Culture
Best grown in light, medium moisture, organically rich, well-drained loams in full sun to part shade. Avoid wet or poorly-drained soils. Plants are easily grown from seed. Division and transplanting are possible but tricky because of the fragile, fleshy root systems of these plants, and it is probably best to leave plants undisturbed once established. Deadheading spent flowers generally prolongs the bloom period. New season plant stems emerge late in spring, so gardeners must be careful not to damage crowns by early cultivation (leaving old plant stems in place throughout winter to the point when the new growth first appears helps mark plant locations). Taller plants often need to be staked because of floppy stems. Consider cutting back plant stems by 1/2 in May to reduce plant height and possibly avoid staking.
‘Astra Semi-Double Blue’ is easily grown from seed. Staking is usually not necessary because of the short stems of this compact cultivar.
Noteworthy Characteristics
Platycodon grandiflorus, commonly called balloon flower, is a clump-forming perennial that is so named because its flower buds puff up like balloons before bursting open into outward-to-upward-facing, bell-shaped flowers with five pointed lobes. Plants are native to slopes and meadows in China, Japan, Korea and Siberia. Purple-blue flowers (to 2-3” across) bloom throughout summer, singly or in small clusters, atop stems typically growing to 30” tall. Ovate to lance-shaped, toothed, blue-green leaves (to 2” long).
Genus name comes from the Greek words platys meaning broad and kodon meaning a bell for the shape of the corolla.
Specific epithet means large-flowered.
The Astra series of balloon flower (see ‘Astra Pink' and ‘Astra Blue’) consists of a variety of different seed-grown forms including single, semi-double and double flowers in white, lavender, blue and pink. Astra series plants reportedly are more vigorous plants with better seed germination rates and better flowering. ‘Astra Semi-Double Blue’ is a dwarf/compact cultivar that produces fluffy, semi-double, blue flowers (to 3” across) singly or in small clusters atop stems typically growing to only 6-12” tall with a spread to 8” wide. Flowers bloom throughout the summer.
Problems
No serious insect or disease problems. Root rot may occur in overly moist soils. Watch for slugs and snails.
Uses
Rock gardens or border fronts. Containers. Edging.