Gardeners, in general, are a diverse mass of good people, but even the soul-building activities of toiling in soil and caring for living plants does not make us immune to the cardinal sin of vainglory (better known to modern sinners as vanity). Most every gardener I know, without exception, craves that occasional rare plant that will make a visitor exclaim "What is that beautiful plant?!" 
During the city garden tour a couple of years back, the plant in my garden that made almost everyone swoon, and ask about, was a surprise even for it's gardener. I don't know where I came across Centaurea macrocephala, but sometime in the past my usual inclination to collecting plants had caused me to purchase and plant it, and by the time the Garden Tour rolled around, it was quite the conversation piece. Centaurea macrocephala, also known as Giant Knotweed, Yellow HardHat, Armenian Basketflower, Globe Centaurea or Lemon Fluff Knapweed (where do they get those names?), is a clump-forming perennial of the Aster family that has essentially two sequential periods of beauty; one when the golden flower buds form, and another when they open to large, yellow, thistle-like flowers. It is attractive to bees and makes a great cut flower, but most importantly it is a standout in the early summer border. At 4 years old, it is a 2 foot diameter by 3 foot tall plant that causes me absolutely no extra care beyond cutting it back to the ground each spring. Rumored to self-seed, I haven't seen any evidence yet that it'll become a pest in my garden, although it has been labeled a Class A Noxious Weed in Oregon and Washington. According to the Internet, it is deer-resistant, drought-tolerant, hardy to zone 3, and thrives in my limey Flint Hills soil. It's a perfect plant except for now, in August, when it's drying up and is a little bit of an eyesore. Luckily for me and my vanity, garden visitors never venture out in the sweltering Kansas heat of August to see that phase. You should try it in your own prairie garden, if you can find it, but until it's more readily available, I'm keeping my swagger over having this plant.
