The Chicago Botanic Garden is releasing results of a long-term study of balloon flower, Platycodon grandiflorus, in its 32nd issue of Plant Evaluation Notes: “A Comparative Study of Platycodon grandiflorus Cultivars.” Between 2001 and 2005, the Chicago Botanic Garden evaluated Platycodon grandiflorus and 19 cultivars in full-sun trials. The goal of the comparative trial was to recommend exceptional balloon flowers for northern gardens. Twelve balloon flower cultivars received high ratings for their strong habits, generally upright stems and good floral displays.
Balloon flower is a bushy, clump-forming perennial, growing to 3 feet tall, but often troubled by floppy stems. Throughout July and August, the buds burst open to blue, pink or white starry flowers streaked with prominent veins. Bluish green leaves, generally oval with toothed margins, are arranged in whorls on the lower portion of the stems but positioned alternately at the tips. In autumn, leaf color changes to dark purple or a mix of light purple and yellow, depending on the cultivar.
Hardy balloon flowers grow best in well-drained soils in full sun to light shade and are long-lived under normal conditions. They have few pest problems, though deer enjoy the stems and flower buds, and staking may be required. Balloon flowers perpetuate themselves in the garden through self-seeding, which sometimes results in subtle new color forms.
In the border or cottage garden, balloon flowers are good companions to other summer-blooming perennials such as Shasta daisies (Leucanthemum sp.), yarrows (Achillea sp.), sages (Salvia sp.) and ornamental grasses. The dwarf cultivars are well suited to rock gardens and seasonal containers.
One drawback to balloon flowers is their often lax stems, which is particularly troublesome for taller plants. Shorter cultivars have been introduced to remedy this problem; however, some short cultivars in the trial grew larger than expected. A compactness of habit was especially notable on 'Astra Blue', 'Baby Blue', 'Misato Purple', 'Sentimental Blue', and 'Zwerg'. These robust cultivars remained mostly upright during the bloom period but occasionally had relaxed or floppy stems by September.
Among the taller balloon flowers that remained fairly upright during the bloom period were Platycodon grandiflorus, 'Blaue Glocke', 'Double Blue', 'Fuji Blue', 'Fuji Pink', 'Fuji White', 'Hakone Blue', 'Hakone White', 'Komachi' and 'Perlmutterschale'.
The Chicago Botanic Garden’s Plant Evaluation Notes provide the latest information on plants suited to the Midwestern climate and growing conditions. To download a PDF of Issue 32, “A Comparative Study of Platycodon grandiflorus Cultivars,” click here.
Photos by Carol Freeman.