How to Grow Onions? A Practical Step by Step Guide for Beginners and Intermediates

Introduction: Why growing onions is easier than you think

Wondering how to grow onions? You can do it in a small backyard bed, a container on a balcony, or a sunny windowsill. Homegrown onions taste fresher, store for months, and cost a fraction of grocery store bulbs. They also let you pick sweet Vidalia types or sharp red varieties for salsa and salads.

This guide walks you through choosing varieties, prepping soil, planting sets or seeds, watering and feeding, thinning, and timing for harvest and curing so your onions keep well.

Onion types and when to plant

When learning how to grow onions, choose the right type first. Bulb onions form a rounded storage bulb, think Walla Walla or Candy, they store for months. Green onions, or scallions, are harvested young for tops and need less space and time.

Decide sets versus seeds. Sets are small bulbs, plantable now, they save time but give fewer cultivar choices and higher bolt risk. Seeds take longer, give more variety control; start seeds 8 to 10 weeks before transplant. Plant sets about 1 inch deep and 4 inches apart; seedlings transplant deeper, keeping necks above soil.

Match daylength to your climate. Short-day varieties suit mild southern winters, plant in fall. Intermediate varieties work in transitional zones, plant late winter. Long-day types need long summer days, plant early spring in northern areas.

Planning your crop and choosing the right variety for your climate

Match onion varieties to your growing zone by day length, not taste. Long-day varieties like Walla Walla suit northern climates with long summer days, short-day or Bermuda types work best in southern zones, and day-neutral types fit the middle bands. Check your USDA zone, then choose accordingly.

Decide plant quantity with use in mind. Plan 10 to 20 mature bulbs per person per year, more if you like pickling. Spacing matters, for bunching onions space about 4 inches, for storage onions space 6 inches. A 10 foot row at 4 inches yields roughly 30 plants.

Make a simple planting calendar. Zone 4 to 7, start seeds indoors 10 to 12 weeks before last frost, transplant in spring. Zone 8 to 11, plant sets or transplants in fall or early winter, harvest in late spring.

Preparing soil and site for big bulbs

Start with a soil test, either a DIY kit or your county extension, so you know pH and nutrient levels. Onions prefer pH between 6.0 and 7.0; if your soil is acidic add lime according to the test, if too alkaline use elemental sulfur.

Aim for loose, well draining soil. Onions have shallow roots, so loosen the top 8 inches and avoid compacted clay; if drainage is poor build raised beds 8 to 10 inches high and mix in coarse sand or grit with topsoil.

Work in 2 inches of compost and a handful of bone meal or rock phosphate for big bulbs, save high nitrogen fertilizers for early growth. For large storage onions space transplants 6 to 8 inches apart, rows 12 inches apart, then mulch 1 to 2 inches to retain moisture and suppress weeds.

Planting, step by step

Searching for how to grow onions? Follow this step by step plan.

1. Sowing seeds, indoors: start 8 to 10 weeks before your last frost. Sow 1 4 inch deep, thin to 1 inch between plants in flats. Keep soil moist, bright, and 60 to 70°F.
2. Transplanting seedlings: move seedlings when they are pencil thick, usually 4 to 6 weeks after sowing. Plant at same soil depth as in the tray, firm the soil, water well.
3. Setting onion sets: press sets 1 inch deep so the top of the bulblet is even with the soil surface.
4. Spacing: for bunching onions plant 2 to 3 inches apart. For medium bulbs use 4 to 6 inches. For large storage onions use 6 to 8 inches, rows 12 to 18 inches apart.
5. Starter fertilizer: mix a balanced 10 10 10 into the planting row, about 1 to 2 pounds per 100 square feet, then side dress with a high nitrogen feed three weeks after transplant.

Watering, feeding and routine care during the season

When learning how to grow onions, consistent water and timely feeding make the biggest difference for bulb size. Water deeply once a week, aiming for about one inch of moisture, increase to twice weekly during heat waves, and always water in the morning. Use drip irrigation or a soaker hose to keep foliage dry and reduce disease.

Fertilize for growth early, then cut back for bulbing. At planting work in compost, then side-dress with a high nitrogen fertilizer when tops reach 6 inches, repeat every 3 weeks for the first 6 weeks. Stop heavy feeding once bulbs start swelling.

Thin seedlings to final spacing early, 4 inches apart for medium bulbs, 6 inches for large varieties; snip extra plants at soil level to avoid root disturbance.

Mulch with 2 to 3 inches of straw or shredded leaves after establishment to conserve moisture, suppress weeds, and increase bulb size. Remove heavy mulch late in the season if soil stays cool.

Common pests and diseases and how to manage them

If you ask how to grow onions? spot problems early. Onion maggot larvae eat roots, thrips strip leaves, and fungal issues include botrytis, downy mildew and neck rot.

Organic control works. Use float row covers to block maggots, rotate crops for three years, and dust diatomaceous earth around plants. Hang yellow sticky traps and spray neem oil or insecticidal soap at first sign, or use spinosad for heavy infestations. For fungi, improve drainage, water at the base, increase spacing for airflow, remove infected plants, cure bulbs for storage.

Harvesting, curing and storing onions the right way

The cue to harvest is simple, watch the tops. When about 50 to 70 percent of the green tops have fallen over and the necks feel soft, the bulbs are mature. For green onions harvest earlier, for storage varieties wait until tops collapse and outer skins turn papery.

1. Stop watering 7 to 10 days before harvest to help necks dry.
2. Loosen soil and lift bulbs gently by hand or fork, avoid damaging skins.
3. Brush off clinging soil, do not wash.
4. Cure in a dry, well-ventilated spot out of direct afternoon sun for 2 to 3 days, then move to a cooler airy area for 2 to 3 weeks.
5. After curing trim roots and cut tops to about 1 inch.

For long term storage keep cured onions in mesh bags or slatted crates, at roughly 32 to 40 degrees Fahrenheit, moderate humidity, and away from potatoes to prevent rot.

Troubleshooting common problems

If you’re wondering how to grow onions? Quick diagnostics with action steps.

• Small bulbs: usually overcrowding, too much nitrogen, or wrong day-length. Thin to 4 to 6 inches for bunching, 6 to 8 inches for storage, stop high-nitrogen feed when tops begin to swell, pick a long-day or short-day variety for your region.

• Bolting: caused by cold shock or stress. Cut stalks early, mulch to stabilize soil, avoid late transplanting.

• Poor germination: use fresh seed, keep soil 60 to 70°F, cover lightly, keep evenly moist.

• Rot: improve drainage, reduce overhead water, rotate crops, discard infected bulbs.

Conclusion and a one page checklist to get started

You now know how to grow onions? Here is a tight summary of the core steps you can actually follow this season. Pick the right variety for your day length, prep loose fertile soil, plant sets or transplants at the right depth and spacing, keep plants evenly watered, feed with nitrogen early, weed often, watch for pests, then harvest and cure for storage.

One page checklist to get started

• Choose variety by day length, short-day for southern regions, long-day for northern regions.
• Test soil, aim for pH 6.0 to 7.0, add compost and a handful of balanced granular fertilizer per 10 sq ft.
• Plant timing, when soil reaches 40 to 50°F; set depth about 1 inch, spacing 4 to 6 inches in rows 12 to 18 inches apart.
• Water schedule, 1 inch per week total, more during bulb swell; keep soil consistently moist.
• Feed, side-dress with a nitrogen source 3 to 4 weeks after planting, repeat monthly until bulbs form.
• Mulch 2 inches to suppress weeds and conserve moisture.
• Pest control, rotate crops, use floating row cover for onion maggot, scout for thrips.
• Harvest when tops flop, cure in dry shade 1 to 2 weeks, trim and store cool and dry.

Start small, take notes, and treat your first season like a test plot; you will improve every year.