For five years now my Maltese Cross (Lychnis chalcedonica) plant has grown with its roots squished between garden pavers that border one of my annual flowerbeds. The plant’s roots aren’t touching any soil that I can see. Despite the fact that its roots are somewhat exposed, it still survived the drought of 2012, the Polar Vortex during the winter of 2013-14 and the brutal winter that followed in 2014-15.
This is not a particularly attractive photo, but you if you look carefully you can make out the stalks sticking straight out of the pavers (and one dead stalk leftover from last year):
Maltese Cross flowers are a beautiful, brilliant scarlet-red. The plants are supposed to grow 30 inches tall, but my defy-all-odds plant has been known to reach 36 to 40 inches tall. The plants prefer full sun and regular garden soil (or apparently tight confinement between clay pavers). If the soil is too rich, the plants can get floppy. If you deadhead this perennial it will continue to bloom throughout the summer.
The plants are hardy in Zones 2-9, and I’m starting to think they could also survive on Mars.