How to Plant Onions: A Step by Step Guide for Beginners
Introduction: Grow Bigger, Tastier Onions This Season
Want bigger, tastier onions this season? Onions are one of the easiest, highest value crops you can grow, whether you have a tiny balcony box or a 20 foot row. A small 4 by 5 foot bed can produce dozens of bulbs, and homegrown onions store for months, so a little effort pays off all winter.
Growing onions is straightforward, they like full sun, well drained soil and a pH close to 6.0 to 7.0. For fast results use sets or transplants, for variety control start from seed. Space bulbs 4 to 6 inches apart, keep soil evenly moist while roots develop, and feed lightly once or twice.
This guide shows exactly how to plant onions, step by step, with timing, spacing and harvest tips you can use right now.
Why Grow Onions in Your Garden
Onions are one of the highest value crops for small gardens, they take little space and deliver big flavor. Use them fresh as scallions in salads, cooked in stews, or cured for months of pantry storage, and try short-day or long-day varieties for your climate. Searching for how to plant onions? You get quick wins and predictable results.
Expect bulbs to mature in about 90 to 120 days, green onions in 30 to 60 days. Labor is low, plan for 10 to 20 minutes weekly for watering, weeding and a midseason feed.
Pick the Right Type of Onion for Your Climate
Onion type matters more than people expect, it drives bulb size and timing. Short day varieties form bulbs when daylight hits about 10 to 12 hours, they are the winners in southern states and regions below roughly 36 degrees latitude. Try short day types if you live in Texas, Florida, or southern California.
Long day varieties need 14 to 16 hours of daylight to bulk up, they do best in the northern US, Canada, and other high latitude zones. Walla Walla and other long day sweets give the biggest bulbs up north.
Day neutral or intermediate types sit in the middle, good for mid latitude gardeners. For green onions and bunching types, pick scallion or bunching varieties, plant them closer and harvest young, they tolerate a wider range of daylight. When learning how to plant onions? start by matching variety to your latitude.
When to Plant Onions
Wondering how to plant onions? Timing depends on seeds, sets, transplants, and your local last frost date.
Start seeds indoors 8 to 12 weeks before last frost. If your last frost is April 15, sow mid February to early March. Harden seedlings 7 to 10 days, then transplant once they have 4 to 6 true leaves.
Plant onion sets or store-bought transplants about 2 to 4 weeks before last frost. Onions tolerate light freezes, so earlier planting often produces larger bulbs.
In mild climates plant in fall, usually October to November, for overwintering. Check frost dates with your extension service or an online frost-date lookup, then mark planting windows on your calendar.
Quick tips, plant when soil is workable not frozen, and stagger sowings every two weeks for a steady supply of green onions.
Choose the Site and Prepare the Soil
If you’re asking how to plant onions? start with a spot that gets at least six to eight hours of direct sun, onions love full sun. Pick loose, loamy soil that drains well, because standing water causes rot.
Do a quick drainage test, dig a 12 inch hole and fill it with water, if it drains within one to two hours drainage is good. If not, build a raised bed or add coarse compost to improve structure.
Get a soil test from your local extension or use a home kit, target pH 6.0 to 7.0. Add garden lime to raise pH or elemental sulfur to lower it, only as the test recommends.
Work in two to three inches of compost, and loosen the soil to eight to twelve inches. For fertility add a small spoonful of bone meal or a balanced fertilizer at planting, avoid fresh manure. These tweaks give onions the loose, fertile soil they need to form large bulbs.
Three Planting Methods Explained
Seeds, sets, transplants, each has a clear playbook. Here is how to plant onions step by step, with pros and cons and when to choose each.
Seeds: Start indoors 8 to 10 weeks before your last frost, sow thinly 1 4 inch deep, keep soil moist and bright. Harden off, then transplant when seedlings have 4 to 6 leaves. Pros, cheapest and widest variety choice. Cons, slow and needs more care. Use seeds if you want unusual varieties or fall planting.
Sets: Plant in early spring, pointy end up, 1 to 2 inches deep, 4 inches apart. Pros, fastest way to get bulbs and low skill required. Cons, sets often produce smaller bulbs and limited variety. Use sets for quick spring harvests.
Transplants: Buy or grow seedlings and move them once they are sturdy. Plant 2 to 4 inches apart in fertile, well drained soil. Pros, reliable bulb size and timing, less chance of bolting. Cons, higher cost than sets. Use transplants for consistent results.
Planting Depth, Spacing, and Row Layout
If you ask how to plant onions, follow these exact measures. Plant sets about 1 inch deep, with 4 inches between plants; for transplants set the top of the root ball 1/2 inch below soil, 4 inches apart. For bulb production thin to 6 to 8 inches between final plants. Bunching onions can sit 1 to 2 inches apart. Space rows 10 to 12 inches apart in small beds, 12 to 18 inches for larger rows. In a 4 by 4 raised bed run four rows 12 inches apart; in a long bed stagger plants in a zigzag to increase light. To maximize bulb size, loosen soil 10 to 12 inches deep, feed nitrogen until tops reach 6 inches, keep evenly watered, and thin early to reduce competition.
Watering and Feeding Onions for Big Bulbs
When wondering how to plant onions? think about water first. Aim for about 1 inch of water per week, more in hot, dry weather. Water deeply once or twice weekly so the top 2 inches of soil stay moist; shallow daily sprinkling makes small bulbs.
Watch the signs. Underwatering causes thin necks, tips that brown and curl, and premature bulbing. Overwatering shows yellowing tops, soggy or soft bulbs, and a rotten smell. Use a finger test to feel soil moisture.
Fertilize at planting, again three to four weeks in, and once when bulbs begin to swell. Use compost or well-rotted manure at planting, then a fish emulsion or blood meal for nitrogen early, and bone meal or kelp for phosphorus and potassium later. Organic and simple.
Common Pests, Diseases, and Quick Fixes
When you learn how to plant onions, expect a few predictable problems, mainly onion maggots, thrips, and fungal diseases like downy mildew or botrytis. Catching them early is key.
Pests, quick fixes: for onion maggots use floating row cover when seedlings emerge, remove old onion debris, and apply beneficial nematodes to soil at planting. For thrips use yellow sticky traps, spray insecticidal soap or neem oil every 7 to 10 days, and avoid excess nitrogen which attracts them.
Fungal issues, quick fixes: improve drainage with raised beds and compost, water at the base in the morning, space plants 4 to 6 inches for airflow, remove infected plants, and treat early with copper fungicide or Bordeaux mixture as organic options. Cure bulbs thoroughly before storage.
Harvesting, Curing, Storing, and Final Checklist
If you followed the steps for how to plant onions, finish strong by harvesting when most tops have fallen and the necks feel soft, usually late summer. Lift bulbs on a dry day, leave soil on them until curing to avoid cuts and rot.
Cure bulbs in direct sun for a few hours, then move to a warm, dry, well ventilated spot for 2 to 3 weeks until skins are papery and necks completely dry. Avoid stacking; spread them out or hang in mesh bags.
For long-term storage, trim tops to about 1 inch, do not wash, and store in mesh bags or crates in a cool, dark place around 32 to 40°F and moderate humidity. Check monthly and remove any soft bulbs.
Quick checklist
- Harvest when tops fall
- Sun dry then ventilate 2 to 3 weeks
- Trim to 1 inch, do not wash
- Store in mesh, cool and dark
- Inspect monthly
