Cardinal flower stalks are turning white and falling over
I have a rain garden with red twig dogwoods, cardinal flowers and turtleheads. The red twig dogwoods look like the have leaf spot and now the cardinal flowers have spots on the bottom of the leaves as well. The cardinal flower stalks turned a reddish color and then white and fell over killing the plants. I pulled out some that had fallen over and the roots seem to be barely underground and very short. Is this leaf spot killing my cardinal flowers or something else?
Baltimore County Maryland
Hi - Cardinal flower can be susceptible to root rot problems and your description of the roots being very short/barely there points in the direction of this being the problem. Cardinal flowers like to be in consistently moist soil with a pH range of between 5.8-7.8. If the moisture or pH is off, it is possible that the soil conditions were favorable for a root rot pathogen to take hold of a stressed plant. Also, cardinal flower is typically a short-lived species; it has a biennial habit -- meaning it will bloom in the second season and then seeds and dies. The plants have to be re-seeded to maintain the population. The affected plant material should be discarded in the trash (not compost). You may want to do a soil test of this area to check the pH and nutrient levels. https://extension.umd.edu/hgic/topics/soil-testing
The Missouri Botanical Garden has noted that some of they hybrid Lobelias have not performed well in their trials, but the reasons for that are unclear. Research-based information on disease problems in this species (and its cultivars) is limited.