After lovingly tending the plants in your flowerbed, you don't want to see weeds rear their ugly heads or see your favorite plants die from an herbicide meant for a weed. Pulling the weeds by hand is effective but labor-intensive, especially if the weeds have gotten a bit out of control. Several options help you kill the weeds you don't want while keeping the beautiful flowers you do.
What They Kill
When your flowerbed is suffering from an infestation of grass and grassy weeds, read herbicide labels carefully to ensure you use the right type to kill them. Herbicides designed to eradicate broadleaf weeds, such as dandelions, might not kill the grass, so choose one specifically designed for grass and grassy weeds such as crabgrass. When sprayed directly on the weeds, most of these herbicides kill the weeds in your flowerbed while keeping your flowers safe. Some herbicides are non-selective, which means they kill nearly any plant they touch. These don't target grass and weeds, and they can harm your landscape plants if the spray touches them.
Before or After Weeds Arrive
Some weed killers work before the weeds sprout, while others are meant to kill weeds as they grow. Pre-emergent herbicides work by stopping the seeds from sprouting, but these are only effective if applied before germination begins. These are best for well-established flowerbeds; some might stop flower seeds from sprouting as well, but they won't harm existing plants. Post-emergent herbicides enable you to attack the weeds you see, using just enough to kill the weeds without the need to cover your entire flowerbed with the herbicide like you must with pre-emergent versions.
When you prefer more natural methods of weed control in your flowerbed, look toward corn gluten meal as a pre-emergent option. Spread about 12 pounds per 1,000 square feet of flowerbed space in the spring, just as the first flowers start to appear, and again in the fall, right after the heat of summer starts to fade. Corn gluten meal is effective against many types of grass and grassy weed seeds, but it might stop some flower seeds from sprouting as well. Spread it only in areas where you have established plants, and wait four to six weeks to plant new seeds. Pouring boiling water or vinegar over weeds and grass effectively kills them, but this also can harm your flowers. Cover your flowers with plastic or cardboard to prevent damage to the plants, and choose a day with little wind. Neither option leaves harmful residue in the soil that could hurt your flowers later, and you can plant new flower seeds immediately. When using boiling water or vinegar, wear the same protective gear you would for chemicals to ensure your skin doesn't get burned by the water or the acid in the vinegar.
Choose chemical weed killers that are designated safe for garden use. Early in the season before weeds sprout, use pre-emergent herbicides containing active ingredients such as prodiamine. Read the manufacturer's application instructions carefully. For prodiamine products, for example, you might be instructed to mix 12 level teaspoons of the dry granules with a gallon of water and apply half a gallon per 1,000 square feet using a garden sprayer. It's safe to spray over most existing landscape plants, although you shouldn't plant new flower seeds for four to six weeks after using most pre-emergent chemicals. Check the manufacturer's label for the exact timing of new plantings. Post-emergent options include those with the active ingredient fluazifop-butyl, often available as a ready-to-use formula, or clethodim. For clethodim, mix about 1/3 ounce of chemical with water unless directed differently by the manufacturer. Spray it over the grass and weeds just enough to wet them. These selective herbicides don't harm most plants in your flowerbed if the liquid touches them, so you don't have to be perfectly precise as you spray. With most post-emergent herbicides, you can plant new flower seeds immediately, but check the manufacturer's instructions for your specific herbicide choice. Always wear protective gear such as long sleeves and pants, closed-toe shoes, gloves and safety goggles when applying chemicals. Keep children and pets away from the area until it's completely dry, or longer if noted by the manufacturer.