Dahlia imperialis, also called the “tree dahlia,” bloomed recently at the Smithsonian. This dahlia is a separate species from those with which most people are familiar. Historically, in the Washington DC area, tree dahlias are killed by freezing before blooming. However, the horticulturists at the Smithsonian Gardens have successfully achieved blooms during two of the last three years. According to James Gagliardi, Horticulturist at the National Museum of Natural History at the Smithsonian, the first time Dahlia imperialis bloomed in the Haupt Garden was in 2011. In 2012, the plant was damaged in the hurricane and did not bloom. However, this year, the plant began flowering in late fall. He estimates that this year’s plant had around 8 large branches that reached around 20 feet in the air. By mid-November, the blooms had become spotty. One can only imagine what the plant would look like if it were to reach full bloom, which is unlikely once the cold temperatures arrive.
The plant can be seen near the northeast corner of the Moongate garden behind the Smithsonian Castle. Gagliardi says “The history of this particular dahlia is that it had been kept in our greenhouse facilities, eventually becoming too large…. we decided to run an experiment, and plant it permanently in the Enid A. Haupt garden behind the Smithsonian Castle.” This area is technically a rooftop garden, as it sits atop multiple floors of underground museums. “The plant was placed in the Moongate garden close to a skylight for the Sackler Gallery,” explains Galiardi. “In this warmer location we have found success with growing the dahlia. During its first summer in the garden in 2011 it reached 9ft tall and bloomed but in 2012,damage from the hurricane winds broke the cane and kept the plant from blooming. This year the plant began to bloom the week before the recent killing freeze, still far from its peak bloom.
 Dahlia Imperialis, NE Corner of Moongate Garden, behind the castle. |
 Photo showing a member of Smithsonian staff, showing immense size of plant |