Onions are a versatile vegetable that add great flavor to many dishes. While they’re easy to find at the grocery store, growing onions yourself can be very rewarding. With some basic knowledge, you can plant and grow an abundant onion crop right in your own backyard. In this beginner’s complete growing guide, we’ll walk through every step of the process in detail.
Choosing the Best Onion Varieties
Many different onion varieties exist, each with their own characteristics. When starting out, consider planting a few different types to see which grow best in your specific climate and soil conditions.
Some of the most popular varieties to try include:
- Yellow onions – The classic all-purpose onion, medium day length
- White onions – Mild flavored, best for raw applications
- Red onions – Sharper flavor, don’t store as long as yellow
- Shallots – Delicate, onion-garlic flavor, easy to grow
- Sweet onions – Mild, sweet flavor, don’t store well
- Scallions – Harvested young for green onions
- Pearl onions – Miniature onions, perfect for pickling
Onions are classified by the length of day they need in order to properly bulb. It’s important to look for varieties suited to your latitude.
Day length types:
- Short day – Best suited for southern regions, need only 10-12 hours of daylight
- Intermediate day – Do well in mid-latitudes, ideal with 12-14 hours days
- Long day – Require 14+ hours of daylight, recommended for northern climates
When browsing seed catalogs or garden centers, pay close attention to each onion variety’s day length classification to ensure you select types that will thrive in your solar conditions. The seed packet or plant tag will specify “short day,” “intermediate day,” or “long day” to guide your choices.
If you are unsure of your latitude or daylight hours, you can look up zone-specific planting calendars online that will provide recommendations for onion varieties suited to your region. Onion seeds and sets sold locally will generally be targeted to appropriate day lengths as well.
When to Plant Onions
Onions grow best when planted in early spring once the soil has thawed and can be worked. Planting in spring gives onions time to establish themselves before summer heat arrives.
In most regions, plan to plant onions 4-6 weeks before your anticipated last spring frost date. Onions are quite hardy and can withstand cooler temperatures and light frosts, so they can usually be planted a few weeks earlier than more cold-sensitive vegetables.
If starting onions from seeds, you’ll want to begin seeds indoors approximately 10-12 weeks prior to your target outdoor transplant date. Onion seeds require some time under grow lights or on a bright windowsill before they will be ready to transplant into the garden bed.
The optimal soil temperature range for planting onions is 45-60°F. Use a soil thermometer to check the temperature at planting depth and delay planting if soils are still too cold.
Onions take 80-120 days to reach maturity depending on the variety, so factor in days to maturity when deciding planting dates as well. You want to be sure to plant early enough so onions have time to fully develop before your first fall frost arrives.
Preparing the Garden Bed
Onions require loose, fertile soil with excellent drainage to grow their best. Dense, heavy, or compacted soil will inhibit proper bulb formation and increase the risk of rot during growth.
Take time to prepare the onion planting area by:
- Loosening the top 12 inches of soil completely using a shovel, garden fork, or rototiller
- Mixing in 2-4 inches of high-quality compost, rotted manure, or other organic matter
- Raking the bed smooth and removing any rocks, clumps, or debris
- Forming raised planting rows/beds to improve drainage
Test your soil pH and make any necessary amendments to bring the pH into the ideal range of 6.0-6.8. Onions prefer slightly acidic soil. Use lime to raise pH or sulfur to lower pH based on soil test results.
By taking the time to create the optimal growing conditions in your onion bed, you will set your crop up for success right from the start.
How to Plant Onion Sets or Transplants
Most home gardeners find it simplest to purchase onion transplants or sets from their local nursery or garden center. Sets are essentially miniature onion bulbs, while transplants are onion seedlings that were started ahead of time indoors under controlled conditions.
Here is a step-by-step guide to planting onion sets or transplants in your garden:
- Separate sets or transplant clumps into individual plants first. Be gentle with onion roots when separating transplants.
- Use your finger or a pencil to poke 1-2 inch deep holes in the prepared soil where you want onions planted. Space holes 3-4 inches apart.
- Drop one onion set or transplant into each hole. Pat soil gently around each onion to eliminate any air pockets.
- Arrange onions in rows 12-18 inches apart to allow ample room for growth and bulb swelling.
- After planting all onion sets/transplants, water well to soak soil and help establish roots.
- Consider constructing a floating row cover over planted onions to protect from pests. Secure cover and allow airflow along the edges.
Growing Onions from Seeds
While onion sets or transplants provide a quick and easy path to onions, you can also grow onions successfully starting from seed. Growing from seed takes more time and practice, but allows you to choose from a wider variety of onion types.
Follow these tips for the best results raising onions from seeds:
- Start seeds indoors 6-8 weeks before your target outdoor transplanting date. Fill starter trays or cells with high quality seed starting mix.
- Sow seeds approximately 1/4 inch deep and keep consistently moist until sprouts emerge.
- Place seeded trays on a propagating mat or near a radiator for bottom heat around 70°F which aids germination.
- Once sprouts emerge, move to a sunny window or under-grown lights on a 14 hour daily light cycle.
- Water carefully to keep soil moist but not saturated. Use fans for air circulation.
- Transplant onion seedlings into garden 4-6 weeks before your expected last spring frost.
- Harden off seedlings before transplanting by setting them outdoors in partial shade for a few days.
- Space transplants 4-5 inches apart in rows 12 inches apart. Handle seedlings gently with their leaves to avoid damaging the fragile root systems.
Caring for Growing Onions
Proper watering, nutrition, and pest protection during the growing season are vital to achieve maximum onion size and yield. Here are some tips for caring for your crop:
- Water – Onions require consistent moisture, about 1-2 inches per week. More watering may be needed in hot weather. Use drip irrigation or direct water at the soil base to avoid wetting bulb neck and foliage.
- Fertilize – Side dress growing onions monthly with a balanced vegetable fertilizer or compost tea to provide essential nutrients.
- Weed & Mulch – Keep beds free of weeds, being careful not to damage onion roots when weeding. Apply 2-3 inches of straw or shredded leaves to retain moisture and reduce weeds. Replenish mulch as needed.
- Support – As bulbs enlarge, use a hoe to gently pull soil up around the onion leaves, covering the bottom 2/3 of each bulb. This supports and branches the bulbs.
- Pests – Floating row covers can protect onions from maggot flies and other pests. Remove covers when plants start to flower for pollination.
Troubleshooting Common Onion Problems
While onions are not difficult to grow, they can encounter a few potential pest and disease issues:
- Thrips – Tiny black or yellow insects that feed on leaves. Knock off with blasts of water or use insecticidal soap sprays.
- Onion maggots – White larvae that burrow into developing bulbs, creating rot. Prevent by using row cover fabric.
- Downy mildew – Fluffy white fungal growth on leaves in cool, damp weather. Improve air circulation and avoid wetting foliage.
- Neck/stalk rot – Fungal disease causes onions to decay in storage, beginning at the neck. Promote air flow and cure bulbs well after harvest.
- Bolting – Premature seed stalk formation. Caused by cold weather or sowing the wrong daylength variety for your region.
Practicing crop rotation from year to year and choosing disease-resistant varieties can help minimize onion problems. Proper curing of bulbs after harvest is also critical.
Harvesting Onions at Peak Flavor
Onions reach maturity and full size around 100-120 days after sowing seeds or setting transplants. Older varieties may take a bit longer.
There are some telltale signs that onions are ready for harvesting:
- Tops turn yellow and fall over
- Above ground foliage dies back
- Bulbs feel firm and solid when gently squeezed through soil
Follow these steps for harvesting onions:
- Use a digging fork to loosen soil and lift bulbs, trying not to nick or slice them
- Gently brush off any loose soil, but don’t wash bulbs yet
- Spread harvested onions in a single layer in a warm, well-ventilated space for curing
- Allow 1-2 weeks curing until outer skins and neck are completely dry
- Clip off dried roots and trim back tops to 1 inch after curing
Curing helps form papery protective skins and ready onions for storage. Proper curing also prevents mold growth and bacterial infections.
Storing Onions for Year-Round Use
Onions can be stored for 2-6 months if properly cured and kept in optimal conditions:
- Ideal storage temperature is 40-50°F – a cold cellar or basement is perfect
- Place cured onions in mesh bags or open crates to allow air flow
- Check onions regularly and remove any that are damp, moldy, or show signs of rot
- Sweet onion varieties have a shorter shelf life than more pungent types
Well-cured dry onions with intact skins will keep the longest in storage. Avoid refrigerating onions which convert their starches into sugars and shortens their shelf life.
Enjoying Your Onion Bounty
Homegrown onions are delicious and can be used in so many ways:
- Caramelize and add pizzas, pastas, salads, dressings, dips
- Saute onions as the flavor base for many savory dishes
- Roast or grill whole onions as a side dish
- Pickle red onions for topping tacos, burgers, sandwiches
- Bake onion into casseroles, quiches, frittatas
- Add diced onions to soups, stews, chili, beans
With this complete growing guide, you now have all the information needed to successfully plant, grow, and harvest onions right at home. There’s nothing quite like the sweet, pungent flavor of fresh onions pulled from your own backyard garden.