Sunflowers are a classic summertime flower that brighten up any garden with their cheery faces. While they are typically direct sown outdoors after the last spring frost you can get a head start on the season by starting them indoors. Proper timing is crucial when starting sunflowers indoors to avoid stunted root-bound plants. Start too late and you may not get any blooms at all if your growing season is short.
This comprehensive guide will teach you exactly when and how to start sunflower seeds indoors for healthy, productive plants. With a few simple steps, you can enjoy earlier blooms and extend your harvest well into fall.
Why Start Sunflowers Indoors?
Here are some of the main benefits of getting a jumpstart on the season by starting sunflowers inside
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Earlier blooms: Sunflowers started indoors will flower sooner than direct sown plants. You can get color in your garden weeks before those planted outdoors.
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Staggered bloom times Succession planting allows you to have flowers over an extended period versus one short burst
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Expand options: Start heat-loving varieties that might not thrive in your area when direct sown. You can try new exotic or rare types.
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Shorter seasons: Get blooms before fall frosts end the season if you have fewer frost-free days.
As long as you time it right and avoid root-bound plants, starting indoors offers huge advantages!
When to Start Sunflower Seeds Indoors
Sunflower seedlings need:
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Warm soil: 65-70°F (18-21°C) minimum soil temperature for germination.
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Time to grow: Around 6-8 weeks before transplanting outside in your area.
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No frost: Transplanted after all danger of spring frosts have passed.
Using these factors, you can calculate the perfect start date:
Step 1: Find Your Average Local Last Frost Date
Your last spring frost date varies based on location. In the U.S. or Canada, you can use this tool to find your closest weather station data.
Outside North America, a web search for “your city last frost date” should find it. Local gardeners are also a great resource.
Step 2: Count Back 6-8 Weeks
Sunflowers grow quickly as seedlings and become root-bound if started too early indoors.
Count back 6-8 weeks from your average last frost date. This is the ideal start time in your area.
Step 3: Make Adjustments as Needed
If your garden has a warmer micro-climate, start 1-2 weeks later. Colder areas should start 1-2 weeks earlier.
For heat-loving varieties or to maximize season length, you can safely push back the start date by a few more weeks if needed.
Step 4: Succession Plant for Extended Blooms
To stagger blooms over months instead of weeks, succession plant a portion of seeds every 1-2 weeks.
Time your last planting so flowers mature before fall frosts. Pay attention to “days to maturity” for each variety.
How to Start Sunflower Seeds Indoors
Follow these simple steps for starting sunflowers inside and hardening off for transplanting:
Supplies Needed
- Sunflower seeds
- Seed starting mix
- Containers (cell packs, peat/cow pots, etc)
- Grow lights
Seed Starting Steps
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Moisten seed starting mix and fill containers.
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Plant seeds 1⁄2 inch deep, 2-3 inches apart.
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Cover containers, provide 65-70°F for germination.
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Once sprouted, provide 14-16 hours of light daily.
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Keep soil consistently moist but not soaked.
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Allow 6-8 weeks of growth before hardening off.
Hardening Off Steps
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Move containers outside to shaded spot for 1-2 hours.
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Slowly increase light exposure and time outside over a week.
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Transplant into garden after last frost, spacing 12-24 inches apart.
Proper hardening off prevents transplant shock!
The Perfect Time for Sunflower Seedlings
With this handy guide, you can confidently determine the ideal starting date for your area and conditions. Just remember these key tips:
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Start 6-8 weeks before your last spring frost date.
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Adjust 1-2 weeks on either side based on micro-climate.
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Succession plant every 2 weeks for extended harvests.
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Allow enough time to maturity before fall frosts.
With the right timing, you can enjoy prolific blooms from cheerful sunflowers all season long. Now go grab those seeds and get growing!
How to Plant Sunflower Seeds Indoors – With Kelly Lehman
FAQ
How early can I start sunflower seeds indoors?
Sunflower seeds should be started indoors 4-6 weeks before the last average frost date in your area, which typically occurs in March.Feb 13, 2023
What is the best month to plant sunflowers?
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Timing:
- Sunflowers thrive in warm weather, so wait until the danger of frost has passed and the soil temperature is consistently above 50°F.
- In Southern California, this typically occurs around late March or early April.
- You can plant seeds directly into the garden or start them indoors and transplant them once they’re large enough.
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Soil:
- Sunflowers prefer well-drained soil.
- Amend the soil with compost or other organic matter to improve fertility and drainage.
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Sunlight:
- Sunflowers need at least 6-8 hours of sunlight per day.
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Spacing:
- Space sunflower plants according to their variety, typically 6-12 inches apart for smaller varieties and 2-3 feet apart for larger varieties.
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Watering:
- Water the plants regularly, especially during dry periods, but avoid overwatering.
Can potted sunflowers survive indoors?
Sunflowers can be grown in pots or sown directly into the ground. They can be started off indoors in early spring and will grow quite happily on a window sill for a time. Alternatively, seeds can be planted outside directly once the risk of frost has passed.
Should I start sunflowers in pots?
You can definitely grow sunflowers in pots/containers. Miniature sunflowers can be easily grown in an 8-inch pot (with proper fertilizer you can even grow 2 to 3 in the same pot). Giant or the large varieties will need at least a 5-gallon container for each plant. The bigger the pot, the bigger the flower will be.
When can I plant sunflower seeds indoors?
If you live in an area with a very long growing season and late first fall frosts, you can sow seeds indoors in early March. Just be sure to provide ample light and space for the seedlings as they grow into young plants over the 2+ months before outdoor planting. Stagger planting sunflower seeds every 2 weeks indoors for continued blooms.
Should you plant sunflowers indoors?
It’s really important to start Sunflowers indoors from seed at the right time – more-so than most varieties – because of their taproot. Sunflowers are fast growers and extra sensitive to becoming root bound. However, if you plant them too late you might miss out on the early harvest advantage of starting indoors.
Can you plant sunflower seeds early?
Starting sunflowers early also gives you the option to plant the flowers as a natural trellis near climbing plants like pole beans. When can you plant sunflower seeds? Plan to plant sunflower seeds indoors about 4 weeks before your area’s last frost date.
How do I start sunflowers indoors?
It is really easy to start Sunflowers indoors. All you need are your sunflower seeds, some paper towels, water, and a bag or container (ziploc-type bags work as well as take out food containers- no need to get fancy).
Do sunflowers need a lot of time to grow?
The smaller, shorter flowers will need less time while the larger, taller mammoth types need more days to maturity. Some people have even grown Sunflowers indoors year round (not just in a greenhouse, but their living room too!) by choosing the right variety.
How long does it take a sunflower to grow?
Sunflowers are hardy in USDA growing zones 4-9 and typically take about 80-120 days to reach maturity (which means grow, flower, and seeds are ready), depending on variety. The smaller, shorter flowers will need less time while the larger, taller mammoth types need more days to maturity.