep the lights on for 14 to 16 hours a day. As the plants grow taller, adjust the height of your lights to keep them about 2 to 4 inches above the foliage.
Thinning and Spacing
If your seeds were sown too closely together, you might need to thin them out. It feels difficult to remove a healthy sprout, but it is necessary for the health of the remaining plants. Use a small pair of scissors to snip off the smaller, weaker seedlings at the soil level, leaving about two inches of space between the ones you keep.
Feeding Your Plants
Because soilless seed starting mixes contain very few nutrients, you will need to start feeding your begonias once they have their first set of "true leaves"—these are the leaves that look like miniature versions of the adult begonia foliage. Use a balanced, water-soluble fertilizer diluted to one-quarter of the recommended strength. Feed them once every two weeks to encourage steady growth.
Potting Up: Moving to Larger Quarters
When your seedlings have two or three sets of true leaves and are starting to crowd each other, it is time to move them into their own individual pots. This is often called "potting up." Usually, this happens about 8 to 10 weeks after sowing.
Use small plastic pots or cell packs filled with a high-quality potting mix. Gently lift the seedling out of the starting tray using a popsicle stick or a small spoon. Be very careful not to tug on the stem, as it is fragile and can easily snap. Always handle the seedling by its leaves rather than the stem if you must touch it.
Set the plant into the new pot at the same depth it was growing previously. Firm the soil gently around the roots and give it a thorough watering. Your plants will likely look a bit wilted for a day or two after the move, but they will soon recover and begin to grow much faster now that they have more room for their roots to spread.
What to do next:
- Monitor your plants for true leaves; this is your signal to start a very weak fertilizer routine.
- Prepare individual 3-inch or 4-inch pots for the first transplanting.
- Keep the lights close to the plants to prevent them from stretching.
- Rotate your trays every few days if they are near a window to ensure they grow straight.
Transitioning to the Great Outdoors
Moving your begonias from the protected environment of your home to the garden is a process called hardening off. This is a vital step because indoor-grown plants are soft and can easily be scorched by the sun or tattered by the wind if moved too quickly.
The Hardening Off Schedule
Start this process about two weeks before you plan to plant them permanently outside. On the first day, place your pots in a fully shaded, sheltered spot outdoors for just one or two hours, then bring them back inside.
Each day, increase their time outside by an hour or two. Gradually move them into slightly more light, such as filtered sunlight under a tree. Avoid direct midday sun, as tuberous begonias prefer the gentler light of morning or late afternoon. By the end of two weeks, your plants should be able to stay outside all day and night, provided the weather remains warm.
Final Planting Site
When choosing a spot in your yard, look for areas with well-drained soil and dappled shade. Tuberous begonias are perfect for Hanging Begonias:
- Hanging baskets on a porch.
- North or east-facing garden borders.
- Window boxes in shaded areas.
- Decorative containers on a patio.
We recommend using a potting mix that contains perlite or coarse sand to ensure excellent drainage. Begonias love moisture, but they do not like to sit in "wet feet," which can cause the stems or the developing tubers to rot.
Key Takeaway: Success outdoors depends on a slow transition. Give your begonias ten days to two weeks to adjust to the wind and temperature changes before planting them in their final summer home.
Summer Care for Maximum Blooms
Once your begonias are settled in the garden, they are relatively low-maintenance, but they do appreciate a bit of consistent attention. For more general care tips, see How Do I Care for a Begonia Plant?
Watering Wisely
Check the soil daily, especially for plants in containers or hanging baskets. Water when the top inch of soil feels dry to the touch. When you water, try to aim for the soil rather than the foliage. Wet leaves can lead to powdery mildew, a white dusty-looking fungus that can weaken the plant.
Regular Fertilizing
To keep the flowers coming all summer long, continue fertilizing every two weeks with a water-soluble flower fertilizer. Follow the instructions on the label for "container plants." Begonias are efficient at using nutrients to produce those large, showy petals.
Deadheading
"Deadheading" is the practice of removing faded flowers. For tuberous begonias, this is simple. When a flower begins to wilt or turn brown, simply snap the flower stem off where it meets the main branch. This keeps the plant looking tidy and encourages it to put its energy into creating new buds rather than setting seeds.
Understanding the Life Cycle: From Seed to Tuber
A fascinating part of growing tuberous begonias from seed is that the plant is actually creating its own tuber underground while it grows and blooms above ground. By the end of the first summer, if you were to gently dig up the plant, you would find a small, solid tuber at the base of the stems.
In the first year, this tuber will likely be small—perhaps the size of a marble or a walnut. As the plant gets older and goes through more growing seasons, the tuber will grow larger, eventually becoming as big as a saucer. The bigger the tuber, the more stems and flowers the plant can produce in future years.
This means that your hard work of growing from seed doesn't just give you one summer of beauty. It gives you a permanent addition to your garden collection that you can save and replant year after year.
Preparing for Winter Dormancy
As autumn approaches and temperatures begin to drop, your begonias will naturally start to slow down. If you are unsure about your local climate, check the Hardiness Zone Map. When the foliage begins to turn yellow or after the first light frost "blacks" the leaves, it is time to bring them in for the winter. Tuberous begonias are not hardy in most parts of the US and will not survive a frozen winter in the ground.
Lifting the Tubers
Cut the stems back to about two inches above the soil. Carefully lift the plants out of the ground or their containers. You will see the small tuber you've grown from seed! Gently brush off the excess soil, but do not wash them with water, as this can encourage rot during storage.
Curing and Storage
Let the tubers sit in a dry, room-temperature spot for about a week. This "cures" the outer skin. Once they are dry, you can remove the remaining bits of stem. Place the tubers in a box filled with dry peat moss, vermiculite, or even shredded newspaper.
For more end-of-season details, see How to Overwinter Begonia Plants. Store the box in a cool, dark, and dry place that stays between 40°F and 50°F. A basement or a cool closet is usually perfect. Check on them once a month during the winter to make sure they aren't shriveling or showing signs of mold. In the spring, you can start them all over again, but this time they will grow even faster because they have that stored energy in the tuber.
"Winter storage turns your annual seed project into a lifelong garden investment. The small tubers you grow this year are the foundation for even bigger blooms next summer."
Achieving the Best Results
Every garden is a little different, and your begonias will respond to your specific climate and soil. However, following the basic principles of "right plant, right place" will solve most issues before they start. If you want more guidance on placement, Where Do I Plant Begonias? is a helpful companion guide.
If you find your plants are not blooming well, they may need a bit more light. While they love shade, "deep shade" (where no light ever reaches) can result in lots of green leaves but few flowers. Moving them to a spot with bright, indirect light often solves the problem.
Conversely, if the edges of the leaves are turning brown and crispy, they might be getting too much direct afternoon sun. Moving them to a slightly more sheltered location will help them thrive. Gardening is a beautiful experiment, and adjusting to your plants' needs is part of the fun.
Conclusion
Growing tuberous begonias from seed is a patient, rewarding journey that transforms a tiny speck of a seed into a spectacular display of summer color. By starting early indoors and providing the right balance of light, warmth, and moisture, you can cultivate a stunning garden that lasts from the heat of July through the crisp days of autumn. Whether you are filling hanging baskets for your porch or creating a lush border in a shady nook, these plants are sure to bring a smile to your face.
- Start seeds in mid-winter to ensure plenty of time for development.
- Never cover the seeds with soil; they need light to germinate.
- Hardening off is the most important step for a successful move outdoors.
- Save your tubers at the end of the year to enjoy even bigger plants next season.
We invite you to explore the many varieties of begonias, including Upright Double Begonias, and other summer favorites available at Longfield Gardens. With a bit of care and the right start, your garden will be a place of beauty and relaxation all season long.
FAQ
How long does it take for begonia seeds to sprout?
Begonia seeds typically take between 10 and 21 days to germinate, though it can take up to a month in cooler conditions. Maintaining a consistent soil temperature of around 70-75°F and providing high humidity with a clear cover will help speed up the process.
Do I really need grow lights to start begonia seeds?
While it is possible to use a very bright, south-facing window, grow lights are highly recommended. Begonia seedlings are very sensitive to light levels and can quickly become weak and spindly if they don't receive 14–16 hours of consistent, direct light each day.
Can I save the seeds from my own begonias to plant next year?
You can collect seeds from dried pods in the fall, but keep in mind that many modern begonias are hybrids. This means the seeds you collect may not grow into a plant that looks exactly like the parent. For a specific color or shape, it is usually best to purchase fresh, high-quality seeds. For product quality and support details, see our About Us page.
Why are my begonia seedlings growing so slowly?
Begonias are naturally slow growers in their first few months as they focus on establishing a root system and a small tuber. Ensure they are being fed a very weak liquid fertilizer every two weeks and that they are not being overwatered, which can stall their growth.