Succulent young shoots are the favorite food of aphids and make them all the more despised by gardeners. Small but mighty, aphids measure just 1-8 inch long and are often green, yellow, or black in color. You can spot them clustered on the undersides of leaves or crawling along stems, where they pierce tissue and suck out valuable sap. Remove aphids from sturdy plants with a strong spray of water from the garden hose. Spray every other day if necessary. Fragile plants, as well as sturdy plants that are heavily infested, may need a pest-control product such as Safer's insecticidal soap, a nonchemical, soap-based mixture that's formulated for soft-bodied insects such as aphids. Apply the product, which is available at garden centers, weekly for 2-3 weeks.