Are you talking about weeds in lawns or bedding areas? For bedding areas, I placed newspaper down around my plants, then bark chips on top. This controlled weeds and helped retain moisture for easier weeding when they popped up. Two years later, I added more mulch and chips (no more paper needed) and the weeds are well under control. As for my lawn, I aerated, removed moss, added more dirt and mulch and reseeded. I'm staying away from chemicals, and find that building up the soil, keeping my lawn and plants healthy, and retaining moisture by mulching and chipping have paid off.