Photo by Melody

PlantFiles: Oyama Magnolia
Magnolia sieboldii 'Colossus'

Family: Magnoliaceae
Genus: Magnolia (mag-NO-lee-a) (Info)
Species: sieboldii (see-BOLD-ee-eye) (Info)
Cultivar: Colossus

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6-8 ft. (1.8-2.4 m)

USDA Zone 5a: to -28.8 C (-20 F)
USDA Zone 5b: to -26.1 C (-15 F)
USDA Zone 6a: to -23.3 C (-10 F)
USDA Zone 6b: to -20.5 C (-5 F)
USDA Zone 7a: to -17.7 C (0 F)
USDA Zone 7b: to -14.9 C (5 F)
USDA Zone 8a: to -12.2 C (10 F)
USDA Zone 8b: to -9.4 C (15 F)
USDA Zone 9a: to -6.6 C (20 F)
USDA Zone 9b: to -3.8 C (25 F)

Sun Exposure:
Full Sun


Bloom Color:
White/Near White

Bloom Time:
Late Spring/Early Summer


Other details:
Flowers are fragrant
Average Water Needs; Water regularly; do not overwater

Soil pH requirements:
5.1 to 5.5 (strongly acidic)
5.6 to 6.0 (acidic)
6.1 to 6.5 (mildly acidic)
6.6 to 7.5 (neutral)

Patent Information:

Propagation Methods:
From seed; winter sow in vented containers, coldframe or unheated greenhouse
From seed; stratify if sowing indoors

Seed Collecting:
Remove fleshy coating on seeds before storing
Seed does not store well; sow as soon as possible

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1 positive
1 neutral
No negatives

Gardeners' Notes:

Neutral coriaceous On Jan 2, 2015, coriaceous from ROSLINDALE, MA wrote:

Nodding fragrant globular flowers with a prominent ring of pink stamens, all summer. (After an initial flush, they come in ones and twos.) The leaves and flowers are twice the size of the species' (the flowers up to 5" wide) and have heavier substance. This cultivar is also more vigorous than the species.

The petals tend to turn brown and hold on instead of dropping---this plant may need regular deadheading.

Best in semi-shade in moist, fertile, well-drained soil.

This is a colchicine-induced hexaploid, which means it has three times the usual amount of genetic material. The polyploidy is also responsible for the additional vigor and the larger leaves and flowers, as well as their additional substance.

Reaches 25' tall, perhaps more. Said to be hardy in Z4. Propagated by grafting, does not come true by seed. Blooms very young, often at 1' tall.

Bred by Dr. August Kehr of Hendersonville, NC.

Positive mcgerm On Sep 7, 2011, mcgerm from Galesburg, MI wrote:

Third year in the ground after receiving a 3 ft stick originally. It really took off this year. I have had flowers since early spring, one or two here or there, all summer. I have heard that as it gets bigger it flowers almost daily from spring to fall. I would die for a Southern Magnolia that could grow in MI, but this is an excellent continuous blooming and fragrant replacement for the warmth deprived.


This plant has been said to grow in the following regions:

Shawnee Mission, Kansas
Galesburg, Michigan
Great River, New York
Marion, Ohio
Downingtown, Pennsylvania
Shoreline, Washington

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