Onions grow well with most vegetables, but a few companions work better than others

Onions pair successfully with beets, carrots, lettuce, spinach, and Swiss chard in the same raised bed. They also grow alongside tomatoes, peppers, and squash without competing for space or nutrients. The key is that onions have shallow roots and take up little horizontal space, so they fit between larger plants or in the gaps of a succession planting schedule. Avoid planting onions near beans, peas, or asparagus — these plants can stunt onion growth or attract the same pests.

The reason onions work as companions is practical: they don't demand the same nutrients at the same time as most vegetables, and their smell deters some common garden pests. A raised bed 4 feet by 8 feet can hold onions plus two or three other crops in the same season without crowding.

Key Takeaways

  • Onions grow well alongside root vegetables like beets and carrots, and leafy greens like lettuce and spinach, because they occupy different soil depths.
  • Plant onions 4 to 6 inches apart and space larger companions like tomatoes or peppers at least 12 inches away to prevent shading.
  • Onions mature in 90 to 120 days depending on variety, so you can plant a second crop of fast-growing greens after you harvest them.
  • Never plant onions near beans, peas, or asparagus, as these combinations reduce yield or attract the same insects.
  • Onions need full sun and well-draining soil; if your bed stays wet, they will rot before they reach full size.

Root vegetables and onions in the same bed

Beets and carrots are the best companions for onions because they grow at different depths. Onion roots stay in the top 6 to 8 inches of soil, while carrot roots go 8 to 12 inches down and beet roots reach 10 to 14 inches. This means they pull nutrients from separate layers and don't compete.

Plant onions in rows 4 to 6 inches apart, and space carrot or beet rows 8 to 10 inches away. Both crops need loose, well-draining soil, so if you've already amended your raised bed with compost, you're ready. Carrots take 60 to 80 days to mature, beets take 50 to 70 days, and onions take 90 to 120 days depending on variety. This means you can harvest the carrots or beets first and use the space for a second planting of greens or radishes before the onions finish.

Leafy greens alongside onions

Lettuce, spinach, arugula, and Swiss chard all grow well with onions because they mature faster and occupy less vertical space. Plant greens in rows between onion rows or at the edges of the bed. Greens need 1 to 2 inches of space between plants, while onions need 4 to 6 inches, so you can fit a row of lettuce in the gap.

Spinach and arugula mature in 30 to 45 days, so you can plant them early in spring, harvest them before the onions need more room, and replant in late summer for a fall crop. Swiss chard grows taller — up to 12 inches — so plant it where it won't shade the onions. All of these greens prefer the same soil moisture as onions: moist but not waterlogged.

Larger plants that work with onions

Tomatoes, peppers, and squash can share a raised bed with onions if you space them correctly. Tomatoes and peppers need 12 to 18 inches between plants, while squash needs 18 to 24 inches. Plant onions in the gaps and around the edges, at least 6 inches away from the base of each larger plant.

Tomatoes and peppers mature in 60 to 85 days and reach 2 to 4 feet tall, so they will shade the onions slightly in midsummer. This is usually not a problem in spring or early summer, but if you're planting onions in late summer for a fall crop, keep them on the south side of the bed where they'll get more direct sun. Squash spreads horizontally and can shade onions if planted too close, so give squash at least 2 feet of space in any direction.

Plants to keep away from onions

Beans and peas stunt onion growth, and onions can reduce the nitrogen-fixing ability that makes beans and peas valuable in a garden. Asparagus attracts the same beetles and spider mites that damage onions, so planting them together increases pest pressure on both. If you want to grow these plants, plant them in a separate bed or at least 3 feet away in the same bed.

Garlic and other alliums (the onion family) can cross-pollinate if you let them flower, and they compete for the same nutrients. If you're growing both onions and garlic, space them at least 8 inches apart and harvest one before the other reaches full size.

Spacing and timing in a 4-by-8 raised bed

A standard 4-by-8 raised bed holds roughly 32 square feet of growing space. If you plant onions in a single row down the middle (32 onions at 4-inch spacing), you have two 18-inch-wide strips on either side for companions. One strip can hold a row of carrots or beets, the other a row of lettuce or spinach. This layout gives you three crops from one bed in a single season.

Alternatively, plant onions in a checkerboard pattern with 6-inch spacing (about 20 onions per bed), and fill the gaps with lettuce or arugula. Harvest the greens at 4 to 6 weeks, then replant with more greens or a fast-growing crop like radishes. By the time the onions are ready to harvest at 12 to 16 weeks, you'll have had two or three companion crops in the same space.

Soil and water needs when planting multiple crops

Onions, root vegetables, and greens all prefer soil that drains well and stays consistently moist without becoming waterlogged. If your raised bed has 6 to 8 inches of a mix of compost and garden soil, all three crop types will thrive. Add a 1-inch layer of compost at the start of the season and again after you harvest the first companion crop.

Water when the top inch of soil feels dry. Onions need less water than tomatoes or squash, so if you're growing those together, water more frequently and mulch around the larger plants to keep the soil from drying out too fast. A 2-inch layer of straw or wood chips around tomatoes and peppers keeps the onions from drying out while preventing the larger plants from sitting in wet soil.

Frequently Asked Questions

Can I plant onions and garlic in the same raised bed?

Yes, but space them at least 8 inches apart. Both are alliums and compete for the same nutrients, so they'll both be smaller if crowded. Garlic matures in 8 to 9 months, while onions mature in 3 to 4 months, so you can harvest the onions first and let the garlic finish.

What's the best way to succession plant with onions?

Plant onions first, then plant fast-growing greens or radishes in the gaps. Harvest the greens at 4 to 6 weeks, replant if you have time before the onions need the space, and harvest the onions last. This gives you three crops from one bed in 16 to 20 weeks.

Do onions need full sun if they're planted with taller vegetables?

Onions need at least 6 hours of direct sun per day. If you're planting them with tomatoes or peppers, put the onions on the south or east side of the bed where they'll get morning and midday sun. Afternoon shade from taller plants is usually fine.

Will onions attract pests to my other vegetables?

No — onions actually repel some common pests like aphids and spider mites. The smell deters them, so planting onions with other crops can reduce overall pest pressure. The exception is onion flies and thrips, which also attack garlic and leeks, so avoid planting those together.

How much space do I need between onions and squash?

Plant onions at least 2 feet away from squash plants. Squash spreads horizontally and shades everything nearby, and the large leaves can trap moisture around the onions, causing rot. If space is tight, plant squash on one end of the bed and onions on the other.