Horseradish

THE WORST THING you can do with horseradish is decide you don't want it anymore," says experienced gardener Gary Coull. "And don't ever rototill; you'll never get rid of it."

The roots of this hardy perennial are the source of both a spicy sauce and many a gardener's headache. "I uprooted my horseradish and left a few strings of root," a gardener in Oregon reports. "I had horseradish growing everywhere!"

In some parts of Canada, the plant is so invasive that it's considered a weed. If you're a horseradish fan, though, follow this advice: Plant root cuttings in a container or in a spot where they won't be disturbed, possibly in the border of the garden. And unless you want to start a horseradish patch, dig carefully when harvesting the roots.