Platycodons, or balloon flowers, are commonly used as attractive, versatile and showy perennials in today’s gardens. They are utilized by gardeners and landscapers as accent plants, border plants and potted houseplants and in rock gardens and container plantings. ‘Miss Tilly’ is a compact F1 hybrid that reaches only 6-8 inches in both height and diameter and produces an abundance of blue, star-shaped flowers above its dark-green foliage. The common name balloon flower refers to the puffy, balloon-like shape of flower buds before they open. On ‘Miss Tilly’ these flower buds open into single, bell-shaped blue flowers during the mid summer.
Unlike most platycodon cultivars, which are suitable for production in USDA Hardiness Zones 3-8, ‘Miss Tilly’ is considered a tender perennial and only hardy in USDA Hardiness Zones 6-8. Platycodons prefer to be grown in full sun, although in the South they perform best when grown under partial shade. This cultivar is heat tolerant in AHS Heat Zones 9-1.
‘Miss Tilly’ is propagated from seed. Sow platycodon seeds in the intended plug flat, and cover them lightly with a germination mix or medium-grade vermiculite. The covering helps maintain a suitable environment around the seed during this phase. Light is necessary for germination. As long as the covering is put on the flats lightly, there is generally enough light available to satisfy this requirement.
The seed flats should be moistened and moved to a warm environment where temperatures can be maintained at 68-72º F for germination. It is important to keep the media very moist (not saturated) during this stage, or the germination rate is likely to decrease. Using germination chambers is optional, but platycodons will successfully germinate in the greenhouse when the proper temperatures and moisture levels are provided.
The seeds should complete germination within 7-15 days. Following germination, reduce the moisture levels somewhat, allowing the growing medium to dry out slightly before watering to help promote rooting. Fertilizers are usually applied once the true leaves are present. Apply 100 ppm nitrogen every third irrigation or 50 ppm with every irrigation using a balanced water-soluble source. When grown at 65° F, ‘Miss Tilly’ will finish the plug stage in approximately 8-10 weeks.
For container production, ‘Miss Tilly’ is suitable for 1-qt. to 1-gal. containers. Most growers receive starting materials of platycodons as finished plug liners. When planting large containers, such as 1-gal. pots, I recommend planting at least two plug cells per container to properly fill out the pot. Platycodons perform best when they are grown in a moist, well-drained medium with a slightly acidic pH of 5.5-6.0.
Plugs should be planted so the original soil line of the plug is even with or just below the surface of the growing medium of the new container. The fleshy tap root is susceptible to root rots, particularly after transplanting or when overly wet conditions occur.
After planting, I recommend drenching with a broad-spectrum fungicide such as Banrot (The Scotts Company LLC) or the combination of Subdue MAXX (Syngenta Professional Products) and Cleary’s 3336 (Cleary Chemical Corporation).
It is beneficial to pinch platycodons prior to or shortly after they are planted in the final container. Pinching increases lateral branching and the total number of flowers produced on each plant. Flowering will be delayed 3-4 weeks when platycodons are pinched. Therefore, growers should modify their crop schedules or ready dates accordingly.
Platycodons can be grown using light to moderate fertility levels. Fertility can be delivered using water-soluble or controlled-release fertilizers. Growers using water-soluble fertilizers should either apply 100-150 ppm nitrogen as needed or feed with a constant liquid fertilization program using rates of 50-75 ppm nitrogen with every irrigation. Growers commonly apply controlled-release fertilizers as a top-dress on the media surface using the medium rate or incorporated into the growing medium prior to planting at a rate equivalent to 1 lb. nitrogen per yard of growing medium.
Platycodons require an average amount of irrigation, as they do not tolerate overly wet or dry conditions. Root zones that remain waterlogged tend to get root rot pathogens and can quickly lead to crop losses. Overly dry growing conditions reduce crop quality and delay flowering. Growers will usually observe yellowing of the leaves if the plants have recently wilted due to moisture stress. When irrigation is necessary, I recommend growers water plants thoroughly then allow the soil to dry slightly between waterings.
Platycodons are relatively free of serious problems associated with insects. Occasionally, aphids, spider mites and whiteflies may appear, causing only a minimal amount of crop injury. Of these insect pests, aphids are the most prevalent. None of these insect pests require preventative control strategies. Most insects can be detected with routine crop monitoring. Control strategies may not be necessary unless the scouting activities indicate actions should be taken. Platycodons can generally be grown free of plant pathogens. The primary diseases growers should watch for are Rhizoctonia crown rot and Heterosporium stem canker. Platycodons are most susceptible to these diseases when they are grown under cool and wet conditions, such as during the fall just prior to entering the winter dormancy. Botrytis is another disease that could become problematic. To control these diseases, it is best to manage the environment by controlling the humidity and providing proper plant spacing and adequate air movement. Growers should carefully watch the moisture levels during adverse times of the year and avoid overwatering their plants. Many growers apply a broad-spectrum fungicide drench before and just after the overwintering period to prevent Rhizoctonia diseases. Stem cankers can be controlled by applying preventative sprays of Compass (OHP) or Cleary’s 3336 when the conditions for the disease are optimal.
‘Miss Tilly’ is a compact cultivar and will usually not require plant growth regulators to control plant height. During the winter months, periods of low light levels or when grown at high plant densities, excessive plant stretching may occur, requiring some type of height management strategy. Most commercially available growth regulators are effective at controlling plant height of platycodons. Before applying these chemicals, the height of platycodons can often be effectively controlled by providing adequate spacing between the plants and by withholding water and nutrients. For toning and shaping purposes, one growth regulator application is often adequate. Whenadditional height control is necessary, make a second application 7-10 days after the first.
For container production, ‘Miss Tilly’ is well suited for forcing into bloom throughout the year. When following a few guidelines, growers can successfully produce uniform, consistent, high-quality flowering plants.
Platycodons do not have a cold requirement that must be met prior to forcing. They will easily bloom from plants started by seed during the first growing season without providing a cold treatment. Established containers of platycodons can successfully be overwintered. Regardless of the size of container being overwintered or vernalized, it is important to avoid moisture extremes and not allow plants to become overly wet or dry.
Platycodons also do not have a juvenility period and have been observed flowering with as few as 13 leaves present. Platycodons are day-neutral plants and can be forced into flower under any photoperiod. They are long-day beneficial plants and will flower 7-10 days faster under long-day photoperiods compared to plants grown under short-day conditions.
The primary factor for flowering is temperature. Platycodons grow relatively slowly compared to other forced perennials. When warm production temperatures (higher than 70º F) are provided, plant development is hastened, and the production time can be reduced. Production of ‘Miss Tilly’ at 65° F will take 12-13 weeks to reach flowering, while plants grown at 75° F will flower in 9-10 weeks.
‘Miss Tilly’ is available to the industry as seed, plug or finished container. Seeds are available from Goldsmith Seeds. Plugs and finished containers can be acquired from many reputable perennial producers or plant brokers.