How Long Does It Take to Grow Onions?
Quick Answer
90–120 days from transplants, 100–130 days from sets, or 130–160 days from seed. Green onions are ready in just 50–65 days.
Typical Duration
50 days160 days
Quick Answer
90–120 days from transplants to harvest for full-size storage onions, making transplants the most popular method for home gardeners. Onion sets (small bulbs) take 100–130 days. Growing from seed takes the longest at 130–160 days but offers the widest variety selection. Green onions (scallions) are the fastest, ready to harvest in just 50–65 days from seed.
Growing Time by Starting Method
| Method | Days to Harvest | Pros | Cons |
|---|---|---|---|
| Transplants | 90–120 days | Fastest to full bulbs, good variety choice | Must buy or start indoors 8–10 weeks early |
| Sets (small bulbs) | 100–130 days | Easy, widely available | Limited varieties, prone to bolting |
| Direct seed (outdoors) | 130–160 days | Cheapest, most variety options | Slowest, needs thinning |
| Indoor seed start | 90–120 days (after transplant) | Best of both: variety + speed | Requires 8–10 weeks of indoor growing first |
Timeline: Seed to Harvest
| Stage | From Seed | From Sets | From Transplants |
|---|---|---|---|
| Germination | 7–14 days | N/A | N/A |
| Seedling growth | 8–10 weeks | N/A | N/A |
| Transplant to garden | Week 10–12 | Day 1 | Day 1 |
| Leaf growth phase | 4–6 weeks | 4–6 weeks | 4–6 weeks |
| Bulbing begins | Week 18–20 | Week 8–10 | Week 6–8 |
| Bulb swelling | 4–6 weeks | 4–6 weeks | 4–6 weeks |
| Tops fall over | Week 22–26 | Week 14–18 | Week 12–16 |
| Harvest | Day 130–160 | Day 100–130 | Day 90–120 |
| Curing | 2–4 weeks after harvest | 2–4 weeks | 2–4 weeks |
Short-Day vs Long-Day vs Day-Neutral
Onions form bulbs based on day length (hours of sunlight). Choosing the wrong type for your latitude means bulbs won't form properly.
| Type | Day Length Trigger | Best Latitudes | When to Plant | Varieties |
|---|---|---|---|---|
| Short-day | 10–12 hours | South of 35°N (TX, GA, FL) | Oct–Jan (fall/winter) | Texas 1015, Vidalia, Red Creole |
| Long-day | 14–16 hours | North of 38°N (OR, NY, MI) | Mar–Apr (early spring) | Walla Walla, Yellow Sweet Spanish, Copra |
| Day-neutral | 12–14 hours | Any latitude | Spring | Candy, Cabernet, Sierra Blanca |
Wrong type = no bulbs. A long-day onion planted in Texas won't receive enough daylight hours to trigger bulbing. A short-day onion in Minnesota will bulb too early and stay small.
Green Onions vs Storage Onions
| Type | Days to Harvest | How to Harvest | Storage Life |
|---|---|---|---|
| Green onions (scallions) | 50–65 days | Pull when pencil-thick, 8–12" tall | 1–2 weeks (refrigerated) |
| Spring onions | 65–80 days | Pull when small bulb forms (1") | 1–2 weeks |
| Fresh eating onions | 80–100 days | Harvest anytime after bulb forms | 1–3 months |
| Storage onions | 100–160 days | Wait until tops fall over, then cure | 3–9 months |
Green onions can be grown year-round indoors on a windowsill or in containers.
Planting Guide
From Seed (Indoors)
- Start seeds indoors 8–10 weeks before last frost.
- Sow seeds 1/4 inch deep in trays, 1/2 inch apart.
- Keep soil at 65–75°F. Seeds germinate in 7–14 days.
- Provide 14–16 hours of light daily (use grow lights).
- Trim tops to 4 inches when they get floppy (encourages stronger growth).
- Harden off for 1 week before transplanting.
From Sets
- Plant sets 1 inch deep, 4–6 inches apart, in rows 12 inches apart.
- Choose small sets (dime-sized) – larger sets are more likely to bolt.
- Point the narrow end up.
- Water well after planting.
From Transplants
- Plant transplants 1 inch deep, 4–6 inches apart.
- Water consistently – onions have shallow roots and need even moisture.
- Fertilize every 2–3 weeks with a nitrogen-rich fertilizer during the leaf-growth phase.
- Stop fertilizing once bulbing begins.
Growing Conditions
| Factor | Requirement |
|---|---|
| Sun | Full sun (6–8+ hours daily) – more sun = bigger bulbs |
| Soil | Loose, well-drained, pH 6.0–7.0, rich in organic matter |
| Water | 1 inch per week; consistent moisture during bulbing |
| Spacing | 4–6 inches apart for bulb onions; 1–2 inches for green onions |
| Fertilizer | High nitrogen during leaf growth; stop when bulbing starts |
| Mulch | Light layer to suppress weeds and retain moisture |
Harvesting and Curing
When to Harvest
- Green onions: Pull when pencil-thick and 8–12 inches tall.
- Storage onions: Wait until 50–80% of the tops have naturally fallen over. Do not force tops down.
- Stop watering 1–2 weeks before harvest to toughen the outer skin.
How to Cure
- Pull onions gently from the soil on a dry day.
- Lay them on the ground or a rack in a warm, dry, airy spot.
- Cure for 2–4 weeks until the necks are completely dry and papery.
- Trim roots and cut tops to 1 inch (or braid if leaving tops intact).
- Store in mesh bags or braids in a cool (35–50°F), dry place.
Storage Life by Variety
| Variety Type | Storage Life |
|---|---|
| Sweet onions (Vidalia, Walla Walla) | 1–3 months |
| Yellow storage (Copra, Patterson) | 6–9 months |
| Red onions | 2–4 months |
| White onions | 2–3 months |
Common Problems
- Bolting (flowering): Caused by cold stress or planting large sets. Remove flower stalks immediately and use that onion first (it won't store well).
- Small bulbs: Usually wrong day-length type for your area, too little sun, or too close spacing.
- Onion maggots: Use row covers at planting. Rotate crops annually.
- Neck rot: Caused by wet conditions during curing. Ensure good airflow while drying.
- Thick necks: The onion hasn't finished bulbing. Be patient and wait for tops to fall naturally.