🧅 Can I Plant Onion in Aurora, CO?

2026 planting guide for Zone 5b · Last frost ~May 7 · Growing season ~150 days

⏳ WAIT — Too late to harvest before first frost (~Nov 2)

Onion needs at least 100 days to harvest, but there are only ~94 days before the average first fall frost around Nov 2. Wait until next spring for best results.

Planting window: Feb 10 – Feb 24 (next spring)
Skip this season. Plan to start onion again around Feb 10 next spring.
Live result based on current forecast for Aurora, CO · Updates every 6 hours
USDA Zone
5b
Last Spring Frost
~May 7
First Fall Frost
October 4
Growing Season
~150 days
Ideal Temp for Onion
45–75°F
Frost Risk
✅ Tolerant

Growing Onion in Aurora

Aurora sits at over 5,400 feet in Zone 5b, sharing Denver's challenging high-altitude gardening environment. The growing season is compact — around 150 days — with late spring frosts and early fall cold snaps. High-UV solar radiation speeds plant development but also increases water evaporation from soil. Raised beds, drip irrigation, and careful variety selection for short seasons are keys to success here.

In Aurora (last frost around May 7), onion can go out around March — approximately 6 weeks before the last expected frost, making it an early-season opportunity. Starting seeds indoors 10 weeks before the last frost date gives you a significant head start.

Onion thrives between 45°F and 75°F. It tolerates temperatures as low as 28°F, making it a candidate for early spring planting before the last frost date. Expect 100–120 days from transplant to first harvest. Long season. Start early indoors or use sets.

Frequently Asked Questions

When can I plant onion in Aurora, CO?

In Aurora (last frost around May 7), onion can go out around March — approximately 6 weeks before the last expected frost, making it an early-season opportunity. For best results, start seeds indoors 10 weeks before that — giving you strong transplants ready to go out at the right time.

What is the USDA hardiness zone for Aurora?

Aurora, CO is in USDA Plant Hardiness Zone 5b. The last expected spring frost is around May 7, and the first fall frost arrives around October 4. This zone classification helps you understand which perennials survive winter and when annual vegetables can safely go outdoors.

Is it safe to plant onion outside in Aurora right now?

That depends on the current weather forecast. Onion needs temperatures above 28°F (ideally 45–75°F) to thrive. CanIPlant checks your real 7-day forecast and any active frost alerts to give you a live YES, NO, or WAIT answer — just enter your ZIP code.

Can I grow onion in Aurora 2026?

Yes — Onion grows well in Aurora, CO. With a Zone 5b climate and a growing season of ~150 days, Aurora is well-suited for cool-season crops like onion. As a frost-tolerant crop, onion can even go out a few weeks before the last frost date.

Grow Onion in Other Cities

New York, NYLos Angeles, CAChicago, ILHouston, TXPhoenix, AZPhiladelphia, PASan Antonio, TXSan Diego, CA

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