There are several natural ways to kill aphids without using dangerous chemicals in your garden. Here are some effective methods:

1. Soap-and-water mixture: Make a homemade aphid spray by mixing a few tablespoons of a pure liquid soap (such as castile) in a small bucket of water. Apply with a spray bottle directly on aphids and the affected parts of the plant, making sure to soak the undersides of leaves where eggs and larvae like to hide. The soap dissolves the protective outer layer of aphids and other soft-bodied insects, eventually killing them.

2. Neem oil: Neem oil is a natural insecticide that can be effective in controlling aphids. It works by disrupting the aphids hormonal balance, making it difficult for them to feed and reproduce. Mix neem oil with water and apply it to the affected plants with a spray bottle.

3. Beneficial insects: Introduce natural predators like ladybugs, green lacewings, and parasitic wasps to your garden. Ladybugs feed on aphids and can consume up to 50 per day. Lacewings are also effective at controlling aphids and can be purchased as adults or as eggs, which will hatch into larvae that feed on aphids. Parasitic wasps are another effective predator of aphids.

4. Strong spray of water: Use a strong spray of water to knock aphids off your plants. With their weak legs, most of the aphids will be unable to crawl back up the plants to feed. Repeat this process every few days until the aphid population is under control.

5. Diatomaceous earth: You can kill aphids by lightly coating them with diatomaceous earth. Make sure its food-grade and apply it with a simple tool for applying DE safely and efficiently.

Its important to catch an aphid invasion early, before the colony has multiplied and become unmanageable. Aphids like to shelter on the undersides of leaves and hide deep in the centers of plants, so inspect your plants regularly, especially during periods of new growth. Be persistent and patient; it may take a little time to see results.