14 Companion Plants for Onions, According to an Expert
Plus what not to plant with the popular veggie.
One of the worst things that can happen while gardening is accidentally sabotaging one plant because you planted the wrong one too close. While the concept of companion planting is pretty simple, learning the specifics of which plants complement each another and which ones don't can be a bit more challenging.
"Companion planting is planning out your garden so that plants near each other help each other, and plants that will harm each other are not planted close together. It's a way to let nature help with your garden. Some plants fertilize others. Some deter pests. Some plants draw in pollinators. It's a little ecosystem to help every plant thrive," says Lindsey Chastain, founder of The Waddle and Cluck, a homesteading blog.
Ahead, we compiled the best companion plants for onions based on which give them the room they need to grow, which keep pests away and more. And if you're searching for what not to grow with onions, we've got that covered, too.
Carrots
Carrots and onions make great garden companions. "They have different root depths so they aren't competing under the soil. The carrot roots help break up the soil for the onion roots. Onions also deter carrot flies, which carrots really don't like," says Chastain.
RELATED: The Real Health Benefits of Carrots
Radishes
Radishes mature more quickly than onions, which means you can use all your garden space effectively throughout the growing season if both are planted strategically. Once the radishes are ready, you can harvest them before your onions need that extra space to continue growing. It's almost like getting double from the same amount of space.
Tomatoes
Onions can help repel pests that typically target tomatoes like aphids and Japanese beetles. Plus, these two plants won't compete for light or space. However, it's important to note that tomatoes are heavy feeders, which means the soil should be fertile and well-composted to avoid potential issues.
Lettuce
Lettuce grows at a much speedier pace than onions, which helps ensure the two don't interfere with one another or fight for space. "Leafy greens, like lettuce, grow low to the ground and grow fast. Their roots don't crown the onion's roots, and they can be harvested before the onions get big enough to need that extra space," says Chastain.
Peppers
Because onions naturally repel certain pests, most varieties of peppers tend to grow well beside them. Still, make sure to give your onions and peppers some breathing room. Although they don't typically fight for space, proper sunlight and airflow is still essential.
Beets
Beets and onions share a few key similarities in terms of growing conditions. "Beets work with onions because they like the same kind of soil, grow in the fall just like onions and share space well. And again, the onions help keep away pests that would go after the beets," says Chastain.
Spinach
Like lettuce, spinach is another leafy plant that can benefit from growing near onions. "Because they grow low to the ground, they act as a kind of mulch, retaining moisture in the soil. They benefit from the onion's pest deterring of aphids and other bugs that like to eat leaves," says Chastain.
Celery
Celery has a deeper root system than onions, which means the two plants can share space without fighting over essential soil nutrients or water. Plus, both celery and onions prefer full sun and plenty of water, making them easy to care for side by side.
Chamomile
Plant a few chamomile flowers next door to onions for a pretty — and tasty — combination. "It's not very well known, but chamomile actually improves the flavor of the plants it lives near. It attracts beneficial bugs to the garden and makes a delicious tea," says Chastain.
Swiss Chard
Onions stay low to the ground while Swiss chard grows upright, allowing you to utilize all the ground space in your outdoor sanctuary. More importantly, these two plants aren't known to inhibit each other's growth.
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Strawberries
There's nothing like picking fresh strawberries in the morning. Luckily, onions can help. "If you live in a warmer zone (7 or higher), and strawberries can survive the fall in your area, onions can deter aphids and slugs that just love to attack strawberries," says Chastain.
RELATED: How to Store Strawberries So They Stay Fresher Longer
Roses
Roses face a few common pests, including aphids and spider mites. Fortunately, onions naturally deter those species while simultaneously inviting beneficial insects and pollinators to the garden.
Marigold
Marigolds are the perfect companion plant for a variety of fruits and veggies. "I like to plant marigolds near all my edible plants in corners or around the outside because they draw in bees and other pollinators, help keep bad bugs at bay and are just happy garden companions," says Chastain.
Cucumbers
Cucumbers and onions don't typically compete for space. Simply plant them 4-6 inches apart so both plants can thrive. Plus, when they're both done growing, you can throw them into a fresh garden salad.
RELATED: 14 Best Companion Plants for Cucumbers to Complete Your Garden
What NOT to Plant With Onions
Now that you know what works with onions, it's time to cross these plants off your list. Chastain discourages gardeners from planting the following alongside onions:
Legumes: "Legumes, like peas and beans, don't like some of the compounds that onions release. It keeps them from properly absorbing the nitrogen in the soil so they just won't grow well."
Aromatic herbs: "Even though onions are aromatics, aromatic herbs like sage, rosemary, basil, oregano and lavender won't thrive near onions because they compete for the chemicals in the soil they need to grow."
Asparagus: "Asparagus and onions are terrible bedfellows because their roots fight for space under the soil. They are also both nutrient hogs. It's best to just give them their own bed with their own blanket of soil."
Laura Millar (she/her) is the assistant lifestyle editor for Good Housekeeping, where she covers home design. Prior to joining Good Housekeeping in 2024, she wrote for NBC's TODAY.com, where she covered everything from entertainment news to pop culture updates.
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