Begonia Seed Starting Schedule: When to Start Begonias Indoors by Zone
Why Timing Is Everything for Begonia Seeds
Begonias are one of the most rewarding flowers you can grow from seed — but they are also one of the most unforgiving when it comes to timing. Start them too late and you will be waiting all summer for blooms. Start them too early without the right setup and you end up with leggy, stressed seedlings that never fully recover.
The good news: once you understand the zone-based schedule, begonia seed starting becomes completely predictable. This guide breaks down exactly when to start begonias indoors based on your USDA hardiness zone, what conditions they need to thrive, and how to get from tiny seed to full, blooming plant by the time warm weather arrives.
Whether you are growing trailing begonias for hanging baskets or tuberous begonias for bold container displays, the principles are the same — only the calendar changes.
Understanding Begonia Seed Starting Basics
Before diving into the zone chart, it helps to understand what makes begonias different from most other flower seeds.
Begonia seeds are dust-fine. They are among the smallest seeds you will ever handle. Most quality begonia seeds are sold as pelleted seeds — coated in a clay-like material that makes them easier to handle and space properly. This is especially important for varieties like the Begonia Groovy Mix Trailing Begonia, where even spacing leads to more uniform germination.
They need light to germinate. Unlike most seeds that prefer darkness, begonia seeds require light to trigger germination. Never cover them with soil. Press them gently onto the surface of a moist, fine-textured seed-starting mix and place them directly under grow lights.
They are slow. Begonias take 14 to 21 days to germinate and then grow slowly for the first several weeks. This is why they need such a long indoor head start — typically 12 to 16 weeks before your last frost date.
They hate cold. Begonias are frost-tender and should never be transplanted outdoors until nighttime temperatures are consistently above 50°F. In most zones, that means waiting until well after your official last frost date.
Begonia Seed Starting Schedule by USDA Zone
Use the chart below to find your zone and calculate your ideal indoor start date. All dates are based on average last frost dates and assume a 14-week indoor growing period, which is the sweet spot for most begonia varieties.
| USDA Zone | Avg. Last Frost Date | Start Seeds Indoors | Safe Transplant Date |
|---|---|---|---|
| Zone 3 | Late May – Early June | Early to Mid-February | Early June |
| Zone 4 | Mid to Late May | Late January – Early February | Late May |
| Zone 5 | Mid-May | Late January – Early February | Mid to Late May |
| Zone 6 | Mid-April | Late December – Early January | Late April – Early May |
| Zone 7 | Early April | Mid to Late December | Mid to Late April |
| Zone 8 | Mid-March | Late November – Early December | Late March – Early April |
| Zone 9 | Late February | Early to Mid-November | Early March |
| Zone 10 | No frost / Year-round | October – November | December – January |
| Zone 11 | No frost / Year-round | Any time (avoid peak heat) | Year-round |
Note: Always verify your specific last frost date using your local extension service or a zip-code frost date tool, as microclimates can shift these dates by 1 to 3 weeks.
Choosing the Right Begonia Variety for Your Zone
Not all begonias perform equally in every zone. Here is a quick breakdown of which types tend to excel where.
Trailing Begonias (Zones 3–9): The Begonia Groovy Rose Trailing Begonia and its siblings in the Groovy series are bred for heat tolerance and cascading growth. They are exceptional in hanging baskets and window boxes and perform well across a wide range of zones. In hotter zones (8–9), they appreciate afternoon shade.
Tuberous Begonias (Zones 4–9): The Prism series, including the Begonia Prism White and Begonia Prism Sunset, produces large, upright blooms with exceptional color saturation. These are ideal for containers and shaded garden beds. They are slightly more cold-sensitive than trailing types, so do not rush transplanting in Zones 4 and 5.
For the full range of available varieties, browse the Begonia Seeds collection.
Step-by-Step: How to Start Begonia Seeds Indoors
1. Gather Your Supplies
You will need a fine-textured seed-starting mix (not potting soil), shallow trays or cell packs, a humidity dome, and a grow light. Bottom heat from a seedling heat mat is highly recommended — begonias germinate best at 70–75°F soil temperature.
2. Prepare Your Trays
Fill trays with moistened seed-starting mix. The surface should be smooth and firm — not fluffy. Begonia seeds are so small that any air pockets near the surface can prevent good seed-to-soil contact.
3. Sow the Seeds
Place pelleted begonia seeds on the surface, spacing them about 1 inch apart. Do not cover with soil. Mist lightly with a spray bottle to settle them in place. Cover with a humidity dome and place under grow lights immediately.
4. Maintain Moisture and Light
Keep the surface consistently moist — never soggy, never dry. Check daily. Germination typically begins at 14 to 21 days. Once sprouts appear, remove the humidity dome gradually over 3 to 4 days to acclimate seedlings to lower humidity.
5. Provide Adequate Light
Begonia seedlings are prone to legginess if light is insufficient. Keep grow lights 2 to 4 inches above the seedling canopy and run them for 14 to 16 hours per day. If you have struggled with leggy seedlings in other crops, the same principles apply — check out our guide on how to fix leggy petunias for light management strategies that translate directly to begonias.
6. Fertilize Lightly
Begin fertilizing with a diluted, balanced liquid fertilizer (quarter strength) once seedlings have their first true leaves. Increase to half strength as they grow. Begonias are light feeders — more is not better here.
7. Pot Up as Needed
When seedlings are large enough to handle (usually 6 to 8 weeks after germination), transplant them into individual 2- to 3-inch pots. This gives roots room to develop before the final transplant outdoors.
8. Harden Off Before Transplanting
Begin hardening off 7 to 10 days before your planned outdoor transplant date. Start with 1 to 2 hours of sheltered outdoor time per day, gradually increasing exposure. Never expose begonias to temperatures below 50°F during this process.
Common Begonia Seed Starting Mistakes to Avoid
Starting too late. This is the most common mistake. Begonias need 12 to 16 weeks indoors. If you miss your window, you will be waiting until midsummer for blooms. Refer to the zone chart above and set a calendar reminder.
Covering seeds with soil. Begonia seeds need light to germinate. Covering them — even lightly — dramatically reduces germination rates.
Overwatering. Begonia seedlings are highly susceptible to damping off. Water from the bottom when possible and ensure trays have drainage. Never let seedlings sit in standing water.
Transplanting too early. Even if your last frost date has passed, wait until nighttime temperatures are reliably above 50°F. A cold snap after transplanting can set begonias back by weeks.
If you are new to indoor seed starting in general, our guide on starting marigold seeds indoors covers the fundamentals of grow light setup, watering technique, and seedling care that apply across most flower crops.
Begonia Seed Starting for Cut Flower Growers
If you are growing begonias as part of a cut flower operation, tuberous types like the Prism series are your best bet. Their large, rose-like blooms have excellent vase life and make striking additions to mixed arrangements. For cut flower production, aim for the earlier end of your zone's start window to maximize your bloom window before summer heat sets in.
Pair begonias with other long-season crops started on a similar schedule. Our guide on growing pansies from seed covers another cool-season flower that benefits from an early indoor start and complements begonias well in spring arrangements.
For growers who want to scale up, bulk pelleted begonia seeds are available through our sister site — Trailing Petunia Bulk Seeds — where you can find larger pack sizes for production-scale planting.
Frequently Asked Questions
How long do begonia seeds take to germinate?
Begonia seeds typically germinate in 14 to 21 days at 70–75°F (21–24°C). Pelleted seeds may take slightly longer to absorb moisture and crack open, so keep the surface consistently moist without overwatering.
Do begonia seeds need light to germinate?
Yes. Begonia seeds are extremely tiny and require light to germinate. Do not cover them with soil — simply press them onto the surface of a moist, fine-textured seed-starting mix and place them under grow lights or in a bright location.
When should I start begonia seeds indoors in Zone 5?
In Zone 5, start begonia seeds indoors 14 to 16 weeks before your last frost date, which typically falls in mid-May. That means starting seeds in late January to early February.
Can I direct sow begonia seeds outdoors?
No. Begonia seeds are far too tiny and slow-growing to direct sow outdoors. They require a long indoor head start — typically 12 to 16 weeks — before transplanting after all frost danger has passed.
What is the difference between trailing begonias and tuberous begonias?
Trailing begonias, like the Begonia Groovy series, have a cascading habit ideal for hanging baskets and containers. Tuberous begonias, like the Begonia Prism series, grow more upright with large, showy blooms suited to beds and pots. Both are started from seed indoors using the same basic method.
How do I harden off begonia seedlings before transplanting?
Begin hardening off begonia seedlings 7 to 10 days before your planned transplant date. Start by placing them outdoors in a sheltered, shaded spot for 1 to 2 hours per day, gradually increasing sun exposure and time outdoors over the week. Bring them in if temperatures drop below 50°F.
Ready to get started? Browse our full selection of begonia seeds and find the perfect variety for your zone and garden style. And if you want to go deeper on seed starting techniques, subscribe to us on YouTube for video guides on everything from germination setup to transplanting day.