Organic Methods for Controlling Aphids in the Garden

Aphids are small pear-shaped yellow-green insects (though some species can also be brown, red, or black) that suck the sap out of the leaves, stems, and roots of plants. An infestation of aphids can cause stunted growth and leaf deformity. You will know that you have aphids by the presence of a sticky substance known as "honeydew" left on the stems and leaves. Also, look for aphids if you notice a lot of ants around and on your plants, since ants love to feed on the sweet honeydew. Aphids cannot only destroy your plants through their dining habits; they can also carry diseases from one plant to another. There are several organic methods that can be used to repel aphids, which are not only effective but also quite easy to employ.

Nasturtiums
In my opinion, the best way to keep aphids off of your plants is to sow nasturtiums. Generally nasturtiums draw aphids to them and away from your other plants; although, I have never noticed any damage to my nasturtiums. [See my article Nasturtium: An Heirloom Plant Perfect for Your Garden.] Grow these hardy flowering annuals - that are also edible - from seeds planted around your ornamentals and among your vegetables.

Water
Aphids like dry conditions; therefore, watering your plants regularly will help keep the aphids at bay. (Allowing your plants to die of thirst will not only harm or kill your plants, it will encourage the aphids to invade.) You can also knock the aphids off your plants by spraying the foliage with water. Be sure to spray a stream of water on the undersides of leaves where aphids like to hide.

Soil
Aphids do not like rich soils, so enriching your soil with compost and/or other organic matter will not only improve your garden but also discourage the aphids. In addition, while you are improving the soil, pull up any plantain that might be around your fruit trees. (Aphids also like fruit trees.) Plantain is a favorite gathering place for aphids.

Ladybugs
One ladybug larva can eat 400 aphids as it is developing, and one adult can eat 5,000 aphids in its lifetime. [Pioneer Thinking: Luring Ladybugs Into Your Garden by Arzeena Hamir] These little red- to orange-colored bugs with black spots are a gardener's best friends. You can attract them to your garden by planting those plants to which the ladybug is particularly attracted; e.g., various herbs (specifically angelica, caraway, cilantro, dill, fennel, tansy, and yarrow), coreopsis, cosmos, and scented geraniums. Ladybugs also like dandelions, which you can plant around your fruit trees. (Dandelions encourage early pollination of fruit trees, too. See my article Dandelion: Herb or Weed?] Refrain from using harmful sprays that kill not only harmful insects but also the beneficials. Almost all of the harmful insects will come back, while only maybe half of the beneficials will return. (I recommend never using harmful chemicals to control pests for this very reason.) If you do not have a lot of ladybugs or need more due to large aphid infestations, you can also order ladybugs commercially. (Do make sure that you purchase the native species called Hippodamia convergens and not the Asian type known as Harmonia axyridis, which likes to hibernate indoors. [Female Forum: Welcome Ladybugs to Your Home's Garden.]) You can purchase ladybugs at home and garden centers or through mail order companies.

Dishwashing Liquid
A tried-and-true method for eliminating aphids is to mix a few drops of dishwashing liquid in a spray bottle with water, shake, and spray directly on the plants. I use this method whenever I happen to notice a few on a plant. (This method is not really feasible for large infestations.)

My experience leads me to believe that aphids are among the easiest pests to control organically. I have also found that using a combination of the methods described above keeps this harmful bugs out of my garden.

References:

J.I. Rodale, editor-in-chief. The Organic Way to Plant Protection. Emmaus, PA: Rodale Press, Inc., 1967.

Janet Marinelli, ed. Natural Insect Control: The Ecological Gardener's Guide to Foiling Pests. Brooklyn, NY: Brooklyn Botanic Garden, Inc., 1994.