Laguna® Dark Blue Lobelia erinus
Photo by: Proven Winners

My favorite color is blue, so I go absolutely giddy every spring when annual lobelias start showing up at my local nursery. Not only do many varieties have true blue flowers, a rarity in the garden world, many also love cool weather and are in full splendor during spring and fall. They are a must-have for my spring containers, and anywhere else in my garden where I want to add a blast of blue.

They're not just a one-color wonder, nor are they always a tender annual. There are more than 400 species that include upright and mounding lobelias, annuals, half-hardy annuals, perennials, and even shrubs and aquatic plants. And although cobalt blue may be their signature hue, you’ll also find blooms in scarlet red, lilac, rose, and vibrant tropical colors.

On this page: The Basics | Varieties | Growing Tips | Care and Maintenance | Pictures | Design Ideas

THE BASICS

Hardiness:

Grown as an annual in most zones; perennials vary by species

Height:

Annuals reach a maximum height of about 12 inches. Perennials can grow to be 4 feet high.

Exposure:

Full sun to partial shade.

Bloom time:

Varies by species. Most annuals will bloom from spring through fall, with a lull during midsummer.

Garden uses:

Hummingbird havens, garden borders and groundcovers, rain gardens, woodland gardens, spillers in container combinations, pollinator gardens.

How rare are blue flowers?

Very! They make up less than 10% of the plant kingdom. Blue lobelias are among this elite group, which also includes blue sea holly (Eryngium planum), Siberian larkspur (Delphinium grandiflorum), Lily of the Nile (Agapanthus africanus), Texas bluebonnets (Lupinus texensis), blue daisy (Felicia amelloides), and blue hydrangeas.

VARIETIES

Although there are hundreds of lobelia varieties, these are the types most commonly grown in the home garden:

  • Edging lobelias (L. erinus) and their hybrids are tender perennials grown as warm-weather garden annuals. Often grown as container and edging plants, they can have bushy or trailing habits. The tiny five-petaled flowers bloom in shades of blue, purple, rose, and white, with some accented by white eyes.
  • Cardinal flower (L. cardinalis), named for its showy spikes of scarlet-red flowers, is the most popular perennial variety. Some varieties also have ornamental reddish-bronze foliage. A North American wildflower native to wet areas, cardinal flower can be found growing in marshes, stream banks, and low woods.
  • Great blue lobelia (L. siphilitica), also called blue cardinal flower, is another native perennial wildflower that bears long-lasting bright blue flowers.
  • Lobelia ×speciosa are popular garden hybrids (usually of L. cardinalis and L. siphilitica) with flowers in shades of blue, lavender, pink or red and a long summer bloom period.

What about Lobelia inflata, commonly called Indian tobacco plant?

Due to serious toxic effects, L. inflata is not commonly grown as a garden plant. It has, however, been used for medicinal purposes for many years.

GROWING LOBELIA

Container combination featuring Laguna® Sky Blue lobelia.
Photo by: Proven Winners.

When to plant:

In spring, after the danger of frost has passed.

Where to plant:

Most prefer moist, hummus-rich, slightly acidic soil. Some perennial varieties, such as cardinal flower, prefer boggy conditions and can even be grown in standing water.

Light requirements:

In midsummer, most will need some shade to keep them blooming, with the exception of those with improved heat tolerance.

Water requirements:

Water regularly to keep the soil evenly moist, especially during hot, dry weather. Container-grown plants may need daily watering to maintain consistent soil moisture.

Growing from seed:

Although annual types are widely available at garden centers in the spring, you can also start your own plants from seed, sown indoors 8 to 10 weeks before the last spring frost date. Don't transplant seedlings outdoors until a few weeks after the last frost date. Perennial lobelias will often self-sow given the right conditions and usually bloom the first year from seed.

Growing in containers:

Plant in a potting mix rich in organic matter. When using them in mixed container combinations, be sure to team them up with other moisture-loving shade-tolerant annuals and perennials, such as violas, impatiens, and sweet alyssum.

CARE AND MAINTENANCE

Fertilizing:

Perennial varieties can usually get by with a yearly application of fertilizer or compost in the spring. For annuals, fertilize more frequently or apply a continuous-release fertilizer for flowering plants to sustain them throughout the growing season.

Pruning and deadheading:

Most annual lobelias are self-cleaning, so you don’t need to deadhead them. If blooming slows during the heat of summer, the best way to revive them is to cut them back by as much as one-half to two-thirds, followed by regular watering. This radical pruning will regenerate new growth, and by the time the cooler weather of fall arrives, your plants should be in full bloom again. You can also pinch back plants at any time if you prefer bushier growth. Avoid pruning back or deadheading cardinal flower and other perennials if you want them to reseed naturally.

Propagating:

Perennials tend to be short-lived, but the plants are easy to propagate by dividing them in the spring or fall or by taking stem cuttings after your plants finish flowering. Unless you plan to let your plants self-sow, divide them every two or three years to extend their lifespan.

Winter protection:

If perennials are covered with heavy mulch over the winter, the roots can rot, especially in warmer southern climates. If you typically mulch your perennial beds to prevent frost heaving and root damage, use a light layer of mulch that won’t completely cover the basal leaves.

LOBELIA PICTURES

Swipe to view slides

Photo by: Proven Winners

Laguna® Dark BlueBuy now from Proven Winners
L. erinus

Type:

Annual; perennial in Zones 9-11.

Height:

6 to 12 Inches

Spread:

12 to 24 Inches

Bloom Time:

Spring until frost

A rare true blue flower with improved heat tolerance. Laguna varieties don't like wet feet, so be sure to let the soil dry out before watering.

See the entire Laguna® series.

Photo by: Proven Winners

Laguna® Sky BlueBuy now from Proven Winners
L. erinus

Type:

Annual; perennial in Zones 9-11.

Height:

6 to 12 Inches

Spread:

12 to 24 Inches

Bloom Time:

Spring until frost

This best seller blooms all season and requires little to no maintenance. Bred to be more heat tolerant than other varieties.

Photo by: Proven Winners

Laguna® WhiteBuy now from Proven Winners
L. erinus

Type:

Usually grown as an annual; perennial in Zones 9-11.

Height:

8 to 12 Inches

Spread:

12 to 24 Inches

Bloom Time:

Spring through late summer

Dainty bright-white flowers with dark green foliage make this an eye-catching spiller to use in container combinations and hanging baskets, where it will trail up to 2 feet. Bred to be more heat tolerant.

Blend Laguna® Dark Blue, Sky Blue, and White for a greater impact.

Photo by: Age Fotostock / Alamy Stock Photo

‘Crystal Palace’
L. erinus

Type:

Perennial in zones 7-11

Height:

4 to 6 inches

Spread:

6 inches

Bloom Time:

Late spring through early autumn

This compact plant packs a big punch with its deep cobalt-blue flowers and glossy bronzed foliage. Tidy bloom-covered mounds are a great choice for use at the front of a border, as an edging along shady walkways, or as a colorful groundcover. Blooms continuously from spring until the first frost.

Photo by RukiMedia / Shutterstock

Great Blue Lobelia
L. siphilitica

Type:

Perennial in zones 4-9

Height:

2 to 3 feet

Spread:

1 to 1½ feet

Bloom Time:

August through September

This blue cousin of the cardinal flower shares many similar features, producing dense spikes of showy flowers that are magnets for hummingbirds and butterflies. It’s also a wetland native that flourishes in moist garden soils.

Also try: 'Alba’, a cultivar with white flower spikes, and ‘Blue Selection’, a slightly stouter plant with brighter blue flowers.

Photo by: Walters Gardens

Cardinal Flower
L. cardinalis

Type:

Perennial in zones 3-9

Height:

3 to 4 feet

Spread:

1 to 2 feet

Bloom Time:

July to September

Its fiery red flowers are a favorite source of nectar for hummingbirds. Cardinal flowers crave water and are perfectly happy growing in a water garden or at the edge of a stream or pond. They can also be grown in containers set in a tray of water on a patio or deck.

Also try: 'Queen Victoria', with bright scarlet-red flowers with dark maroon foliage, and ‘Ruby Slippers’, with ruby-colored flowers.

Photo by: John Richmond / Alamy Stock Photo

Mexican Cardinal Flower
L. laxiflora

Type:

Perennial in zones 7-11

Height:

2 to 3 feet

Spread:

5 feet or more

Bloom Time:

Spring through fall; nearly year round in mild climates.

Rather uncommon, this exotic and tropical-looking variety has trumpet-shaped salmon-red flowers with bright yellow and orange throats that hang in clusters on thin red stems. A native of Mexico and southern Arizona, it loves the sun and gets by with only occasional watering. With a spreading, bushy growth habit (that can be invasive), this plant works especially well as a showy groundcover or tall border.

Photo by Walters Gardens

'Starship Deep Rose'
Lobelia ×speciosa

Type:

Perennial in zones 6-10

Height:

20 to 24 inches

Spread:

12 to 24 inches

Bloom Time:

June through September

Dazzling rose-pink blooms are set off by dark bronze foliage. This long-blooming hybrid bears flowers on tall, upright stalks and thrives in moist conditions. Use as a vertical accent in containers, well-watered garden beds, and aquatic gardens. Also a good choice for cut flower arrangements.

Photo by Walters Gardens

‘Starship Scarlet’
Lobelia ×speciosa

Type:

Perennial in zones 6-10

Height:

20 to 24 inches

Spread:

12 to 24 inches

Bloom Time:

June through September

Scarlet red flowers bloom from midsummer to early fall on dense, upright spikes. An excellent choice for borders and beds with moist soil. Hummingbirds love the bright red flowers.

DESIGN IDEAS

  • Cascading varieties make attractive spillers in hanging baskets and window boxes.
  • Upright varieties work perfectly as a centerpiece (or ‘thriller’) in containers or along borders. They also add height to cut arrangements.
  • Add in rock gardens, butterfly gardens, or in a deer-resistant landscaping design.

RELATED:
Flowering Plants for the Fall Garden
Flower Garden Design
Container Gardening Ideas

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