String trimmers, which cut greenery with whirling plastic lines, can trim right up to trees, steps, and rocks. They're great for maintaining a neat edge along walks and beds, and they can tidy a rocky hillside that's too irregular to mow. Many can also accept a metal blade for leveling tough scrub and small saplings.
Roger Cook, This Old House landscape contractor, keeps two trimmers in his truck—one with plastic string, the other with a blade. He switches to the latter the minute the string stops cutting and wraps around a tough stem. String comes in a range of thicknesses and textures, but you're limited by what your machine can accept. "In most cases, heavier is better," says Roger. "The right texture, on the other hand, depends on your landscape. You have to experiment."
The trimmers themselves come in two basic varieties: the more costly and powerful gas models (2-cycle or 4-cycle engine, the latter up to $350) and the economical electric (cordless or corded, some less than $50). The right choice depends on the property's size, its terrain, and your tolerance for noise and pollution. Keep in mind: Trimmer tips spin at close to 400 mph, so don't forget eye and ear protection, as well as boots, long pants, and gloves. And stay clear of outdoor wiring, lest you zap yourself instead of the weeds.