Dahlias produce wonderful blooms in a plethora of colors and shapes in mid-summer and into fall. These popular plants are traditionally grown from tubers, but did you know you can also grow dahlias from seeds and even harvest dahlia seeds from your existing plants to grow new ones?
Harvesting dahlia seeds is simple, though there is no guarantee that the seeds you germinate will replicate the parent plant. If you want a specific type of dahlia, then taking cuttings or dividing tubers is the best way to go. As dahlias cross-pollinate easily, it will be a surprise what blooms come from harvested dahlia seeds.
If you are not fussy about what dahlias you get and are happy to experiment, then we get some expert advice for when to harvest dahlia seeds and store them correctly to ensure you have lots of saved seeds to sow come spring.
When to collect dahlia seeds
Dahlias will flower profusely whether you are growing them in flower beds, a cut flower garden, or you have your dahlias in pots. It is important to resist the urge to go out and deadhead all your dahlias throughout the blooming season. Rather than pruning every dahlia, leave some flower heads to develop seeds that you can collect.
That time for collecting and saving seeds from dahlias comes in the fall. Jennifer Gulizia, an experienced flower grower from The Flowering Farmhouse, collects seeds from her dahlias in September and October towards the end of each growing season. Pollination is key to producing seed, and Jennifer has a trick when it comes to fading blooms that increase the chances of having dahlia seed to harvest.
She says: ‘Once the dahlia flower has started to die back, I help by gently pulling off some of the petals so that the stamen is more readily visible and accessible to the bees.
‘Once the flowers have been pollinated, the dahlia flower heads will start to close up and form a seed pod. This usually takes about 4-6 weeks.’
When pollination has occurred a green seed pod will form inside the old blooms, which then turns brown when it is ready to be harvested. Swan Island Dahlias in Oregon recommends that it is ‘best to leave blooms on your plant for about a month prior to frost and then harvest the seed pods after frost, allowing them time to fully develop’.
Jennifer Gulizia runs The Flowering Farmhouse, a small flower farm on less than a 1/4 acre located in Hood River, OR. She has been growing dahlias since 2014 and collecting and growing dahlias from seed for the past three years.
How to collect dahlia seeds
The process of harvesting dahlia seeds is a simple one and you need only a pair of clean and sharp pruning shears or garden scissors and a brown paper bag to collect the dahlia seed heads in. Using a paper bag is a tried-and-tested method when it comes to collecting seeds. Paper bags are available on Amazon or in stores and are commonly used when collecting flower seeds, including when harvesting coneflower seeds among many others.
Identifying ripe and ready seed pods is important, making sure they are brown in color and dried up. Use your pruning shears or scissors to snip the seed heads from the plant and collect these into a brown paper bag.
The seed heads will need to be dried and then gently opened to be able to collect and store the seeds inside. The seed heads can be left in the paper bag in a dry and cool room for two or three weeks, or spread out on a tray so they naturally dry in the open air. Then comes the time to harvest the dahlia seeds from inside the seed pod. The dahlia seeds themselves are small and flat, dark brown or black in color, and each seed pod may have up to 20 seeds inside it.
Miguel Palma, professional gardener and owner of JardinTienda, says: ‘These are the dahlia seeds you'll use for propagation. To separate them from any remaining plant material, gently rub the seeds between your fingers.’
You need to have a plate or container to hand to separate the seeds into. Having a vessel to catch the seeds ensures you do not lose any of your precious harvested seeds.
Miguel Palma is a professional gardener with over 20 years of experience in the horticultural business. He is the owner of JardinTienda, a site dedicated to reviewing gardening products and providing independent buyers guides.
Storing harvested dahlia seeds
Whenever you are collecting seeds, it is important to ensure that they are completely dry before storing them away. Proper storage is important to ensure the viability of the seed. A failure to dry seeds properly before storing means they are likely to start going moldy in storage.
Once the seeds are dry, Miguel Palma recommends: ‘Placing the dry seeds in an airtight container, such as a small envelope or a glass jar with a tight-fitting lid. To further protect the seeds, store the container in a cool, dry, and dark place, such as a refrigerator. You can add a packet of silica gel or a desiccant to absorb excess moisture.’
It is important to label and date the collected seeds for record-keeping purposes. Your harvested dahlia seeds can be sown in the following spring to germinate. The resulting dahlias are then planted out into a sunny spot in the garden once the risk of frosts has passed.
Do dahlia seeds turn into tubers?
Dahlia plants grown from seed will produce tubers. When I grew dahlia seeds at home the plants developed a small set of tubers at the end of their first year. As dahlias are tender perennials they do need to be lifted and stored to overwinter dahlias in US hardiness zone 7 and below. They can be planted outside again each spring or summer and the tubers will develop in size year-on-year. The resulting flowers each year will be the same as the first year’s blooms.
Are dahlias hard to grow from seed?
Dahlias are simple to grow from seed. You can buy packets of dahlia seed, like these from True Leaf Market, that will grow into a specific variety, or you can harvest your own dahlia seed to grow into a new unique type of dahlia. Dahlia seeds are sown into seed compost in spring and should germinate quickly, though placing the containers on a heat mat will help speed up germination. The time to transplant seedlings out into the garden comes when the risk of frosts has passed and the young plants are large enough to handle.
Any time you are growing dahlias you want the best blooms possible. There are ways to keep dahlias blooming and that includes keeping your eyes peeled for dahlia pests and dahlia diseases – taking prompt action as required. With a bit of care and attention, you can easily have fantastic blooms for months.
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Drew’s passion for gardening started with growing vegetables and salad in raised beds in a small urban terrace garden. He has gone on to work as a professional gardener in historic gardens across the UK and also specialise as a kitchen gardener growing vegetables, fruit, herbs, and cut flowers. That passion for growing extends to being an allotmenteer, garden blogger, and producing how-to gardening guides for websites. Drew was shortlisted in the New Talent of the Year award at the 2023 Garden Media Guild Awards.
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