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Onions make great companions for many other vegetables. Find out which ones grow best together.
Wondering about companion planting with onions? Find out who belongs in Mr. Onion’s Neighborhood.
Companion planting goes by vegetable family, which makes it easier to understand. Onions are in the allium family along with their smelly cousins: leeks, chives, and garlic.
We have an article on the basics of companion planting if you want an overview.
Plants function as good or bad neighbors to each other for several reasons.
Physically plants get along if their roots spread at different depths in the soil—they literally will not crowd each other.
Biologically plants can work in harmony as “trap crops” that attract insects away from other vegetables, or a plant’s aroma may repel insects from the general area.
Chemically plants can alter the composition of soil, as when peas fix nitrogen from the air into soil.
Plants can also be bad neighbors for any of those reasons too.
Lettuce, carrots, and onions grow roots that go down to different depths—and these vegetables can grow comfortably side by side.
Onions form a fat bulb a few inches underground and then fine roots move out 1 foot on each side of the bulb, and will grow down into the soil to a depth of 39 inches, on occasion. It’s most important not to block the onion bulb. Plant onions six inches apart.
Grow onions as physical companion plants with very shallow-rooted vegetables like lettuce, or narrow-rooted vegetables like carrots.
The aromatic onion will repel many insects and it’s often grown as a companion plant for this very reason. Planting different kinds of herbs and vegetables together in clusters is called “intercropping”.
Cornell University suggests planting onions with these crops to deter insects:
All members of the cabbage family (also called Cole crops or Brassicas): Broccoli, Brussels Sprouts, Cauliflower, Cabbage, Kale, Collards, Radishes, Kohlrabi, Rutabaga, Turnip, Mustard
Onions also do well with:
North Dakota State University Extension recommends Summer Savory and Chamomile to enhance the flavor and growth of onions.
Some onion combos are destructive though. Onions will stunt the growth of peas and beans, from the legume family.
Now that you know where to plant onions, go find out more about which onions will do best in your climate. That whole long-day, short-day thing? We explain it all in an article here and in our video about growing onions.
Onions are useful companion plants for so many of your vegetables. You get sweet, homegrown onions too!