Aphids are common garden pests that suck the sap out of plants. While there are over 4,000 kinds of aphids, they’re all very similar: small, oval-shaped, and typically light-colored with two rear projections called cornicles. Aphids, as a group, feed on all parts of the plant: leaves, stems, buds, flowers, fruit, and/or roots, depending on the species. Most are partial to new growth, though any succulent growth is in danger of aphid attack. Small populations typically do little damage, but large populations can cause correspondingly large amounts of damage. They cause leaves to curl and turn yellow and can stunt the growth of new shoots. When they attack root systems, entire plants can wilt. In some cases, they even lead to gall formation and they are often responsible for flower and fruit deformation. In addition, they secrete a sticky substance called honeydew that can attract other insects (e.g., ants, wasps) and become the site of sooty mold growth. In addition to being ugly, sooty mold reduces photosynthesis.
One especially dangerous effect of aphids is virus transmission.
Eliminating aphid populations after you find them is unlikely to save your plants from viruses. It only takes one aphid minutes to transmit a virus to a plant. Furthermore, aphids can reproduce asexually, so aphid populations can grow rapidly. You should try to prevent aphid colonization. If you have aphids on plants, you must address it immediately.
Here, we’ll cover a method of aphid control known as companion planting or intercropping, in which certain types of vegetation are planted with desired plants to protect the desired plants from aphids. There are three primary control methods:
- Trapping – planting vegetation that aphids like with the goal of attracting them to the trap plants instead of your primary plants
- Deterring – planting vegetation that repels aphids
- Attracting natural aphid enemies – this reduces aphids through predation or parasitism
Plants that attract aphids
What plants do aphids eat? Common aphid targets include a wide variety of food plants such as fruit trees, melons, vine-grown vegetables, underground vegetables, leafy vegetables, and some herbs. They also feed on ornamentals, shrubs, and non-fruit trees. They are also attracted to some weedy plants like sowthistle and milkweed.
If you plant any of these varieties in your garden, you should check them for aphids regularly. If you’re looking for aphid-trapping plants, mustards, sowthistle, nasturtiums, and sunflowers are particularly useful.
Plants that repel aphids
Most plants that repel aphids are herbs such as garlic, chives, catnip, rosemary, mint, dill, cilantro (coriander), oregano, savory, thyme, basil, rue, and lavender. Onions, citrus, marigolds, petunias, ageratum, tansy, pigweed, and marsh Labrador tea plants are all considered aphid repellents as well.
Choosing the right plants
So, how do you choose the right plants to get rid of aphids naturally? That depends on how you want to deal with aphids. If you want to keep them from colonizing your garden to begin with, any of the three methods will be suitable. For trap plants or repellents, the plants mentioned above have been shown to work if planted correctly. If you don’t want to go the route of attracting additional bugs to your garden, avoid the plants mentioned below. If you want to remove a current population of aphids, though, your best bet will likely be attracting aphids’ natural enemies, which include predators such as hoverflies, ladybirds, lacewings, and spiders and parasitoids such as wasps.
Many aphid predators are also attracted to plants that attract aphids, such as sowthistle and mustard. Some aphid deterrents like chives, cilantro, basil, and marigolds also harbor lacewings and ladybirds. These species are further found around fennel, cosmos, and sweet alyssum. Hairy vetch, beret, and wild chamomile additionally attract ladybirds, while lacy phacelia and buckwheat attract hoverflies. Alfalfa attracts both lacewings and spiders. Flowering wildflowers are great for bringing in hoverflies, lacewings, ladybirds, and parasitic wasps. Wasps and Asian ladybirds are especially fond of plants with yellow flowers, though the efficiency of wildflowers depends on high abundance and quality of nectar and pollen.
Where to plant
For effective trapping, attractant crops must have a small footprint and you have to plant them earlier than your primary plants. The best trap plants form a protective barrier around the valuable plants. Where possible, they should be taller than the main crop. Nasturtium is especially protective around broccoli and fruit trees. Soybean, sorghum, and winter wheat are effective around potatoes. Feverfew is good to plant near roses while crepe myrtle is great in nurseries to protect young plants.
The deterrents onion, garlic, and chives are great for protecting lettuce, peas, mustard, and roses.
The strong smell of both onions and garlic can mask the scent of roses and other flowering plants, making them almost invisible to aphids.
The same is true of marigolds. Chives, lavender, marigolds, and rosemary can be planted around peppers. Ageratum, basil, and savory protect pears well, while marsh Labrador tea causes birch trees to produce repellent compounds that they can’t produce on their own. Broad beans should be planted with savory and/or basil. Pigweed protects barley plants. Don’t plant basil and rue together.
When attracting natural aphid enemies, type and placement also matter. Hairy vetch is good to plant in pecan orchards, while lacy phacelia and coriander have shown good protection in cabbage crops. Pretty much any flowering attractant can be planted with broccoli. Plant summer savory, ageratum, and basil between the rows in pear orchards and mint, marigold, ageratum, and basil in apple orchards. Buckwheat planted between rows will protect peach trees. Alfalfa offers good protection in cotton fields, while wildflower strips protect potatoes and wheat.
Companion planting is a natural and effective way to both prevent and combat aphid infestations. Here, we’ve provided a guide to the different methods of companion planting, which depend on your specific needs. We’ve covered plants that attract aphids, plants that deter aphids, and plants that attract the aphids’ natural enemies. Finally, we offer an overview of companion plants known to protect certain types of primary crops. Companion planting is a critical part of an integrated pest management plan. Good luck!