How Long Do Begonias Take to Grow From Seed

Table of Contents

1. Introduction
2. The Overall Timeline for Begonia Seeds
3. Stage 1: Sowing and Germination (Weeks 1 to 3)
4. Stage 2: The Seedling Phase (Weeks 4 to 10)
5. Stage 3: Transplanting and Strengthening (Weeks 11 to 16)
6. Factors That Influence Growth Speed
7. Moving Your Begonias Outdoors
8. Why Growing From Seed is Worth the Wait
9. Simple Care Tips for Healthy Begonias
10. Summary of the Begonia Seed Journey
11. Conclusion
12. FAQ

Introduction

There is a unique kind of magic in watching a tiny, dust-like seed transform into a lush, flowering begonia. Whether you are dreaming of trailing blossoms in hanging baskets or neat rows of wax begonias in your garden borders, starting from seed is an incredibly rewarding way to fill your landscape with color. It offers a sense of accomplishment that only a gardener truly understands, allowing you to witness every stage of a plant's life cycle from the very beginning.

At Longfield Gardens, we want to help you succeed with every planting project, no matter how ambitious it may seem. While many gardeners choose to start with tubers or nursery-grown plants, growing from seed allows you to access a much wider variety of colors and leaf patterns. This guide is designed for home gardeners who are ready to start their seeds indoors and want to know exactly what to expect regarding timing and care. If you want to explore our begonias, that’s a good place to start.

Growing begonias from seed requires a bit more patience than growing sunflowers or zinnias, but the process is straightforward once you understand the timeline. You can expect the journey from sowing the seed to seeing your first bloom to take anywhere from four to six months. By starting early and providing the right environment, you can ensure your begonias are sturdy, healthy, and ready to shine all summer long.

The Overall Timeline for Begonia Seeds

When you decide to grow begonias from seed, the most important thing to remember is that they are slow starters. In the gardening world, we often refer to them as "long-season" plants. This means they need a significant amount of time indoors before the weather warms up enough for them to move outside.

On average, begonias take about 12 to 16 weeks to reach a size where they are ready to be transplanted into the garden. If you want them to be in full bloom by the time you set them out in late May or early June, you should plan to start your seeds in mid to late January. For zone timing, check the hardiness zone map.

Here is a quick look at the major milestones you will see:

• Germination: 15 to 21 days
• First true leaves: 5 to 7 weeks after sowing
• Transplant readiness: 12 to 14 weeks after sowing
• First blooms: 18 to 22 weeks after sowing

Because the seeds are so small and the initial growth is so gradual, it is easy to think nothing is happening. However, during those first few months, the plant is focusing its energy on building a complex root system and sturdy stems. This slow and steady approach is what makes begonias so resilient once they finally reach the garden.

Stage 1: Sowing and Germination (Weeks 1 to 3)

The first step in the journey is getting the seeds into the soil. Begonia seeds are famously tiny—they look more like fine dust or grains of pepper than traditional seeds. Because of this, they have very specific needs when it comes to light and moisture.

Surface Sowing for Light

Unlike many other seeds that need to be buried deep in the earth, begonia seeds need light to germinate. This means you should "surface sow" them. Simply sprinkle the seeds on top of a sterile, moist seed-starting mix. Instead of covering them with soil, gently press them into the surface with your fingertip or a flat piece of cardboard. This ensures the seeds have contact with the soil while still being exposed to the light they need to wake up.

Temperature and Moisture

During these first three weeks, warmth is your best friend. Begonia seeds prefer a consistent temperature between 70°F and 75°F. Many gardeners use a waterproof heat mat designed for plants to keep the soil at the perfect temperature.

Moisture is also critical, but because the seeds are so small, a heavy watering can wash them away or bury them too deep. Use a fine misting bottle to keep the surface of the soil damp. To hold in that moisture, cover your seed tray with a clear plastic dome or a sheet of plastic wrap. This creates a miniature greenhouse environment that protects the seeds while they begin to sprout.

Key Takeaway: Begonia seeds must be sown on the surface because they require light to germinate. Keeping them warm and consistently moist is the secret to seeing sprouts within the first three weeks.

Stage 2: The Seedling Phase (Weeks 4 to 10)

Once you see the first tiny green specks appearing in your tray, the germination phase is over and the seedling phase begins. This is often the stage where gardeners need the most patience. Begonia seedlings grow very slowly at first, and it may take several weeks before you see a second set of leaves.

Providing Ample Light

As soon as the seeds sprout, remove the plastic cover and move the tray directly under grow lights. While a sunny windowsill might seem like a good spot, the winter sun in many parts of the US isn't strong enough or consistent enough for begonias. For more light guidance, see Are Begonias Shade or Sun Plants?

Keep your grow lights about 2 to 3 inches above the tops of the plants. You will need to leave the lights on for 14 to 16 hours a day. This consistent light helps the plants grow strong and prevents them from becoming "leggy," which is when a plant grows tall and weak because it is searching for light.

Feeding Your Young Plants

Around week four or five, your seedlings will benefit from a very light feeding. Use a water-soluble fertilizer at about one-quarter of the strength recommended on the package. Because the plants are still delicate, "weak and frequent" is a better approach than one heavy dose of nutrients. This provides the building blocks the plants need to start producing their first "true leaves," which are the leaves that actually look like begonia foliage rather than the simple rounded leaves of a new sprout.

Thinning and Spacing

If you find that your seeds were sown too closely together, you may need to thin them out. If seedlings are crowded, they will compete for light and air, which can lead to stunted growth. You can use a pair of small scissors to snip away the smaller, weaker plants, leaving the strongest ones with plenty of room to expand. If you are planning a bed, How Far Apart Should Begonias Be Planted? is a helpful next step.

Stage 3: Transplanting and Strengthening (Weeks 11 to 16)

By the time your begonias are about three months old, they should have several sets of true leaves and look like miniature versions of adult plants. At this stage, they are ready to be moved from their starter trays into individual pots.

Moving to Individual Pots

Moving the seedlings into 3-inch or 4-inch pots gives the roots more room to grow. Use a high-quality, soil-less potting mix that offers good drainage. Drainage refers to how quickly water moves through the soil; you want the soil to stay moist but never soggy.

When you move the plants, be very gentle with the stems. It is often safest to lift the plant by its leaves or by the root ball using a small spoon. Once they are in their new pots, continue to keep them under the grow lights. You will notice that once they have more space and a bit more fertilizer, their growth rate will start to pick up.

What to Do Next: Mid-Growth Checklist

• Check the roots: If roots are starting to poke out the bottom of the tray, it is time to transplant.
• Adjust your lights: As the plants get taller, move your grow lights up to maintain that 2-to-3-inch gap.
• Monitor moisture: Larger plants in individual pots will dry out faster than seeds in a covered tray. Check the soil daily.
• Pinch for bushiness: If you want a fuller, bushier plant, you can pinch off the very top set of leaves once the plant has six to eight leaves. This encourages the plant to grow outward rather than just upward.

Factors That Influence Growth Speed

While the four-to-six-month timeline is standard, several environmental factors can either speed up or slow down the process. Understanding these variables helps you adjust your care routine to keep your plants on track.

Soil Temperature

Begonias are tropical plants by nature. If your indoor space is cool (below 65°F), the plants will grow much slower. Using a heat mat not only helps with germination but can also be used in the early seedling stages to keep the root zone warm, which encourages faster nutrient uptake and cell division.

Light Intensity and Duration

The "how long" of begonia growth is directly tied to "how much" light they receive. If the lights are too far away, the plant spends its energy growing a long, thin stem instead of leaves and roots. By keeping the lights close and running them for at least 14 hours, you maximize the plant's ability to create energy through photosynthesis.

Variety Differences

Different types of begonias have slightly different growth rates.

• Wax Begonias: These are generally the fastest to grow from seed and are often the first to show blooms.
• Tuberous Begonias: These take the longest. They are busy building a tuber (a thick, underground storage stem) while they grow, which requires a lot of energy.
• Dragon Wing and Angel Wing: These fall somewhere in the middle, typically taking about 18 weeks to reach a substantial size.

Moving Your Begonias Outdoors

After months of indoor care, the final step in the timeline is moving your plants to their permanent home in the garden. However, you cannot move them directly from a controlled indoor environment to the great outdoors all at once. They need a transition period called "hardening off."

The Hardening Off Process

Hardening off typically takes about 7 to 10 days. Start by placing your pots in a sheltered, shady spot outside for just an hour or two during the warmest part of the day. Each day, gradually increase the amount of time they stay outside and slowly expose them to a bit more sunlight (if they are a sun-tolerant variety).

This process allows the plant's cell structure to toughen up, making it more resistant to wind and temperature swings. If you skip this step, the tender leaves can easily become scorched by the sun or damaged by a light breeze.

Timing the Final Planting

Never plant your begonias in the ground until all danger of frost has passed and the soil has warmed up. In many parts of the US, this is usually a few weeks after the last frost date. We recommend waiting until nighttime temperatures consistently stay above 50°F. Begonias love the warmth, and planting them too early in cold soil can cause them to stall or "sulk," negating all the progress you made indoors. Before you ship or plant, review shipping information.

Key Takeaway: The hardening off process is the bridge between indoor success and outdoor beauty. Taking one extra week to acclimate your plants ensures they thrive immediately upon planting.

Why Growing From Seed is Worth the Wait

It is true that you could go to a garden center in May and buy a flat of begonias in five minutes. So, why spend five months growing them yourself? For many of us at Longfield Gardens, the answer lies in the variety and the value.

When you grow from seed, you can choose from specialized mixes that include bi-colored blooms, unique bronze foliage, or cascading habits that aren't always available at local stores. Furthermore, a single packet of seeds can produce dozens of plants for a fraction of the cost of buying individual starts. For a broader overview, All About Begonias is a useful companion guide.

There is also a deep sense of satisfaction in knowing you raised those plants yourself. When neighbors ask where you found such beautiful, unique begonias, you can proudly tell them you grew them from a tiny speck of a seed. That connection to the growing process makes every bloom feel a little more special.

Simple Care Tips for Healthy Begonias

Once your begonias are established in the garden, they are surprisingly low-maintenance. To keep them blooming until the first frost of autumn, follow these simple rules:

• Watering: Begonias like consistent moisture, but they don't like to sit in "wet feet." Water the soil, not the leaves, to prevent fungal issues. Let the top inch of soil dry out slightly before watering again.
• Fertilizing: To support those long-lasting blooms, give them a balanced liquid fertilizer every two to three weeks throughout the summer.
• Mulching: A thin layer of mulch around the base of the plants helps retain moisture and keeps the roots cool during the heat of July and August.
• Deadheading: For most modern wax begonias, the old flowers fall off on their own (this is called "self-cleaning"). However, for tuberous varieties, removing faded flowers helps the plant focus its energy on producing new ones. If you want more pairings, see What Plants Grow Well With Begonias?

Summary of the Begonia Seed Journey

Growing begonias from seed is a marathon, not a sprint. While the 20-week average timeline might seem long, the actual work involved is minimal once you have your indoor setup established. By starting in January, you turn the quietest months of the gardening year into a productive season of growth.

The key to success is providing that early warmth, consistent light, and plenty of patience during the slow seedling phase. Before you know it, those tiny green specks will be the stars of your summer containers and garden beds.

What to Do Next:

• Order your seeds by early January so you are ready to plant.
• Set up your light station and heat mats in a quiet corner of your home.
• Mark your calendar for 16 weeks after your sowing date—that is your target for moving plants outdoors!

Conclusion

Growing begonias from seed is a wonderful way to expand your gardening skills and enjoy a wider variety of these spectacular flowers. While the timeline is longer than many other annuals, the process is very manageable for any home gardener with a bit of space and some basic equipment. At Longfield Gardens, we believe that the time you invest in your plants is always returned in the form of beauty and garden joy.

By following the steps of surface sowing, providing consistent heat and light, and properly hardening off your plants, you can create a professional-quality display in your own backyard. Whether you are filling window boxes with trailing tuberous begonias or edging a walkway with colorful wax varieties, the results of your hard work will be evident in every vibrant blossom. For a quick refresher on growing habits, Are Begonias Annual Plants? can help you plan.

The beauty of a begonia garden is a testament to the gardener's patience. Starting from a seed that is barely visible and watching it grow into a show-stopping plant is one of the most rewarding experiences you can have in the garden.

We hope this guide gives you the confidence to start your own begonia seeds this season. It is a rewarding journey that turns the late winter months into a celebration of new life and the promise of a beautiful summer ahead.

FAQ

Can I start begonia seeds in March and still get flowers?

Starting in March is possible, but your plants will be quite small when it is time to move them outside. You likely won't see significant blooming until late August or September. For a full season of color, it is much better to start in January or February.

Why are my begonia seedlings not growing?

Begonias go through a very slow growth phase right after germination. They are often building roots that you cannot see. Ensure they have enough light (14+ hours) and that the room temperature is above 70°F. If they have their true leaves, a very weak fertilizer can also help jumpstart their growth.

Do I need to cover begonia seeds with soil?

No, begonia seeds should not be covered with soil. They are "photoblastic," which means they need light to trigger the germination process. Simply press them gently onto the surface of your moist seed-starting mix so they stay in place but remain exposed to the light.

How do I water begonia seeds without washing them away?

Because the seeds are so small and sit on the surface, you should never use a watering can or a hose. Instead, use a spray bottle set to a fine mist. This provides the necessary moisture without disturbing the seeds' position on the soil surface.