Ask gardeners where they learned about plants, and most will tell you about a parent, grandparent, or favorite aunt or uncle who passed along a love of digging in the dirt. Certainly these green-thumbed mentors did a lot right. It was, after all, their colorful perennial borders and bountiful veggie patches that inspired the next generation to pick up a trowel. Amid all their sound advice, though, they probably passed down some less-than-scientific lore, too. Many homegrown gardening tricks simply don't live up to their hype when researchers put them to the test. But old ways are slow to change. After all, most gardeners learn from one another rather than by brushing up on the latest university study. So we've done the research for you. The next time a well-intentioned neighbor offers up one of these time-tested "tips," you'll be able to weed out fact from fiction.