When growing dahlias, the season ends with big, bold flowers that fill the backyard with color. The tall ones add height at the back of the border and the single-flowered ones provide a source of food for bees and butterflies. The cut-and-come-again habit of dahlias makes them a great source of fresh flowers for the house.
Dahlias bloom from mid- summer to late fall, but you might be wondering when to plant them. Hailing from Central America, dahlias shouldn’t be planted outside until the weather warms. If you have stored or bought tubers, this is why planting dahlias in the spring is best time, usually March or April. Under cover in the late spring is the best time to start dahlias. After the risk of frost has passed, potted dahlias should be put in the ground.
You can choose from a wide range of colors and shapes to suit your garden style. The cactus and ball varieties bring retro glamour, the single and anemone forms fit into jungle-style flower bed ideas, and the huge dinner-plate dahlias are a must-have for a cutting garden.
Oregon-based landscape architect and garden designer, Bethany Rydmark, likes to intersperse dahlias among other plants. As an accent in a mixed border, or as an infill in a parterre, dahlias work well.
How to Plant Dahlias
When planting dahlias in spring, around March or April, you can put up a potted hodge tuber in a greenhouse, and then plant it outside in May or June. Planting tubers will give you earlier flowers because they will produce multiple shoots which will not need pinching out.
Young plants should be hardened off to acclimatize them to the outdoors before planting. By placing them in a cold frame or sitting them outdoors during the day for a week covered with fleece, they can gradually remove the fleece.
When to plant dahlias outdoors
Wondering when to plant the dahlia tubers outdoors? Dahlia can be planted out between April and May. The earlier you can plant, the warmer the climate is. You can plant earlier in the US if you live further south.
In most parts of the UK and the northern US, it is safe to plant dahlia tubers in the middle of April.
During the late spring and early summer months, the tubers will grow their roots and begin sending up new shoots. In warm spring weather, they may shoot early. This won’t hurt the plant in the long run.
Dave and Sue say that growth that emerges too early may be stopped by spring frosts. The plants will recover and it will result in bushier plants earlier on, as they will have had a natural pinch.
In the middle to late spring, you can find mini plants from suppliers of dahlias. They can produce a better flower color and are more reliable than tuber’s.
If possible, plant them under cover in the spring. Dave and Sue Hall say that Dhulia roots can be planted directly outside, but they will benefit from being potted up and grown on for at least a few weeks before planting out. In the south of the UK, planting out can be done from early to mid May. You wouldn’t plant out until June in the north and Scotland. We don’t recommend planting out before the last expected frost in your area.
Prepare the dahlias for the weather by cutting off the young plants. By placing them in a cold frame or sitting them outdoors during the day for a week covered with fleece, they can gradually remove the fleece.
When to plant flowers.
In late spring and early summer, ready-grown dahlias can be purchased from nurseries. When to plant dahlias? Once the risk of frost has passed, they can be put into sunny borders.
Dave and Sue Hall advise against buying plants that have become pot bound. Being pot bound will make them slower to get away.
To see what the roots look like, look underneath the plant. If they are old and in a dense knot under the plastic container or if you can slide the plant out of the container, avoid purchase.
Planting Dahlias in Pots
If you want to grow dahlias in pots on the patio or terrace, plant them in well-drained containers of compost under cover in March or April. Once the risk of frost has passed, move the pots outside into a sunny position.
They are ideal for containers, as they reach around 2.5ft (75 cm). The dahlias like moist compost.
When to sow flowers.
It is much easier and quicker to grow dailies from tubers. If you like a challenge, they can be raised from seed. In the early spring, sow the seed in a greenhouse or on a bright windowsill. Once they are large enough, plant into borders in June.
How late can you plant dahlias?
In most regions, you can start planting dahlia tubers as late as May or June. They should carry on until frost.
Can you leave dahlias in the ground over winter?
Yes, you can leave dahlias in the ground over winter; however, like many other flowering plants, their roots are still able to succumb to root rot or freeze. Dahlias are not considered a hardy plant, therefore, if you live in cooler climates where the ground freezes, you may want to consider transplanting them to pots before winter. This also allows you to find a new spot to plant them when planting dahlias in the spring.