Some years ago along an Arizona highway in the middle of nowhere, I saw Penstemon ambiguus in bloom and fell instantly in love. The clumps were scattered and about 18" high in full bloom. After taking many pictures (all slides, alas), I carefully noted the kind of soil in which it grew (sand, old sparkplugs, shredded bits of rubber from tire blowouts, sand, cigarette stubs). I grew it from seed and ended up with half a dozen seedlings ready to plant. They were planted in different spots in the garden. Three died quite quickly when we had rain on and off for several weeks. Three made it in the sand bed but only one looked really strong. That is the one that survives still in the sand bed (very coarse sand and nothing else). It blooms each year and each year it looks better. It's so different from any other penstemon I grow. I think you can see the difference in the flower shape from the pictures, it's quite open and flat. The flowers are large and very lovely. The color looks the same as the wild plants I saw. It is considered xeric but it is an example of why you should never listen when people say something won't grow in the northeast or wherever you happen to live - you never know when something will decide it's found a second home.