Lobelia is a plant family with over 350 species, including a well-known annual species L.erinus used most often in hanging baskets or low edgings. This article, however, will focus on the perennial Lobelia species known as cardinal flowers.
Botanical Information and How to Grow Lobelia
Cardinal flower grows native along streambeds all over the Southern United States and is a real treasure in the garden by providing one of the truest reds available. Is thrives in areas where other perennials would rot and adds bold color to shady corners of the garden.
Cardinal flowers also boast a long bloom time, which is a huge bonus as the plant also attracts hummingbirds. The delicate looking, but boldly colored flowers create a strong presence near water features or planted in masses.
Botanical Name: Lobelia cardinalis is the scientific name.
Hardiness Zones: Lobelia cardinal flowers can handle cold weather climates remaining hardy in zones 2-9.
Bloom Time & Color: Cardinal flowers produce dozens of red or blue flowers on tall stalks in midsummer through fall. Some varieties have later bloom times but all are long lasting.
Plant Category: A short-lived Perennial.
Foliage: Cardinal flower (Lobelia cardinalis) has lance shaped leaves approximately 4-5" long in most varieties. Some cultivars and varieties have purple or burgundy colored foliage and the others have a true green color that contrasts nicely with the blooms and looks attractive all season.
Growth Habit: A strong vertical element in the garden, the foliage is closer to the ground in shallow rooted clumps with the taller flower stalks lifted above.
Dimensions: Most cardinal flowers are 2-4 feet tall.
Preferred Conditions: Cardinal flowers grow well in moist soil that would cause other perennials to rot. Dappled sun or light shade is preferred but that depends on location; plant the Lobelia in shadier spots further south and in sunnier areas north of zone 5. Dry soil can be tolerated with frequent watering and rich soil is preferred.
Maintenance: Individual cardinal flower plants can be short lived but the fibrous rooted crown is easily divided in the fall to provide you with new plants. They will reseed if the flower stalks are allowed to remain after blooming. Mulch generously to preserve moisture, and be sure to mulch during the winter as well, since the shallow root system makes them susceptible to root heaving, when freezing temperatures can actually lift the entire plant out of the ground.
Pests or Diseases: No specific pests or diseases. Root heaving is the main thing to watch out for if in areas with freezing winters.
Propagation Methods: You can grow Lobelia from seeds sown outdoors in the fall, or indoors in the winter. Also consider stem cuttings and division.
Using Lobelia in the Garden Landscape
Companion Plants: Combine Lobelia with any plant that enjoys moist soil conditions such as Astilbe and Iris. Shady conditions such ferns and hostas will make good companion plants for cardinal flowers also. Consider other plants attractive to hummingbirds to provide a real feast for the flying jewels!
Seasons of Interest: The foliage is attractive spring through fall and the flowers have a long bloom time midsummer through autumn as well.
Uses in the Garden: Cardinal flowers are fantastic near water features, so consider using around ponds, pools, stream beds or boggy areas. They also do well in shade borders, woodland areas, hummingbird gardens, for a cut flower border or native, naturalized areas. (For more information about growing Lobelia and other native plants consider 100 Easy-to-Grow Native Plants by Lorraine Johnson, a great book that details how to create an easy-to-maintain garden using native plants like cardinal flower.)
Other Uses: Cardinal flowers are great cut flowers and work nicely in arrangements.
Lobelia Species & Varieties
- L. cardinalis – The native cardinal flowers naturally has red blooms. Some cultivars have beautiful burgundy foliage like ‘Bee’s Flame’ growing 30" x 12" and Queen Victoria growing 3’ tall and 9" wide. Hardy zones 2-9
- L. siphilitica – Called Azure Sage, this Lobelia has deep blue flowers that make their appearance in the fall. Longer leaves grow to 6" but the plant itself grows 3’ tall and 18" wide. Hardy zones 4-8
- L. vedrariensis (also called L. gerardii) – Hybrid forms with purple blooms that are very tall growing 3-4’ high and are prized as cut flowers. These bloom summer through fall and are hardy zones 5-8
Angela England - Angela England is a problogger, mother of four (yes I know what causes that), speaker, teacher, labor doula, gardener and so much more.
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