Onions have quickly managed to gain a good reputation due to its multiple benefits. These plants come with a bulb-like structure at the top, which is a common feature found in all Allium family members. Texture-wise, the leaves are flat and somewhat yellow to bluish-green.
Cultivated and used around the world, onions are native to Southwestern Asia. Some of its most famous close relatives are garlic, shallot, leek, and chive, among many others.
Not only is planting onions easy but they also harvest early and are the least vulnerable to diseases. However, to further improve the quality and yield, companion planting is a method every gardener should definitely consider.
In this article, find some of the best and worst onion companion plants, along with tips on how to boost harvest and reap the maximum benefits of this heavily profitable plant.
Table of Contents
Why Companion Planting?
Interplanting has long been used by gardeners to mainly use their garden space with efficacy. Certain plants in companionship with others have proved to be rewarding not only to those plants but also to the gardener’s property as a whole.
These are the three P’s of companion planting that usually help companion plants thrive.
Companion planting can drastically improve the productivity of the garden. When two or more companion plants are planted in proximity to each other, they not only mutually benefit one other but also effectively save space.
One great example is the three-sisters method of companion planting. This method is widely considered and used by many harvesters while planning their garden.
It includes growing corn, squash, and beans together. These three “sisters” thrive when planted together, while also saving space in the garden.
2. Pest Control
Many plants, especially flowering plants, are used for their scent to keep pests away from the main crop. Some plants have such a pungent smell that insects and pests are repelled by it; others have a strong enough smell to cover the main crop’s scent.
A few plants also act as trap crops by attracting insects and pests, thus deterring them away from the main crop. Although, these are always planted at a distance from the main crop.
Some aromas also attract beneficial insects. They are also commonly called predatory insects. But, these are often planted close to the main crop.
Attractive flowering plants not only improve the aesthetics of the garden but also act as a magnet for pollinators. Though we often find ways to get rid of wasps in the garden, some of these are great pollinators besides bees, birds, butterflies, and so on.
Onion Companion Plants: What to Plant
Now that we know why to opt for companion planting, let’s take a look at some of the best onion companion plants that can be planted in your garden.
However, more than providing their unique benefits, onions are often good hosts for other plants, thus making them good onion companion plants as well. Few of them are listed below.
1. Cabbage Family
- Scientific name: Brassicaceae
- Also called cruciferous vegetables
- Includes cabbage, brussels sprouts, kale, broccoli, cauliflower, kohlrabi
The cabbage family members are commonly known to benefit from onion plants. This is because onions are great at repelling insects and pests that often plague the cabbage family. These insects mainly include cabbage worms and cabbage maggots.
Cruciferous vegetables such as Bok choy, cauliflower, broccoli, etc. too prefer growing conditions similar to that of onions, sunny spots with well-drained soil, and a nitrogen-rich organic fertilizer.
Thus, the above-mentioned vegetables can all benefit as onion companion plants.
- Scientific name: Lactuca sativa
- Eaten fresh or cooked
- Comprises of Calcium. Vitamin C, Beta carotene, and Iron
Onion grows on a shallower root plane as compared to lettuce. It is the difference in root planes that allows them both to grow cordially without fighting for nutrients.
This gives a chance to maximize and use the garden space to the most without compromising the plants or the soil.
- Scientific name: Fragaria × ananassa
- Easy to grow
- Antioxidant properties
Onion makes for one of the best strawberry companion plants. These juicy fruits are often prone to various pests and diseases; aphids especially love them. But, onions have a pungent smell which can deter these pests away, including marauders.
Contrary to what some gardeners believe, planting these two in proximity does not affect the taste of either of the plants. Neither do the strawberries end up tasting like onions, nor do the onions taste like strawberries.
- Scientific name: Matricaria chamomilla
- Apple-like scent
- Calms anxiety and an upset stomach
Chamomile is one of the best onion companion plants to plant in the garden as it has tremendous antifungal and antibacterial properties that protect the plant.
Since it is an herb, it does not solely elevate the aesthetic value of the garden with its beautiful leaves, instead it also drastically improves the flavor of the onions.
- Scientific name: Daucus carota
- Besides orange, they are also cultivated in purple, black, white, yellow, and red
- Improves eye health
Carrots are highly susceptible to carrot flies. These attack the root of the plant, thus damaging it completely. Onions help with repelling these dangerous insects.
However, since they are both root plants, extra care must be taken while harvesting them. Since young carrots are very fragile and can be uprooted prematurely while harvesting onions, carrots and other root plants often make controversial onion companion plants.
6. Summer Savory
- Scientific name: Satureja hortensis
- Mild peppery taste
- Medicinal and culinary uses
Summer savory is an excellent herb to grow in companionship with onions as it enhances the flavor by making it slightly sweeter, and also encourages its growth.
- Scientific name: Beta vulgaris var. crassa
- Various culinary uses
- Low in cholesterol and saturated fat
Beets benefit as onion companion plants. Onions protect beets from garden pests like sugar beet-flea beetles and aphids. They also act as a natural repellent against animal pests that may be harmful to beets, like rabbits and deer.
Garlic and leek can also provide similar protection to beets.
8. Swiss Chard
- Scientific name: Beta vulgaris var. cicla
- Slightly bitter flavor
- Exceptional source of various vitamins and fibers
Swiss chard has huge leaves that can help to retain the moisture in the soil. This provides a healthy soil environment for onions since it grows on a shallow root plane.
Other members of the Allium family like chives or shallots can also benefit from swiss chards.
- Scientific name: Solanum lycopersicum
- Low in calories
- Reduces the risk of cardiovascular diseases and cancer
Similar to how onions protect strawberries, they make great tomato companion plants by repelling insect pests with their pungent smell. Other close relatives of the onion family like garlic and chives also aid tomato plants similarly.
- Scientific name: Tagetes
- Annual plants
- Edible flowers
Marigolds come in many attractive colors like bright yellow, orange, and rusty red. They help in attracting beneficial insects that help with better pollination.
These annuals also repel harmful insects that may be trying to ruin your onion garden.
Onion Companion Plants: What Not to Plant
Certain plants can prove to be harmful when planted in companionship with onions. They have been listed below:
1. Onion Family Plants
Onions often endure onion maggots. These extremely harmful pests can travel quickly from one plant to another. Thus, planting garlic, shallots, leek away from onions is a good idea.
Space out all your onion plants so the maggots cannot ruin the plants. This will also help other plants reap the benefits of onion as a companion plant.
All types of peas usually hate being planted close to any Allium family member. In fact, onions, shallots, garlic, chives, can all deteriorate the growth rate of peas.
They also have wildly different conditional needs. Onions require high levels of nitrogen, while peas cannot bear too much nitrogen in the soil since they are legumes. Even if they are planted together, both the plants will require extensive care.
Again, avoid planting any member of the onion family near beans. Onions contain antibacterial properties that can kill the beneficial bacteria present on bean roots, thus stunting its growth. Most importantly, it also inhibits the release of nitrogen from its roots into the soil.
Other Diseases and Pests
Just like any other plant, onions too are susceptible to various diseases and pests. Here we discuss some of the most concerning ones that gardeners need to look out for:
- Onion maggots: little eggs are laid at the base of the plant. Most common symptoms include stunted, wilting seedlings, weak plant, and deformed bulbs. Prevention techniques include good sanitation, insecticides, and companion planting.
- Bulb mites: stunted growth; rotting bulbs with cream-white pests. Avoid onion plant clutters and space them out with enough distance to prevent bulb mites.
- Leaf miners: small yellow and black pests that lay eggs on the leaves and leave back thin white trails. Even worse, they can cause early drooping leaves and a diminished harvest.
- Black mold: causes black discoloration on the leaves and the bulb. The plant should be treated with a fungicide before planting to prevent this.
- Botrytis leaf blight: older leaves are prone to this fungal disease which is caused by high humidity and warm temperatures. Symptoms include white abrasions with light green outer rings that may expand. It can be prevented by spacing out plants.
- Fusarium basal plate rot: continuous crop rotation every 4 years or so can prevent this disease. Causes discoloration on stems, and yellow wilted leaves usually form in high temperatures.
- Rust: apply weed control measures and fungicides for prevention. Rust can cause tiny white dots that turn into orange eruptions, and may lead to complete damage of roots and stem if not checked.
- Smut: causes dark thick stems, and blisters on the base; reduces growth rate, and can kill the plant within a few weeks. Smut stays in the soil for years and can be prevented by crop rotation.
- Leaf streak and bulb rot: common symptoms are burnt leaf tips, burnt inner scales, and dark green streaks on leaves. Avoid fertilization during winters and use organic bactericidal sprays for prevention and control, respectively.
- Pythium seed rot: causes severely stunted growth in older plants; grey roots and mushy leaves in seedlings. For prevention, constantly check on soil moisture and apply fungicides.
Health Benefits of Onions
- Onions contain flavonoids which, according to multiple studies, lowers the bad cholesterol levels in the blood and promote better cardiovascular health. It also reduces the risk of a stroke or a heart attack by a great percentage, due to the blood-thinning properties of thiosulfate.
- Flavonoids also help relax the muscles of the isolated trachea, thus helping asthma patients with breathing easily.
- With the high calcium content, onions can strengthen your bones and joints. Moreover, its antioxidant properties can boost immunity and reduce the risk of cancer.
- Many natural eye-drops often contain onion extract as one of the main components since it contains selenium. Remember, selenium can boost vitamin E production in the body, thus keeping eye problems like conjunctivitis away.
- Onions can also improve oral health, sexual health, give a natural glow to the skin and help with scalp-related issues like dandruff and lice.
Gardening is a highly subjective area. It requires a lot of practice and experience. However, the higher the risk, the higher the reward. Make sure you seriously consider companion planting in the garden. If the most successful and long-term hobbyist gardeners believe companion planting brings benefits to their land and plants, then why not give it a shot?
You can also refer to a companion planting chart to experiment with other combinations in your garden.