What to plant with onions companion planting

Onions are a garden staple, but they do even better when paired with the right neighbors. Companion planting with onions can deter pests, improve growth, and maximize your space. Here’s what to plant with onions, what to avoid, and how to do it successfully in your garden this season.

Why Companion Planting with Onions Works

Onions belong to the allium family, and their strong sulfur compounds naturally repel many common pests, including aphids, carrot flies, and Japanese beetles. In return, certain plants can help onions by providing ground cover, attracting beneficial insects, or improving soil n utrients. The key is to choose companions that don’t compete for the same resources and that thrive under similar conditions.

Best Onion Companions

Here are the top plants to grow alongside onions, with specific varieties and spacing tips.

Carrots

Carrots and onions are classic companions. The onion’s scent masks the carrot’s aroma, deterring carrot flies, while carrots help break up the soil for onion roots. Plant them in alternating rows or scatter carrot seeds between onion sets.

• Varieties: ‘Nantes’ or ‘Danvers’ carrots work well.
• Spacing: Space onion sets 4 inches apart, and sow carrot seeds 2 inches apart in rows 12 inches apart.
• Planting time: In USDA zones 3-7, plant both in early spring as soon as soil is workable. In zones 8-10, plant in fall for winter harvest.

Beets

Beets and onions are mutually beneficial. Beets add minerals to the soil, and onions repel leaf miners that attack beets. They also have different root depths, so they don’t compete.

• Varieties: ‘Detroit Dark Red’ or ‘Golden’ beets.
• Spacing: Plant onion sets 4 inches apart, and beet seeds 3 inches apart in rows 12 inches apart.
• Planting time: Early spring in zones 3-7; fall in zones 8-10.

Lettuce

Lettuce is a quick-growing crop that can be tucked between onion rows. It provides living mulch, shading the soil and retaining moisture, while onions deter slugs and aphids.

• Varieties: ‘Buttercrunch’ or ‘Black Seeded Simpson’.
• Spacing: Plant lettuce 6 inches apart between onion rows.
• Planting time: Spring and fall in most zones.

Tomatoes

Tomatoes and onions are a classic pairing in the garden and kitchen. Onions repel spider mites and aphids that can plague tomatoes, and tomatoes provide some shade for onions in hotter climates.

• Varieties: ‘Celebrity’ or ‘Roma’ tomatoes; ‘Red Burgundy’ or ‘Walla Walla’ onions.
• Spacing: Plant tomatoes 24 inches apart, and onions 4-6 inches apart in a nearby row, at least 12 inches away from tomato roots.
• Planting time: Set out tomatoes after last frost (zones 3-7: May; zones 8-10: March-April). Plant onion sets in early spring.

Strawberries

Strawberries and onions are good neighbors. Onions help repel pests like slugs and aphids, while strawberries provide ground cover that suppresses weeds.

• Varieties: ‘Seascape’ or ‘Albion’ strawberries; ‘Red Creole’ onions.
• Spacing: Plant strawberries 12 inches apart, and onions 4 inches apart in a separate row, 12 inches away.
• Planting time: Plant strawberries in spring or fall; onions in early spring.

Chamomile

Chamomile is a beneficial herb that attracts pollinators and beneficial insects. It also is said to improve the flavor of onions.

• Varieties: German chamomile.
• Spacing: Plant chamomile 6 inches apart around the edges of onion beds.
• Planting time: Sow seeds in early spring.

Summer Savory

Summer savory is a culinary herb that pairs well with onions in the garden and kitchen. It attracts bees and may improve onion growth.

• Varieties: ‘Kouznetzov’ or common summer savory.
• Spacing: Plant 12 inches apart near onions.
• Planting time: Sow after last frost.

What NOT to Plant with Onions

Some plants do poorly when planted near onions. Avoid these combinations to prevent stunted growth or poor yields.

Beans and Peas

Legumes and onions are a bad match. Onions release compounds that inhibit the growth of beneficial bacteria that legumes need for nitrogen fixation, resulting in smaller yields.

Asparagus

Asparagus and onions compete for nutrients and space, and onions can stunt asparagus growth.

Sage and Parsley

These herbs can inhibit onion growth. Keep them in separate beds.

Other Alliums

Avoid planting onions with garlic, leeks, or shallots. They share the same pests and diseases, so planting them together increases risk.

How to Plan Your Onion Companion Garden

Here’s a step-by-step approach to integrate companions with your onions.

1. Choose your onion type: For storage, plant ‘Copra’ or ‘Redwing’. For fresh eating, try ‘Walla Walla’ or ‘Texas Sweet’. In zones 7-10, choose short-day varieties like ‘Red Creole’.

2. Prepare the bed: Onions prefer loose, well-drained soil with a pH of 6.0-7.0. Work in 2 inches of compost before planting.

3. Plant in blocks or rows: For companion planting, use a 4-foot-wide bed. Plant onions in rows 12 inches apart, with 4 inches between sets. Interplant companions in between or along edges.

4. Use succession planting: Plant fast-growing companions like lettuce or radishes between slower onions. Harvest them before onions need full space.

5. Water and mulch: Keep soil evenly moist, and mulch with straw to retain moisture and suppress weeds.

Sample Planting Plan for a 4x4 Bed

Here’s a practical layout for a 4x4 raised bed in zones 5-7.

Row	Crop	Spacing
1	Onions (e.g., ‘Copra’)	4 inches apart
2	Carrots (e.g., ‘Nantes’)	2 inches apart
3	Onions	4 inches apart
4	Beets (e.g., ‘Detroit Dark Red’)	3 inches apart
5	Lettuce (e.g., ‘Buttercrunch’)	6 inches apart

Plant onions in early spring (March-April in zones 5-7). Sow carrot and beet seeds at the same time. Lettuce can be planted a few weeks later.

FAQ

Can I plant onions with garlic?

No, avoid planting onions with other alliums like garlic, leeks, or shallots. They share pests and diseases, and they compete for the same nutrients.

How close should companion plants be to onions?

Keep companions within 12 inches of onion rows for pest-deterrent benefits, but ensure they don’t shade onions. Tall plants like tomatoes should be at least 12 inches away.

What is the best onion variety for companion planting?

Any onion variety works, but choose based on your day-length needs. For zones 3-6, long-day varieties like ‘Copra’ or ‘Yellow Sweet Spanish’ are best. For zones 7-10, short-day varieties like ‘Red Creole’ or ‘Texas Sweet’.

Do onions repel pests from all plants?

Onions repel many pests, including aphids, carrot flies, and Japanese beetles, but not all. They are not effective against all insects, so use other methods like row covers if needed.

The Bottom Line

Companion planting with onions is a low-cost, effective way to improve garden health and yields. Pair onions with carrots, beets, lettuce, tomatoes, strawberries, and herbs like chamomile. Avoid beans, peas, asparagus, sage, and other alliums. Plan your bed with proper spacing and timing, and you’ll enjoy a productive onion patch with fewer pest problems. Start with a small bed this season and expand as you see what works in your garden.