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January 16th 2024

How to Grow Dahlias from Seed

Written by
Floret

One of the most exciting and surprising discoveries I made on my dahlia-growing journey was learning how new varieties were created. 

Unlike tubers or cuttings, which produce an exact clone of the plant they come from, dahlias grown from seed offer a treasure trove of new possibilities, each one something that’s never existed before. 

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. 

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. 

Dahlias do best in rich, heavily amended soil. We prepare planting beds with a generous dose of compost and organic fertilizer and then install drip irrigation. Learn more about soil preparation here.

Although they can handle the heat of summer, we recommend providing some afternoon shade in extremely hot climates. 

Space plants 12 in (30 cm) apart and water deeply twice a week. (Dahlia seedlings can be grown much closer together, with as little as 4 in [10 cm] between plants. This method will produce a jungle of towering stems and is how most professional breeders increase the number of seedlings they can grow in a season.) 

Slugs and snails love tender dahlia seedlings. We apply Sluggo immediately after transplanting to protect them while they get established. 

Plants inevitably grow tall and heavy and will require sturdy staking, which should be placed before they grow too large and topple over from the weight of their showy blossoms. 

If you’re growing dahlias in garden beds, you can pound individual stakes next to each seedling at planting time and tie them up as they grow. 

If you’re planting in long rows, plants can be corralled and held upright by pounding heavy stakes or T-posts around the perimeter of the bed and creating a string-lined box using bailing twine.

To increase the overall number of flowers and encourage long, strong stems, you’ll want to pinch them. Once plants are 8 to 12 in (20 to 30 cm) tall, use sharp pruners to snip off the top 3 to 4 in (7 to 10 cm), just above a set of leaves. This causes the plant to send up multiple stems below the cut. 

Unless you’re leaving seedpods to mature for breeding purposes, remove spent blooms often so the plants put their energy into flower production rather than making seed. 

If you discover varieties you love, you can dig them up at the end of the season to replant the following year. 

Dahlias grown from seed produce miniature clumps of tubers that are often not big enough to divide, so we store the entire bundle in a Ziploc bag filled with peat moss or vermiculite in a cool place that doesn’t freeze, between 40°F and 50°F (4°C–10°C). 

Dahlias are not terribly long-lasting cut flowers, but you can get about 5 days by picking at the right stage and using floral preservative. Dahlias won’t unfurl much after harvesting, so pick when they are almost fully open for large, full blooms. 

For singles and other open-centered varieties, pick just as the petals are unfurling and before the bees get to them.

If you haven’t grown dahlias from seed, I highly encourage you to give it a try—it’s the ultimate treasure hunt.

I’d love to hear about your experience with dahlias grown from seed and some of the discoveries you’ve made in your garden. 


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17 Comments

  1. Darlene MacDonald on

    Ive ordered dahlia seeds (shooting star) so starting from seed for first time. I’ll start 8 weeks before frost as recommended. I will plant seedlings in raised bed. I understand can plant them 4 inches apart but how close can I plant each row apart? I didn’t understand that part in the library? So I can put seedlings close 4 inches but how close are the rows? Thank you

    Reply
  2. Melody on

    Living in Iowa, surrounded by corn and cattle sun and wind; is there any of your varieties of dahlia you suggest? We are fully prepared for staking..

    Reply
  3. Val Schirmer on

    Hi guys! I’m going to start the seeds indoors now — do you recommend sowing into 72s and can I then bump them to a 4″ pot and grow on until it’s warm enough to put them in the ground? OR should I start them in the 4″ pot? It will be under lights and with a heat mat.

    Reply
    • BriAnn, Team Floret on

      We start ours in 72s and then transplant them into the ground from there without potting up. We recommemd starting them 4-8 weeks before it’s time to plant them outside. It’s important not to start them too early so they don’t get stressed in the seed trays.

  4. Gwen on

    thank you for what you offer to the world!

    Reply
  5. Cynthia O’Connor on

    I live in Northern Nevada where the summer highs can get in the high 90s. Not usually 100s but my backyard is full sun from probably 10am on. Would these flowers do well?

    Reply
  6. Germaine Licht on

    I am looking for container cut flowers that can take the heat and humidity of New Orleans, Zone 9.

    Reply
  7. Marley on

    What temperature do the dahlia seedlings need to be to survive and thrive? I am trying to figure out if I can grow them in trays in our potting shed (not insulated) with a lamp, or if they need to be truly indoors. We are located in the Bay Area, CA.

    Reply
    • Erin on

      You’ll want to keep the temp between 60-70* for them to stay in active growth.

  8. Fiela Winston on

    I just bought four varieties of your dahlia seeds. I have never planted a flower in my life but I want o give it a try come spring on my east facing balcony in Southern California. These are the most beautiful flowers I have ever seen in my life and hopefully, I get to see them in person if can manage this process correctly! :)

    Reply
  9. Sara on

    If you were to grow dahlias in pots from seed, what sort of spacing would be ideal? Say in a 14” diameter pot, just one seedling?

    Reply
  10. Donna on

    Where can we purchase dahlia seeds ?

    Reply
  11. Lyndy on

    And what do you fertilise them with please and how often?

    Reply
    • BriAnn, Team Floret on

      We use a combination of organic compost mixed into the soil and Nature’s Intent 7-2-4 fertilizer. Then we use compost tea biweekly throughout the growing season.

  12. Whitney on

    I started saving seeds from my dahlias and it was truly amazing! The beautiful first year seedlings that I grew. Such a rewarding experience. I’ll try to upload a photo and send you my absolute favorite.

    Reply
  13. Kate on

    I am so excited to start growing dahlia from seeds this year. After re-watching Floret show and reading a book Discovering Dahlias, I am very excited to try dahlia from seeds and come up with new varieties.

    Reply

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