Onion Planting Guide

May

onion this month

This page is about onion in general. For your zone's exact planting and harvest dates, pick your county below.

Sun full sun

Water moderate

Days to harvest 90–120

Plant depth 1″

Spacing 6″

How to water onion
Consistent moisture matters more than volume for onion. Little and often beats occasional drenching.
Where to put onion
onion wants at least 6 hours of direct sun. Less than that and you'll get leggy plants with weak yields.
Check your local forecast before planting
Your zone determines the exact week to plant onion. Pick your county below and we'll line everything up against your frost dates.

Get onion planting dates for your county →

Onions are a fundamental kitchen staple available in yellow, white, and red varieties. Choose long-day, short-day, or intermediate types based on your latitude.

Allium cepa · Vegetable · Amaryllidaceae family · 90–120 days to maturity

Get Your Personalized Onion Planting Dates

Enter your ZIP code to see exact planting dates, soil compatibility, and growing tips specific to your county.

Where Can You Grow Onion?

Zone Compatibility for Onion Zones 3a – 10b

1a 1b 2a 2b 3a 3b 4a 4b 5a 5b 6a 6b 7a 7b 8a 8b 9a 9b 10a 10b 11a 11b 12a 12b 13a 13b

Ideal (data available) Suitable Marginal Not recommended

Planting Dates by Zone

Zone	Start Indoors	Direct Sow	Transplant	Harvest
Zone 3a	Apr 3	May 8	May 15	Aug 14 – Sep 18
Zone 3b	Mar 29	May 3	May 10	Aug 9 – Sep 13
Zone 4a	Mar 25	Apr 29	May 6	Aug 5 – Sep 23
Zone 4b	Mar 20	Apr 24	May 1	Jul 31 – Sep 18
Zone 5a	Mar 21	Apr 11	Apr 25	Jul 25 – Sep 12
Zone 5b	Mar 14	Apr 4	Apr 18	Jul 18 – Sep 5
Zone 6a	Mar 6	Mar 27	Apr 10	Jul 10 – Aug 28
Zone 6b	Feb 27	Mar 20	Apr 3	Jul 3 – Aug 21
Zone 7a	Feb 18	Mar 11	Mar 25	Jun 24 – Aug 12
Zone 7b	Feb 11	Mar 4	Mar 18	Jun 17 – Aug 5
Zone 8a	Feb 1	Feb 22	Mar 8	Jun 7 – Jul 26
Zone 8b	Jan 21	Feb 11	Feb 25	May 27 – Jul 15
Zone 9a	Jan 13	Jan 20	Feb 10	May 12 – Jun 30
Zone 9b	Dec 28	Jan 4	Jan 25	Apr 26 – Jun 14
Zone 10a	Dec 4	Dec 11	Jan 1	Apr 2 – May 21
Zone 10b	Dec 4	Dec 11	Jan 1	Apr 2 – May 21

Why are some columns showing "—"?

Transplant shows "—" because Onion is best direct sown where it will grow. Transplanting can disturb the roots and slow growth.

How to Plant Onion

Planting Depth

Between Plants

12"

Between Rows

🍂 Fall planting: Sow 10 weeks before your first frost date for a fall harvest.

Growing Conditions

☀️ Sun

Full Sun (6-8+ hours)

💧 Water

0.7"/week

Water when the top inch of soil feels dry. Consistent moisture produces the best results.

🧪 Soil pH

6 – 7

Prefers neutral to slightly acidic soil — ideal for most garden beds.

🗺️ Hardiness Zones

Zone 3a – 10b

📅 Days to Maturity

90–120 days

Medium-season crop. Start early for best results in shorter seasons.

👪 Plant Family

Amaryllidaceae

Rotate with other families yearly to prevent soil-borne diseases. Don't plant in the same spot where Amaryllidaceae family crops grew last year.

How Much Onion to Grow

Onion takes 90–120 days to mature. In most zones you'll get one harvest per season, so plant enough to last.

Companion Planting for Onion

✅ Good Companions

Carrots Lettuce Beets Cabbage

❌ Keep Away From

Peas Green Beans Asparagus

Check more combinations with our Companion Planting Checker →

Growing Tips for Onion

Start seeds indoors 8-10 weeks before transplanting. Match day-length type to your latitude. Stop watering when tops begin to fall over and cure bulbs for 2-3 weeks before storage.

💧 Watering: Onion needs approximately 0.7 inches of water per week during active growth. Adjust based on your local rainfall — check your county page for a monthly watering guide specific to your area.

Saving Onion Seeds

Recommended for Your Garden

🌱

Seed Starting Trays $8-20

Start seeds indoors with reusable cell trays and humidity domes.

🧪

Soil Test Kit $12-25

Test your soil pH, nitrogen, phosphorus, and potassium levels before planting.

🏷️

Garden Plant Markers $6-12

Keep your garden organized with durable, weather-resistant plant labels.

Reader favourite

Seed Saving & Storage Guide

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Most saved seeds go bad before next season. This shows exactly when to pick, how to dry, and where to store seeds from 200 plants so yours don't.

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Bonus: searchable Google Sheets tracker + custom GPT assistant

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Onion by State

Frequently Asked Questions

How long does it take to grow Onion?

Onion (Allium cepa) takes 90 to 120 days from planting to harvest. Exact timing depends on your variety, growing conditions, and USDA zone.

What zones can Onion grow in?

Onion can be grown in USDA zones 3a through 10b. Use the planting calendar above to find the exact dates for your zone.

How much sun does Onion need?

Growing Onion requires Full Sun (6-8+ hours), Moderate — regular watering, and soil pH of 6 to 7.