Germination temperature
About 21-27 °C (70-80 °F); germination slows below 16 °C (60 °F).
Flower growing guide
Garden dahlias grow easily from seed, flower in their first season and form their own tubers by the end of it. Every seedling is different, which is part of the fun: this guide covers sowing, growing on and keeping the best plants.
About 21-27 °C (70-80 °F); germination slows below 16 °C (60 °F).
About 6 mm (1/4 in).
7-21 days.
Cover the seed lightly; seedlings need strong light as soon as they emerge.
None needed.
Start in trays and transplant; direct-sown plants flower late or not at all in the first season.
Dahlia seeds are flat and slender, easy to sow one or two per cell. Sow dry seed into a moist, fine seed compost.
Not needed. The seed coat is thin and absorbs water readily.
Not needed. Dahlia is frost-tender and has no cold requirement; what it needs is warmth.
Not needed. Warm, evenly moist compost is enough for good germination.
Best at 21-27 °C (70-80 °F). Below about 16 °C (60 °F) germination is slower and fewer seeds come up, so use a warm room or a propagator in cool weather.
Cover with about 6 mm (1/4 in) of fine compost or vermiculite. A cell tray (for example 72 cells) makes later transplanting easy.
A light, free-draining seed compost. Avoid heavy garden soil in trays, which stays wet and invites damping-off.
Keep compost evenly moist but never waterlogged; water from below if possible.
Light is not needed to germinate, so a light cover is fine. As soon as seedlings appear they need bright light: commercial growers give long days, around 16 hours, with extra lighting to keep them compact.
Usually 7-21 days, quicker at the warm end of the range.
Sow about 8 weeks before planting out. Prick seedlings into small pots when large enough to handle, harden them off and plant out once there is no risk of frost; plants must stay protected until temperatures stay above 5 °C (41 °F).
Space bedding dahlias from seed about 30-45 cm (12-18 in) apart; larger plants need 60 cm (24 in) or more. Feed seedlings with a liquid fertiliser every two weeks, starting 3-4 weeks after sowing.
Seed-grown plants can flower within a few months and develop small tubers by the end of the season. These tubers can be lifted and stored to grow the same plant again next year.
Cause: dahlias do not come true from seed; seedlings vary in colour, form and quality, and many have single or semi-double flowers. Fix: grow plenty, then keep the tubers only from the plants you like best.
Cause: too little light or too much warmth after germination. Fix: move trays to the brightest place or under lights as soon as seedlings appear and grow them slightly cooler.
Cause: slugs and snails, which favour young dahlia growth, or earwigs that chew leaves and petals. Fix: protect plants at planting and during early growth; trap earwigs in rolled newspaper or straw-filled pots.
Cause: aphids (blackfly) and thrips, which also spread viruses. Fix: wash off aphids early, use insecticidal soap if needed and pull out plants with mottled, stunted, virus-like growth.
Cause: powdery mildew, which develops when plants are dry. Fix: water well in dry weather and give plants space for air flow.
In the Indian plains dahlias are planted in September-October and flower through the cool season; in the hills they are planted from March to May. Sow seed early in that window so seedlings are ready to plant out on time.
Choose a warm, sunny spot with fertile soil that stays moist but drains freely. Dahlias struggle in very dry soil and rot in waterlogged soil, which matters during heavy rain.
Pinch out the growing tip at about 30 cm (12 in) tall to get more branches and more flowers. Avoid excess nitrogen, which gives leaves instead of blooms.
Where tubers cannot stay in the ground, lift them when the foliage dies back, dry them upside down, trim stems to 5-15 cm (2-6 in) and store them in dry compost, sand or vermiculite in a cool, dark place above about 10 °C (50 °F). Check regularly and remove any that rot.
Grow a colourful mixed bed of dahlias from seed and keep the tubers of your favourites.
Yes. Started indoors about 8 weeks before planting out, seed-grown dahlias can flower within a few months. Plants sown directly outdoors may flower late or very little in the first season.
Yes. Seedlings form tubers by the end of their first season. You can lift and store them and replant them next year to grow the same plant again.
No. Dahlias do not come true from seed, so each seedling can differ in colour and flower form. Keep the tubers of the plants you like best.