Caren White is a Master Gardener and instructor at Home Gardeners School. She has been associated with Rutgers Gardens for over a decade.
I was introduced to the Great Blue Lobelia when it popped up unexpectedly in my garden. I'm not sure how it got there. My guess would be it was courtesy of the birds who tend to excrete seeds all over my yard. But however it got there, I have enjoyed its beautiful blue flowers for many years.
What is Great Blue Lobelia?
Great Blue Lobelia is often called the Blue Cardinal Flower. It is, in fact, related to the well-known red Cardinal Flower. They are both Lobelia. The Cardinal Flower is L. cardinalis while the blue cardinal flower is L. siphilitica. It was named siphilitica because it was mistakenly thought to be a cure for syphilis. The Native Americans used the plants medicinally like aspirin to relieve aches and pains.
Like its cousin the Cardinal Flower, the Great Blue Lobelia is native to North America. It is hardy in zones 4 through 8. The plants prefer moist soil and semi-shade. They are often found along the sides of streams or in moist woodlands. They are short-lived perennials, lasting just a few years unlike most perennials which live anywhere from 7 to 9 years on average. You don’t need to worry about the plants dying out. The Great Blue Lobelia will readily reseed itself in your garden so you will always have plenty of plants. They do not produce so much seed that they become a nuisance which is a good thing because the plants are quite large, growing between 2 and 3 feet tall. You can pinch back the plants to make them bushier.
The tubular blue flowers appear in late summer through early fall, August to October. They attract butterflies and hummingbirds. They do not attract deer. The Great Blue Lobelia is deer resistant, a real plus in areas like mine that suffer from an over-population of deer.
How to Divide Great Blue Lobelia
Great Blue Lobelia plants stay healthier if they are divided every 2 to 3 years. Over-crowding causes them to grow poorly and encourages disease. It’s easy to divide them. New plants develop in the form of leafy rosettes on the sides of the parent plants. In the fall, using a garden fork, carefully dig up your clump of plants. With a sharp knife, cut the side rosettes from the main plant, making sure that each rosette has its own root system, and plant them in another part of your garden, 8 to 12 inches apart, or in an entirely new location. Great Blue Lobelia can also be divided in the spring using the same technique. I prefer dividing my plants in the fall so that they have a head start the following spring.
How to Make Cuttings From Great Blue Lobelia
Another easy way to propagate your plant is by cuttings. In mid-summer, before the plants bloom, make 4 to 6 inch cuttings from actively growing branches. Remove the leaves from the bottom of the cuttings and dip the cut ends into rooting hormone. Set the cuttings in a container filled with soil. Roots should develop in 2 to 3 weeks. You will know that roots have grown because you will see new leaves on your cutting. Plants that have no roots cannot grow new leaves. After the cuttings have developed roots, you can set them outside in your garden, 8 to 12 inches apart, so that they will be able to grow their rosette of leaves before winter. Plants that do not develop their rosette of leaves will not survive the winter.
How to Grow Great Blue Lobelia From Seed
Growing Great Blue Lobelia from seed is easy. You can either direct sow your seeds in the spring after all danger of frost or start them indoors 8 weeks before your last frost. Surface sow the seed. Do not cover. The seeds need light to germinate. Germination will occur in 14 to 30 days. You can plant your seedlings outdoors after all danger of frost spacing them 8 to 12 inches apart. Unlike most perennials, Great Blue Lobelia will bloom the first year.
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Allowing your plants to self-sow is the easiest way to create new plants. Instead of deadheading the flowers to make the plants appear neater, allow some to go to seed. In the spring, you will rewarded with seedlings. After a few years, you will have a whole clump of Great Blue Lobelia adorning your garden.
Questions & Answers
Question: Can I grow lobelia in a hanging basket?
Answer: It depends on which kind of lobelia you are growing. Both the Cardinal Flower and the Great Blue Lobelia are unsuitable for hanging baskets because of their size and growth habit. Both are upright plants that are tall, between 2 and 3 feet high. Flowers that work best in hanging baskets either drape or are very short.
Question: Can blue lobelia survive winter in pots?
Answer: It would be difficult to overwinter these plants indoors because they have a very specific growing environment. They need shade and soil that is constantly moist. They grow along streambanks which are wet year-round. They also do well in my backyard which is shady and on the edge of a wetlands area so the soil is always wet. If you want to overwinter in pots outdoors, no, they will not survive.
© 2016 Caren White
Caren White (author) on April 04, 2016:
You're quite welcome Flourish! I've owned 2 homes, both of which had shady yards so I've become rather knowledgeable about shade gardening.
FlourishAnyway from USA on March 31, 2016:
Finding shade loving flowers has been a challenge for me so thank you!