Step-by-step instructions on how to grow dahlias from seed.
The 2025 Winter Gardening Series is supported by Gubba Garden Store.
Once thought of as a bit old fashioned, dahlias have made a bold and beautiful comeback over the last few years. The resurgence began with the blushy queen: Café au Lait – a favourite among brides and florists. But the craze caught on, and dahlias are now a hot favourite among the everyday gardener. With their many colours, structural forms and almost endless varieties, it’s no wonder dahlias have captured the hearts (and wallets) of a new generation of growers.
Part of what makes dahlias so captivating is their genetics. They’re octoploids, meaning they carry eight sets of chromosomes (compared to the usual two in most plants). This gives them an extraordinary range of colour, form and size.
If you’re growing dahlias this year and keen to increase your patch, raising them by seed is a rewarding and surprisingly simple way to do just that.
In this article, we’ll walk you through how to multiply your dahlias by seed propagation.
Why grow dahlias from seed
Growing dahlia from seed is an exciting and cost effective way of filling your garden blooms.
The unique thing about growing dahlias from seed is that, unlike growing from tuber or cuttings where you get a clone of the parent plant, seed propagation will give you a brand new hybrid variety every time. This is because the seed contains genetics from both seed parents but can look completely different, because of the dahlia’s eight sets of chromosomes.
A dahlia will flower in its first year from seed, but it won’t flower as prolifically as a tuber grown dahlia will. In the first year you will get an idea of its colour and form, but it isn’t entirely stable and can change the following year.
Every seed will turn into its own unique dahlia that will form a clump of tubers by the end of the season.
How to grow dahlias from seed
Now, if you are keen to get started, there are a few important points to consider first:
Check viability
Viable seeds are slightly harder and darker in colour than non-viable seeds, and they will not bend easily. If you’ve saved your own seed, it is likely there will be many seeds that are not viable due to lack of pollination.
Sometimes as a beginner (or even pro!) it can be hard to tell the difference. That’s when presprouting using the ‘paper towel method’ comes in handy – as it will help you save on soil and space.
If you have purchased seed from a supplier, you can go ahead and start in pots or trays.
Know your frost zone
Young dahlia seedlings are particularly vulnerable to the cold, so it’s important to know your frost zone.
For many it will be too early to start dahlia seeds in winter – waiting until 6-8 weeks before your last frost date is recommended.
Check the depth
Do not bury the seed with too much soil. A light sprinkle is fine, but I always prefer to create a small indent in the soil using a pen, and then I push the seed in before covering with vermiculite.
Dahlia seeds are particularly prone to rotting. Covering with a heavy amount of soil will increase this risk.
Keep it warm
Dahlia seeds need warmth to germinate. I would recommend grabbing a heat mat and setting it around 24°C at this time of year (late winter) to get things going.
If you don’t have a heat mat, above the fireplace, heater or another warm environment will help – but make sure it’s not too hot or germination could be slowed.
Bring the humidity
Keep a lid over your tray or place pots inside a Sistema tub to keep up the humidity. The seeds need moisture to germinate, and a lid will help trap heat to build that humidity and prevent drying out.
Step-by-step instructions: How to grow dahlias from seeds
Sowing dahlia seeds in pots or trays
1. Harvest dahlia seed heads in autumn, once they turn brown and dry. Alternatively, purchase a packet of dahlia seeds.
2. Sow directly on top of a good quality seed raising mix and sprinkle with a light layer of vermiculite.
3. Place in a warm position indoors or on a heat mat until germination occurs, which should take 10-14 days.
4. Once germinated, carefully prick out seedlings into individual pots to grow on until established enough to be transferred into the garden in late spring.
5. Keep pots protected from frost – the seedlings are tender.
Sowing dahlia seeds using the ‘paper towel method’
1. Place seeds between wet paper towels or a wet cloth.
2. Evenly space out the seeds so they are not touching. This will avoid the spread of damping off, should it occur.
3. Keep seeds warm at around 24 degrees Celsius (preferably using a heat mat).
4. Seeds typically sprout within 2-14 days.
5. Make sure to keep checking the seeds inside the paper towel every day.
6. If you notice seeds starting to go mouldy, quickly remove the affected seed to avoid the spread.
7. When you notice a small white root sprouting from the seed, carefully transfer into seed starting mix with the sprout tip down. Position seeds so half of each seed sticks out of the soil.
8. Keep the pots on a heat mat or warm windowsill until you notice the first true leaves emerge from the top.
9. If using a heat mat, make sure to provide grow lights for at least 12 hours each day to prevent the seedlings from becoming leggy.
10. Once seedlings reach 5-7cm tall, move them outside into low tunnels or tubs to grow on. These protected environments will help the seedlings acclimate to outdoor conditions which can still be unpredictable in the spring.
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Do you feel encouraged to try your hand at propagating dahlias this winter? I hope so!
There’s something so satisfying about turning a single seed into a clump of tubers by the end of a growing season – with the added bonus of breeding your very own new hybrid variety of dahlia.
Whether you’re dreaming of full garden borders, overflowing vases or buckets of blooms to gift to friends, seed propagation is the new way to grow more for less.
More help for growing dahlias —
Everything you need to know about growing & caring for dahlias
A dahlia grower’s autumn checklist | How to prolong dahlia flowers & prep tubers for next season
Preparing dahlias for winter | A guide to digging & storing dahlia tubers
Dahlia propagation | How to grow dahlias from cuttings
How and when to dig & divide dahlia tubers
The Winter Gardening Series is proudly supported by Gubba Garden Store.
www.gubba.co.nz | @gubbagardenstorenz
