Dahlias are beloved for their stunning diversity of colors, shapes and sizes But when is the optimal time to sow dahlia seeds to get these spectacular blooms in your garden? Here is a complete guide to understanding when and how to plant dahlia seeds for success.
An Overview of Dahlia Seed Germination
Before diving into planting times it’s helpful to understand some basics about dahlia seed starting
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Dahlia seeds have relatively low germination rates, typically 30-75%.
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They take 1-2 weeks to germinate after planting.
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Germination is sporadic over this time.
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Seeds need warm soil temperatures around 70°F to germinate well.
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Starting dahlia seeds indoors is recommended. Direct sowing outdoors is difficult.
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Give seedlings 14-16 hours under grow lights or sunlight daily.
Knowing these key facts provides helpful context for determining the best planting time based on conditions in your region.
When to Start Dahlia Seeds Indoors
Dahlia seeds should be started indoors 4-8 weeks before the intended planting date. This gives enough time for the seeds to germinate and seedlings to grow large enough to transplant.
Here are some general indoor starting guidelines based on your zone:
Zones 3-6
- Start seeds indoors 6-8 weeks before your last expected spring frost date.
Zones 7-9
- Start seeds indoors 4-6 weeks before your average last frost date.
Zones 10-11
- Start seeds in late winter, 8-10 weeks before your spring planting timeframe.
You may want to begin on the earlier side of these ranges if hoping to get earlier blooms. Just be prepared to provide supplemental lighting and warmth.
Transplanting Dahlia Seedlings Outdoors
The ideal window for moving dahlia seedlings into the garden is typically 3-4 weeks after the last average spring frost date for your area.
Some guidelines for transplanting seeded dahlias outside include:
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Harden off seedlings for 7-10 days first to transition them to outdoor conditions.
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Wait until nighttime temperatures remain above 50°F consistently.
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Plant in full sun in fertile, well-drained soil.
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Space plants 12-18 inches apart in rows or clusters.
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Provide support for stems immediately after transplanting.
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Pinch out the center stem once seedlings reach 6 inches tall.
With proper hardening off and spacing, your seedling dahlias should thrive when moved outdoors at the right planting time for your zone.
Direct Sowing Dahlia Seeds Outdoors
Direct sowing dahlia seeds into garden beds is possible but more challenging than starting seeds indoors. Here are some tips if you want to try direct sowing:
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Wait 2-4 weeks after your average last spring frost to sow.
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Choose the warmest, sunniest part of your garden.
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Prepare soil by mixing in extra compost to retain heat.
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Sow seeds 1/4-1/2 inch deep in rows 18-24 inches apart.
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Water gently daily until seeds sprout, which takes 10-15 days outdoors.
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Use row cover to maintain soil warmth and moisture.
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Thin seedlings to 12-18 inches apart.
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Provide support for plants immediately after thinning.
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Pinch out center stem once seedlings reach 6 inches.
Even when direct sown, be prepared to protect young dahlia seedlings from any late frosts with coverings as needed.
Fall Planting of Dahlia Seeds
In frost-free climates (zones 9-11), dahlia seeds can be planted in late summer or early autumn to produce winter and early spring blooms. Follow these fall planting guidelines:
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Sow seeds 8-10 weeks before first expected fall frost.
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Choose warm, protected planting sites against south-facing walls or structures.
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Use cloches, cold frames, or mini-hoop houses over seeded areas for extra cold protection.
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Transplant seedlings to protected areas of the garden once they reach 6 inches tall.
With proper timing and protection from cooler weather, you can enjoy unique winter-blooming dahlias from seeds planted in the fall.
Adjusting for Your Microclimate
Always take your specific garden microclimate into account when deciding planting times. Gardens in cooler pockets or zones should wait a week or two longer when scheduling both seed starting and transplanting dates.
Likewise, warmer sites can often safely move up timelines by a week or two for earlier blooms. Pay attention to weather patterns in your area, and adjust dates accordingly for planting success.
Get Ready to Plant Dahlia Seeds!
One of the joys of starting dahlias from seed is discovering the variety of colors and forms that develop from your planting. Just be sure to provide warm growing conditions, consistent moisture, and protection from frost when starting and transplanting dahlia seeds.
With the right timing for your climate, you’ll soon be rewarded with vibrant, diverse blooms unlike any other flower. So get your seeds and supplies ready to plant dahlias at the perfect time this season!
Planting Dahlia Seeds In Seed Trays Under Grow Lights
The other method is to plant your seedlings directly onto your seed trays. Fill your seed starting trays with seed starting mix. Poke a small hole in each of the seed cells. Take dahlia seeds and sow seeds, with one in each seed cell. Bottom water the seed tray and cover with a clear acrylic dome. I like to place my seed tray on a heat mat and underneath a grow light. This ensures that the soil is warm enough for germination. Dahlia seeds need a warm location to germinate and grow. Seedlings should emerge within 3-5 days.
I did an experiment this winter and tried starting dahlia seeds using both of the methods above. I actually found that the dahlia seeds sprouted in about the same amount of time using both methods. However, the seeds that were germinated underneath grow lights in the cell plug flats actually grew better initially. Within a week of both being planted in cell plugs, it was hard to tell the difference in either method. The only downside to direct sowing is that you may end up with empty seed cells because of low germination rates with dahlia seeds.
When you should plant dahlia seeds
When growing dahlias from seed, you want to plant dahlia seeds indoors about 6-8 weeks prior to your last frost date. If you do not know your growing zone’s last frost date, you can find it here. This will give your dahlia seeds time to start growing and to be ready to plant outside. You do not want to transplant your dahlia starts outside until all danger of frost has passed.
How To Grow Dahlias From Seed
FAQ
When should you start dahlias from seed?
We typically transplant them 3 to 4 weeks after our last spring frost. Seeds should be started indoors at least 4 to 8 weeks before you want to plant them out. Dahlia seeds germinate sporadically, so be patient—they will come up but it can take up to two weeks. Direct-seeding into the garden isn’t recommended.
Do dahlias grown from seed come back next year?
Yes, dahlias are perennial plants, which means they can grow back every year. However, they are sensitive to freezing temperatures. In colder climates, their tubers need to be dug up and stored over the winter to ensure they return the following year.
What is the best month to plant dahlias?
Spring to early summer is the best time for planting dahlia tubers in the ground. Depending on what variety you choose, you’ll see flowers from summer through autumn, and in some cases (such as with Tree Dahlias) even into early winter.
Is it better to grow dahlias from seed or tuber?
However, as tubers store more energy than seeds, you’re more likely to see longer and better flowering in year one.
How do you grow dahlias from seed?
To grow Dahlias from seed, start by sowing them indoors 6-8 weeks before the last expected frost. Use a seed tray with well-draining soil and keep it moist but not waterlogged. Once seedlings have at least two leaf sets, transplant them into individual pots. Move outdoors after the danger of frost has passed.
When can you plant dahlia seeds?
“Dahlias can be started indoors from seed six to 10 weeks before your desired planting date,” says Marina Sideris, co-owner of Dooryard Farm, an organic farm in Camden, Maine. Alternatively, you can sow dahlia seeds directly outside after the risk of frost has passed in spring.
How long do dahlia seeds take to grow?
This will give your dahlia flower seeds enough time to get growing so that they can flower in the summer months. Dahlias will bloom until your first frost. It takes about 100-120 days for the seeds to produce flowers. There are several ways you can get your dahlias seeds to germinate.
When should I transplant my Dahlia seedlings?
The opportunities are endless, and if you find one you love, you get to name it! Dahlia seedlings are extremely cold sensitive, so don’t plant them outside until the weather has sufficiently warmed. We typically transplant them 3 to 4 weeks after our last spring frost.
How do you grow dahlias in the summer?
Prepare your soil with nutrients before you plant tubers four to six inches in the ground. Cut dahlias back regularly throughout growing season to encourage more blooms, and dig up tubers in fall. Lush dahlias are one of the most delightful summer sights in the garden.
When should you plant dahlias outside?
Dahlias are tender annuals, meaning you’ll need to wait until the danger of frost has passed before you can start planting outside. “The last frost date is the average date of the last light freeze in the spring,” says Caitlin Meredith, owner of Quietside Flower Farm in Downeast Maine.