Onions are one of the most useful vegetables you can grow at home. They can be added to soups, sauces, stir-fries, salads, roasted vegetables, and countless everyday meals.

They are also surprisingly versatile in the garden.

You can grow onions for:

• Large storage bulbs
• Fresh green onions
• Small bunching onions
• Mild sweet onions
• Strong cooking onions

Although onions are not especially difficult to grow, they do require good timing. The variety you choose, the length of your growing season, and the amount of daylight your garden receives all affect whether your plants form large bulbs.

In my Maryland Zone 7 garden, I have grown onions from seeds and sets, including Texas Grano and other bulbing varieties. Onions take time, but watching the small seedlings slowly develop into full-sized bulbs is incredibly rewarding.

Here is everything you need to know about how to grow onions successfully.

Understanding How Onions Grow

Onions are biennial plants, although gardeners usually grow them as annual vegetables.

During the first growing season, the plant produces leaves and forms a bulb. If it survives winter and continues growing into its second year, it may produce a flower stalk and seeds.

Each green onion leaf corresponds to a layer inside the developing bulb. Healthy leaf growth early in the season is therefore important for producing a larger onion later.

Onions begin forming bulbs in response to day length. That means choosing the right onion type for your location is one of the most important parts of growing them successfully.

Choose the Right Onion for Your Day Length

Onions are generally divided into three groups:

Short-Day Onions

Short-day onions begin forming bulbs when daylight reaches approximately 10 to 12 hours.

They are best suited to southern regions with mild winters.

Examples may include:

• Texas Grano
• Red Grano
• Merlin
• Vidalia
• Red Rock
• Red Creole
• Cipollini Yellow

Short-day onions are often planted in fall or winter in warm climates and harvested in spring or early summer.

Intermediate-Day Onions

Intermediate-day onions begin bulbing when daylight reaches approximately 12 to 14 hours.

They perform well in the central portion of the United States and can also grow successfully in parts of Zone 7.

Examples may include:

• Candy
• Avalon
• Scout
• Red Candy Apple
• Super Star

Long-Day Onions

Long-day onions begin forming bulbs when daylight reaches approximately 14 to 16 hours.

They are best suited to northern regions with long summer days.

Examples may include:

• Walla Walla
• Caliber
• Ruby
• White Spanish
• Yellow Spanish
• Purple Haze
• Patterson
• Copra
• Red Wing

Choosing the wrong type may result in small bulbs, even when the plants otherwise appear healthy.

Should You Grow Onions from Seeds, Sets, or Transplants?

Onions can be started in several ways.

Each method has advantages and disadvantages.

Growing Onions from Seeds

Starting onions from seed gives you the widest selection of varieties.

It is also usually the least expensive option when growing many plants.

Advantages include:

• More variety choices
• Lower cost per plant
• Greater control over plant health
• Reduced risk of premature flowering compared with large sets

The main disadvantage is that onion seedlings grow slowly and must often be started indoors several months before planting outside.

In Zone 7, onion seeds are commonly started indoors in winter, often from January through February, depending on the variety and local conditions.

Growing Onions from Sets

Onion sets are small, dormant bulbs produced during the previous season.

They are convenient and easy to plant, making them popular among beginner gardeners.

Advantages include:

• Easy planting
• Quick early growth
• No indoor seed-starting setup required

However, larger sets are sometimes more likely to bolt or produce flower stalks. Sets also provide fewer variety choices than seeds.

Choose small, firm sets rather than the largest ones for better bulb production.

Larger sets can still be useful when growing green onions.

Growing Onions from Transplants

Onion transplants are young seedlings sold in bundles or small containers.

They offer a convenient middle ground between seeds and sets.

Advantages include:

• Faster than starting from seed
• More reliable bulbing than large sets
• Less indoor work
• Good variety selection from specialty growers

Transplants should be planted soon after purchase so their roots do not dry out.

When to Plant Onions

Onions are cool-season vegetables that tolerate chilly weather.

They are generally planted outdoors several weeks before the average last spring frost.

In Zone 7, onion transplants and sets are often planted from late winter through early spring, depending on soil conditions and the weather.

The soil should be workable rather than frozen, waterlogged, or extremely muddy.

Onion seedlings tolerate cool temperatures, but newly planted onions may still benefit from protection during severe cold snaps.

In warmer regions, short-day onions are often planted in fall and grown through winter.

How to Start Onion Seeds Indoors

Onion seeds should be started early because the seedlings grow slowly.

What you need

• Onion seeds (always use fresh seeds)
• Seed-starting mix
• Shallow trays or containers
• Grow lights
• Water
• Labels

Steps

1. Fill the container with moist seed-starting mix.
2. Sow the seeds approximately ¼ inch deep.
3. Space them closely because onions tolerate growing together while young.
4. Keep the mix moist but not saturated.
5. Place the seedlings under strong grow lights after germination.
6. Trim the tops if they become excessively tall and floppy.
7. Harden the seedlings off before transplanting them outdoors.

Onion seeds often lose viability faster than some other vegetable seeds. For better germination, use relatively fresh seed.

How to Prepare the Soil for Onions

Onions grow best in loose, fertile, well-drained soil.

Heavy, compacted soil can restrict bulb development and make harvesting more difficult.

Before planting:

1. Remove weeds and old roots.
2. Loosen the top several inches of soil.
3. Add finished compost.
4. Break apart large clumps.
5. Level the planting area.

The ideal soil pH for onions is generally slightly acidic to neutral.

Raised beds can work especially well because they offer improved drainage and loose soil for bulb expansion.

Avoid planting onions in an area that stays constantly wet. Excess moisture can contribute to root and bulb rot.

How Much Sun Do Onions Need?

Bulbing onions grow best in full sun.

Provide at least six hours of direct sunlight each day, although eight or more hours is preferable.

Plants grown in too much shade may produce healthy green tops but small bulbs.

Green onions are somewhat more tolerant of partial shade because they are harvested before developing large bulbs.

How to Plant Onion Sets

Plant onion sets with the pointed end facing upward and the root end facing downward.

Place them approximately 1 inch deep, with the tip close to or slightly above the soil surface.

Do not bury onion sets too deeply. Deep planting can interfere with bulb formation.

Space sets approximately:

• 1 to 2 inches apart for green onions
• 4 to 6 inches apart for full-sized bulbs

Rows may be spaced around 12 to 18 inches apart, depending on the garden layout.

How to Plant Onion Transplants

Separate the seedlings gently if they arrive in a bundle.

Trim damaged roots if necessary, but avoid removing healthy roots unnecessarily.

Plant each seedling so the root system is covered while the base of the leaves remains close to the soil surface.

Avoid burying the stem deeply.

Space transplants approximately 4 to 6 inches apart for large bulbs.

Closer spacing produces smaller onions, while wider spacing allows more room for bulb development.

Growing Green Onions

Green onions are one of the easiest forms of onion to grow.

They can be grown from:

• Seeds
• Sets
• Transplants
• Bunching onion varieties

Plant them approximately 1 to 2 inches apart and harvest them whenever the stems reach a useful size.

Because green onions do not need to form large bulbs, they are ideal for:

• Containers
• Raised beds
• Small gardens
• Bed edges
• Succession planting

You can sow a small amount every few weeks for continuous harvests.

Watering Onions

Onions have relatively shallow root systems, so they need consistent moisture.

Provide approximately 1 inch of water per week, adjusting for rainfall, temperature, soil type, and container conditions.

The soil should stay evenly moist but not soggy.

Irregular watering may contribute to:

• Small bulbs
• Slow growth
• Split bulbs
• Stress
• Premature decline

Water near the soil rather than repeatedly wetting the leaves.

As the bulbs approach maturity and the tops begin falling over naturally, reduce watering. Excessive moisture near harvest can increase the risk of rot and shorten storage life.

Should You Mulch Onions?

A light layer of mulch can be helpful.

Mulch can:

• Conserve soil moisture
• Reduce weeds
• Moderate soil temperature
• Prevent soil crusting

However, avoid piling thick, wet mulch directly against developing bulbs.

As bulbs enlarge, their shoulders may become visible above the soil. This is normal. Do not cover the exposed bulb with additional soil.

Fertilizing Onions

Onions need adequate nutrients to produce healthy leaves and large bulbs.

Before planting, amend the soil with compost and, if needed, a balanced fertilizer or a bone meal.

Nitrogen supports leafy growth early in the season. However, too much nitrogen later can delay maturity and produce excessive foliage instead of well-finished bulbs.

A practical approach is to:

• Improve the soil before planting.
• Feed lightly during early active growth.
• Stop high-nitrogen feeding once bulbing begins.

Always follow the application instructions for the fertilizer you use.

Do not place concentrated fertilizer directly against the roots or bulbs.

Keep Onion Beds Free of Weeds

Onions do not compete well with weeds.

Their upright leaves create very little shade, allowing weeds to grow easily around them.

Weeds compete for:

• Moisture
• Nutrients
• Sunlight
• Growing space

Pull weeds while they are still small. Work carefully because onion roots grow close to the soil surface and can be damaged by deep cultivation.

Mulch can help reduce the amount of weeding required.

When Do Onions Start Forming Bulbs?

Bulbing begins when the plant receives the appropriate number of daylight hours for its type.

Before bulbing, onions focus on producing leaves and roots.

Once the necessary day length is reached, the base of the plant begins swelling.

This is why early leaf growth matters so much. The more healthy leaves the plant produces before bulbing begins, the greater its potential to form a large onion.

A plant that is stressed, stunted, or planted too late may begin bulbing while still small.

Why Are My Onion Bulbs Small?

Small onions may result from several factors.

Common causes include:

• Planting the wrong day-length variety
• Planting too late
• Insufficient sunlight
• Crowded spacing
• Inconsistent watering
• Poor soil fertility
• Heavy weed competition
• Transplant stress
• Early pest or disease damage

Small onions are still edible. However, improving the timing, variety selection, and early growth conditions can lead to larger bulbs in future seasons.

Should You Remove Onion Flowers?

An onion that produces a flower stalk is called a bolting onion.

Bolting may be triggered when a plant experiences certain temperature fluctuations and then interprets the conditions as a second growing season.

Large onion sets may also be more prone to bolting.

Once an onion bolts, the bulb usually does not store as well.

You can remove the flower stalk, but this will not reverse the plant’s internal change.

Harvest bolted onions early and use them first rather than placing them into long-term storage.

Common Onion Pests

Onion pests vary by region, but several may cause problems.

Onion Thrips

Thrips are tiny insects that feed on the leaves.

Damage may appear as:

• Silvery streaks
• Pale patches
• Distorted foliage
• Reduced growth

Inspect plants regularly, especially during dry weather.

Onion Maggots

Onion maggot larvae feed on roots and bulbs.

Affected plants may wilt, yellow, or collapse.

Crop rotation and sanitation can help reduce recurring problems.

Allium Leaf Miners

Allium leaf miners can damage onions, garlic, leeks, and related crops.

Signs may include:

• Rows of small feeding marks
• Distorted leaves
• Tunneling
• Damage inside stems or bulbs

Insect netting applied before the adult flies become active can help protect allium crops.

Remove badly infested plant material rather than leaving it in the bed.

Common Onion Diseases

Onions may develop fungal or bacterial diseases, especially in wet or poorly drained conditions.

Possible problems include:

• Downy mildew
• Neck rot
• White rot
• Botrytis
• Bacterial soft rot

Reduce disease risk by:

• Providing good airflow
• Avoiding overwatering
• Rotating crops
• Using clean planting material
• Removing infected plants
• Allowing bulbs to cure thoroughly

Avoid storing onions that are bruised, soft, damaged, or diseased.

When Are Onions Ready to Harvest?

Bulbing onions are usually ready when:

• The bulbs have reached a useful size.
• The necks soften.
• The leaves begin yellowing.
• Most of the tops fall over naturally.

Do not force the tops down early. Allow the plants to finish naturally whenever possible.

Once approximately half to three-quarters of the tops have fallen, the crop is usually close to harvest.

Choose a dry period if possible.

How to Harvest Onions

Loosen the soil carefully around the bulbs with a garden fork or hand tool.

Lift the onions by supporting the bulbs rather than pulling hard on the tops.

Brush away loose soil, but do not wash storage onions before curing.

Fresh onions can be used immediately, but onions intended for storage should be cured first.

How to Cure Onions

Curing dries the outer layers and prepares the onions for storage.

Spread the harvested onions in a single layer in a dry, shaded, well-ventilated location.

Depending on humidity and weather, curing may take approximately two to three weeks.

The onions are ready for storage when:

• The outer skins feel dry and papery.
• The necks are completely dry.
• The roots are dry.
• The tops no longer contain green or moist tissue.

After curing:

1. Trim the roots.
2. Cut the tops, leaving approximately 1 inch of stem, or braid suitable varieties.
3. Remove loose dirt and outer skin gently.
4. Inspect every bulb for damage.

Use damaged or thick-necked onions first.

How to Store Onions

Store cured onions in a cool, dry, dark, well-ventilated location.

Good storage containers include:

• Mesh bags
• Open baskets
• Ventilated crates
• Onion sacks

Avoid sealing onions inside airtight plastic bags because trapped moisture can encourage rot.

Check stored onions regularly and remove any that become soft or begin spoiling.

Sweet onions generally do not store as long as strong, pungent storage varieties.

Can You Grow Onions in Containers?

Yes. Onions grow well in containers when they have enough space, sunlight, and moisture.

Choose a container with:

• Drainage holes
• At least 8 to 10 inches of soil depth
• Enough surface area for proper spacing
• High-quality potting mix

Space bulbing onions approximately 4 inches apart.

Green onions can be planted more closely.

Containers dry out faster than raised beds, so check the soil regularly.

Can You Regrow Onions from Kitchen Scraps?

Green onion bases can regrow additional leaves when placed in water or replanted in soil.

However, this method usually produces green tops rather than a new full-sized storage bulb.

For the healthiest long-term growth, transfer the rooted base into potting mix and provide bright light.

Growing from seed, sets, or transplants remains the better choice for producing full bulbs.

Tips for Growing Larger Onions

For the best chance of producing large onions:

• Choose the correct day-length type.
• Plant early enough.
• Provide full sun.
• Use loose, fertile soil.
• Space plants properly.
• Water consistently.
• Keep the bed free of weeds.
• Encourage strong leaf growth early.
• Avoid excessive nitrogen once bulbing begins.
• Protect plants from pests and disease.

Final Thoughts

Onions require patience, but they are one of the most practical vegetables to grow at home.

The key is to choose the right variety for your location and give the plants enough time to develop healthy leaves before they begin forming bulbs.

You can start onions from seeds, sets, or transplants, depending on how much time and space you have. Seeds offer the widest variety, sets are convenient, and transplants provide a reliable option for many home gardeners.

Even if your onions do not become as large as those sold at the grocery store, they are still useful and delicious. Small bulbs can be used fresh, while green onions can be harvested throughout the season.

With the right timing, consistent moisture, full sun, and proper curing, you can enjoy homegrown onions from the garden and store them for use long after harvest.

Frequently Asked Questions

What is the easiest way to grow onions?

Onion sets are often the easiest option for beginners because they are simple to plant and establish quickly. Transplants are another reliable choice for producing full-sized bulbs.

How long do onions take to grow?

Bulbing onions may take approximately 90 to 120 days or longer, depending on the variety and whether they are grown from seeds, sets, or transplants. Green onions can be harvested much sooner.

How many onions grow from one bulb?

A standard onion set usually produces one main bulb. Some multiplier onions and shallots divide into clusters, but ordinary bulbing onions generally produce one onion per plant.

Do onions need full sun?

Yes. Bulbing onions grow best with at least six hours of direct sunlight, although eight or more hours is preferable for strong growth and larger bulbs.

How deep should onions be planted?

Onion sets should be planted shallowly, approximately 1 inch deep, with the pointed tip near the soil surface. Transplants should be planted deeply enough to cover the roots without burying much of the stem.

Why are my onion tops falling over?

Onion tops often soften, yellow, and fall over naturally when the bulbs approach maturity. If young plants suddenly collapse, check for pests, disease, root damage, or excessive moisture.

Should onion bulbs be covered with soil?

No. As the bulbs expand, their shoulders may rise above the soil. This is normal. Avoid covering developing bulbs with additional soil.

Can onions survive frost?

Young onion plants tolerate light frost and cool weather. Severe freezes may damage exposed growth, especially newly planted or poorly established plants.

Can I eat an onion that has flowered?

Yes. A bolted onion is still edible, but the center may become tough and the bulb will not store as well. Harvest and use it soon.

When should I stop watering onions?

Reduce or stop watering as the tops begin yellowing and falling over naturally. Drier conditions near harvest help the bulbs mature and prepare for curing.

Related Articles

• How to Grow Green Onions
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• What to Plant in Early Spring
• Best Vegetables to Grow in Raised Beds
• How Often Should You Water Your Garden?
• How to Prepare Soil for a Vegetable Garden
• How to Protect Alliums from Leaf Miners
• How to Grow Garlic
• What to Do in Your Garden in August
• Best Vegetables to Plant in Fall

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