Onion Growing Made Easy: How to Plant and Care for Any Variety

No vegetable is more universally loved than the onion, yet most people have never experienced what a homegrown one tastes like. Fresh onions are crisper, more flavorful, and far more satisfying than anything sitting in a grocery store.

Before you put a single bulb in the ground, let’s peel back what we’ll cover:

• Choosing seeds, sets, or transplants
• How to plant at the perfect depth
• Tips to cure bulbs for long storage
• Avoiding myths that cause rot

Let’s get started!

Step #1: Choose the Right Onion Variety

Onions are biennials, which means they live for two years. In the first year, you’ll get leaves and bulbs; in the second, you’ll see just flowers and seeds.

They are also photoperiodic, meaning they bulb based on total daylight hours. Once your garden receives a specific amount of daily sunlight, the plant stops producing new leaves and shifts all its energy into the bulb.

If you choose an onion variety with sunlight requirements that don’t match your local day length, your onions will either bulb too early and stay small or fail to bulb at all.

There are three day-length categories. Knowing which one applies to your region is the single most important decision you will make before buying a seed packet or transplant.

Onion Varieties and Their Sunlight Needs

• Short-Day Onions: These onions bulb with 10 to 12 hours of daylight. They are best for southern regions; plant in fall or early spring and harvest before summer heat. Varieties include Texas Legend, Southern Bell, and Red Creole.

• Intermediate-Day Onions: These onions bulb with 12 to 14 hours of daylight, and they’re well-suited for Middle America gardeners between the two main zones. Varieties include Super Star, Candy, and Red Candy.

• Long-Day Onions: These onions require 14 to 16 hours of daylight to bulb. They’re ideal for northern gardeners in regions like the Pacific Northwest and upper Midwest. Varieties include Walla Walla, Highlander, and Red Zeppelin.

Growing other fruits and vegetables also requires picking the right varietal, learn how to choose the best tomatoes in our guide here.

4 Main Onion Colors and Flavors

The onion variety you choose does impact the final flavor:

1. Yellow Onions: Pungent, sulfurous flavor.
2. Red Onions: Sharp and spicy when raw.
3. White Onions: Clean, sharp flavor.
4. Sweet Onions: Very mild and sweet.

How to Choose the Right Onions

1. Is your location best for short-day, intermediate-day, or long-day varieties?
2. Will you cook, store, or use your onions raw?
3. Purchase only onions labeled with variety names and day-length categories.

Step #2: Start With Seeds, Sets, or Transplants

Next, you’ll need to determine how you will start your onions.

There are three main methods, and each offers a unique balance of convenience, cost, variety selection, and final bulb size.

Start Onions From Seed

Starting from seed gives plants the most time to develop leaves before bulbing begins, which results in bigger bulbs.

You can easily find several varieties of onion seeds in seed displays or online. Then, follow these steps:

• Sow seeds 1/2 to 1-inch deep in trays, and keep the soil evenly moist.
• Thin seedlings when they reach about 3 inches tall.
• Transplant outside as soon as the soil can be worked.

Onion Transplants

Transplants are young onion plants that are sold by variety, so you can confirm day-length type, flavor profile, and storage quality before buying.

Transplants are generally easier than starting from seed and typically produce better bulbs than starting from sets. When selecting transplants, look for thin stems to avoid flowering.

Onion Sets

Sets are small dormant bulbs sold in mesh bags or cardboard boxes and are the fastest, most convenient way to start onions.

The trade-off is variety uncertainty. Sets are usually labeled only by color, which makes matching them to your day-length zone a gamble.

Tips and Tricks for Starting Onions

• For maximum bulb size, start seeds indoors 10 to 12 weeks before your last frost date.
• If buying transplants, use suppliers that label cultivars and day-length categories and certify plants are disease-free.
• If using sets, choose only the smallest and firmest bulbs, no larger than a dime in diameter.
• If you plan to grow green onions, you can use larger sets.

Step #3: Select and Prepare Your Planting Site

Onions are particular about two things: sunlight and soil. Get these right, and you’ve given your crop the foundation it needs to thrive.

Sunlight

Onions need a minimum of 6 to 8 hours of direct sunlight. Shaded onions consistently produce small, underdeveloped bulbs.

Early-season light is especially important because it powers leaf and root development. It also determines how large your bulbs will ultimately grow.

Strawberries, too, require at least 6 hours of sunlight. Read our guide and learn how to grow these sweet berries in addition to onions.

Soil

Well-drained, loose, fertile soil is essential for onions. Sandy loam or silt loam are ideal, but if you’re working with a different kind, most garden soils can be improved with the right amendments.

Onions have a shallow root system, so the nutrients they need must be available in the top layer of soil. This also means drainage, fertility, and soil structure all matter more for onions than most other vegetables.

Prepare the Soil and Choose a Planting Site

• Choose a spot that offers 6 to 8 hours of direct sunlight daily throughout the growing season.
• Conduct a soil test and aim for a pH between 6.0 and 7.0.
• If needed, amend soil with lime (to raise pH) or sulfur (to lower pH).
• Work 2 to 3 inches of organic matter into the top 6 to 8 inches of soil.

If your soil is heavy clay or slow to drain, use a raised bed. Additionally, you’ll want to avoid planting onions in any site with poor drainage, compaction, or a history of onion or garlic diseases.

Step #4: Plant at the Right Time and Depth

Onions are cold-hardy plants that actually benefit from an early start. Transplant onions right after your last frost or as early as your local climate safely allows.

Every extra week your onion plant grows and produces leaves before it forms a bulb contributes to a bigger onion at harvest.

If onion seedlings seem top-heavy, trimming the tops can help them stand upright.

Planting Depth

Planting depth is crucial because onions form bulbs at or just above the soil surface, not underground.

So, you should plant onions no deeper than the white shank at the base of the plant. Whether you are handling a small onion seedling or a larger green onion-type plant, you can usually see the white portion clearly.

Burying onions too deeply restricts bulb expansion and results in smaller bulbs. A shallower depth keeps the developing bulb in the right environment for airflow and drying, reducing disease risk.

How to Plant Onions Properly

1. Plant onions early in spring; don’t wait for warm weather.
2. Plant sets 1 inch deep with the pointed tip facing upward.
3. Plant transplants at the same depth they were growing.
4. Plant green onions or scallions from sets 1.5 to 2 inches deeper.
5. Space dry bulb onions 4 to 6 inches apart in rows spaced 12 to 18 inches apart.
6. Space green onions 1 to 2 inches apart.
7. In raised beds or wide rows, use a 4-inch grid to maximize yield without overcrowding.

Step #5: Water Onions Consistently

If possible, you should set up your watering system at planting time. Drip irrigation or soaker hoses should run along each row, placing water exactly where onions need it. (Plus, you won’t have to worry about displacing onions later with a hose.)

If you’re using a watering timer, adjust it to keep moisture steady rather than delivering occasional heavy soakings.

As your onions grow, make adjustments based on the weather. Increase the watering frequency during hot, dry periods; you can reduce or pause watering after steady rainfall. Avoid letting soil swing between soaked and very dry.

How to Properly Water Onions

1. Install drip lines or soaker hoses along each row at planting.
2. Monitor soil moisture regularly, checking 1 to 2 inches below the soil surface.
3. Maintain even moisture with light, consistent watering.
4. Add 2 to 3 inches of mulch to stabilize soil moisture and temperature.
5. Adjust watering based on rainfall and weather conditions.
6. Stop watering entirely when tops naturally yellow and fall over.

Step #6: Fertilize for a Better Harvest

Fertilization is one of the biggest drivers of onion size and overall crop success. Onions convert leaf growth directly into bulb development later in the season. So, if nutrients are insufficient early on, the plant produces fewer leaves, which affects bulb size.

Onions are unusually sensitive to nutrient timing. Excess nitrogen late in the season encourages leaf production when plants should transition into bulb finishing. This leads to bulbs that look mature but break down quickly in storage.

Step-by-Step Onion Fertilization

1. Add fertilizer once plants are actively growing.
2. Use a higher-nitrogen fertilizer (a 10-5-5 ratio) applied lightly and regularly.
3. Place fertilizer beside the row, a few inches away from the plants.
4. Water after each application to move nutrients into the root zone.
5. Monitor plants for yellow leaves or slow growth; adjust if needed.
6. Stop all nitrogen as soon as bulbs swell at the soil surface.

Step #7: Control Weeds, Pests, and Diseases

Weeds

Weeds can permanently stunt onion growth if left unmanaged even temporarily. Onions have shallow root systems and tall, thin tops, and weeds will compete against them for light, moisture, and nutrients.

Luckily, young weeds are easy to remove. Mature weeds with deep root systems, on the other hand, are far more disruptive to onions. During the first six weeks after planting, weeds will be the worst, but removal will be easiest.

When weeding, keep your hoe shallow. Onion roots are close to the surface, so going too deep will cause damage and crop delay.

If you’re concerned about onion or garlic pests and diseases, read our guide on growing garlic here.

Pests and Disease

There are three major pests and diseases that target the allium (onion) family that you should watch for:

1. Onion Thrips: Tiny, slender insects that create streaking on the leaves, followed by yellowing and browning.
2. Onion Maggots: Small fly larvae that feed on roots, then burrow into the base of bulbs, causing wilting and collapse.
3. White Rot: A disease that causes plants to collapse and “melt” at the base as a white, fluffy fungal growth appears on the bulb.

The most effective disease prevention strategy is crop rotation. Never plant onions, garlic, leeks, or any other allium crop in the same bed in consecutive years.

Bolting 

Bolting is an environmental issue that occurs when a plant stops bulb development and sends up a flower stalk.

Once bolting begins, it cannot be stopped, and the plant won’t produce a storable onion. Triggers include:

• Planting oversized sets
• Extreme cold or heat
• Inconsistent growing conditions

Neck Damage

There is a common myth that you should break the necks of your onions to speed up bulbing.

Not only does this not help bulbing, but it also damages the neck tissue, creating an entry point for rot fungi that destroys bulbs in storage.

How to Control Weeds, Pests, and Diseases

1. Purchase only certified disease-free sets and transplants.
2. Hand-pull or shallowly cultivate weeds every few days during the first six weeks.
3. Apply a 2- to 3-inch layer of mulch around onions to suppress weed germination.
4. Do not use chemical pre-emergents; it can inhibit development.
5. Inspect foliage weekly for signs of thrips, maggots, or fungal growth.
6. Install row covers at planting time if onion maggots have been a problem previously.
7. Rotate allium crops to a fresh bed every season, using a two- to three-year cycle.
8. Dispose of all diseased plant material immediately.

How to Harvest Onions

Pulling your onions at the wrong time, even if you’re just one or two weeks too early (or late), can decrease your final harvest.

Harvest onions too early, and you’ll wind up with undersized bulbs with thick, moist necks that won’t cure or store properly. Harvest too late, and you risk the outer skins cracking, splitting, or deteriorating in your garden.

However, onions will let you know when they’re ready. If you know what to look for, the signs are fairly clear and consistent.

Signs Onions Are Ready to Harvest

• 50 to 75 percent of the tops have fallen.
• Necks feel thin, soft, and pliable.
• Outer skin is dry and turning papery
• The shoulder of the bulb is visible without digging.

Begin monitoring tops daily once it’s been 90 to 100 days since planting (for sets) or 100 to 120 days (for seeds or transplants).

How to Lift and Harvest Bulbs

When it’s time to harvest onions, technique matters. You should:

• Grip the bulb near its base, not by the top.
• Gently pull upward, allowing the roots to release from the soil naturally.
• If bulbs resist, use a garden fork to loosen the ground a few inches away from the plant.
• Avoid using force, which can tear roots and bruise or crack bulbs.

Always Cure Onions Before Storing

Harvesting your very own onions is rewarding, but it’s not the finish line. Curing is critical if you intend to store your harvest long-term.

Curing gradually pulls moisture out of the neck, roots, and outer skin layers, allowing the onion to essentially seal itself. As moisture leaves the neck, tissue tightens, forming a natural barrier that locks out pathogens and slows internal breakdown. The outer skin layers dry into a papery protective wrapper.

Signs of Properly Cured Onions

• Completely dry, papery outer skin
• Firm, completely dry necks
• Shriveled, brittle, and wiry roots

When your bulbs display all three of these characteristics, they are ready for long-term storage.

Create the Perfect Curing Environment

To cure onions, they need the right environment. Temperature, airflow, and protection from rain and direct sun are the three variables you can control, and each one matters.

• Warm temperatures speed evaporation.
• Airflow carries evaporated moisture away so it doesn’t settle on bulbs.
• Shelter prevents new moisture from re-entering necks and skins.

Expert Tip: A box fan is great for airflow, as it speeds up drying and is especially valuable in humid climates.

How to Cure and Trim Onions

1. Move harvested onions to a warm, shaded, well-ventilated curing location immediately.
2. Spread bulbs in a single layer on screens or wire racks so air circulates freely around each one.
3. Protect from rain and sun while maintaining 80 to 90 degrees Fahrenheit to provide fast moisture removal.
4. Cure for a minimum of one to two weeks; humid or cool climates may require three or more weeks.
5. Test readiness by pinching each neck for complete dryness and hardness.
6. Check neck color, too; green necks need additional curing time.
7. Once fully cured, trim roots and cut tops down to 1 to 2 inches above the bulb.
8. Transfer to your storage area.

Storing Your Onions

Curing readies onions for storage, but there’s one more step to complete: sorting.

A bulb placed into storage with a flaw will deteriorate and spread rot to healthy bulbs. Sorting before storage can be the difference between onions that last six months or six weeks.

Examine every single bulb individually and divide your harvest into three groups:

1. Long-Term Storage: Bulbs are completely firm, outer skin is papery and dry, and necks are thin, sealed, and dry.
2. Use First: Necks are thick or slightly soft, skin is cracked, bruised, or has surface blemishes that break the outer skin.
3. Discard Immediately: Bulbs showing active mold, softness, or rot.

Storage Environment

Once sorted, onions need a cool, dry, and well-ventilated environment to stay dormant and resist mold. A root cellar or cool basement (32 to 40 degrees Fahrenheit) works well.

Avoid temperatures around 50 to 60 degrees Fahrenheit, as that is prime sprouting temperature.

Airflow is also critical, as trapped moisture will ruin even a perfectly cured onion. Never store onions in sealed plastic bags or containers. They trap moisture and can cause rot within days.

Onion Storage Tips

1. Mesh bags or crates allow the airflow that every bulb needs.
2. Soft-necked onions can be woven into hanging braids for excellent airflow and easy monitoring.
3. Keep onions away from potatoes, which release moisture that encourages onion rot.

Monitor Your Stored Onions

Storage is not a set-it-and-forget-it situation. You’ll need to check your stored onions every two to three weeks.

During these checks, remove any bulb that has softened, sprouted, or shown early signs of mold. If sprouting becomes widespread, move them all to a cooler location, or use them up quickly.

The main issue to watch for is neck rot, which appears as water-soaked, discolored tissue and then progresses into gray, moldy rot.

How Long Can Onions Be Stored?

Different onion varieties can survive in storage for various lengths of time. In general, the sulfur compounds that make onions taste sharp also act as natural preservatives, which is why pungent types store longer than sweet onions.

The milder the onion, the shorter its shelf life. Here’s how long common onion varieties can sit in storage:

• 3 to 12 Months: Copra, Stuttgarter, and Cortland

• 3 to 6 Months: Red Zeppelin and Redwing

• 2 to 4 Months: Candy and Super Star

• 1 to 3 Months: Walla Walla and Sweet Spanish

Final Advice

Producing flavorful, long-storing onions is a season-long project that rewards attention to detail.

The biggest influences on any onion harvest will come from planting depth, proper water and fertilizer, and waiting to harvest until onions are fully mature. Slight adjustments in these areas can make a major difference in bulb size and quality.

Follow these steps, and you’ll be reaching into a crate of firm, beautifully preserved onions well into winter.

Happy growing!