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Growing Onions in Pots

Onions are a kitchen essential, and you can grow them successfully in containers - whether you want quick green onions in weeks or full bulb onions over a season. Container onions are perfect for balconies and patios, and you can even regrow onions from kitchen scraps for endless green tops.

Quick Reference

Container Depth

6-10 inches

Spacing

4-6" (bulbs), 1-2" (green)

Sunlight

6+ hours full sun

Days to Harvest

21-120 days

Watering

Consistent, moderate

Difficulty

Beginner

Day-Length

Match to latitude

Best Start

Sets or transplants

Onion Types for Containers

Green Onions (Scallions)

Timeline: 3-4 weeks from sets
Container: Any 4+ inch deep pot
Spacing: 1-2 inches apart
No bulbing: Day-length doesn't matter
Varieties: Evergreen, Tokyo Long White
Cut-and-come-again: Regrows from roots

Bulb Onions

Timeline: 90-120 days from transplants
Container: 8-10 inch deep, wide pots
Spacing: 4-6 inches apart
Day-length critical: Match to latitude
Short-day: Texas Sweet, Vidalia (zones 7-10)
Long-day: Walla Walla, Yellow Sweet (zones 3-6)

Understanding Day-Length

Onion bulb formation is triggered by day length - getting this wrong is the #1 reason for onion failure:

Short-Day (10-12 hrs)

Zones 7-10 (South)

Plant fall, harvest spring

Intermediate (12-14 hrs)

Zones 5-6 (Middle)

Most flexible option

Long-Day (14-16 hrs)

Zones 3-6 (North)

Plant spring, harvest summer

Step-by-Step Planting Guide

1Choose container and onion type

Select wide container at least 6-8 inches deep. Decide: green onions (any container, fast) or bulb onions (need more space, longer). Choose short-day or long-day varieties based on your latitude.

2Select planting material

Options: Onion sets (small bulbs - easiest), transplants (young plants), or seeds (cheapest but slowest). Sets and transplants are faster for beginners.

3Prepare loose soil

Fill with loose, well-draining potting mix. Onions need loose soil to form bulbs - heavy or compacted soil restricts growth. Mix in compost for fertility.

4Plant at proper depth

Sets: plant 1 inch deep, pointed end up. Transplants: bury to white part. Seeds: 1/4 inch deep. Space 4-6 inches apart for bulbs, 1-2 inches for green onions.

5Position in full sun

Place where onions get 6+ hours direct sun. Sunlight drives bulb formation. Insufficient light = small bulbs or just greens.

6Water and feed consistently

Keep soil evenly moist but not wet. Onions are shallow-rooted. Feed every 2-3 weeks with balanced fertilizer until bulbing starts.

7Harvest at right time

Green onions: harvest when pencil-thick. Bulb onions: harvest when tops fall over and yellow. Cure bulb onions in sun for a few days, then store.

Growing Onions from Scraps

Regrow green onion tops from kitchen scraps - it's nearly free!

Save 1-2 inches of the root end when cutting onions
Plant root-down in soil, just covering the white part
Place in sunny window and keep moist
Green tops emerge in 1-2 weeks
Harvest tops repeatedly - they regrow!
Note: This produces greens only, not new bulbs

Expected Yield

4-5

Bulb onions per 12" pot

15-20

Green onions per 12" pot

3-4 mo

Storage life (cured bulbs)

Common Problems

No Bulb Formation

Cause: Wrong day-length variety for your latitude

Solution: Grow short-day in South, long-day in North. Check variety requirements before planting.

Small Bulbs

Cause: Overcrowding, insufficient sun, or not enough growing time

Solution: Space 4-6 inches apart, ensure 6+ hours sun, start early in season

Bolting (Flowering)

Cause: Temperature fluctuations or planting too early

Solution: Protect from cold snaps, don't plant sets too early. Cut flower stalks if they appear.

Onion Maggots

Cause: Fly larvae in bulbs

Solution: Cover with row cover when planting, rotate containers, don't plant where alliums grew

Frequently Asked Questions

What size container for onions?

Onions need at least 6-8 inches deep for bulb formation, 10+ inches for large bulbs. Width matters more - space onions 4-6 inches apart. A 12-inch pot holds 4-5 bulb onions or 15-20 green onions. Rectangular containers work well for maximizing onion production.

Can I grow onions from kitchen scraps?

Yes! Cut 1 inch from the root end of an onion and plant in soil. It will regrow green tops in 1-2 weeks for continuous harvest. However, it won't form a new bulb - just greens. For new bulbs, plant onion sets, seeds, or transplants.

What's the difference between short-day and long-day onions?

Day-length determines when onions form bulbs. Short-day onions (for South, zones 7-10) bulb with 10-12 hours of daylight. Long-day onions (for North, zones 3-6) need 14-16 hours. Planting the wrong type for your latitude results in no bulbs or tiny ones.

How long do onions take to grow in containers?

Green onions: 3-4 weeks from sets, 8-10 weeks from seed. Bulb onions: 90-120 days from transplants, 5-6 months from seed. Onion sets planted in early spring produce bulbs by mid-summer. Container onions may be slightly smaller than ground-grown.

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