How to Grow Cardinal Flower – General Description and Facts
The Cardinal Flower (Lobelia cardinalis) is a perennial flower native to most of North America. Also known as Cardinal Plant, it grows 3-4′ tall in optimum conditions producing several stalks or spikes of bright red flowers. This is a very showy flower. Let me say this – I love this plant. I don’t know of a more beautiful flower to have blooming in the late summer months. The individual flowers are tubular with a couple petals above, and then below the tube. The tubes are quite long meaning that only hummingbirds (yay!) and butterflies can pollinate it.
In the wild, the Cardinal Flower generally grows along streams or ponds, and therefore prefers wet soil. Growing in these locations provides it a steady supply of water and generally gives it partial shade as well. I’ve observed them along cold mountain spring streams a few miles from where I live. In all of my hiking, I’ve never come across a specimen that wasn’t near water. An additional benefit of Cardinal Flower is that it is Black Walnut tolerant! So, while many plants will not survive when planted near black walnut trees due to Allelopathy, Cardinal Flower will thrive!
Planted in a grouping it can make an absolutely stunning display of red. The more you have, the more likely you will bring in the hummingbirds as they are generally attracted to the color red, and this plant does the trick.
Apparently the Native Americans used this plant medicinally, making tea from leaves or roots to treat a variety of ailments. However, I wouldn’t recommend doing this as all research I’ve read has shown this plant to be poisonous / toxic. I guess you need to consume quite a bit for it to be toxic, but you shouldn’t consume any part of this plant in any form. Sometimes it is better to just observe nature….
Cardinal Flower Growing Requirements and Care
Cardinal Flowers should be spaced 1-2′ apart. I typically go ‘closer’ to reduce the number of weeds that pop up, since that will remove more sunlight/real estate. They can be in full sun to partial shade, but might require watering in full sun. I’ve not seen any pest problems or disease on any that I have grown.
Cardinal Flowers grow well in partial shade with moist soil, as this is how you will find them in the wild. Typically along stream banks. In a flower bed it will require a bit of maintenance, but it can easily be done by following two main rules.
Never let the soil dry out completely (remember, they grow along stream banks!)
Never let the basal rosette of leaves at the base dry out completely
The basal rosette will stay green all winter long. If it gets covered up, the plant will die. Remember the ‘growing along stream’ thing? Well, that matters a lot for this plant, as rising waters will remove any debris on the basal rosette, or at least remove enough leaves, etc.
But don’t let those two rules prevent you from growing this amazingly beautiful flower! Having this planted in your flower bed is one of the best ways to attract hummingbirds. They are the primary pollinators followed by Swallowtail butterflies. So if you enjoy the wildlife, this plant is for you.
I’ve not had any issues with wildlife eating this plant. I often need to protect certain species from rabbits/deer – but I’ve never seen any damage on any of my Lobelia species. So that is another large benefit of this plant in the garden.
Be sure to scroll to the bottom of this article for our reference table on this plant. As it summarizes all the necessary grow/care info into one convenient source.
How to Grow Cardinal Flower from seed
Growing Cardinal Flower from seed is pretty easy, and economical. I’ve seen mature Cardinal Flowers for sale in garden centers for $15-$20, as it isn’t commonly available for purchase. I’ve never seen it for sale in big box stores. Well, I will tell you how you can get dozens of these beautiful perennials for about $2.50 (standard price for pack of seed).
Just direct sow / sprinkle some seeds on top of the soil, and keep moist. The seeds of this plant are incredibly tiny. They are so small it is almost like powder, so be careful not to sneeze when planting or you might blow all your seed away!
Most of what you read state that you should cold/moist stratify these seeds, or winter sow them. Since I like to experiment, I’ve tried growing without stratification, and have always had success. So it is up to you. If you are reading this in the winter, then go ahead and winter sow them in pots and protect them. There is no harm in doing so, and you will have mature plants sooner.
When I sow them in pots the biggest issue I have that is unique to this species is thinning. Since the seed is so small I usually end up getting out the tweezers to remove unwanted seedlings a couple times. Once the basal rosette of leaves gets to be about 1″ diameter, I will plant out into the garden.
How long from seed to bloom?
How long does it take to get a flower? Well that will depend on how early you start your seeds, and ultimately how early you transplant out into the garden. Most of the time I will get blooms on Blue Lobelia flowers (albeit smaller stalks). But for Cardinal Flower I’ve gotten blooms the first year a few times. Mainly when I had the flowers transplanted into the flower bed by late June (also, I’m in zone 6).
Harvesting Lobelia Seed
When saving seed from Cardinal Flower, or really any Lobelia you need to follow many of the same principles as other species. Let the seed pods dry out on the stalk until they are brown/dry before collecting them. If you collect the pods too early the seeds may not have developed fully, and therefore may not be viable to germinate.
Saving seed from the Cardinal Flower can be really easy, or a bit more work. If you just want some seeds, and aren’t worried about chaff then it is really easy. Just crush some of the pods and save the seeds in a ziplock bag. However, if you want to separate the chaff, then you better get out your kitchen strainer and sift the seed/chaff multiple times until you are satisfied. The video I’ve linked to below gives a very thorough description of how to save seeds from this plant, and its cousin the Great Blue Lobelia.
Common Uses of Lobelia Cardinalis
This plant prefers medium to wet soil, so this is a perfect plant for a rain garden. I generally grow them in my flower beds and just ensure that they are watered when necessary. As long as they don’t dry out, the plant will be fine in full sun, as I’ve only had them in full sun locations at my homes. They can make a wonderful border in a garden or along a fence, or a nice grouping to attract more hummingbirds.
This plant can also be used in a micro-prairie, assuming the soil doesn’t get too dry. I plant on adding 6-12 of these to our micro prairie this year. I will keep an eye on them to make sure they get enough moisture. Check out our article on starting a micro prairie here.
In fact, if you are in the process of making a butterfly or hummingbird garden, then this plant must be on your list. And remember, the more the merrier. More Cardinal Flowers should equal more hummingbirds. One single specimen will provide some food, but if you want to have hummingbirds frequently visit then you should consider many, many more. Since the spacing on this plant is so small you can really pack them in. I generally will try for about a dozen in a single bed, just to make sure my red blooms ‘advertise’ food to the hummingbirds.
Mixing this plant with the Blue Lobelia is always a great idea, as they are similar but their bloom times often overlap, which gives you longer bloom duration for that section of your perennial garden. I’ve added some pictures below of how I’ve used Cardinal Flower in my gardens over the years. I hope you enjoy them!
Companion Plants for Cardinal Flower
A few species of plants that seem to do well with Cardinal Flower include the Great Blue Lobelia, Purple Coneflower, Blazing Star, and most varieties of Black-Eyed Susan (Rudbeckia). Just make sure you ‘protect’ the Cardinal Flower from encroachment. I have seen these species push right through other foliage, but it is best if they have their own small space.
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Cardinal Flower Facts & Reference Table
Cardinal Flower, Cardinal Plant, Red Cardinal Flower
Late Summer – July / August
Approximately 4 weeks
Tubular flowers approximately 1/2″ diameter by 1″ long
Single or multiple stalks containing many flowers
3-4′ (1-1.3 m)
1-2′ (30-60 cm)
Typically partial shade, but can tolerate full sun (will need water)
Varied – medium loam to clay.
Medium to Wet – mustn’t dry out completely
Medium. Basal rosette of leaves at the base mustn’t get covered by mulch. Must have moist soil (watering).