Jenny, not sure what you mean by cardinal flowers. If you have a picture or a latin name it would help people be clear on what plant you're referring to. There is a "cardinal vine" that would flop because it's a vine and does grow pretty fast this time of year.

On a more general note, plants often flop because they aren't getting enough sun.

Other than this, can't help without more specificity.

Thank you; I finally found the right forum - and posted a photo. I guess I need stakes.