Weeds are judged by the gardener. Wild flowers to some are weeds to another. Then there are those plants that are by anyone's definition a bother to have in the flower bed. They steal nutrients and water away from roses and dahlias. They rob sunlight from low-growing flowers such as alyssum and lobelia. And they look, well, unsightly. The only sure way to stop weeds is to use an herbicide. But what kills the weeds will also kill your flowers.
Water the flower bed. Cover it with black plastic. The weeds will sprout and die. Remove the black plastic and plant the flowers. This method can also be used in a garden with well-established flower bushes such as roses. Carefully arrange the plastic between the bushes but not directly up against their trunks. Remove after a few weeks.
Mulch between the flowers with a natural mulch, shredded newspapers, grass clippings or a commercial mulch. The mulch prevents sunlight from reaching the soil. Weeds can't grow in the dark once they've sprouted. If you use newspapers or grass clippings and don't like the way they look, cover them with a second layer of more attractive mulch. An advantage to natural mulches is that they add nutrients to the soil as they decompose.
Remove the weeds as soon as you see them growing. Some weeds spread by seed, but others spread by runners underground. The longer you wait to pull the weed, the more the runners will spread. Use a hand fork--a hand-held gardening tool that looks like a claw--to remove all the runners.
Pull weeds by the roots. Leaving the root by just clipping the top of the weed may mean the weed will resprout. Use a weeder, another hand-held tool that looks like a long, flat screwdriver with a "V" cut in the end of the blade. Plunge the weeder next to the weed's stem and pop it up. The V provides more leverage.
Remove weeds from all of your landscaping, not just the flower beds. When the weeds go to seed, the wind, birds and animals can spread the weeds into flower beds.
Spray troublesome weeds that just won't die otherwise with a systematic herbicide that works through the plants' leaves. Spray on a windless day. Keep the spray away from the flowers. Do not water for at least 24 hours.