Home » Gardening » Garden Flowers » Dahlia imperialis, a marvel in fall

Dahlia imperialis, a marvel in fall

Dahlia imperialis towers tall above, blooming

Dahlia imperialis or tree dahlia is a perennial herbaceous flower that is simply beautiful.

Dahlia Imperialis facts

NameDahlia imperialis
Type – bulb plant

Height – 6 to 13 feet (2 to 4 meters)
Exposure – full sun, part sun
Soil – enriched ordinary soil

Flowering – September to November
Hardiness to freezing – 23°F (-5°C)

Sometimes called giant dahlia, it can reach a height of 13 feet (4 meters)!

Planting imperial dahlia

Dahlia imperialis blooms in winter but cannot withstand temperatures below 23°F (-5°C). You must thus first check that your climate allows for planting before purchasing it.

Planting dahlia imperialis bulbs

Dahlia imperialis bulbs are best planted during the months of April and May, when the last frosts are past.

Plant them about 4 inches (10 cm) deep, and space the bulbs 40 inches (100 cm) apart, because dahlia imperialis requires sunlight and likes having space to spread out!

  • Avoid windy locations that could break the stems of your dahlia imperialis.
  • A blend of flower plant soil mix and garden soil is ideal for planting.
  • Dahlia imperialis must be staked upon planting.
  • Water regularly the 1st year but not too much because dahlia dislikes moisture.
  • Amend with bulb flower fertilizer in the following years.
  • Mulch enables you to protect the bulbs in winter.

Propagating dahlia

  • To sow, start with sowing in a tray in early March, repot in April and transplant in the ground in May.
  • Propagating through tuber division in spring.

Pruning and caring for dahlia imperialis

Single flower of the tree dahliaDahlia imperialis is a flower that requires a little specific attention if you want to see it bloom year after year.

Dahlia imperialis is inclined to rather warm, rich and well drained soil.

Tree dahlia also appreciates being watered in summer but fears excess moisture that could destroy the plant.

  • Remove wilted flowers regularly (deadheading).
  • Once stems are completely wilted, cut them as short as you can.
  • Dahlia imperialis plants can resist freezing temperatures down to around 23°F (-5°C).
  • In winter, it is important to protect the base of your plants with plant-based mulch.

If you fear particularly strong freezing:

After the blooming, at the beginning of winter, bring the tubers indoors when the first frost spells hit, and keep them in a dark, dry place until the following spring.

Watering dahlia imperialis

As mentioned above, the watering of tree dahlia is important because it must be regular but never excessive.

One of the most common problems that this plant meets is the rotting of its roots. It thus requires very well drained soil.

  • Water the dahlia imperialis but avoid wetting the foliage. This will keep fungal diseases at bay.
  • Water preferably in the evening to reduce evaporation and also save water.

Dahlia imperialis in winter

Dahlia imperialis cannot survive freezing temperatures.

If you live in an area where the weather frequently drops below 23°F (-5°C), bringing your bulbs indoors before it freezes is your only hope.

This can be performed after the blooming and before temperatures have dropped under 23°F (-5°C).

  • Wait for leaves to have withered completely, and then cut them 4 inches (10 cm) above ground level.
  • Pull out the rhizomes and dry them off for 2-3 days in the sun.
  • Clean them with a brush.
  • Keep them in a cool, dry and dark place.
  • Replant them outdoors when the last frosts are past, in spring.

In other regions, protect your tubers with dead leaf mulch for instance.

Diseases and parasites that impact dahlia imperialis

The major difficulty encountered with dahlia imperialis is the rotting of the tuber.

This happens when the soil is too moist and doesn’t drain well enough, thus preventing excess water from being evacuated.

This also leads to various fungus such as powdery mildew or gray mold.

As for parasites, the dahlia can occasionally fall victim to aphids.

Learn more about dahlia imperialis

bamboo dahlia - tree dahliaNative to Mexico, the dahlia imperialis or tree dahlia exhibits a very peculiar stem similar to bamboo.

Its flowers are as beautiful as ever, a cute pink that can also be white, and always very large. Tree dahlia flowers can grow to be 8 inches (20 cm) across.

In temperate climates, the foliage is evergreen.

It is also called Imperial Dahlia, tree dahlia, Lehmann dahlia or Bamboo dahlia because of the strong resemblance of its stem with bamboo.

Read also:

Smart tip about Dahlia imperialis

This is a plant that can grow quite large and will always be at its best in a sheltered spot where it can grow while being protected from wind.

Image credits (edits Gaspard Lorthiois):
CC BY 2.0: chuck b.
A comment ?

Your email address will not be published. Required fields are marked *