Onions (Allium cepa) are a kitchen staple and surprisingly easy to cultivate at home. Whether you’re growing them from seed, sets (small bulbs), or transplants (starts), you can enjoy fresh, flavorful onions in just a few months. This beginner-friendly guide covers everything you need to know—from choosing the right type and planting method, to care, harvest, curing, and storage. Ideal for container gardens, raised beds, or backyard plots.
1. Types of Onions & When to Plant
Onions fall into three main types:
Short-Day Onions
- Require 10–12 hours of daylight to bulb.
- Best for regions with mild winters (US Zones 7–10).
- Varieties: ‘Texas SuperSweet’, ‘White Bermuda’, ‘Yellow Sweet Spanish’.
Long-Day Onions
- Require 14–16 hours of daylight.
- Ideal in northern regions (US Zones 3–6).
- Varieties: ‘Walla Walla’, ‘Yellow Sweet Spanish’, ‘Red Wing’.
Intermediate-Day Onions
- Suitable for mid-latitudes.
- Clear-weather adaptable.
- Varieties: ‘Candy’, ‘Copra’.
You can start from:
- Seeds: cheapest and widest choice; takes longer (~120–150 days).
- Sets: small bulbs; faster (~90 days) but limited varieties.
- Transplants: nursery-grown seedlings; good compromise.
☀️ In mild climates, plant in late fall or early winter. In colder zones, plant onion sets or starts in early spring as soon as soil is workable.
2. Planning & Soil Preparation
Sunlight & Site
- Onions need full sun (minimum 6-8 hours daily).
- Avoid shaded areas—bulbing depends on light intensity.
Soil Requirements
- Well-draining, loose soil is essential.
- pH between 6.0–7.0.
- Before planting, work in:
- Compost or well-rotted manure (2–4 inches).
- Balanced organic fertilizer (e.g., 5-10-10) or bone meal.
Raised beds help improve drainage and ease harvest. Containers should be at least 6–8 inches deep and wide enough to hold clumps of onions spaced as needed.
Timing Summary:
- Long‑day: plant March–May.
- Short‑day: fall planting in early winter regions.
- Succession plan by staggering planting every 2–3 weeks for longer harvest window.
3. Planting Onions
From Seeds
- Start 8–12 weeks before last frost in trays.
- Sow ~¼ inch deep, spacing 1 inch apart.
- Thin or transplant seedlings after 4–6 leaves emerge.
From Sets
- Press sets just below soil surface (~1 inch deep).
- Space sets 4–6 inches apart in rows 12 inches apart.
From Transplants
- Space transplants 4–5 inches apart; plant up to soil level of original pot.
- Firm soil gently and water in thoroughly.
Water Immediately
- After planting, water deeply to settle soil and promote root growth.
- Mulch with straw or compost to conserve moisture and suppress weeds.
4. Watering & Feeding
Watering
- Onions need 1 inch of water per week, more in hot/dry weather.
- Water directly at soil, avoiding damp foliage to reduce disease.
- In containers: adjust frequency as soil dries more rapidly.
Feeding
- Side-dress plants with compost tea or organic fertilizer every 3–4 weeks.
- High nitrogen early promotes green leaf growth, but reduce nitrogen once bulbs form to avoid soft necks.
Mulching
- Mulch with straw or shredded leaves to retain moisture and moderate soil temperature.
- Helps suppress weeds and keep bulbs tidy.
5. Support, Weeding & Common Care
- Onions don’t require support structures, but need consistently clean beds.
- Weed carefully to avoid disturbing shallow roots—hand pull or use weeding tool.
- Remove any yellowing, limp leaves promptly.
- Early removal of weeds helps avoid competition for nutrients and moisture.
6. Milestone Growth & Bulb Formation
- As day length increases (or temperature rises), bulbs begin to swell.
- Green tops may fall over or turn yellow—a sign bulbs are nearing maturity.
- Fertilize lightly one last time at first sign of bulbing.
- Stop high watering when tops flop to help dry out necks for curing.
7. Harvesting, Curing & Storage
Harvest Time
- Harvest onions 2–3 weeks after tops fall over and begin to yellow.
- On dry days, gently lift bulbs with a fork to avoid bruising.
Curing Process
- Lay bulbs in a single layer in a dry, well-ventilated area (shed, garage, porch).
- Allow them to cure for 2–3 weeks until outer skins are papery and necks dry.
- Trim roots and cut tops to 1–2 inches (or retain foliage for braiding softneck types).
- Brush off soil; do not wash onions before storage.
Storage Conditions
- Store in cool, dry, well-aerated place (55–60°F or 13–15°C).
- Mesh bags, hanging braids, or slotted baskets work well.
- Long‑term storage onions (softneck types) will keep 6–9 months; hardneck keep 4–6 months.
8. Pests, Diseases & Troubleshooting
Common Pests
- Onion maggots: lay eggs at base; use row covers early, rotate planting annually.
- Thrips: tiny pests feeding on leaves; control with neem oil, avoid planting near other alliums.
- Cutworms: can sever young seedlings—use collars around new transplants.
Common Diseases
- Downy mildew: fuzzy leaf mold; ensure good airflow, water early, remove infected leaves.
- Purple blotch: dark lesions on leaves; mitigate with crop rotation and disease-resistant varieties.
- Neck rot: post-harvest fungal decay—cure thoroughly and avoid neck moisture.
Preventive Measures
- Rotate on onion family crops every 3 years.
- Clean gardening tools and containers between use.
- Intercrop with herbs like garlic or chamomile to deter pests.
9. Container Growing Tips
- Use large containers holding 4–6 sets or transplants in one planter.
- Must be well-draining and deep (8 inches or more).
- Maintain consistent soil moisture until tops bend.
- Containers heat up faster: water slightly more during heat.
- Cure harvested bulbs outside, trimming tops after curing.
Container onions can give satisfying harvests even in urban gardens or balconies.
10. Using Homegrown Onions & Culinary Ideas
- Use freshly harvested bulbs in sauces, sautés, soups, and salads.
- Pickled onions are excellent long-term storage and flavor.
- Store cured garlic and onions separately—protect flavors and avoid cross-sprouting.
- Make onion-infused oils or roast bulbs for a mellow, sweet taste.
Final Thoughts
Growing onions at home is incredibly rewarding: the plants are hardy, versatile, and supply your kitchen with fresh, high-quality flavor. From seeds or sets to harvest and cure, homegrown onions add satisfying depth to meals and reduce waste. With proper spacing, watering, and care, your onion patch or container will flourish each season. And once you experience growing your own onions, store-bought versions will never taste the same.