How to Plant, Grow, and Care For Cardinal Flower

Cardinal flower (Lobelia cardinalis) is a perennial wildflower native to the central and eastern United States and Canada. It loves wet soils and partially shaded garden locations. It is a very showy plant for your rain garden or a wetland edge where you may have difficulty finding suitable plants that love constant soil moisture. 

These tall, leafy perennials provide plenty of lush greenery during the spring and summer. By the end of summer, be prepared for some eye-popping colors and fluttering visitors! Hummingbirds adore the gorgeous spikes of intensely bright red tubular flowers. These flashy flowers will keep your garden well-adorned right into fall. 

If your landscape has the right growing conditions, these plants are very low-maintenance. Grow them with other wildflowers that thrive in similar conditions, such as the great blue lobelia, southern blue flag iris, and marsh milkweed. You will create a pollinator paradise and a spectacular flower garden with immense curb appeal.

Keep reading for more information about growing and caring for the magnificent cardinal flower plant.

Natural History

The cardinal flower is a member of the Bellflower family (Campanulaceae) which encompasses over 2,000 different species around the world, including bellflowers, balloon-flowers, and a variety of beautiful and colorful Lobelia species. There are also several spectacular cultivars available commercially.

These plants are native to central, southern, and eastern North America. They are partial to moist soils and most commonly found around wetlands and floodplains. Cardinal flowers are an important species in moist prairies and meadows, as well as along shaded forest edges.

Characteristics

This herbaceous perennial grows two to three feet tall but can reach up to four feet tall in ideal conditions. These plants have a dramatic, upright growth form. The erect, leaf-lined stems are lined with alternate, shiny leaves with toothed margins. These plants remain fairly inconspicuous for most of the spring and summer, providing attractive green foliage. 

In mid-to-late summer, cardinal flower plants send up flowering spikes lined with very showy scarlet red flowers. The flowers start opening at the bottom and continue their way up the spike. They bloom well for a few weeks before the flowers start to fade and drop off, leaving behind bulging seed capsules.

Native cardinal flowers are typically brilliant scarlet red. Blue species are similar in appearance but with beautiful purple-blue flowers. Other varieties and cultivars have showy red, pink, white, blue, and purple flowers. All lobelia flowers tend to be somewhat tubular with prominent lips at the opening.

These plants spread by self-seeding and rhizomes. Within a few years of planting, they form expanding clumps and clusters, naturalizing into very attractive colonies. They are considered short-lived perennials. In their natural environments, they self-seed and maintain vibrant populations. In cultivation, you can allow your plants to self-seed or spread a little each year to colonize their plot. 

Do not attempt to eat any part of the plant, and keep them away from your pets as well. All parts of the cardinal flower plant are toxic if ingested. 

Propagation

Easily propagate these flowers by division of mature clusters. They can also be started from seed, but this method requires a bit more work and patience.

Seed

Cardinal flower plants can be successfully grown from seed and will self-seed in ideal growing conditions. Plants grown from seed will typically start to bloom during their second summer. 

The seeds need about two months of cold stratification before they will sprout. You can do this by placing the seeds in a refrigerator for two months before sowing or direct sowing them outdoors in the fall. The seeds are tiny and need light to germinate, so don’t bury them under the soil.

After sowing, keep the soil continually moist until germination. Keep your seedlings moist as well because the young plants are very sensitive to drying out.

Division

Dividing mature clusters is the quickest and easiest way to propagate cardinal flowers. Don’t dig plants from the wild, but if you already have a patch in your yard, you can divide them in the early spring or late fall and transplant part of the divided cluster to a new location. 

Transplanting

When you are ready to transplant, try to time this activity on a cool, overcast day. Prepare your transplant site in advance by digging a hole, enriching the soil, if necessary, and pre-moistening the soil.

Gently remove the plant from its pot and transplant it into the prepared hole. Immediately backfill the space around the roots with soil and water the area well, allowing enough time for the water to soak into the soil rather than just moisten the surface. Keep your plant well-watered for the next several days. 

How to Grow

Cardinal flowers are easy to grow if you have good conditions for them. The most important things to remember are that they love moist soil and a bit of protection from prolonged intense sunlight.

Sunlight

Cardinal flowers perform well in full sun to partial shade but generally prefer partially shaded locations. Allow them anywhere from two to six hours of bright sunlight each day. In cooler climates, they tolerate more direct sun exposure, while in warm climates, they will appreciate more afternoon shade.

Water

Cardinal flower plants like moist to wet soil. If your site is prone to drying out completely, you’ll need to do some supplemental watering to keep your cardinal flowers happy. Check the soil moisture frequently during dry periods and places where you know the soil dries quickly.

Soil

Provide high-quality soil to give your cardinal flower a distinct advantage. The soil should be high in organic matter and have good moisture retention. The soil pH should be neutral to slightly acidic.

Climate and Temperature

Cardinal flowers are hardy in USDA Plant Hardiness Zones 3 – 9. Cardinal flowers perform well in both warm and cold climates as long as they get a bit of shade and have plenty of moisture.

Fertilizing

You won’t need to fertilize your cardinal flower plants. As long as you have rich soil, this will provide all the nutrients your plants need. If your soil is poor quality, enrich it at planting time with some organic compost and mulch.

Maintenance

These plants are wonderfully low maintenance. Apply mulch in the fall to protect the roots from extreme temperature fluctuations and help the area around your plant retain moisture throughout the year. As with any garden planting, routinely pull weeds to reduce competition and keep your flower garden looking great.

Garden Design

These flowers would look fabulous and be the center of attention in any setting as long as you can provide consistently moist soil. Cardinal plants are not drought tolerant and would not be suitable for a xeriscape or any situation with frequently dry soils. 

If, however, you have a rain garden or a low, moist location in your landscape, this plant would be a great choice. Grow it along a streamside, pond, or wetland edge. It shouldn’t be standing in the water, but growing along the edge for a showy statement. If you have a wet or soggy area in your yard and you just don’t know what to do with it, try growing a cardinal flower.

Cardinal flower is also an ideal choice for a moist pollinator garden or hummingbird garden. Though you must wait awhile for cardinal flowers to bloom, the end-of-summer rewards are worthwhile. Grow these plants with some other interesting moisture-loving wildflowers that bloom at earlier times so there are always beautiful, nectar-rich flowers to entice hungry pollinators to your yard. Allow at least one foot of space between individual plants because they will quickly fill in their available space.

You can even grow cardinal flowers and other native plants in container gardens. Use a rich, moisture-retentive potting soil. Place your potted cardinal flowers in partially shaded areas and check on them regularly. You’ll probably need to provide regular watering to container-grown cardinal flowers to help keep them sufficiently moist.

Varieties

There are several species of wild and cultivated Lobelia with versatile colors and forms.

Blue Cardinal Flower, Lobelia siphilitica

The blue cardinal flower is native to eastern North America and hardy in zones 4 to 9. This plant has spectacular lilac-blue trumpet-like flowers with prominent lower lobes. Blue lobelia also grows well in partial shade and moist soil, making it an excellent companion for the red cardinal flower. Butterflies and hummingbirds also love this species of Lobelia. 

Downy Lobelia, Lobelia puberula

Downy lobelia is native to the eastern United States, particularly in the southeastern region. This perennial wildflower is very similar in appearance to the blue cardinal flower, but it will grow well in dryer sites. Downy lobelia leaves are slightly downy on the undersides, giving them a soft, fuzzy appearance. The pale purple flowers attract hummingbirds and butterflies.

Trailing Lobelia, Lobelia erinus

This cascading lobelia is a perennial only in zones 10 and 11 but can be easily grown as an annual in cooler climates. It reaches only about 10 inches tall and makes a good annual ground cover or container garden plant. The purple, blue, or pink flowers bloom through much of the summer and attract plenty of butterflies.

Lobelia x speciosa ‘Starship Deep Rose’

This cardinal flower cultivar has stunning dark pink flowers. It is hardy in zones 6 through 10 and thrives in consistently moist soil. ‘Starship Deep Rose’ grows up to two feet tall and blooms from summer into fall. The showy flowers will attract plenty of admirers as well as butterflies and hummingbirds.

Lobelia cardinalis ‘Queen Victoria’

‘Queen Victoria’ blooms in mid-to-late summer with a dazzling profusion of intensely red flowers. These plants love rich, moist soil and perform well in zones 3 to 9. One of the most obvious differences between the native cardinal flower and ‘Queen Victoria’ is that this cultivar sports deep maroon-red leaves and stems, adding long-season color to a moist garden plot.

Wildlife Value

Cardinal flowers are wonderful plants for a wildlife-friendly landscape. They provide nectar for hummingbirds and are a seasonal favorite hummingbird plant with their bright red, tubular flowers. Cardinal flowers also attract numerous butterflies, bees, and a host of other beneficial insects. Deer and rabbits typically do not bother these plants. 

Common Problems

If you have good growing conditions for a cardinal flower plant, you should not encounter too many problems. Since these plants like moist conditions, keep an eye out for damage from slugs and snails. The most likely problem you may encounter is your plants drying. This can be easily prevented by simply keeping the soil moist. 

Slugs

Slugs and snails are common garden pests but rarely cause serious problems for cardinal flowers. You may, however, occasionally encounter some of these pests feeding on your plant’s leaves.

If you notice holes in the leaves and the telltale slime trail of a slug or snail, you’ll know what was eating the leaves. Slugs can be difficult to deter, and since they are unlikely to decimate your plants, you don’t typically need to take further action. You can hand-pick or trap large populations, though.