Aphids are small insects in the family Aphididae belonging to the order of the true bugs (Hemiptera). The most significant characteristic to identify aphids is the presence of cornicles, or tube-like projections extending from the insect’s abdomen. These extensions are used to secrete pheromones or defensive compounds.
Honeydew is another fluid secreted by aphids that contain waste products, including excess sugar and moisture from plant sap. This waste product is a tempting treat for ants which will farm aphid honeydew by hiding aphids from predators, moving them to the best feeding spots, and aggressively protecting their herd.
There are many species of aphids, and they come in many colors, from green and brown to pink and orange. They use their tube-like mouthparts to extract fluid from plants and are mostly found among nutrient-dense parts of plants like fresh flower bugs, young stems, and the underside of leaves. Their color is usually dictated by the plants that they feed on. Below is a list of plants that are known to attract common aphid species.
1) Cabbage and mustard (Brassica spp.)
Aphids frequently target cabbages and mustards in the genus Brassica due to their nutrient-dense leaves and large size. The cabbage aphid (Brevicoryne brassicae) is the primary culprit in most Brassica gardens. They will target young leaves, flowers, and stalks of the plant and can transmit diseases to plants through their saliva, such as the cauliflower mosaic or cabbage ring spot viruses. Generally, gardeners do not want aphids on vegetable crops. Luckily, they can easily be removed with a strong water spray or food-safe insecticides.
2) Zinnia (Zinnia spp.)
These annuals have colorful, puff-ball-like flowers with yellow centers. There are many species of zinnia, but the common zinnia, Zinnia elegans, is the most popular. In addition to a stunning array of colors, zinnias have been bred to produce different flowering forms that vary in the number of petals. They need full sun and well-draining soil with an acidic to neutral pH (5.5. to 7.5).
In addition, zinnias require warmer temperatures and will only grow if daytime temperatures are at least 60°F (16°C). Zinnias make excellent garden plants, given their beautiful blooms and drought tolerance, but weakened plants may be a target for aphids that feed on the developing flower bugs.
3) Cosmos (Cosmos spp.)
Aphids feed on cosmos, but they possess chemical compounds, like phenolic acids, that attract natural enemies like ladybugs and spiders that defend a garden from pests. This plant produces simple, flat flowers that come in various colors. They can be grown in the spring and fall in most growing zones and during the summer in cooler regions of North America.
Cosmos can be started indoors or sown directly into the ground. It will take around three months to produce their beautiful blooms. Bees, butterflies, and other pollinators will be attracted to the cosmos’ vibrant flowers, and the seeds produced after the blooms are spent can be saved for the next season.
4) Sunflower (Helianthus spp.)
Sunflowers are famous for their large, yellow flowers. Some plants can grow taller than a human, with one variety capable of growing more than 30 feet (9 meters) tall. They also produce delicious seeds. As attractive as they are for humans, sunflowers are also a beautiful food source for aphids and ants.
The extrafloral nectaries on sunflowers are designed to attract insects early during the sunflower’s growth to pollinate the sunflower when it blooms. Unfortunately, ants plus aphids can result in an aphid infestation. Sunflowers are easy to grow and thrive in areas with deep, well-draining soil and plenty of sun.
5) Nasturtium (Tropaeolum spp.)
The genus Tropaeolum has about 80 species of flowering plants that are initially found in South America. Nasturtiums have leaves that resemble pennyworts (Hydrocotyle spp.) and are shield-shaped, although the nasturtium produces much more vibrant flowers and is not an aquatic plant.
Generally, they grow in small bushes and can be annual or perennial, depending on the climate. Nasturtiums are often used as trap crops for aphids and other plant pests. Fortunately, they are resilient and can sustain more feeding than many crops. Nasturtiums also tolerate various growing conditions but prefer slightly acidic soil (pH 6.5).
6) Pot marigold (Calendula officinalis)
Pot marigolds are daisies (family Asteraceae) with disk-like yellow or orange flowers. Their petals are sometimes dried and used as a natural remedy for dermatitis and minor skin inflammation. Pests love Calendula, and they are fantastic trap crops as a result. A patch of pot marigolds will draw away not only aphids but also other garden pests like thrips and whiteflies. More importantly, it attracts beneficial predators to deal with the problems. Fortunately, Calendula is notoriously easy to grow with tolerance to various soil and light conditions, although they will develop the best in full sun and nutrient-rich soils.
7) Nettle (Urtica spp.)
The genus Urtica is named after their stinging or urticating hairs, which resemble hypodermic needles and deliver irritating compounds into the skin of anything that comes into contact with them. Their defensive qualities make them a haven for aphids (and the insects that eat them!) which are too small to be affected by the nettle’s sting. In addition, cooked nettles are edible and can be cooked into a soup. Be sure to wear thick gloves when handling nettles.
8) Chervil (Anthriscus cerefolium)
This next plant is an herb with a flavor between tarragon or anise and parsley. Other sources report that it tastes like fennel and licorice. Chervil, also known as French parsley, is native to Europe and is sometimes grown as an herb in the northern regions of North America. New growth and chervil budding leaves attract aphids. Gardeners should plant trap crops or introduce natural enemies to avoid an infestation to keep aphid populations manageable.
9) Sorrel (Rumex acetosa)
Also known as spinach-dock due to its resemblance to the typical salad green, sorrel is an edible perennial that contains healthy antioxidants. Sorrel leaves contain oxalic acid, responsible for its slightly sour taste. While sorrel is an herb commonly used in cooking, it is essential to understand that large amounts of sorrel can cause kidney damage and other unpleasant side effects. Aphids are also attracted to these nutrients and may infest the new growth of sorrel plants.
10) Milkweed (Asclepias spp.)
Milkweeds belong to the genus Asclepias in the family Apocynaceae, which includes about 73 species native to North America. Milkweeds are essential plants for pollinators, particularly the monarch butterfly (Danaus plexippus). Depending on the species, milkweed plants can range in size from a few inches tall to over 6 feet tall (1.8 m). One plant in the genus Calotropis can grow over 15 ft (4.6 m)!
The leaves are typically broad and oval-shaped, and the flowers are large and showy, with five petals that are often pink or purple. Milkweed contains a toxic cardiac glycoside, which can be harmful or fatal to animals if ingested in large quantities. Aphids infest new growths of milkweed plants and are often found near flower buds or fresh leaves at the top of the plant.
11) Lupine (Lupinus spp.)
With one of the most exciting arrangements of flowers, lupines possess vibrant flowers that come in an array of purple, pink, and even orange. Unfortunately, the plant hosts the lupin aphid (Macrosiphum albifrons), which can be found on its host throughout the year. Gardeners can use an aphid-killing Entomophthora fungus that grows when aphid colonies become too dense. The fungus appears during the rainy season, but gardeners can encourage its growth early by misting aphid infestations with water.
Do Aphids Have Benefits?
Aphids will be present in the environment whether humans like it or not and have been on earth since before the age of dinosaurs. Thankfully, a few aphids are generally acceptable for most gardens. Issues arise when aphid populations grow out of control. Their populations can explode without predators, most common in monoculture (single species) gardens or greenhouses where predators cannot access plants. As mentioned before, ants can tend and protect aphids as well.
One way to defend against aphid outbreaks is to provide plants that aphids like more than our crops or beloved flowers. These are called “trap crops” and can help keep pests’ attention off other plants. On the other hand, attracting aphids also means attracting beneficial insects that can attack aphids and other insect pests. For example, aphids attract lacewings, ladybugs, syrphids, and soldier beetles that feed on other soft-bodied prey items that might infest plants, so having a handful of aphids around may increase the number of natural predators in the garden. This population of predators will naturally prevent large outbreaks of pest insects.
How to Deter Aphids in Gardens
Aphids are among the easiest pests to identify and remove from the garden, even if ants tend them. Once found, a strong stream of water can obliterate colonies of aphids. For fragile plants, safer soap will kill any aphid colonies when sprayed on plants.
If a herd of aphids is protected and maintained by a colony of ants, it is essential to eradicate all aphids and eliminate the ants. Unfortunately, ants will move aphids around and restore removed herds, ruining any efforts to keep aphids off plants. Parasitic wasps, like Aphidius colemani, also demolish aphid populations.
