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How to Grow Cardinal Flower (Lobelia cardinalis): Must-Have Plant for Hummingbirds

Juvenile male Ruby-throated Hummingbird feeding on a cardinal flower (Lobelia cardinalis)

The vivid blooms of Lobelia cardinalis attract hummingbirds of all ages, including this juvenile male Ruby-throated.

Photo Credit
Patrick Jennings
Botanical Name
Lobelia cardinalis
Plant Type
Perennial Flowers
Sun Exposure
Full Sun
Part Sun
Soil pH
Slightly Acidic to Neutral
Bloom Time
Summer
Fall
Flower Color
Red
Hardiness Zone
2
3
4
5
6
7
8
9
Special Features
Attracts Hummingbirds
Attracts Pollinators

Brilliant Red Blooms: Planting, Growing, and Caring for Cardinal Flowers

Written By: Lauren Landers Master Gardener and Contributing Writer

What plant is as red as a flame, loves wet feet, and keeps hummingbirds coming back for more? If you guessed cardinal flower, you guessed right! Cardinal flowers have become staples in my garden, partly because of their pollinator appeal, but also because they have a high tolerance for damp conditions and thrive in water gardens and poorly draining spots. In this guide, you’ll find out why cardinal flowers are so very special, and learn the cardinal rules of keeping them.

About Cardinal Flower Plants

Cardinal flowers have a large native range that stretches from southeastern Canada to Florida, and as far west as California. In the wild, you’ll often spot these perennials growing on damp streambanks and along pond edges, or in marshes, bogs, and forest margins that stay damp. Cardinal flowers thrive in woodland gardens, wildlife habitats, and rain gardens, too, and they can be grown near or even in ponds and other water features!

Belonging to the bellflower, or Campanulaceae, family, cardinal flowers are closely related to plants like great blue lobelia and Indian tobacco (Lobelia inflata), but their bright red, tube-shaped flowers are all their own. Ruby-throated hummingbirds are especially drawn to these plants and are their main pollinators. However, you can expect cardinal flowers to also serve as magnets for butterflies, bees, and other wildlife.

When mature, cardinal flowers produce tall, erect stems that typically stretch to about 4 feet high, and they look best when planted in groups or drifts. I like to pair these plants with other water-loving natives, like Joe Pye weed and swamp milkweed, but they can be mixed and matched with non-native plants as well.

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Planting

Cardinal flower (Lobelia cardinalis) bright red blossoms
Image credit: Nikolay Kurzenko / Shutterstock

Cardinal flowers can be grown either from potted nursery plants or seeds, and they’ll often bloom in their first year. I recommend not growing cardinal flowers in pots, as they have high water needs and tend to dry out too quickly in containers. Here’s how to plant them!

When to Plant Cardinal Flower

Potted cardinal flower plants grow best when they’re planted in spring, after the risk of frost has passed. Seeds, on the other hand, should be planted outdoors in the fall or cold-stratified indoors for 60 days before spring planting.

How to Plant Cardinal Flower

Seeds in Fall

Prepare the planting site by removing weeds and raking the area flat before the ground freezes. If needed, blend some compost or aged manure into the soil too. Once the ground freezes solid, lightly scatter cardinal flower seeds over the soil, cover the seeds with a light dusting of straw mulch, and only water the plants when they sprout in spring.

Seeds in Spring

Place cardinal flower seeds on a damp paper towel, seal them in a Ziploc bag, and keep the bag in your fridge for 60 days. Then, fill seedling trays or pots with pre-moistened seed starting mix, scatter the seeds over the soil line, and keep the seeds evenly moist and in bright, indirect light. Once the seedlings sprout true leaves and are a few inches tall, harden them off over a period of 1 to 2 weeks and then plant them outside when the risk of frost has passed.

Planting Potted Plants

Dig a hole that’s slightly larger than your plant’s root ball and amend the soil with compost or aged manure if needed. Then, plant your cardinal flower at the same depth it was growing in its nursery container, add mulch, and water well.

Growing

Butterfly on bright red Cardinal Flower
Image credit: MargJohnsonVA / Shutterstock

Cardinal flowers are much easier to care for if you plant them in an area that stays naturally damp. These plants can even be grown in areas that flood regularly, or along pond margins where the plants are partially submerged. If you keep these plants in standard garden beds, make sure to add mulch to keep the soil insulated, and water them often and well! You can use a mulch calculator to quickly estimate how much mulch to use.

Water
The most important part about growing cardinal flowers is making sure they receive enough water. If you’ve planted cardinal flowers in a poorly draining location, they may not need any supplemental water. But in other areas, cardinal flowers should be watered regularly and deeply so that the soil never dries out.
Light
Full sun to partial shade locations are appropriate for these plants. In hot climates, cardinal flowers may do best in areas that receive morning sun and light afternoon shade.
Humidity
Water-loving cardinal flowers prefer humid conditions, but can grow in a range of humidity levels.
Temperature
Winter hardy in Zones 2 or 3 and warmer, cardinal flowers are very cold-colerant plants and generally don’t need winter protection.

Fertilizer

Amending your garden beds with compost before planting cardinal flowers will give these plants the boost they need to bloom and grow. After that, top dress the soil with an annual application of compost in spring or fall, and skip the fertilizer entirely. Like other native plants, cardinal flowers can develop floppy stems if they get too much fertilizer!
Toxicity
These plants are toxic to humans, pets, and livestock and should not be planted in areas where pets can get to them.

Gardening Products

Pests/Diseases

Most pests leave cardinal flowers alone, and these plants are plagued by few problems. However, they can sometimes struggle with:

  • Slugs and snails may target cardinal flowers and are particularly problematic with young plants. Hand-picking slugs and snails off your plants, and installing ‘slug pubs near areas with slug activity can help.
  • Fungal issues can also affect cardinal flowers and cause spotting and other problems on their leaves. These issues are most common when cardinal flowers are grown in areas with poor air flow or if they’re watered from the top down.
  • Leggy plants are often the result of low light conditions, but can also be caused by overfertilizing.

Propagation

Rain Drops on Lobelia cardinalis
Image credit: Peter Turner Photography / Shutterstock 

Cardinal flowers are short-lived but self-sow readily and produce offsets that can keep plant colonies going for decades. If you leave the old flowers in place, these plants will naturally self-sow, but you can also divide cardinal flowers using the following tips:

  • Time it right — The best time to divide cardinal flowers is in autumn, about 4 to 6 weeks before frost is expected. You can divide plants when they look overgrown or about once every two to three years.
  • Divide correctly — Use a shovel to dig a circle a few inches out from the base of your plants, and then lever the plant’s root ball up from the soil with your shovel blade. Use a spade or two gardening forks back-to-back to cut the cardinal flower clump into sections that each have a clump of roots, and healthy stems and leaves.
  • Replant quickly — Replant the divided cardinal flowers at the same depth they were previously growing as soon as possible, then water them in and add mulch. If you’re planting multiple plants together, space each cardinal flower plant about 1 to 2 feet from its neighbor.
     

Seasonal Care

Although cardinal flowers don’t need winter protection, adding mulch around the base of your plants can prevent frost heaving that disturbs plant roots. Pruning is usually not needed with these plants, but you can cut away old leaves and stems throughout the year and cut dead stems down to the ground in spring before cardinal flower starts growing. If desired, you can also deadhead old flowers to trigger plants to rebloom and pinch back leggy stems to a leaf node to make plants a little bushier.

Wit and Wisdom

  • Cardinal flowers get their name from their bright red petals, which are the same color as the robes of Roman Catholic cardinals.
  • Traditionally, cardinal flowers were used by indigenous communities as a tobacco substitute and to remedy issues like swelling. 
     

Flowers
About The Author
Lauren Landers

Lauren Landers

Master Gardener and Contributing Writer

Lauren is a gardener, writer, and public speaker with over a decade of experience helping others learn about gardening, homesteading, and sustainable living.She combines years of practical gardening a...
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