The color blue in the garden does not have a better representation than lobelia. The South African perennial Lobelia erinus, and its cultivars have graced garden beds and trailed from balcony plantings for years. Traditionally grown as an annual, lobelia is a key component to any bedding-plant grower’s product mix.
As many traditional bedding plants have done before, lobelia has made the crossover to a vegetative crop. Many question the advantages of vegetative crops over seeded ones, especially when habits and color forms do not differ greatly. Vegetative lobelia, however, has proven itself superior in many ways to its seeded counterparts. Many breeders have been working with this crop to explore and develop these improved traits. Series such as Hot, Laguna and Waterfall are just some of the big names in vegetative lobelia. Color range and flower size are some of the clearest improvements that can be seen at a consumer level; however, many improvements have been developed to assist at a production level for growers.
One of the main advantages of vegetative lobelia over seeded lobelia is that most vegetative cultivars are sterile. One might ask why sterility is seen as an advantage. Simply put, when traditional seeded lobelias undergo stress, usually from lack of water or exposure to adverse levels of heat, the plants go into a reproductive state and set seed. This decreases the quality and quantity of bloom and the overall appearance of the plant. Vegetative forms, which have received their bloodlines from interspecies crosses, are sterile and have the ability to recover from stressful conditions and continue to bloom.
Lobelias are native to coastal South Africa in and around the Cape of Good Hope. This climate provides high light and cool temperatures. In response to this heritage, lobelias do not fare well in hot weather and low-light conditions. This adversity to heat is another reason vegetative forms have proven better; they have increased heat tolerance. One series that touts heat tolerance as its key feature is the Hot series from Westhoff in Germany. Cohen Nurseries of Israel is responsible for the stock and cutting production of this series and has had great success producing cuttings in 100° F days. Series like this can now let consumers enjoy lobelia from spring until frost. In milder climates vegetative lobelias can be grown as tender short-lived perennials.
The development of additional color lines and increased flower sizes have also helped lobelia establish itself as a key item in the vegetative annual market. Traditionally, lobelia has been offered in every shade of blue known. Now, lobelia has started to break into the pink, lavender and dark-purple color ranges. White is another traditional color of lobelia, but bicolors of white and blue, and white and lavender are starting to become available. Two exciting new cultivars that show this bicolor trend are lobelia ‘Hot White Spot’ from Westhoff and lobelia Á ‘Waterfall White Sparkle’ from Ball FloraPlant. Blue, however, is still the key color in lobelia.
Flower size has also been a key development. Flowers that double the size of traditional seeded forms are not uncommon in recent introductions. Lobelia ‘Big Blue’, also from Westhoff, has flowers close to 1 inch in size. These larger flowers with their intense colors can be a real attention grabber when grown in larger containers and baskets. Anyone who visited Fischer’s 2005 California Pack Trials could not help but notice lobelia ‘Techno Blue’ screaming from the corner. Grown in baskets covered with intense blue flowers, these plants challenged you to find the green foliage.
Traditionally, lobelia has been a great mounding and trailing plant. Its trailing habit has made it a key item in window boxes in places like Northern Europe. This trailing habit has been accentuated in the vegetative forms and has made lobelia an ideal component in mixed containers and hanging baskets. Lobelia’s habit matches well with other trailing plants such as bacopa and calibrachoa. Lobelia can easily be grown with these plants and will not be overwhelmed or overrun other plants. Lobelia can also be grown as a stand-alone plant; baskets of pure lobelia can make an impressive statement, especially when grown in full sun, so they can achieve their full glory. Some development has also been made toward more mounding and upright habits. Lobelia ‘Bavaria’ and ‘Periwinkle Blue Improved’ both have habits that are suited to container culture.
There are some key elements to growing a successful lobelia crop. High light is essential to producing quality lobelia. The light intensity and day length both play into how a crop will do. Lobelia should be grown in full sun, ideally with light in the range of 5,000-8,000 foot-candles. Lower light levels will cause Á overgrown, soft plants. Photoperiod is the other key element that will affect flowering and flower quality of lobelia. Lobelias are long-day plants, typically flowering naturally in late spring and summer. Some development has been made in producing varieties that are less sensitive to photoperiod, but the majority of lobelias require supplemental lighting to induce flowering at early times in the year.
Lobelias are naturally vigorous plants with habits that tend toward the trailing side. This vigor and habit can be great when growing crops in larger containers or baskets, but it can pose a challenge when trying to finish crops in 4-inch containers. Lobelias respond well to chemical growth regulators. I have had success with paclobutrazol sprays and drenches, as well as sprays of B-Nine (Chemtura Corporation) to control growth. At Pacific Plug & Liner we treat lobelia in propagation with a low-rate paclobutrzol drench prior to root development. This greatly reduces stretch during propagation and creates a better quality young plant for transplanting.
Lobelias also respond well to pinching. Varieties vary greatly in the need for more or less pinching. Some forms that basal branch need almost no pinching at all; other forms need multiple pinches to create a quality finished plant. Typically, vigorous trailing varieties are most appropriate in baskets or mixed containers where their full potential can be appreciated. Mounding and more compact varieties are better suited for smaller containers where they can easily be controlled.
Lobelia requires evenly moist, well-drained soil. Excessive drying will aversely affect the crop; however, the vegetative varieties will rebound with better success than seeded types. Lobelia is a good indicator plant of nutrient levels. Plants will show chlorosis when nutrient levels are off balance. A moderate 200-ppm nitrogen fertilizer given constantly should be adequate for most plant needs. Lobelia prefers cooler temperatures but can handle hot spells. An average temperature of 55-65° F should work well for most varieties.
Considering the lack of true blue flowering plants, lobelia has made its presence known as the key component for blue in any garden. The advancements in color range and more compact habit have made lobelia an even more important plant for both growers and gardeners. Vegetative lobelia varieties have taken away many of the challenges seeded varieties once posed. If growers have not worked with lobelia very much, these new developments make this crop worth a second look. Lobelia definitely deserves a place in production schedules and will likely not disappoint.
The California Pack Trials are a great opportunity to see the most current varieties available. Cohen, Fischer, S&G Flowers, Ball FloraPlant, Bodger Botanicals and Proven Winners are just a few locations that have lobelia varieties in their programs.