Can anyone help me identify this plant?! I have searched the web for hours and cannot put in an accurate enough description to find the plant. I am an avid gardener and have gardened in both zones 6 & 7 and have not seen this before. It is in the existing garden of our new house in zone 6b. It is very tall at about 4 feet, a perennial, and has tiny spines along its flat blueish foliage. It is just about to flower and produces these thistle-like white globe flower heads. It seems to love full sun and relatively dry to normal soil. It resides amongst some mature peony bushes and cone daisies. Thank you to whoever can help me figure this one out... I am stumped!