Dahlias burst into bloom from mid-summer to late fall, and knowing the best time to plant them ensures a spectacular display.
These stunning flowers extend the gardening season with their vibrant colors. They typically grow tall, adding vertical interest to your garden borders, and the single-flowered types attract bees and butterflies. Additionally, dahlias keep producing, offering fresh blooms for indoor arrangements.
Our guide outlines the ideal times for planting dahlias to maximize their colorful presence.
Timing for Planting Dahlias
Originating from Central America, dahlias should only be planted outdoors once the weather has warmed. If you have tubers to plant, pot them indoors (like in a greenhouse) during March or April. Rooted dahlia cuttings are best started under cover in mid to late spring. Once the frost risk is gone, typically in May or June, you can safely plant potted dahlias in the ground.
Dahlias come in a wide array of colors and forms, allowing you to choose the varieties that complement your garden style. For example, cactus and ball types add a retro touch, while single and anemone forms fit well into tropical-style flower bed concepts. The impressive dinner-plate dahlias are essential for any cutting garden.
'I like to mix dahlias with other plants,' shares landscape architect and garden designer Bethany Rydmark from Oregon. 'They work beautifully in modern meadows, add interest to mixed borders, or fill spaces in formal gardens.'
Starting Dahlia Tubers Indoors
If you've stored or purchased dahlia tubers, pot them in a sheltered place (like a greenhouse) in March or April, and plant them outside in May or June.
'Starting tubers early often leads to quicker blooms,' say dahlia nursery experts Dave and Sue Hall from Halls of Heddon, near Newcastle upon Tyne, UK. 'Tubers usually produce multiple shoots that don't require pinching back.'
It's wise to acclimate young plants to outdoor conditions before planting. This can be done by placing them in a cold frame or bringing them outside during the day for a week, covered with fleece. Then, gradually remove the fleece.
Planting Dahlia Tubers Outdoors
When should you plant dahlia tubers outdoors? 'You can safely plant them between April and May,' advise Dave and Sue Hall. 'The warmer your climate, the earlier you can plant. If you're in southern regions, you can start earlier.'
In most areas of the UK and northern US, it's safe to plant tubers directly outdoors from mid to late April.
Typically, tubers will establish roots in late spring and start sprouting new shoots in early summer. Sometimes, they may shoot up prematurely in warm weather. This won't harm the plant overall.
'If early growth is hit by spring frosts,' note Dave and Sue, 'the plants will bounce back, often resulting in bushier growth sooner, as they naturally pinch themselves.'
Planting Rooted Dahlia Cuttings
Mini plants known as 'rooted cuttings' are typically available from suppliers in mid to late spring. They tend to establish faster and yield better flower color compared to tubers.
Whenever possible, pot them in a sheltered area (like a greenhouse) during spring. 'Rooted cuttings can be planted straight outside, but they thrive better if potted and nurtured for a few weeks first,' Dave and Sue advise. 'In southern regions of the UK, you can plant them out by early to mid-May. In northern and Scottish areas, wait until June. Always plant after the last expected frost date in your area.'
Harden off young plants before transplanting to prepare them for outdoor conditions. For example, place them in a cold frame or leave them outside during the day for a week, gradually removing the fleece cover.
Planting Potted Dahlias
In late spring and early summer, you can acquire ready-grown dahlias in pots from nurseries. Once all frost danger has passed, they can be planted directly into sunny borders.
'Choose fresh, healthy plants that aren't pot-bound,' advise Dave and Sue Hall. 'Pot-bound plants will struggle to grow and take longer to establish.'
To determine if a plant is pot-bound, check the roots underneath. If they're tightly coiled in the container, or if you can slide the plant out and see roots circling the compost, it's best to avoid that plant.
Sowing Dahlia Seeds
While dahlias are commonly grown from tubers for simplicity, they can also be cultivated from seeds for those seeking a challenge. Sow seeds indoors (like in a greenhouse or on a bright windowsill) in early spring. Once the seedlings are large enough, harden them off and plant them in borders by June.
When to Start Dahlia Tubers?
Begin your dahlia tubers in March or April by potting them under cover; they can be planted outside in May or June. If space is an issue, dormant tubers can go directly outdoors between April and May.
How Late Can You Plant Dahlia Tubers?
In most areas, you can plant dahlia tubers as late as May or June. They should continue blooming until the first frost hits.
