I caught the dahlia bug many years ago, but haven’t won the lottery yet so, as much as I’d like to, I can’t fill my garden with piles of new tubers each spring.
So you’d better believe I threw a garden party when I mastered growing dahlias from seed.
For the price of one tuber, I can buy enough seeds to fill up my entire garden with dahlias, and even collect them from my existing plants!
We link to vendors to help you find relevant products. If you buy from one of our links, we may earn a commission.
Our guide to growing dahlias has all you need to know to cultivate these beautiful flowers in your landscape.
If you want to breed dahlias to create new and unique specimens, growing from seed is a skill you must have.
When you take a cutting or divide a tuber, you’ll grow an exact genetic replica of the parent. But plants started from seed combine the characteristics of both parent plants.
You might end up with something magical and new that no one has seen before. Just imagine the accolades as you share your new dahlias with friends and fellow growers.
And it all started from a little seed. Are you dreaming of growing dahlias on the cheap or producing new types?
Here’s what we’ll go over in this guide so you can make that happen:
Dahlias grown from seed will develop tubers by the end of the summer.
You can save these and store them over the winter, if you want, or leave them in the ground if you live in the right climate in Zones 8 to 11.
But, before you can do that, we’ve got to plant those puppies.
When to Start
Dahlias are sensitive to cold temperatures and unless you live somewhere that never freezes, you’ll need to start the seeds indoors before putting them outside when it’s warm enough.
You should start the process of germination a month or two before the last predicted frost date in your area with the idea of planting out a month after the last predicted frost date.
If you are starting them in a cold basement or your other seedlings tend to take a long time to grow, give them two months. Otherwise, a month should be fine.
You can also direct sow into the garden if you live somewhere warm enough that dahlias can stay in the ground year-round.
This process is less reliable since you don’t have any control over the environmental conditions and herbivores like birds and voles seem to particularly love stealing them.
If you go this route, wait until the soil has warmed to 65°F before sowing.
Where to Buy Seeds
You won’t find seeds for some of the more elaborate dinnerplate dahlias or ball cultivars available, but there are many open-faced (single) or semi-double options out there.
If you aren’t sure what these types are, learn more about dahlia groups in our guide.
For example, Eden Brothers carries the stunning ‘Figaro,’ which has daisy-like flowers in deep purple with sunny yellow centers.
‘Figaro’
Or, if you want something with a bit more color, consider Unwins Bedding, a mix of a variety of colors also available at Eden Brothers.
Unwins Bedding
These daisy-like dahlia flowers come in multiple bright colors including white, yellow, orange, red, and pink.
If you’re ready to harvest your own, keep reading.
Harvesting Seeds
As mentioned, dahlias started in this way won’t grow true, which means they won’t look exactly like the plant you collected the seeds from.
If you want an exact replica, you need to grow from tubers.
Dahlias are octoploids, which means they have four more sets of chromosomes than most flowering plants.
This provides incredible genetic diversity, but it also makes it extremely challenging to predict what plants grown from seed will look like.
You can try to cross two plants you love and hope the traits you desire will appear, but you can’t be sure. It’s a hit-and-miss process.
If you want to try crossing two plants, you will first need to cover your chosen receptive flowers in mesh or nylon bags to prevent natural pollination.
Then, when the dahlia flowers have fully opened and pollen has developed on the stamens, take the pollen from an open flower using a toothpick. Types with large, full heads make it a bit more difficult for you (and other) pollinators to find the pollen.
You might need to pluck some of the petals away from the center of the flower to find the pollen.
Rub this pollen on the stigmas of your chosen flowers. You’ll find the pods on the inside of the blossoms, but they aren’t ready until the blooms have aged and faded.
This happens in the fall for most types. Leave the blossoms on the plant until the first freeze is on the horizon.
Keep the blossoms covered in mesh bags to prevent birds from making off with your seeds.
To harvest the heads, cut the spent flower head away from the dahlia stem and gently rub the pods in your hand to release the seeds inside.
Some pods might be empty and some might have heaps. Set them on a towel or baking sheet to allow them to dry.
Once they feel totally dry, put the seeds in jars or envelopes and place them in a cool, dry area to store them until sowing time in the late winter or early spring.
Some may not be viable, but there’s no way to really know until you sow them and wait for them to germinate. I always sow more than I think I’ll need to compensate for any duds.
Sowing Seeds
To start, fill a tray with seed starting mix. You can also use potting soil, but don’t use one that contains fertilizer.
A seed starting mix is made without soil for a light, airy, water-retentive substrate that supports germination and growth without becoming oversaturated.
Arbico Organics carries an excellent product called Tank’s Pro-Lite Seeding & Potting Mix. It’s available in 16-quart bags.
Tank’s Pro-Lite Seeding & Potting Mix
Moisten the soil and then gently sprinkle the seeds on top. Place a thin layer of the medium over them and gently press down on the surface of the soil with your hands.
Set the containers on a heat mat set to maintain temperatures of 70 to 80°F and don’t panic if you don’t see any seedlings for a few weeks.
Dahlias aren’t in a hurry to pop up but that doesn’t mean they won’t.
Your setup should be near a window with bright, indirect light as the seedlings will require light as soon as they emerge. You don’t want any direct sunlight at first, though.
If you’d like to, you can cover the tray with plastic or glass to help the soil retain water. Whether you go this route or not, keep the soil moist but not wet – it should feel like a well-wrung-out sponge at all times.
As the seedlings emerge, you’ll eventually want to thin them out so they are about four to six inches apart. But, because the seeds tend to germinate sporadically, wait until the majority of the seeds have sprouted. I generally wait a month before thinning.
When the seedlings are about six inches tall and all risk of frost has passed, you can transplant them outdoors after a period of hardening off.
To harden them off, take the whole tray outside and set it in a sunny spot that’s protected from the wind for about an hour. Then bring it indoors. The next day, leave it outside for two hours. Keep adding an hour a day over the course of about a week.
After they are hardened off, transplant into the garden or into permanent containers. Dig holes six inches apart and make sure each hole is large enough to accommodate the roots.
Gently remove the seedlings from the tray, set them in the prepared holes, backfill with soil, and water in well.
If the resulting plant is one that you love, propagate it via tubers in the future so you can guarantee that it will be replicated faithfully.
Let’s Get This Party Started!
I have to confess that for me it isn’t all about saving money or developing new cultivars. I take a lot of pride in turning a little seed into a big, beautiful plant. It’s extremely fulfilling.
What’s your goal with growing dahlia seeds? Are you hoping to breed a few new styles and shapes? Or just looking to save a few bucks? Let us know in the comments section below.
There’s so much more to learn about these colorful flowers. If you’d like to expand your knowledge about growing dahlias, you might find these useful:
