Houseplants need to be dusted or they can’t breathe.

Partially true. Over time dust can block plants’ pores, which allow water vapor to escape (transpiration) and food production to occur (photosynthesis). Don’t feel obliged to take a feather duster to your philodendron every time you wipe down the TV screen, but most houseplants do benefit from having their leaves cleaned once or twice a year, says David Ellis of the American Horticultural Society. He suggests wiping the tops and bottoms of broad-leaved plants with a damp cloth or sponge. Even quicker: Pop them under a soft shower, or spray them gently with the garden hose.

Standing in front of a microwave oven while it’s operating can give you cancer.

False…probably. Despite a few studies suggesting possible cause for concern, according to a Food and Drug Administration spokesperson, “there are no established adverse health effects, including cancer, from using or standing in front of a standard microwave oven.” The nonionizing radiation that ovens use to change the chemical structure of food is different from the ionizing radiation that causes cells in the body to mutate. Research is ongoing, though, so to be safe, the FDA advises, don’t stand directly in front of a microwave “for long periods of time” while it’s working. If you’re standing there watching last night’s kung pao chicken reheat, you’re much more likely to die of boredom.

The shorter you cut grass, the less often you have to mow it.

True only because if you cut it too short, you’ll kill it. “You’re taking away the leaf, which is the plant’s food factory,” explains John Buechner, the Marlboro, New Jersey–based director of technical services for lawn-service provider Lawn Doctor. The plant will compensate by diverting energy from growing roots to regrowing the leaf. What should you do? When you mow, never cut off more than one-third of the blades. This ensures that the grass is long enough to shade the soil and keep its temperature down, allowing the roots to grow deeper and increasing drought tolerance. Plus, “a healthy lawn that’s well nourished and thick is the best defense against weeds,” says Buechner.