Companion planting is the practice of growing different plants together for mutual benefit. While growing onions is a relatively simple task, a more complicated consideration is what you should grow near them.
Adding an onion's suitable companion plants can help your garden produce abundant, flavorful, and pest-free crops.
The onion's main role as a companion plant is as a pest repellant, giving the other plants a greater chance of success. Luckily the onion has several companion plants to choose from to fill out your garden and keep your plates full and your taste buds tingling.
What Is Companion Planting?
Companion planting is the strategic planting of a crop with another crop to gain a mutual advantage in production, flavor, or protection from pests.
Benefits of Companion Planting
Companion planting is not a new idea. Native Americans used companion planting to balance soil nutrients and environmental support that corn, bean, and squash plants require. By planting these crops in close proximity, they could share or replenish the nutrients the other crops needed while also creating a hospitable habitat for growth. The corn provided a trellis for the beans, the beans replenished the nitrogen in the soil, and the squash leaves provided shade to maintain moisture and reduce weeds.
This example shows how planting just those three plants could improve the growing conditions in a garden. Adding other plants can also increase crop productivity and control pests.
Onions are a great example of a plant that excels at pest control. Using a plant to help control insects is an environmentally friendly method that can be used as an alternative to using pesticides or other synthetic chemicals.
Before planting a vegetable or herb garden, look at your plant list and see what plants work together or not and if they should be neighbors and plan your garden accordingly. The benefits will be worth the little bit of extra planning.
Best Onion Companion Plants
- Beets: Beets and onions prefer the same soil conditions. The beet is one of many root vegetables on the list of onion companion plants.
- Spinach: Spinach is often attacked by hungry insects who love to nibble on the green leaves and rabbits who make this leafy plant a diet staple. Interspersing your spinach with some onion plants will help keep these pests at bay and let you enjoy the fruits of your labor just as much, if not more, than your garden invaders.
- Other plants in the onion genus, such as garlic, leeks, shallots, and chives, make excellent companion plants for onions. They need the same nutrients, so fertilizing them is simpler. Keep in mind when growing onions next to other plants in the onion genus that special attention must be paid to pests because pathogens can pass easily between plants in the same plant family.
- Brassicas: The mustard and cabbage family plants make great companion plants for onions as they are highly susceptible to insect damage and are a favorite snack for pesky rodents. Planting onions near cabbage, cauliflower, broccoli, mustard greens, kale, collards, and Brussels sprouts is an invaluable way to keep those little annoyances from eating your crop before you get a chance to harvest them.
- Tomatoes: Onions do very well as companion plants to vegetables in the Solanaceae (nightshade) family. Onion is a pest deterrent to these tasty veggies and will help you get a healthy, bountiful crop when it is time to harvest.
- Peppers: Another member of the nightshade family, this sweet or hot vegetable can attract insects and rodents to a garden patch. Onions can do a great job repelling insects away from the pepper plants and confusing hungry rodents with the unpleasant onion smell. Planting the two together makes it more likely that those precious peppers will survive the season.
- Eggplant: This versatile fruit is yet another nightshade crop and a perfect companion to be planted alongside onions not just for utility, which is fantastic because rodents love to eat eggplant, but for taste. Planting eggplant, onion, and tomato together practically invites the ingredients to hop to create amazingly fresh ratatouille during those warm summer nights when fresh garden meals are perfect.
- Strawberries: Like most items on the list, planting onions near your strawberry patch will keep pests away from your sweet harvest of candy red berries so that you can enjoy them rather than the insects or furry critters that frequent your garden.
- Potatoes: Potatoes, a root vegetable in the nightshade family, have the same favorite conditions as onions. It seems the biggest benefit is that onions deter pests from infesting potatoes as they grow.
- Lettuce: Onions and lettuce go perfectly together in a salad and in a garden. Lettuce tends to get eaten by both insects and rodents, and onions do a remarkable job of acting as a deterrent from letting this happen. Plant these two together near some tomatoes when it gets warm and prepare a salad for a delicious meal.
- Parsnips: Onions do an amazing job keeping pests and rodents away from the late-growing root vegetable, the parsnip. Having the best taste when harvested after the first frost, onions will keep critters at bay long enough to get a good harvest.
- Carrots: Onions will help keep rodents from digging for your delicious carrots by confusing their scent and taking them off the trail of the sweet-smelling vegetable they are after. Both plants enjoy the same conditions and have a similar growing season making them an almost no-brainer of a companion plant when combined with the pest-repelling benefits.
- Chamomile: Some herbs and onions make great garden bed-fellows. One, in particular, is chamomile. Up until now, the plants on this list have all been aided by planting onions nearby, but this situation is the other way around. Planting chamomile next to your onions will give the onions a noticeable boost and increase their flavor.
- Parsley: The herb parsley is akin to the vegetable carrot. The same benefits you get from planting onions with carrots will be achieved by planting onions next to your parsley.
- Dill: This herb instills great flavor into your onions while the onions boost dill flavor when grown together.
- Savory: An herb often used in soups and stews, savory is known to help make onions grow larger and more flavorful, lessening the sharpness or bite of the onion and increasing its sweetness. Planting them near each other seems like a no-brainer if you are a big fan of making soup!
- Marigolds: Marigolds are a great way to brighten up any day, but they are also functional as companion plants. This warm-weather flower does a great job at repelling rodents, but the biggest effect marigolds have on gardens is as a repellant to roundworms called nematodes, specifically the root-knot nematode, which specifically attacks onions and garlic.
- Roses: Roses are often infested by aphids, which, while usually just a nuisance, can hinder a rose plant's flower production. Onions are known to serve as a mild aphid repellant, making them a good plant to aid in a pest management regime.
What should not be planted with onions?
While there are many plants you want to grow near onions, there are a few that should definitely be avoided. Onions should not be planted with peas, beans, asparagus, or sage. Onions can stunt the growth of these crops and also negatively affect their flavor.
What plants benefit from onions as a companion plant?
Onions make great companion plants for many fruits, vegetables, herbs, and flowers, including beets, spinach, alliums, brassicas, tomatoes, peppers, eggplant, strawberries, potatoes, lettuce, parsnips, carrots, chamomile, parsley, dill, savory, marigolds, and roses.
Do onions needs a lot of space to grow?
Onions are the perfect crop to grow in a tight space and are great for growing in containers. You can even grow them in a food-safe, quality plastic five-gallon container. Expect to yield six to eight onions in a container of that size.
The Science of Companion Planting in the Garden. Montana State University Extension Office
Companion Planting. West Virginia University Extension Office