Love the concrete block idea. I was going to make raised beds for vegetables with them this year and someone mentioned the fly ash and other contaminates. I don't think it would affect flowers.
This was on Facebook in 2013 by ''Container Gardening Alliance''
The EPA is and has for the last year been doing a study to decide whether or not to label Fly Ash as a Hazardous Waste due to the high levels of mercury, arsenic, and lead; leaving some "Industry Folk" to refer to concrete as the "New Asbestos" or the "New Lead Paint".
"Carl, saw your post on ATP--Francelle Edwards is an elderly lady that lives in Glendale AZ, a Western suburb of Phoenix, here is a photo of her from my presentation in Phoenix a week ago."