How to Grow Cardinal Flowers

Cardinal flower plant with bright red petals hanging closeup

The Spruce / Adrienne Legault

In This Article

Typically found in moist areas such as by streams, swamps, and low wooded areas, the cardinal flower (Lobelia cardinalis) makes a wonderful addition to gardens with wet soil.

This toothed, lanceolate leaved plant boasts erect, terminal spikes of brilliant red flowers. Each flower has five petals, three on the lower half and two on the upper half. The three lower petals are more prominent than the upper two, creating a unique, showy display.

These fancy flowers not only catch the eye of passersby but also of hummingbirds and butterflies, who are primary pollinators of these deep, bell-shaped blooms.

Cardinal flowers bloom in late summer when many other perennials are spent for the season. This makes them a wonderful addition to perennial flower gardens to achieve a longer season of blooms.

Botanical Name Lobelia cardinalis
Common Name Cardinal flower
Plant Type Perennial 
Mature Size 2 to 4 feet tall; 1 to 2 feet wide 
Sun Exposure Full sun to partial shade
Soil Type Rich, moist soil
Soil pH Slightly acidic to neutral
Bloom Time Summer to early fall
Flower Color Red, pink, or white
Hardiness Zones 3 to 9, USA
Native Area The United States and Canada
Toxicity Toxic to humans and pets

Cardinal Flower Care

Because the cardinal flower is naturally found in wet areas, keeping the soil evenly moist is key to their health These perennials are short-lived with a lifespan around three to four years long.

Allowing your cardinal flowers to reseed themselves is ideal. This ensures that they will continue to come back every year full and beautiful. Dividing your plants every two to three years will also help prolong life and create more plants.

With decent light, well-saturated soil, and a bit of propagating, you can grow these bright red flowers for years on end. It's also handy that cardinal flowers are generally not plagued by common pests or diseases, making them easier to cultivate.

Cardinal flower plant spike with bright red petals and buds closeup

The Spruce / Adrienne Legault

Cardinal flower plant spike with toothed, lanceolate leaves and bright red flowers

The Spruce / Adrienne Legault

Cardinal flower plant with toothed and laceolate leaves on spike

The Spruce / Adrienne Legault

Light

Depending on where you live, the cardinal flower grows best in full sun to part shade. In colder areas, they appreciate full sunshine. In hotter climates, the cardinal flower will do best with afternoon shade to provide shelter from the intense heat.

Soil

The cardinal flower loves rich, moist to wet soil. Unlike other plants that develop rot in wet areas, this plant thrives in these conditions. To help retain soil moisture, try adding a layer of mulch around your plants.

Water

It's no surprise that this plant variety appreciates plenty of water. In fact, the cardinal flower can even tolerate flooding. So be sure to maintain a consistent watering schedule that keeps the soil evenly moist.

Temperature and Humidity

These flowers can handle a wide range of temperatures. However, giving them protection from frost and freezing temperatures will help them overwinter successfully. Add a layer of mulch will protect the plants and help to ensure that they grow back healthy again the next year.

Since cardinal flowers love moisture, higher humidity levels are great. Because of this, cardinal flowers make great additions to rain gardens or areas near bodies of water.

Fertilizer

Cardinal flowers do not require large amounts of 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 growing activity.

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.

Propagating Cardinal Flowers

Cardinal flowers can be propagated by seed, division, or by transplanting young plants that develop around the mature plant.

Here is how to propagate by division (but bear in mind that the plants rarely live longer than around four years):

1. In the spring or fall, gently dig up your plant.

2. Cut its root system and foliage into two or three sections.

3. Plant each division in its own spot around your garden.

If you would like to remove young plants forming around your mature plant, simply dig them up in the fall and place them wherever you would like another cardinal flower to grow.

Growing Cardinal Flowers 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 to encourage propagation. If you would like to collect seeds to start indoors, here’s how:

1. Once the seeds pods begin to open, collect the seeds.

2. Store them in the refrigerator. You can keep these seeds for several years. When you are ready to start them, sow them on top of moist soil six to eight weeks before the last frost. Do not press them into the soil as they need light to germinate.

3. Keep the soil evenly moist and place your seeds in a bright location.

4. After the last threat of frost, you can plant your new cardinal flower in the garden.