HARDINESS: Frost tolerant
PREFERRED SOIL pH: Adaptable
PREFERRED SOIL TYPE: Average
PREFERRED LIGHT: Sun or partial shade
ATTRIBUTES: Intense true blue, violet-blue, or white flowers on cascading or mounding plants, for edging, window boxes, and containers
SEASON Of INTEREST: Spring to fall
FAVORITES: For edging, blue 'Blue Moon' or white 'Paper Moon'; 'Midnight Blue' has bronzy red foliage; the 'Fountain' series for its cascading habit
QUIRKS: Plants stop blooming and may die in hot weather
GOOD NEIGHBORS: Yellow dwarf marigold, dusty miller, petunia, snapdragon, zinnia
WHERE IT GROWS BEST: Cool summer climates, and a site in full sun
POTENTIAL PROBLEMS: Excessive warmth can wither plants
CRITTER RESISTANCE: Good
SOURCE: Seeds, cuttings
DIMENSIONS: 6 in (15.2 cm) high, 6-12 in (15.2-30.5 cm| wide, depending on variety
Lobelia in the Landscape
Here is the perfect plant for the edge of anything. Edging a garden bed, filling a window box, or spilling out of containers or hanging baskets. If you enjoy teaming up different annual combinations in containers, lobelia will quickly become an essential source for that hard-to-find shade of true blue, as well as contributing purple, violet, and white to the scene. The tiny, 3/4 in (2 cm) flowers are prolific, and plants always have new flowers to offer throughout the season with no fuss whatsoever.
These annual edging lobelias grow best when summer nights remain between 50°F and 70°F (10° and 21°C), but they are such prompt and continuous bloomers that gardeners in warm climates can enjoy them as lovely, but fleeting flowers from spring to early summer when nights turn from cool to warm. Petunias have similar weather preferences, so the two make an unbeatable combination in beds or containers. Yellow dwarf marigolds are also excellent companions, and lobelia is a great way to hem a patchwork of multicolored snapdragons or compact zinnias. Weave lobelia among silver-leaved dusty miller for a neat, trouble-free edging in foundation beds.
Lobelias grow to 6 in (15.2 cm) tall, but varieties vary in growth habit. Some form rounded mounds, while others are more intent on spreading, making them suitable for cascading over the edges of containers. If you want to use lobelia to edge a bed, choose a mounding variety, such as violet-blue 'Blue Moon' or white 'Paper Moon'. 'Midnight Blue' has bronzy foliage that contrasts vividly when paired with silvery dusty miller or any plant with white or pale yellow flowers. Choose a cascading variety, such as the Fountain series for containers, baskets, or for planting at the top of a stone wall.
Lobelias need an 8- to 10-week start from seeds before they reach transplanting size, so in this case, bedding plants are a good buy. Keep the soil in their containers moist until you plant them. Set the bedding plants in the garden after your last spring frost date, spacing them 6 in (15.2 cm) apart. Lobelias grow best in a cool spot with partial shade in areas where days are often above 80°F (26°C). Before planting lobelias in beds, mix a balanced, organic, or controlled-rel ease fertilizer into the soil. Fertilize pot-grown lobelias every 2 weeks during the growing season, using an all-purpose plant food.
In midsummer, you can rejuvenate lobelia by cutting the plants back by half their height, reapplying fertilizer, and watering them well. This is worth a try in all climates, but it may not succeed in hot, humid areas, where lobelias often wither away in July. However, this is an honorable end after their many weeks of valiantly producing intense, nonstop color.
Lobelias are easy to propagate by rooting 4 in (10.2 cm) long stem cuttings taken at any time. Remove leaves from the lower 2 in (5.1 cm) of stem and insert the cuttings halfway into moistened potting soil. Set the containers in a shady spot and keep the soil moist until new growth signifies that they are rooted. Plants can be cut back and wintered over indoors on a sunny windowsill, where they'll keep on blooming and be ready to go out to the garden the next spring.