Sowing Bedding Dahlias: They’ll Typically Flower After 100-120 Days
Elizabeth is a Permaculture Garden Designer, Sustainability Consultant and Professional Writer, working as an advocate for positive change. She graduated from the University of St. Andrews with an MA in English and Philosophy and obtained a Diploma in Applied Permaculture Design from the Permaculture Association.
Reviewed By DAN ORI
Dan has over 27 years’ under his belt caring for plants and gardens. Working as a Horticultural Instructor and Consultant, he draws on a diverse range of experience that includes working as a Head Gardener, Tree Surgeon, Garden Centre Trouble Shooter, and writer of academic papers. Dan has a Level 3 Diploma in Horticulture and is currently a candidate for the RHS’s most prestigious award – The Master of Horticulture.
IN THIS GUIDE
Dahlias are attractive plants which can work well in many gardens, sporting a hugely varied group of flowering plants.
Fast-growing bedding dahlias are suitable for growing from seed, while other dahlias are best propagated by means of planting tubers, or from cuttings.
However, you can also use the same method to sow seeds you have collected yourself from an existing dahlia in your garden the previous season.
This can be a very interesting thing to do because it can throw up a range of new varieties, as you can not be entirely sure of what the plants sown from seed will actually look like, and how their flowers will be.
Of course, if you purchase seeds, this is also a very affordable way to obtain new dahlia plants.
It will cost far less than growing potted plants or purchasing tubers to plant.
To grow bedding dahlias from seed, sow undercover in late winter or early spring:
- Fill a seed tray or small pots with moist potting mix.
- Gently push the dahlia seeds into the potting medium.
- Wait for seeds to germinate.
- Once true leaves form, transplant the dahlia seedlings into individual pots.
- Harden off seedlings before transplanting to their final growing positions in May.
Read on for more detail on each of the steps outlined above.
| Difficulty | Easy |
| Equipment Required | Seeds, pots or seed trays, covers or a propagator lid, potting medium |
| When To Sow | February to April |
| When To Plant Out | May |
1) Prepare To Sow
Dahlias are best sown indoors from February to get them off to the best start, though you can also sow them where they are to grow in April, once the risk of frost has passed in your area.
Take a seed tray or small plugs, soil blocks or pots, and fill these with a suitable, moist, peat-free seed starting compost.
“I recommend augmenting peat-free seed compost with one part fine-grade vermiculite to two parts compost,” shares Dan Ori, a Horticultural Instructor and Consultant.
“My personal favourite mix is one part fine-grade vermiculite, one part hydrated coir and one part peat-free seed compost.
“I will pot plants onto a similar mix of one part vermiculite (any grade), one part hydrated coir and one part peat-free multipurpose compost, adding some 6-month controlled release fertiliser.”
2) Sow Your Seeds
Dahlia seeds are long and thin, and blackish in colour.
Gently push the dahlia seeds vertically down into the compost, making sure that they are in good contact with the growing medium around them.
Place these in a bright location with reasonable humidity.
3) Wait For Germination
Dahlia seeds should germinate within around 2 weeks.
Ensure that the medium remains moist but not damp during this time.
4) Pot Up The Seedlings
Once the dahlia seeds have germinated, wait for the first leaves to grow.
As soon as a couple of leaves have grown and the seedlings are large enough to handle, you can gently tease each one out of the growing medium and place each one into its own individual pot to grow on.
Pots should be around 10cm in size and should be filled with a peat-free, multi-purpose compost.
Water in the plants well on transplantation and grow them on indoors or under cover until around the middle of May.
5) Harden Off & Plant Out
From around the middle of May, you can begin the hardening-off process.
This simply means slowly acclimatising indoor grown plants to outdoor conditions.
Gradually place them outdoors for longer and longer periods, bringing them in at night, or use a cold frame for the hardening-off process if you have one.
Dahlia seedlings can be planted out into their final growing positions once all risk of frost has passed where you live.
Bedding dahlia planted out in May should flower the same year.
Typically, bedding dahlias will flower from 100-120 days after the seeds are sown, but with other dahlias, you may have to wait longer for blooms to emerge.