The dahlia bed is in full bloom this month and located just west of the Sharps Cabin.  The Bellevue Botanical Garden’s display is planted and maintained by Lee Bowen, Roger Walker, and other volunteers associated with the Bellevue Botanical Garden and the Puget Sound Dahlia Association.

Cultural notes:

Reliably long flowering season, often until the first frost in cool, temperate climates.

Use support stakes for specimens with large inflorescence. Most Dahlia species require staking to show off the variety of color and texture displayed by these brilliantly flowering plants. The lower growing, single flowering group can be on display unstaked in a mixed border.

Plant tubers in mid to late spring, placing them 4 in. deep with a 3 ft.  stake towards one side. Set the tuber on its side, with the growing shoot close to the stake. Tie the growing plant to the stake at 2 ft. after growth has become established and again as required to provide support.

Tip newly emerging stems to encourage branching and a more robust flower display. Remove tips after 3 sets of leaves have established on the central leader to encourage branching.

Dahlias have a high water requirement.  Mulch with compost to retain moisture and suppress weed growth.

Propagate from tubers or cuttings to ensure parental flowering traits.

Lift tubers from ground in mid to late autumn for over-wintering. All Dahlia species are frost tender and require lifting and storing to ensure viable spring growth.

Dahlia species are divided into 10 distinct groups according to their flower morphology. The groups are: Single-flowered, Anemone-flowered, Collerette, Waterlily, Decorative, Ball, Pompon, Cactus-flowered and Semi-cactus-flowered. The Miscellaneous Group includes Peony-flowered, Star and Orchid-flowered forms.

References: 
RHS, Sunset