How long do onions take to mature fully?
Written by
Olivia Mitchell
Reviewed by
Prof. Martin Thorne, Ph.D.Understanding onion maturity timelines will help you determine which ones to plant, based on your specific goals. Green onions are ready in 30 days, while the larger bulb varieties require 100-150 days. I plant both, as I hate to be without onions; your patience will determine if you have scallions or storage bulbs.
Variety selection affects length of time to harvest dramatically. In warm climates, we can afford to use short-day types like 'Granex' because they mature quickly. Long-day types, such as 'Ailsa Craig', require long northern summers to reach maturity. I test several varieties every year. Your climate zone will indicate how long you can expect to wait for your harvest to be ready.
Choose your planting methods carefully to dictate your timelines. Sets shave off three weeks from seed timelines. Transplants speed up the process from starting indoors. My spring-planted seedlings are harvested 25 days sooner than the same seed when direct-sown outdoors. You must weigh the trade-offs with which you're most comfortable.
Climate Control
- Use cloches for 2-week head starts
- Apply black plastic mulch to warm soil
- Install shade cloth above 85°F
Nutrition Management
- Apply phosphorus at planting for root development
- Use fish emulsion every 3 weeks during leaf growth
- Stop nitrogen 60 days pre-harvest
Environmental Monitoring
- Track growing degree days (GDD)
- Ideal: 1500-2000 GDD for bulbing onions
- Use soil thermometers to optimize growth
Recognize harvest readiness signs accurately. Green onions should have 12-inch stems. Bulb onions are ready when half of the tops turn yellow and fall over. Squeeze bulbs gently to check for firmness. Your timely harvest prevents bolting or rot in your garden bed!
I make a monthly calendar to track growth milestones as they develop. For guides and research, I use leaves of 8 to 10 leaves at 60 days. Around day 90, I will record the production of swollen bulbs. Each week, I take photographs of development. This way, I can see patterns that will allow for plants to be modified in future plantings.
Weather Extremes That Change Timelines Heat Waves Promote Growth Cold Snaps Delay Growth My Covered Hoops Preserve Growing Times Between Temperature Fluctuations Your Interventions Provide Consistent Growth Regardless of Weather Fluctuations
Plant by succession for continuous harvests. Plant seeds of green onions every couple of weeks, and several bulbs at three different intervals. I enjoy my fresh onions from May through October, thanks to your good planning, so that no matter the length of time needed, a fresh supply is assured.
Read the full article: How to Grow Onions Successfully at Home
