How To Grow Dahlias From Seed

Dahlias are a beautiful flower to cultivate in any garden because they come in a wide range of colors and sizes, and you can easily grow Dahlias from seed right at home. The plant size varies from species with plate-sized flowers on 6-foot plants to small border variants. Despite their wide variety, dahlias often have long, upright stems that allow the blooms to stand out.

Dahlias prefer loamy, rich soil with lots of organic content and is well-draining. Add some compost to your soil if you are not sure if it is rich enough. Additionally, if the soil in your garden has a tendency to be clayey, add some sand, peat moss, or manure to soften the texture and improve drainage. A pH of 6.5 or above is considered neutral for dahlia growth. Let’s talk about growing dahlias from seed.

Growing dahlias from seed

The best way to grow dahlias from seed is by planting them in a low, flat tray filled with high-quality, organic potting soil 4-5 weeks before your final frost date of the year. Sprinkle your dahlia seeds over the top of the soil and then very very lightly cover the seeds with soil. Once you’ve planted the seeds, use a spray bottle to gently moisten the soil. Keep your potting soil moist but not soaking wet and within 7-10 days, you should begin to see seedlings coming up.

When the seedlings have reached 3 inches tall, you can transplant them into small pots filled with the same organic potting soil you used before. Once you’ve moved the seedlings to their individual pots, continue keeping the soil moist but not soaking wet.

Keep these 3-inch seedlings in their pots for approximately one month before transplanting outdoors. Be sure to plant your dahlias outside only after the danger of frost has passed.

Transplanting dahlias outdoors

Up until now, your dahlia seedlings have been enjoying their lives inside of your warm house, but during the early spring months, it is still pretty chilly outside at night. Your dahlias can handle it, but they need to be hardened off before they can be planted outdoors. The hardening process involves moving them outside during the warmer hours of the day, then bringing them back inside at night. This helps prevent a deadly shock when transplanting them outdoors.

When they’re hardened off and ready to be transplanted outside, select a full sun location in well-draining soil. Plant your seedlings and keep the soil most but not waterlogged for 2 weeks after planting. This helps the roots of your new dahlias get established. After 2 weeks, you can provide them with a 5-10-10 or 10-20-20 fertilizer. Reapply this fertilizer every month. If blooms appear weak or stunted, it’s a sign you may be giving too much fertilizer.

How to harvest dahlia seeds

Dahlia seeds can be harvested in the fall when summer and fall blooms have begun to die back and dry up. Don’t get too ahead of yourself though – just because the flowers have started to die back does not mean the seeds are ready to be harvested. Wait to harvest dahlia seed pods until you’ve experienced your first frost of autumn. Once it has frosted, you can cut seed pods from their stems. Each pod should contain as many as 20 seeds.

Dry the seed pods over winter and in the spring, you will have plenty of dahlias seeds to get started for your next garden.

Thomas Nelson
Gardening Expert
Hi! I'm Thomas, one of the founders of The Garden Magazine. I come from a long line of gardeners who used the art of gardening as a way to live long, healthy lives. I'm here to share my knowledge of gardening with the world!