Written by Mary Nelson

Great blue lobelia (Lobelia siphilitica) is a stunning native Wisconsin plant! It grows 2 to 4 feet tall with a spread of 2 to 3 feet. Bright-blue, trumpet shaped flowers cover tall spikes, blooming from July through September.  The flowers are rich in nectar and attract hummingbirds, butterflies, and bees. Although numerous types of bees can pollinate great blue lobelia, the structure of the flowers make bumble bees, mainly due to their larger size, the most successful pollinators. The trumpet shaped flowers have five petals; the three lower petals are fused, and the upper two petals are usually curled back. A bumble bee lands on the lower petals, pressing them down, and then pushes the upper petals aside. The bee then dives headfirst into the flower to access the nectar and pollen. It is entertaining to watch bumble bees climb up the spike going from flower to flower until they reach the top and then fly off to another flower spike.

Here’s what you need to know if you plan to include great blue lobelia in your landscape. It prefers medium to moist soil in part shade but will tolerate full sun if it is mulched and watered periodically to ensure its roots stay cool. It can be short lived, but it will self-seed under the right conditions to form colonies, but it is not overly aggressive. Since the plants have fibrous roots, small seedlings that result from self-seeding can easily be dug and moved elsewhere. If you are interested in collecting seeds from the plant in the fall, wait until the flower spikes have started to turn brown. Cut off the spikes and place them in a paper bag. After a couple of days, empty the bag over a seed screen to separate the seed from the chaff. The seeds are very tiny and remind me of paprika.

An upclose view of a single flower. 

When you consider all the medicinal uses of great blue lobelia through the years, it is quite surprising to find out that it, as well as all other lobelias, contains a host of toxic alkaloids, including lobeline, lobelanine, and lobelanidine. Ingesting large amounts of lobelia can cause symptoms ranging from vomiting and excessive sweating to  coma and even death. Lobelia can also cause skin irritation or allergic reactions, such as redness, itching, or a rash. Considering this, it is also surprising to see how readily available lobelia products are for purchase. These products have been touted to protect against ailments such as asthma and other respiratory disorders, depression, attention deficit hyperactivity disorder (ADHD), and drug abuse. However, there is no scientific evidence to support the efficacy of these products for these disorders. At one time, lobelia products containing lobelia lobeline, particularly Lobelia inflata (Indian tobacco), were sold in tablet form for smoking cessation. However, in 1993, the U.S. Food and Drug Administration (FDA) prohibited the sale of smoking products containing lobeline. Again, the main reason for this was that there is limited evidence of efficacy. Another contributing factor to this decision was the fact that lobeline has a narrow therapeutic index, meaning that the potentially beneficial does is very close to the toxic dose.

Due to its toxicity and unpleasant taste, most mammals will avoid nibbling on this plant. The deer-resistant label, however, does not stop our Wisconsin four-legged critters from taking the occasional bite.

A bumble bee enjoys nectaring. Photo by Mary Nelson