I was wondering why my cardinal flowers are falling over. We live in SE Michigan, the climate is 60-90 degree mostly around 80 for the summer. Dirt with clay foundation, the morning is sunny and shade in the afternoon.
Thank you for contacting the Toronto Master Gardeners with your enquiry.
Lobelia cardinalis is a native American wildflower, native to many states including Michigan. It is a short lived perennial with tall spikes of brilliant red trumpet shaped flowers that bloom all summer long. Hummingbirds love this flower more so than bees. They are native to wet lands, marshes, stream banks but can be grown in gardens as long as similar growing conditions are met.
They like morning sun and afternoon shade. Their soil should be moist and fertile. Moisture is essential, especially if is hot with little rain. From your photo it looks as if the soil is bone dry and very hard, a difficult environment for such a moisture loving plant to survive in. As well, your plant is planted next to a brick wall which will reflect the sun and increase the temperature even more, thus stressing your plant even more.
You will want to replace your dirt/clay soil with moisture retaining nutrient rich loam or find a new location with this kind of soil. In your hot summers you will have to water your plants deeply and regularly if it does not rail.. A layer of mulch around your plant will keep the water from evaporating. In the fall fertilize with a layer of compost.
Lobelia will propagate by self seeding. Just remove the mulch from around your plants when the seeds are ready to allow them to fall on soil. Once the new plants are higher than the mulch, you can carefully replace the mulch.
The following web site will provide you with detailed information on how to keep your lobelia flowering and healthy.
Michigan also has an extensive Master Gardener Association that can assist you with any gardening questions for your climate and environment.