Aphids are tiny, lime-green, pear-shaped pests that appear in the garden in the early summer. Sucking the juice from tender new shoots, aphids are among the most destructive garden pests outside of the tropics, attacking everything from roses to potatoes to pine trees. Once aphids have begun to colonize a plant, quick action must be taken or a colony can rapidly evolve into a swarm capable of destroying your entire garden.
Spray infected plants with the garden hose. The pressure from the water will knock the insects off the foliage and wash them away. Once the aphids have been physically removed from the plant, it is unlikely they will attempt to recolonize it. Take care not to use too much water pressure so you don't harm the flowers.
Apply insecticidal soap following the manufacturer's instructions.
Make your own anti-aphid soap if you cannot find it at the store or if the price is off-putting. Combine 2 tsp. of liquid dish soap, 1 cup of vegetable oil and 2 cups of water. Stir the ingredients until well blended and then transfer the solution to a plastic spray bottle. Use the soap to thoroughly coat the foliage of any affected plants, being sure to spray the bottoms of the leaves as well as the tops.
Plant marigolds near your other flowers to encourage the growth of beneficial insects such as ladybugs or lacewings. If you can't seem to attract them, purchase them from a garden center or over the Internet and release them into your garden.
Sprinkle diatomaceous earth over infected plants. The abrasive white powder is nontoxic and safe for people and pets, but the sharp edges created by the fossilized remains can easily shred the aphid's exoskeleton.
Plant garlic, chives or onions near the flower beds. The aroma is a natural repellent for aphids and other destructive insects. For the greatest effectiveness, these plants should be placed near the flowers early in the spring, prior to the first aphid invasion.