How Long Do Onions Take to Grow? Practical Timeline, Planting Tips, and Troubleshooting

Introduction: How Long Do Onions Take to Grow?

If you’ve ever asked how long do onions take to grow?, the short answer is: it depends. Expect anything from 30 days for green onions to 120 to 150 days for storage bulbs, with most garden onions maturing in about 90 to 120 days. Variety, day length, and whether you start from seed, sets, or transplants all change the timeline. For example, short-day varieties form bulbs faster in southern climates, long-day types need more time up north, and sets usually give harvestable bulbs sooner than seeds. In this guide you will get a practical timeline by variety and planting method, step-by-step planting tips to shave weeks off growth, and troubleshooting for slow or small bulbs so you can plan your harvest with confidence.

Onion Types and Typical Growth Timelines

If you are wondering how long do onions take to grow, the first thing to nail is day length. Onions form bulbs when they sense a certain number of daylight hours, so choose the type that matches your latitude. Short-day onions set bulbs at about 10 to 12 hours of daylight, they are best for southern states and usually reach harvest in roughly 12 to 16 weeks from planting. Long-day onions need 14 to 16 hours, they thrive in northern climates and typically need 18 to 26 weeks to mature. Intermediate-day varieties sit between those ranges, they do well in mid-latitudes and usually take 14 to 20 weeks.

Practical tip, if you want faster bulbs pick a short-day variety like Texas 1015 in warm areas. If you want larger storage onions and you live up north choose long-day types like Walla Walla. Plant on the local recommended schedule and you will hit those week ranges reliably.

Key Factors That Affect How Fast Onions Grow

Several things determine how fast your onions grow, and each one can add or subtract weeks from the timeline.

Day length matters most for bulbing. Short-day varieties, used in southern states like Texas and Florida, start forming bulbs at 10 to 12 hours of daylight, so they bulb earlier. Long-day types, for places like Maine or Minnesota, need 14 to 16 hours, so bulbing can be later in the season. Day-neutral types are more flexible.

Climate and temperature affect pace. Onions prefer cool nights and daytime temperatures around 50 to 75 F; extreme heat can stall bulb formation or cause bolting. Consistent moisture speeds growth; drought slows it.

Variety and planting method change timing. Onion sets often mature fastest, in 60 to 90 days; transplants 90 to 120 days; direct-seeded varieties commonly take 100 to 150 days. Storage varieties usually need longer.

Soil fertility counts. Rich, well-draining soil with steady nutrients speeds bulb growth; excess nitrogen promotes top growth and delays bulbing. Soil test, add compost, and side-dress moderately as bulbs swell.

Timeline by Planting Method: Seeds, Sets, and Transplants

If you wonder how long do onions take to grow, here is a practical, step-by-step timeline for each planting method, with realistic weeks to bulb formation and to harvest.

Seeds

• Weeks 0 to 2, germination, thin to 1 inch between seedlings.
• Weeks 3 to 8, fast green growth, start hardening off at week 6.
• Weeks 12 to 16, bulb initiation for long-day varieties in spring, short-day types may form earlier.
• Harvest window, weeks 18 to 24 for mature storage onions, earlier for bunching onions.

Sets

• Weeks 0 to 1, shoots appear after planting.
• Weeks 3 to 6, rapid top growth.
• Weeks 6 to 10, bulbs usually form because sets were partially matured already.
• Harvest window, weeks 8 to 12 for small bulbs, 12 weeks plus for larger sizes.

Transplants

• Weeks 0 to 1, transplant shock recovery.
• Weeks 2 to 8, active leaf growth.
• Weeks 8 to 12, bulb formation begins.
• Harvest window, weeks 12 to 16 typically for full-sized bulbs.

Tip, check the seed packet or nursery tag for variety daylength and plan timelines around local frost dates for best results.

When to Plant: Building a Simple Planting Schedule

Pick your last frost date, choose the right day‑length type, then count backward from your target harvest. Quick rule of thumb, for sets or transplants plant 4 to 8 weeks before your last frost; for seed start indoors 8 to 12 weeks before transplanting. Match type to zone: long-day onions for northern climates (zones 3 to 6), intermediate-day for transition zones (5 to 8), short-day for southern climates (8 to 10). Soil temperature matters too; plant when soil is consistently above about 45 to 50°F.

Examples: Zone 5, last frost May 15, plant long-day transplants around April 15. Zone 8, want spring bulbs, plant short-day sets in October for an overwinter crop. To answer how long do onions take to grow, add the variety’s days to maturity to your planting date, that gives a realistic harvest window.

Soil Preparation and Planting Steps That Speed Growth

If you wonder how long do onions take to grow, start with soil that helps them sprint to maturity. Steps that actually speed growth, 1. Loosen soil to at least 12 inches, remove rocks, work in 2 inches of compost for immediate fertility. 2. Test pH, aim for 6.0 to 7.0. Add lime if below 6.0. 3. Planting depth, sets and transplants: bury onion sets so the tip is about 1 inch below the surface, transplant seedlings at the same depth. For seeds, sow 1/4 inch deep. 4. Spacing: 4 to 6 inches between bulb onions, rows 12 inches apart; bunching onions can be 2 to 3 inches apart. 5. Mulch 2 inches and water about 1 inch per week, side dress nitrogen when tops begin to swell. These tweaks shorten your timeline and increase bulb size.

Watering and Feeding: A Practical Care Schedule

For the first two weeks after planting, keep soil evenly moist, not soggy, so seedlings establish. Aim for about 1 inch of water per week total, split into two deep waterings. Once bulbs begin to swell, roughly the last three to four weeks before harvest, increase to 1.25 to 1.5 inches per week, especially in hot dry weather. Use drip irrigation or soaker hoses, avoid overhead watering late in the season to reduce disease.

Fertilizer schedule, simple and effective:

• At planting, work in compost plus 1 to 2 pounds of 10-10-10 fertilizer per 100 square feet.
• When tops hit 6 inches, side dress with a nitrogen source, for example 1/2 cup blood meal or 1/3 cup urea per 10-foot row.
• Repeat that side dress 4 weeks later.

If you wonder how long do onions take to grow, consistent moisture and timely nitrogen will shorten the timeline and increase bulb size.

How to Tell When Onions Are Ready to Harvest

If you wonder how long do onions take to grow, here is the short checklist to know harvest time. Primary signs of maturity, pull when 70 to 80 percent of tops have fallen over, necks are thin and flexible, and outer skins are papery and dry. Bulbs should feel firm when squeezed, not soft or hollow.

Quick field tests

• Lift a sample bulb, brush soil away, press the neck. If it cracks and feels dry, it is ready.
• Slice one open. The layers should be tight with no green center.
• Stop irrigation two weeks before harvest. If bulbs continue growing after you stop water, wait another week.

Timing to maximize size and storage life

• Harvest in dry weather, leave onions on the soil for 2 to 3 days to dry, then cure in a warm ventilated place for 2 to 3 weeks.
• Only trim tops after curing, store at 32 to 50 degrees Fahrenheit with low humidity for best long-term storage.

Common Problems That Slow Onion Growth and How to Fix Them

Pests like onion maggots, thrips, and cutworms chew growth time, leaving stunted plants and slow bulbing. Fix it, use floating row covers during seedling stage, apply spinosad or insecticidal soap for thrips, and hand-pick cutworms at night. Plant trap crops and keep the bed weed free.

Fungal problems such as downy mildew, fusarium rot, and neck rot also stall progress. Improve air flow by wider spacing, remove infected rows promptly, and rotate out of allium crops for at least three years. Use seed treated for fungus or apply copper fungicide at first sign.

Nutrient issues show as thin leaves or pale color. Do a soil test, side-dress with a balanced fertilizer early, avoid excess nitrogen late in the season to encourage bulbing.

Water stress, poor drainage, compacted soil, and wrong variety for day length slow growth. Practical steps, crop rotation, clean seed, and raised beds speed recovery so you get a better sense of how long do onions take to grow.

Curing, Storing, and Using Your Onions

After harvest, cure onions for two to three weeks in a warm, dry, well-ventilated spot, such as a garage or a sunny shed. Lay them on racks or cardboard, keeping tops intact until the necks are papery. Once cured, trim tops to about 1 inch and snip roots. For long-term storage, keep bulbs cool, 32 to 40°F, with moderate humidity, 60 to 70 percent, in mesh bags or crates so air can circulate. Sweet onions store only one to two months, storage types four to six months. Use any surplus quickly: caramelize and freeze in ice cube trays, quick-pickle slices in vinegar and sugar, roast whole and vacuum seal, or dehydrate into onion powder. Check monthly and remove soft bulbs.

Conclusion: Quick Checklist and Final Insights

Quick takeaways, then a printable checklist you can use in the garden today. If you asked how long do onions take to grow? Expect about 100 to 175 days from seed, 90 to 120 days from transplants or sets, and 30 to 60 days for bunching onions. Use full sun, loose soil pH 6.0 to 7.0, one inch depth, and space bulbs 4 to 6 inches.

Printable planting checklist

• Start seeds indoors 8 to 12 weeks before last frost, or plant sets as soon as soil is workable.
• Feed with nitrogen early, reduce feed when bulbs begin to swell.
• Water about 1 inch per week, more in hot weather.
• Thin to final spacing by month 2.

Harvest checklist

• Harvest when tops fall over and yellow.
• Cure 1 to 2 weeks in a dry, ventilated spot.
• Store at 32 to 40 F with low humidity.

You now have a clear timeline and steps to start growing onions this season.