Mulch ado about nothing : a Jane Jeffry mystery / Jill Churchill.

Enhanced descriptions from Syndetics:

No one could ever accuse Jane Jeffry or her equally green-thumbless best friend Shelly Nowack of being modern reicarnations of Luther Burbank. Their ineptitude in all things vegatative has inspired them to sign up for a botany class at the local community center, even though the gods of gardening seem to be warning Jane to steer clear.

Jane trips on a curb and badly bangs up her foot, but his gamely hobbles to class on crutches and in a cast, only to learn that the glamorous and celebrated microbiologist teacher, Julie Jackson, has been beaten into a coma by a person or persons unknown. But the class must go on, even though the substitute teacher, Dr. Stewart Eastman, is the arrogant creator of his patented plant species and more interested in his personal ambition to achieve botanical fame and fortune than imparting knowledge or a love of gardening. He's propaganding only his ego and his latest floral coup.

When a murder occurs, there's and abundant crop of suspects in the class, Is the perp who plants a body in Dr. Eastman's compost pile the conspiracy nut Ursula Appledorn, who's' convinced that they are being stalked by a cabal involving the U.S. Department of Agriculture, Queen Elizabeth, and the French Dauphin? Or maybe the obsessively tidy computer nerd Charles Jones? Or the milquetoast widoer Arnold Waring? Perhaps it's the terrifying knowledgeable Miss Martha Winstead with her strong opinions on gardening?

Jane's beau, police detective Mel VanDyne, who admits to a secret longing to drive dieselpowered earth-moving equipment, is on the case, but hasn't seen the gardens the classmates have created -- wherein flourishes the floral clue to the grimy crime. Jane's afraid he'll pluck out the wrong suspect.

And Jane, her nuisance injury ignored, is willing to get her gardening gloves, and Shelly's as well, dirty to uneath the gardener who's responsible for one bashing and one buried.