All Flesh is Grass

Novel, first published: Doubleday 1965

"All Flesh Is Grass" centers all of its action in the little town of Millville, and most of the story is told through the thoughts and actions of the small town. The unlikely hero, Brad Carter, is an unsuccessful realtor who aspired to be an artist but stayed on in Millville, a failure in the eyes of the town. Strange things are happening in Millville - someone has erected an invisible barrier around the town and only inanimate objects can move in or out, voices come over cordless and dial-less telephones, and the village idiot, Tupper, who vanished ten years ago, reappears in Carter's backyard, "naked as a jaybird." The only connection Brad can make among these events is some purple flowers grown in his father's greenhouse.
The residents of Millville are in a panic and suspicious of Brad. Suddenly, the barrier moves, stripping the soil bare, and a storm of seeds descends on the bare ground. Tupper disappears again, and Carter follows Tupper's trail into an alternate world where the purple flowers cover everything. The flowers, an alten group mllld, are running out of living space and want to make a deal with the human race. In exchange for more "lebensraum", the flowers will provide Earth with food, shelter, and best of all, their accumulated knowledge. The flowers explain that they had often been in contact with many minds on Earth - could they be responsible for humanity's achievements? Brad is uneasy about the flowers' offer, especially after he finds some human bones.
Brad returns to Millville and tries to get the authorities to believe his story (the military and the Feds have now arrived). As a goodwill gift and a demonstration of their powers, the flowers grow fifty-dollar bills on trees in Brad's garden. The flowers have one other very specIfic condition - the human race must banish nuclear war. Radiation is the one danger the flowers fear.
The story reaches the inevitable Simak stalemate: will the flowers continue to take over the Earth, or will the government drop an atomic bomb on Millville to stop the flowers? Stiffy, the town bum, turns up with the answer. Despite the incredible age and knowledge of the flowers, no other race but humans has ever grown them and appreciated their beauty.

Ewald, Robert J.: When the Fires Burn High and the Wind is from the North, p.83-84