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How to Grow Dahlias from Seed

Dahlias grown from seed won't look like the parent plant, so you'll get a new, unique variety every time. Here's how to grow dahlias from seed!

how to grow dahlias from seed

Dahlia flowers come in an astonishing variety of colors, forms, and sizes. Smaller flowers are about an inch across, and huge "dinner plate" varieties reach 12 inches or more in diameter. You can find dahlias in almost every conceivable color and shape.

Most people grow dahlias from tubers, which will be a genetic match to the parent plant. However, you can also grow dahlias from seed, which will then form tubers over the growing season. 

Every dahlia grown from seed is a never know what kind of flower you'll get! Who knows, maybe you'll discover the next Cafe Au Lait! If you find a keeper, you can dig up the tuber in the fall and replant it the following year.

cafe au lait dahlias

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Growing Dahlias from Seed

If you buy dahlia tubers or commercial seeds, they will grow out true to the parent type. However, if you collect dahlia seeds or buy a mixed packet like these, they will produce new forms that are totally unique!

Most dahlia seeds will have some genetic traits from single bloom, open faced flowers such as the collarette variety. It's easier for bees to access the pollen in these types of flowers, leading to cross-pollination with other dahlias.

collarette dahlia

What do dahlia seeds look like?

Dahlia seeds are long and fairly large, with one pointed end and one rounded end. They are typically dark brown or black when dried.

How to collect dahlia seeds

Growing dahlias from home-harvested seeds cross-pollinated by bees can be a fun and exciting project. You can also do the work of cross-pollinating dahlia flowers yourself, aiming to get specific results in color or flower form.

Collect ripe dahlia seeds in the fall after the flowers bloom and the seeds are dried out inside the seed heads. Store the seeds in a cool, dark, dry place until the following spring.

The video below shares more details about how to harvest dahlia seeds from your existing plants.

How to plant dahlia seeds

Planting dahlia seeds is a fairly straightforward process. You'll want to start about six weeks before your last frost date to give your new plants enough time to grow large enough to flower in late summer.

planting dahlia seeds in seed tray

Here are the basic steps for planting dahlia seeds:

  • Sow in clean, sanitized seed trays with one to two seeds per cell. 
  • Plant the seeds approximately ¼ inch deep in pre-moistened seed starting mix
  • Keep the soil surface damp, but don't let it get soggy. 
  • Put the containers in a location at approximately 70°F in bright light during the day. You can use a heat mat to keep the temperature even. 
  • When the seedlings have at least two sets of true leaves, transplant them outdoors in full sun and well-draining soil.
  • When the seedlings have four leaves, pinch off the top to encourage more abundant side branching. 

Dahlia seeds germinate in 3 to 14 days and will start blooming approximately 100 to 120 days after transplanting. Flowering continues until the first frost. 

Planting dahlias in the garden 

Once your seedlings have put on a few inches of growth and the soil is warm, you can plant them outside. Choose a spot in the garden with full sun and excellent drainage.

different colors of dahlias growing in the sun

Dahlias are sensitive to how much room their roots have to grow. If your soil is hard packed or there are lots of rocks or roots in the way, the tubers will have a difficult time reproducing underground.

To loosen up the soil around your future tubers, dig a hole two feet deep and wide. Then, mix two-thirds of the soil from the hole with one-third of high-quality compost or decomposed cow manure. In acid soils, incorporate some agricultural lime into the mix to raise the pH to 6.5 to 7.

Fill the hole with the soil mixture, and plant the seedling in the center. Place a four foot stake into the ground next to each seedling, so you can tie the stem to it as the plant grows. If you wait until the plant is taller, you risk puncturing the tuber with the stake when it's pressed into the ground. 

Now that you know how to grow dahlias from seed, you can create an entire field of unique, gorgeous flowers! When you decide on your favorites, you can dig up the tubers and store them for next year. Check out this article for more information about how to store dahlias tubers properly and how to know if they survived the winter!