Lobelia cardinalis and Lobelia siphilitica, Family Campanulaceae.
The small-flowered lobelia commonly sold in spring hanging baskets, Lobelia erinus, is an annual and not considered in this profile.
Great Blue Lobelia, Cardinal Flower
4-8, but may be marginally hardy in zone 3
Partial sun or dappled shade
Mid summer, lasting up to two months
Many small florets on each flowering spike make the lobelia a lovely asset to the wildflower and cutting garden. Each floret has five lobes, sporting two erect upper petals and three descending lower petals. The tubular flowers are appealing to hummingbirds, but not too deep to deny butterflies their nectar.
The plants form clumps, which you can divide in the spring to produce more plants. Foliage color varies, with species bearing olive green lance-shaped leaves, but some hybrids bear bronze or reddish leaves.
Lobelia plants thrive with abundant moisture, and make good specimens for bog or rain gardens. You can also plant lobelia along riverbanks or streams, as the plants will tolerate an occasional flood. Lobelia plants like rich soil, so amend the planting site with compost or aged manure at planting time.
If you choose to grow lobelia plants from seed, sow them on top of the soil, and do not cover the seeds. The seeds need light to trigger germination.
- Although lobelias like wet conditions, they don’t like a thick layer of mulch. If a dry spell occurs, you’ll have to keep them moist with extra irrigation, not extra wood chips.
- As a perennial, lobelia plants are short-lived, and will fade after a few years no matter what care the gardener offers. Divide the plants every two years to replenish plants in decline.
- Diseases that bother lobelia include rust and leaf spots. Mite infestations may occur in drought stressed plants.
- Alba: White flowers
- Fried Green Tomatoes: A scarlet cardinal flower with some red tinting on the foliage
- Pink Flamingo: Rose colored flowers
- Ruby Slippers: Vivid red flowers on hardy plants
- Russian Princess: Purple foliage, red flowers, requires more shade than others
- Vedariensis: Dark purple flowers, red hues on foliage