In my garden with the Blue Cardinal flower (Lobelia siphilitica)

Blue Cardinal flower, blue lobelia, Lobelia sipiliticaLast year I added this beauty. I love the color of the Blue Cardinal Flower (Lobelia siphilitica) in my shade garden where it receives morning sun and a bit of dappled afternoon sun. I have to keep it regularly watered because it does not like to dry out. It has reached about 32″ tall in the clay soil under the Oak tree and it started blooming about 2 weeks ago (Mid July) and will continue until early fall.

Lobelia siphilitica, Blue lobelia, Blue Cardinal flowerThe Blue Cardinal flower loves morning sun and moist soil here in zone 7 under the Oak tree where I keep it regularly watered. Lobelias need moist soil and will tolerate full sun in colder areas (zone 4 & 5) where they can grow in either moist to wet areas in your garden or in ditches and along streams and swampy areas. This native beauty is seen in the eastern part of the United States and received its name ‘siphilitica’ because it was once used to treat the venereal disease syphilis.Lobelia siphilitica, Blue lobelia, Blue Cardinal flower

The cardinal flower can be divided in spring or sown from seeds in the fall because they need to be cold stratified (seeds need to be chilled to prior/ start germination). I hope to collect and sow the seeds this year. I bought my Cardinal flower as a blooming plant last summer. I love the bright blue/purple of this flower against the green of the ferns where I had planted it. If you have a shady and moist area this would be a great plant to add. There are other companion plants that could be mixed in such as ferns, Turtlehead (Chelone obliqua, and even Trout lily). If you do not have a moist area, then just do as I do and keep it regularly watered. Blue Cardinal Flower, Lobelia syphilitica, blue lobelia

The recommended soil is moist humus rich soil but I have red clay soil that was amended 7 years ago with horse manure and kept mulched. I want to add that this area was hard sterile ground that weeds did not even grow before I made it my shade garden. I was worried that my Cardinal flower would struggle since the information out there says humus soil and do not mulch. I have only about an inch of mulch around the plant and it was standing upright until rainstorm the other day. Rain in SE Virginia comes down in sheets or in buckets and so many times my plants take a beating.

Blue Cardinal flower, Lobelia syphilitica, blue lobelia

After a rainstorm the Cardinal flower is leaning a bit

Another good reason to add Cardinal Flower? The deer do not seem to eat it and it has no real insect or disease problems in my garden (some sites suggest slugs, rust, and even leaf spot)

Happy gardening everyone!

Creating. Inspiring. Gardening without the rules!

2015 copyrighted material C Renee Fuller @The Garden Frog Boutique

  • other info:
  • shade to part sun in southern climates and shade to full sun in northern climates
  • swampy to moist areas in zones 4-9 (some sources say 5-9)
  • 2-3′ H and clumps reaching 1 1/2′ wide
  • late summer to early fall blooms
  • native
  • hummingbird magnet
    Blue Cardinal flower, Lobelia syphilitica seed


    Blue Cardinal flower, Lobelia syphilitica, Blue lobelia leaf identification

    Leaf Identification

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