Emily ParkerBy Emily Parker

Updated November 2026

Cabbage and onion companion planting works because the two crops support each other in a small, practical way: onion odor can confuse some pests that target brassicas, and the low, upright onion foliage takes up little space. You will learn how to space and time the planting, which pests this pairing helps with, and where it falls short, so you can decide whether to use it in your own beds.

What the Pairing Does and Doesn’t Do

Onions produce sulfur compounds that many gardeners believe discourage aphids, cabbage root flies and some moths. Cabbage, in turn, is a heavy feeder that grows large, so the onions sit in the gaps without competing much for light. The benefit is mostly a reduction in pest pressure, not a guaranteed protection. Expect fewer hits from some insects, but keep checking your plants and use row covers if flea beetles or cabbage worms show up in numbers.

Shopping for one? See our guide: 6 Best Onions and Potatoes Companion Planting Books and Guides for 2026.

How to Plant Cabbage and Onions Together

Start with transplants for cabbage and sets or transplants for onions, timed to your local frost dates. In most of the US, set cabbage transplants out two to four weeks before your last spring frost, then add onions once the soil is workable.

  1. Prepare the bed with 2 to 3 inches of compost worked into the top 8 inches of soil.
  2. Space cabbage 12 to 18 inches apart, depending on the variety. Larger head types need the full 18 inches.
  3. Plant onion sets or transplants about 4 to 6 inches apart in the gaps, or in a separate row between cabbage rows about 12 to 18 inches away.
  4. Water both crops at the base to keep foliage dry, and mulch lightly to hold moisture.

Spacing for Different Cabbage Types

Early varieties and smaller heads, such as those sold as “baby” or early types, can be planted slightly closer. Late storage cabbage needs more room for airflow and head development, so keep onions at the outer edges of those beds.

Managing Pests and Timing the Harvest

Onions mature earlier than most cabbage, so you can pull them as the cabbage heads fill. Harvest onions when the tops fall over and begin to yellow, then cure them in a dry, shaded spot for two to three weeks. Leaving the onions in place longer than necessary can crowd the cabbage roots and reduce head size.

If you already grow other crops in the same bed, check your rotation plan. For a broader look at how these crops pair with others, see Companion Planting with Cabbage: Best Partners, Spacing and Pitfalls and Companion Planting for Cabbage Worms: 6 Plants That Deter Them. If you plan to grow onions beside other brassicas, Onions and Broccoli Companion Planting: A Step-by-Step Guide for Beginners covers similar spacing.

Common Mistakes

  • Planting onions too close to cabbage, which shades and crowds the roots of both crops.
  • Expecting onions alone to stop cabbage worms or flea beetles. Use row covers as a backup.
  • Letting onions bolt by planting too early in cold weather, which produces small, woody bulbs.
  • Skipping compost. Both crops need steady nitrogen and moisture, especially in the first six weeks.
  • Failing to rotate. Keep brassicas and onions out of the same spot for at least three years.

Lightweight row covers help keep cabbage moths and flea beetles off young plants, and they pair well with onions that do not need cover. A soil thermometer helps you confirm that the bed is warm enough for onion sets to root properly.

  • Insect row cover fabric: protects brassica seedlings from egg-laying moths. View on Amazon
  • Soil thermometer: helps you time onion planting by checking soil temperature. View on Amazon

FAQ

Do onions really keep cabbage worms away?

Onions may reduce some pest activity, but they do not reliably stop cabbage worms on their own. Use row covers and check the undersides of leaves weekly for eggs.

How far apart should I plant onions and cabbage?

Plant cabbage 12 to 18 inches apart and onions 4 to 6 inches apart in the gaps, keeping them at least 12 inches from cabbage stems.

Can I plant cabbage and onions in the same bed every year?

No. Rotate both crops out of the same spot for at least three years to reduce soilborne disease and pest buildup.

Conclusion

Cabbage and onion companion planting is a low-effort way to add some pest deterrence to a brassica bed, as long as you space the crops well and do not rely on onions alone. Plant cabbage first, tuck onions into the gaps, and use row covers as backup. Rotate the beds each year and you will get steadier, healthier harvests.

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Emily Parker

About Emily Parker

Emily Parker is part of our editorial team and reviews and edits our vegetable & edible gardening guides, checking product details against manufacturer specifications and owner feedback.