Cardinal Flower (Lobelia cardinalis)

Lobelia cardinalis is a light green stem plant that has attractive salad-like leaves. While the leaves can be purple when grown, the submerged leaves are generally totally light green, with the slightest hint of purple under very high light. It originates from America and grows in moist soil along river banks and the sides of ponds. The round leaf “mini’ cultivar is gaining popularity as it has rounded leaves that serve as a good contrast to many plants. It is therefore very popular in Dutch style planted tank layouts where contrast between leaf shapes and colors is important. 

I. Appearance and Characteristics 

Lobelia cardinalis, the cardinal flower (syn. L. fulgens), is a species of flowering plant in the bellflower family Campanulaceae native to the Americas, from southeastern Canada south through the eastern and southwestern United States, Mexico and Central America to northern Colombia.

It was introduced to Europe in the mid-1620s, where the name cardinal flower was in use by 1629, likely due to the similarity of the flower’s color to the vesture of Roman Catholic Cardinals.

It is a perennial herbaceous plant that grows up to 1.2 m (4 ft) tall and is found in wet places, streambanks, and swamps. The leaves are up to 20 cm (8 in) long and 5 cm (2 in) broad, lanceolate to oval, with a toothed margin. The flowers are usually vibrant red, deeply five-lobed, up to 4 cm across; they are produced in an erect raceme up to 70 cm (28 in) tall during the summer to fall. Forms with white (f. alba) and pink (f. rosea) flowers are also known. It grows along streams, springs, swamps, and in low wooded areas.

Lobelia cardinalis is related to two other Lobelia species in to the Eastern United States, Lobelia inflata (Indian tobacco) and Lobelia siphilitica (great lobelia); all display the characteristic “lip” petal near the opening of the flower and the “milky” liquid the plant excretes. L. siphilitica has blue flowers and is primarily pollinated by bees, whereas L. cardinalis is red and is primarily pollinated by the ruby-throated hummingbird (Archilochus colubris).

As a member of the genus Lobelia, it is considered to be potentially toxic. Symptoms of ingestion of large quantities include nausea, vomiting, diarrhea, salivation, exhaustion and weakness, dilation of pupils, convulsions, and coma. The plant contains a number of toxic alkaloids including lobelamine and lobeline.

II. How to Grow and Care

Sunlight

In colder areas, cardinal flowers appreciate full sunshine. In hotter climates, it will do best with afternoon shade to provide shelter from the intense heat.

Temperature and Humidity

Cardinal flower can routinely handle the wide range of temperatures across USDA zones 3 to 9. It is known to survive down to minus 34 degrees Fahrenheit, and some zone 2 gardeners have grown it successfully. The named cultivars and hybrids, however, may be somewhat less cold-hardy than the native species plant.

Since cardinal flowers love moisture, higher humidity levels are ideal; these plants aren’t well suited for arid climates.

Watering

This plant appreciates plenty of water. Cardinal flower can even tolerate prolonged seasonal flooding. Be sure to maintain a consistent watering schedule that keeps the soil evenly moist. Heavy twice-a-week watering may be necessary during hot months if no rain is falling.

Soil

The cardinal flower loves rich, moist-to-wet soil that often causes other plants to collapse with rot, but it struggles in dry, barren soils. To help retain soil moisture, try adding a layer of mulch around your plants. Amending soil with heavy amounts of compost can also improve soil moisture levels.

Fertilizing

Cardinal flowers generally do not require fertilizer throughout the year. Adding compost and organic material in the late winter or early spring will provide the necessary nutrients for the growing season ahead. This one-time application is generally sufficient for healthy growth.

Pruning

You may want to remove spent flower spikes to keep your plant looking clean and to encourage further blooming. Just keep in mind that this may not allow the plant to self-seed, which could impact next year’s colony.

If you find your plant getting a bit unruly during its growing season, feel free to trim it back to help maintain a bushier, less leggy look.

Propagation

Cardinal flowers can be propagated by seed, division, or by transplanting young plants that develop around the mature plant. Here’s how to propagate by division:

• In the fall, carefully dig up the entire colony.
• Divide the root clumps into individual sections, each containing a healthy network of roots and a piece of the crown.
• Plant each division in the desired location. If re-establishing a colony, plant the pieces about 1 foot apart.
• If you would like to remove young volunteer plants that have formed around your mature plant by self-seeding, simply dig them up in the fall and place them wherever you like.

How to Grow from Seed

To propagate by seed, you have a couple of options. These plants easily self-seed, so you can simply leave the seed pods on the plant and allow them to fall naturally. Another option is to collect the seeds, sowing them around the plant when they are ripe If you would like to collect seeds to start indoors, here’s how:

• Once the seed pods begin to open, pick them off the plant and collect the seeds. They can be replanted immediately in the garden, if you so choose, or stored in the refrigerator to plant in the spring.
• If you plan to start seeds indoors. give them several weeks in the refrigerator to provide the necessary cold stratification. Fill a container with moistened potting mix, sow the seeds on top of the mix, as they need light to germinate, water with a spray bottle, cover the container, and place in the refrigerator. Do not allow the seeds to dry out. Remove from the refrigerator in later winter, and place in a warm spot inside under lights.
• Place the pots in a bright location at about 70 degrees Fahrenheit, Keep the soil moist as the seedlings sprout and develop. Move the pots into direct sunlight to continue growing.
• When the seedlings have two sets of true leaves, pot them up into a larger container filled with potting soil.
• After the last threat of frost, harden off the seedlings in the garden for about 10 days.
• Once the seedlings have been hardened off, you can plant them in the garden.

Potting and Repotting 

Cardinal flower is not a common choice for planting in pots and other containers, but it can be done. Use a large, well-draining pot filled with ordinary commercial potting mix. These moisture-loving plants will require frequent watering when grown in containers.

These are not plants that can be moved indoors to grow as houseplants for the winter. Instead, move the potted plants to a sheltered location out of the wind for the winter months.

Overwintering

In most regions, cardinal flowers require no special preparation or protection. Do not cut stalks in the fall–wait until spring.

In regions where their hardiness is borderline (zone 3), a layer of mulch over the root crowns will moderate freeze-thaw cycles over the winter and ensure the plants return the following spring. These plants can survive extremely low winter temps but frequent thaw-refreeze cycles may cause them to perish.

Pests and Diseases

Common Pests and Plant Diseases

The cardinal flower is a very hardy plant troubled by very few pests or diseases. The most common pests are snails and slugs, so take protective measures against them if they show up.

Fungal infections such as rust and leaf spots may arise if the plants are crowded and if airflow around them isn’t good. Fungicides can usually treat the problem, but you can also simply cut the plants down to the ground and allow them to grow back fungus-free. Make sure to keep neighboring plants cut back so that the cardinal flowers have room to breathe.

Common Problems With Cardinal Flower

Like many native wildflower species, cardinal flowers are pretty fuss-free plants. The common complaints are fairly easy to address:

Yellowing Leaves

If you find that the leaves of cardinal flowers are turning yellow, it might indicate nutrient-deficient soil. A rich compost applied around the base of the plants can help.

Toppling Flower Stalks

When a cardinal flower grows in shady conditions, the stalks may become overly leggy as they reach for the sun. In some cases, you may need to use stakes or hoops to support the flower stalks against the wind.

Clumps Become Sparse

Cardinal flower is a fairly short-lived plant that dies back after flowering, though a colony will continue to sustain itself by the offshoots that are created. But an older clump may spread out and become sparse. The solution is to dig up the plant, divide the crown, and replant the pieces with closer spacing.

III. Uses and Benefits 

• Ornamental uses

This common perennial provides handsome red clusters of late summer flowers. Because of its unusual bloom time and appeal to pollinators, the cardinal flower is a welcome addition to most types of gardens, from butterfly to cottage to bog gardens. This plant does well near water as well, adding a touch of color to pond or stream banks. Swamp milkweed, swamp rose, and water parsnip make great companion plants for cardinal flower.

• Medicinal and other uses

The Zuni people use this plant as an ingredient of “schumaakwe cakes” and used it externally for rheumatism and swelling. The Penobscot people smoked the dried leaves as a substitute for tobacco. It may also have been chewed.