Dahlia: planting cultivation care and flowering

Dahlias are tuberous plants of which there is a multitude of varieties. These plants of the family of Asteraceae bloom generously from July until frost, and there is even a giant winter-flowering Dahlia more suited to regions with mild winters. Here’s everything you need to know to grow dahlias to enhance your outdoor space.

Plant the Dahlia

This is in spring that dahlias can be planted in the ground, from the end of April, or even later in areas where late frosts are to be feared. The planting method is as follows.

  • Loosen the soil of the massif,
  • Dig holes that are wide enough and 12 to 15 cm deep, which should be spaced out:
    • 40 cm for dwarf varieties,
    • 50 cm for medium variety dahlias,
    • from 80 to 100 cm for large dahlias.
  • Install a tutor for large varieties,
  • Place a tuber in each planting hole,
  • Cover with a mixture of 50% loosened garden soil and 50% compost,
  • Tamp down,
  • Water.

When the stems of large dahlias reach about 30 cm in height, they can be tied to stakes so that the wind does not break them.

You should know that only dwarf dahlias can be grown in a jar. We choose a container with a pierced bottom at least 35 cm in diameter so that the tuber has enough space. The ideal is to opt for a soil that retains humidity, such as that suitable for geraniums.

Growing the Dahlia

The Dahlia likes to be installed under the sun because it appreciates the heat, in a soil rich in humus, cool, well drained and deep.

The dahlias are all gorgeous. But for an even more spectacular effect, you can plant a dahlia arborescent. It is more precisely the Dahlia imperalis. Under the right conditions, this extraordinarily beautiful giant can reach 3.50 to 4 m high and 1.30 wingspan ! Its very large, sculptural flowers appear in November and bloom lasts until January. But the resistance to cold of this Dahlia being weak, it is a little complicated to cultivate it north of the Loire. This Dahlia needs sufficient space, i.e. 1 m² per foot.

Caring for your dahlias

The Dahlia is quite easy to live with as it requires little maintenance.


It is especially in summer that it is essential to water the dahlias so that they shine despite the drought and the strong heat. The ideal is to water at the start of the evening because water evaporates less quickly at night. But be careful not to have too heavy a hand: the tubers must absolutely not be immersed in stagnant water as this causes them to rot. When watering, care should also be taken to do not wet the foliage because it promotes fungal diseases.


Every 4 weeks, it is very useful to do a fertilizer supply for flowering plants to dilute in a watering can of water, for the duration of flowering.


Putting a mulch at the foot of the dahlias is essential to maintain a sufficient freshness in summer.


Dahlias can withstand a maximum of -8°C for a short time. In colder regions, where even lower temperatures are common and long-lasting, care is taken to cut the stems before the first fall frosts. The tubers are dug up and must be brushed to get rid of the soil. Then all you have to do is place them in boxes in order to store them under cover, in a frost-free, healthy, dry and ventilated room, but also without windows.

If you overwinter different varieties of dahlias, it is very useful to note on labels their name, their color and their size. This will allow the following spring to organize your beds well and to make successful associations by planting them, for example, with Phlox, large Lavatera, grasses, etc.

Pests and diseases

Beware of slugs and snails who delight in the young leaves of dahlias. A mulch of flax chaff prevents these voracious gastropods from gaining access to plants. It is also possible to set beer traps to avoid invasions.

The aphids are also attracted to dahlias. These pests can cause the growth of these plants to slow down. The right solution is to opt for pyrethrum sprays.

L’powdery mildew is a common fungal disease in dahlias. These should be treated with a sulfur fungicide spray.

As to necrotic mosaic virus responsible for yellow spots on the leaves, it can cause damage. It is necessary that to cut and of burn all affected parties because there is currently no no treatment allowing it to be overcome.

Flowering of the Dahlia

Dahlia flowers come in a very rich palette of colors and shapes. Each gardener can therefore have fun planting different varieties to enhance his garden, create monochrome lovely or areas multicolored while playing on the shape of the flowers. There are indeed all kinds of dahlias: with pompom, collar, semi-cactus, cactus, decorative, lace or even dahlia ball, dahlia camellia, dahlia anemone…

Pour promote flowering of its dahlias, it is recommended to cut off the faded flowers as you go. After the flowering period, all stems should be cut short as soon as they have completely faded.

Finally, note that the Dahlia flower holds up well in a vase. We can therefore create sumptuous bouquets of cut flowers to bring color to any room in the house.

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