Beginner’s Guide to Growing Onions: A Step-by-Step Guide

Onions are a staple in countless recipes worldwide, prized for their unique flavor, versatility, and nutritional benefits. While growing onions might seem intimidating to beginners, onions are actually quite simple to cultivate with the right knowledge and a bit of patience. They can be grown in gardens, raised beds, and even containers, making them a flexible option for many types of gardeners.

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Choosing the Right Type of Onion for Your Climate

Onions are a staple in kitchens around the world, and growing them at home can be a rewarding experience. However, not all onions are suited to all climates, and selecting the right type is key to successful harvests. Onions are classified into three main types—long-day, short-day, and day-neutral—and the best choice for your garden will depend on your local climate and day length.

Types of Onions by Day Length

Day length refers to the number of daylight hours that an onion plant needs to mature and form bulbs. Different onion varieties are adapted to different day lengths, so choosing the right type is essential to ensure your crop thrives.

Long-Day Onions

Long-day onions are suited to regions with longer summer days. These onions require 14-16 hours of daylight in order to trigger bulb formation. They are typically grown in northern climates, where the growing season has longer daylight hours during the summer months.

Ideal Climate: Long-day onions thrive in northern regions or areas with longer daylight hours, especially during the late spring and summer.

Varieties:

Walla Walla: A mild, sweet onion variety that’s perfect for raw use, like in salads or sandwiches.
Yellow Sweet Spanish: Known for its sweet flavor and large bulbs, it is a great all-purpose onion.
White Spanish: This variety produces large, round, white onions with a mild flavor. They store well and are often used for cooking or fresh salads.

Long-day onions typically have a longer growing season, meaning they need more time to mature before harvesting. They are a good choice for gardeners with a longer growing season or those in areas further north with extended daylight hours.

Short-Day Onions

Short-day onions require fewer daylight hours—about 10-12 hours—making them perfect for regions with shorter days or warmer climates. These onions are best suited for the southern parts of the United States or regions where winters are milder and the daylight hours don’t extend as long.

Ideal Climate: Short-day onions are perfect for southern climates, such as areas in the southern United States, where winters are mild and day lengths remain shorter.

Varieties:

Texas Sweet: A popular variety in southern states, known for its very mild flavor and sweetness. It’s commonly grown in Texas and the surrounding areas.
Granex: A sweet, mild onion that is often used in fresh dishes or raw on sandwiches and salads. It has a white bulb and is grown primarily in warm climates.
Red Creole: A short-day variety with a slightly more pungent taste, red Creole onions are ideal for cooking and adding color and flavor to dishes.

Short-day onions are typically planted in the fall in the south and harvested in the late spring or early summer. Their ability to mature with shorter daylight hours makes them a good choice for gardeners in the southern regions who experience milder winters and shorter daylight periods.

Day-Neutral (Intermediate) Onions

Day-neutral onions, also called intermediate onions, are a hybrid of both long-day and short-day types. These onions can grow well in most regions and are considered more flexible because they don’t require extremely long or short days to mature. They can adapt to a variety of climates and are a good option for beginner gardeners or those living in areas with intermediate day lengths.

Ideal Climate: Day-neutral onions are well-suited for regions with a range of daylight hours, including most areas in the United States.

Varieties:

Candy: Known for its sweetness and mild flavor, Candy onions are perfect for fresh use, such as in salads or as a topping for burgers.
Superstar: A versatile onion that grows well in a variety of climates, it’s an excellent all-purpose onion for cooking or fresh eating.
Cippolini: These small, round onions are sweet and mild, making them a popular choice for roasting or caramelizing.

Day-neutral onions are the most adaptable option, making them an excellent choice for gardeners in regions with a range of growing conditions, or those new to growing onions.

Selecting Onion Varieties by Use

Once you’ve selected the right type of onion for your climate, the next step is to consider how you plan to use the onions. There are several types of onions, each with its own characteristics that make them better suited for specific culinary uses.

Storage Onions

If you’re growing onions that you plan to store for long periods, you’ll want to choose varieties known for their ability to stay fresh through the winter months. These onions tend to have thicker skins and a more robust flavor.

Varieties:

Yellow Globe: A classic storage onion with a rich, pungent flavor. It has a golden-brown skin and is commonly used for both cooking and storage.
Patterson: Known for its long storage life, Patterson onions are large, with a strong, sharp flavor. They’re great for making onion rings or adding flavor to soups and stews.

Storage onions are perfect for harvesting in late summer or early fall, and with the right curing techniques, they can last for several months in a cool, dry environment. They are particularly useful for gardeners who want to enjoy homegrown onions year-round.

Sweet Onions

Sweet onions are characterized by their mild, sweet flavor and are great for eating fresh. These onions typically have a higher water content than other varieties, which contributes to their sweetness. They are perfect for use in salads, sandwiches, and as a topping for burgers.

Varieties:

Vidalia: A well-known sweet onion from Georgia, Vidalia onions are renowned for their crisp, sweet flavor. These onions are perfect for fresh dishes or raw use.
Walla Walla: A sweet and juicy onion, Walla Walla is often grown in the Pacific Northwest and is excellent for fresh eating.

Sweet onions are best harvested in the early summer, before they lose their moisture content, and should be used fresh or preserved shortly after harvest. These onions are a gardener’s choice for eating raw or making mild, sweet onion dishes.

Red Onions

Red onions are distinct for their deep purple-red color and crisp texture. They have a milder flavor than white or yellow onions, making them a great choice for raw dishes or salads. Red onions are commonly used in salsas, salads, and sandwiches, where their vibrant color can add a burst of visual appeal.

Varieties:

Redwing: A medium-sized red onion with a mild flavor, great for fresh dishes and pickling.
Red Baron: Known for its rich red color and mild taste, this variety is commonly used raw or in dishes where the onion’s color is a feature.

Red onions are typically harvested in the summer, and they tend to store for a shorter period than other types of onions. They can be enjoyed immediately or pickled for longer shelf life.

Final Considerations for Onion Selection

When deciding which type of onion to grow, you’ll want to consider not only your local climate and day length but also your personal preferences for taste and usage. For example:

If you enjoy fresh, mild onions for salads and sandwiches, sweet onions such as Walla Walla or Vidalia are the way to go.
If you prefer onions that you can store for several months, varieties like Yellow Globe or Patterson might be more suitable.
For gardeners in regions with milder climates and shorter day lengths, short-day varieties such as Texas Sweet or Granex will thrive.

It’s also important to consider your growing space and the type of soil. Onions prefer well-draining, loose soil, so be sure to prepare your garden bed accordingly. With the right variety and care, you can enjoy a bountiful harvest of onions in your garden, whether you are a beginner or a seasoned gardener.

Selecting the Best Location and Soil Preparation

Onions need full sun to grow well, so choose a location in your garden that receives at least 6-8 hours of sunlight per day. Good drainage is essential, as onions dislike wet feet and will rot if left in soggy soil.

Preparing the Soil

Test and Adjust Soil pH: Onions prefer slightly acidic to neutral soil with a pH between 6.0 and 7.0. You can test your soil pH with a basic kit from your local garden center.
Loosen the Soil: Loosen the top 8-10 inches of soil to provide a well-aerated environment for onion roots.
Add Organic Matter: Mix in compost or well-rotted manure to improve soil structure and boost nutrient content. Onions are heavy feeders and thrive in nutrient-rich soil.
Add a Balanced Fertilizer: Before planting, add a balanced fertilizer (10-10-10) to the soil and mix it in well.

Planting Onions: Seeds, Sets, and Transplants

Onions can be started from seeds, sets, or transplants, each with its own advantages. The method you choose depends on your timeline, garden space, and preference.

Starting Onions from Seeds

Starting onions from seeds is the most traditional way of growing them, but it requires a bit more time and attention. It’s an ideal option for gardeners who want to start their onions early and have the patience to nurture them through their growing stages.

Timing: When to Start Onion Seeds

Onions require a long growing season, so starting them from seed means you’ll need to plan ahead. For most onion varieties, you’ll want to start your seeds indoors 8-10 weeks before the last expected frost in your area. This timing allows your onions to grow into healthy seedlings before being transplanted into the garden.

For Northern climates where the growing season is shorter, starting seeds indoors early is essential to get enough growing time.
For Southern or warmer climates, you may have a longer growing season, but starting seeds early will still give you stronger plants.

Planting Depth and Technique

When planting onion seeds, it’s important to use a well-draining seed-starting mix. Onion seeds are tiny, so they should be sown about 1/4 inch deep into seed trays or small pots. Make sure to space the seeds about 1/2 inch apart to give them room to sprout without overcrowding.

Watering: Keep the soil consistently moist, but not soggy. Onions like their soil to be moist but not waterlogged, so be mindful of drainage.
Light: Once the seeds sprout, make sure they receive at least 12-14 hours of light per day. If you don’t have access to bright sunlight, you can use grow lights to encourage healthy growth.

Transplanting Seedlings

After about 8-10 weeks, your onion seedlings should be about 4-5 inches tall and ready to move outdoors. The outdoor soil temperature should be above 50°F (10°C) to ensure healthy growth, so wait for the right moment in your growing season.

Acclimate seedlings to the outdoors by hardening them off. Gradually expose them to outdoor conditions for a few hours each day, increasing the duration over the course of 7-10 days.
When transplanting, gently separate the seedlings and plant them into prepared garden beds or containers, making sure to space them about 4-6 inches apart to allow for proper growth.

Planting Onions from Sets

Onion sets are small, immature onions that were grown from seed the previous season. These sets are a convenient and popular method of planting because they provide a quicker start to the growing process, and they’re easier to handle for beginners.

What Are Onion Sets?

Onion sets are typically sold as small bulbs, about the size of a marble. They’ve already started growing, meaning they can be planted directly into the soil. Unlike seeds, they don’t require time to sprout, making them a faster option for gardeners who want to grow onions without waiting for seedling growth.

Advantages: Sets tend to grow faster and require less care than seedlings. They’re also less prone to bolting (flowering prematurely) than seedlings or seeds.
Disadvantages: The variety of onions available as sets can be more limited than the seeds, so you may have fewer options when it comes to selecting onion types.

Planting Onion Sets

When planting onion sets, you’ll want to follow a simple process:

Planting Depth: Push each onion set about 1 inch deep into the soil. The pointed end should face up, as this is the end where the new growth will emerge.
Spacing: Space each onion set 4-6 inches apart. If you’re planting in rows, make sure the rows are about 12-18 inches apart to give the onions plenty of room to mature without crowding.
Soil: Like all onions, sets prefer well-draining, fertile soil. Make sure to amend the soil with compost or well-rotted manure to ensure healthy growth.

Watering and Care for Sets

Once you’ve planted the sets, water them gently to settle the soil around them. During the growing season, keep the soil moist but not overly saturated. Regular watering is key, especially when the bulbs are forming. As the onions mature, reduce watering to allow the bulbs to dry out a bit before harvesting.

Onion sets usually require about 100-120 days to grow from planting to harvest. You’ll see the green tops start to fall over and yellow as the bulbs mature, signaling that it’s time to harvest.

Using Onion Transplants

Onion transplants are young onion plants that have been grown for several weeks or months in a nursery or greenhouse before being sold to gardeners. They’re slightly larger than onion sets and offer the benefit of already being established, making them an excellent choice for gardeners who want an earlier harvest or those who don’t want to start from seeds themselves.

What Are Onion Transplants?

Onion transplants are typically sold in bundles, with each plant being 4-6 inches tall. These transplants have been carefully nurtured and are ready to be planted directly into your garden.

Advantages: Since they’re already established, transplants often grow more quickly than onions started from seeds. They also tend to be less prone to bolting, making them an ideal choice for growers in regions with unpredictable weather.
Disadvantages: Transplants can be more expensive than sets or seeds, and the available varieties may be more limited. Additionally, if you’re not careful when transplanting, you could damage the young plants.

Planting Onion Transplants

Planting onion transplants follows a similar process to planting onion sets:

Planting Depth: Set each transplant into the soil so that the base of the plant is level with the soil. You do not want to plant the transplants too deep, as this can hinder growth.
Spacing: Space the transplants about 4-6 inches apart in rows that are 12-18 inches apart. This will allow the onions room to spread out and form large bulbs.
Soil: Onions require loose, well-draining soil, so prepare your garden bed by loosening the soil to a depth of at least 6-8 inches and adding organic matter to improve fertility.

Caring for Onion Transplants

Once planted, water the transplants thoroughly to help them settle into the soil. Be sure to keep the soil consistently moist during the growing season, especially as the onions start to develop bulbs. Once the onions are established, you can mulch around the plants to retain moisture and suppress weeds.

Growing Asparagus in Your Garden

Onion transplants tend to grow faster than sets, so you can expect to harvest them in 90-120 days, depending on the variety

Comparing Seeds, Sets, and Transplants

Method	Time to Start	Difficulty	Growing Speed	Risk of Bolting	Variety Available
Seeds	8-10 weeks before last frost	Moderate	Slow	High	High
Sets	Directly in the ground	Easy	Fast	Low	Moderate
Transplants	4-6 weeks before last frost	Easy	Fast	Low	Moderate

Watering and Fertilizing for Healthy Growth

Consistent watering is crucial for onions, especially during the initial stages of growth and bulb formation.

Watering Guidelines

Frequency: Water onions deeply once or twice a week, depending on rainfall. Aim for about 1 inch of water per week.
Avoid Overwatering: Onion roots are shallow, and overwatering can lead to rotting. Ensure the top layer of soil dries out between watering sessions.

Fertilizing Onions

Onions benefit from a steady supply of nutrients, particularly nitrogen, which supports healthy leaf and bulb development.

Initial Fertilizing: Apply a balanced fertilizer before planting.
Follow-Up Fertilizing: Side-dress onions with a nitrogen-rich fertilizer (such as a 21-0-0) every 3-4 weeks until they start forming bulbs. Reduce nitrogen application at that point to encourage bulb growth rather than leaf production.

Onion Care: Weed Control and Mulching

Onions are vulnerable to competition from weeds, which can sap nutrients and water.

Weeding Techniques

Hand Weeding: Because onions have shallow roots, hand-weeding is the safest method to avoid disturbing their growth.
Hoeing: If using a hoe, work carefully between rows to prevent root damage.

Mulching for Weed Control

Applying a layer of mulch around your onions can help control weeds, retain moisture, and regulate soil temperature.

Organic Mulch: Straw or shredded leaves make good mulch options for onions, as they allow airflow and slowly decompose, enriching the soil over time.
Mulch Depth: Apply a 2-inch layer of mulch around the onion plants, but leave some space around the stems to prevent rot.

Managing Pests and Diseases

While onions are relatively pest-resistant, they can sometimes fall victim to certain insects and diseases.

Common Pests

Onion Maggots: These small maggots feed on onion roots, causing plants to weaken and wilt. Prevent them by rotating crops and using row covers.
Thrips: Thrips are tiny insects that can cause leaves to become silvery and curled. Insecticidal soap sprays can help control them.

Common Diseases

Downy Mildew: This fungal disease can cause yellow spots on leaves. Space plants properly and ensure good air circulation to reduce the risk.
Botrytis Leaf Blight: This disease creates small white spots that turn brown on onion leaves. Remove infected leaves and avoid overhead watering.
White Rot: White rot causes plants to wilt and die. Unfortunately, it persists in the soil, so crop rotation is essential to prevent it.

Harvesting and Curing Onions

Understanding when to harvest and how to cure onions ensures that you can enjoy your harvest for months to come.

Harvesting Bulb Onions

When to Harvest Onions

Timing is critical when it comes to harvesting onions. If harvested too early, the bulbs may not be fully developed and could have a short shelf life. On the other hand, leaving them in the ground too long could lead to the bulbs rotting or sprouting prematurely. Here are some key indicators that your onions are ready to be harvested:

Yellowing Tops: One of the first signs that onions are ready for harvest is when the tops (green stems) begin to yellow and start to flop over. This is a natural part of the onion’s life cycle, signaling that the plant is no longer sending nutrients to the top and is instead focusing energy on the bulb.
Drying of the Neck: The neck of the onion (where the bulb connects to the stem) should begin to dry and tighten. If the neck is still soft or moist, the onion may not yet be fully mature.
Timing: Harvesting typically happens in late summer or early fall, depending on your climate and the variety you planted. In areas with longer growing seasons, onions might be ready for harvest earlier in the season, while in cooler climates, they may require more time to mature.

How to Harvest Onions

Harvesting onions requires a delicate touch to avoid damaging the bulbs, which can affect their ability to store properly. Here’s how to do it carefully:

Digging Up the Bulbs: Use a garden fork or hand trowel to gently lift the onions out of the soil. Start by loosening the soil around the onion, taking care not to pierce the bulb with your tool. Once the soil is loosened, carefully lift the onion out of the ground, allowing the roots to break free naturally.
Avoiding Damage: Be sure to handle the onions with care. Avoid pulling on the tops too hard, as this can cause the neck to break and compromise the bulb’s ability to store. If you’re pulling by hand, gently grasp the onion stem and wiggle it out of the soil.
Leave the Tops Intact: When you pull the onions, try to leave the green tops (stems) intact for now. This will help in the curing process. If the tops are damaged during harvest, that’s okay, but it may speed up the need to cure the onions.
Check for Size and Maturity: After harvesting, inspect the size of the onions. If they are small or underdeveloped, you may want to leave them for a bit longer in the garden. Onions that are fully mature will have a firm, plump bulb and will feel heavy for their size.

Curing Onions for Storage

Curing is the process of drying out the onion bulbs to ensure they store well over the winter months. Proper curing is essential because it helps to prevent rot, ensures the onions’ skins are tough enough for storage, and allows the flavors to fully develop.

Drying Process

Once you’ve harvested your onions, it’s important to allow them to dry out before storing them. This drying or “curing” process should be done in a dry, well-ventilated space. Here’s how to cure your onions:

Find a Suitable Area: Select a dry, well-ventilated area out of direct sunlight. A shed, garage, barn, or even a basement with good airflow can work well. The key is to avoid moisture buildup and direct sunlight, which could affect the onions’ drying process.
Lay Onions in a Single Layer: Spread the onions out in a single layer on a clean, dry surface such as a table, countertop, or even newspaper. Make sure that the onions are not touching each other to allow for good air circulation around each bulb. This will help them dry evenly and prevent any moisture from being trapped between the bulbs.
Allow the Onions to Dry: Let the onions cure for 2-3 weeks. During this time, the outer skins will dry out, and the necks of the onions will tighten. The tops should also be completely dry by the end of this period. A properly cured onion will have papery, dry skins, and the neck will be tight and no longer moist.
Temperature and Humidity: For optimal curing, the temperature should be around 75°F (24°C) with low humidity. If you are curing your onions in an area with high humidity, you may need to extend the drying time or use fans to improve air circulation.

Cleaning the Onions

Once the onions are fully cured, it’s time to clean them up for storage. Here’s what you need to do:

Brush Off Excess Dirt: Gently brush off any dirt or soil that is still attached to the onions. Be careful not to damage the outer skins. You can use a soft brush or your hands to remove debris.
Trim the Tops: Cut the dried tops off the onions, leaving about 1-2 inches of the neck. This will help prevent moisture from seeping into the bulb and causing rot. If the neck is still soft, it might indicate that the onion wasn’t fully cured, so give it more time to dry before trimming.
Trim the Roots: Trim the roots of each onion to about 1 inch. Be gentle to avoid damaging the bulb. Removing the roots helps make the onions easier to store.
Check for Damage: As you clean your onions, inspect each one for any signs of damage or disease. If you find any soft spots, mold, or bruises, remove those onions immediately to prevent them from spoiling the others.

Storing Cured Onions

Once your onions are properly cured and cleaned, it’s time to store them for long-term use. The right storage conditions are essential to ensuring your onions last throughout the winter.

Storage Containers: Onions should be stored in a cool, dry, well-ventilated area. You can store them in mesh bags, onion crates, or even pantyhose (hanging onions in the legs of the hose) to provide proper airflow. Avoid storing onions in plastic bags, as this can trap moisture and lead to rot.
Temperature: The ideal temperature for storing onions is 32-40°F (0-4°C), which is similar to the temperature of most home basements or root cellars. Onions stored in too warm of an area will begin to sprout, and if stored in too cold of an area, they may freeze.
Humidity: Onions need a low-humidity environment for storage. If the storage area is too humid, the onions may begin to rot or sprout prematurely. To avoid excess moisture, keep onions in a place with good air circulation.
Check Regularly: It’s important to check your stored onions every few weeks for any signs of rot, mold, or sprouting. If you find any onions that are beginning to go bad, remove them immediately to prevent the spread of decay to the other bulbs.

Signs Your Onions Are Ready to Harvest and Cure

Yellowing and Drooping Tops: The first sign that your onions are ready for harvest is when the tops (the green stems) turn yellow and begin to fall over. This indicates that the bulbs have matured and the onions are beginning to go dormant.
Dried Necks: The necks of the onions should feel tight and dry by the time you’re ready to harvest. If the necks are still soft and moist, the onions aren’t fully mature yet and should be left in the soil for a little longer.
Firm Bulbs: When you dig up your onions, the bulbs should be firm to the touch. A soft or squishy bulb indicates that the onion is not yet ready for harvest.

Tips for Using Your Homegrown Onions

Your homegrown onions can enhance a wide range of dishes, adding flavor, texture, and nutrition.

Cooking Ideas

Raw in Salads and Sandwiches: Fresh onions are perfect for adding crunch and flavor to salads, burgers, and sandwiches.
Caramelizing: Slowly cook onions until golden brown and sweet, perfect for topping burgers or adding to sauces.
Pickling: Pickled onions make a delicious condiment for tacos, salads, and more.

Storage for Cooking Convenience

Consider chopping and freezing extra onions, which can be a time-saving option for future recipes.

Bottom Line

Growing onions may take time and patience, but the payoff is well worth it. With these beginner-friendly tips, you’ll soon enjoy the satisfaction of harvesting your own fresh onions right from your garden. Whether you’re looking to enjoy them fresh, store them for winter, or experiment in the kitchen, onions are a versatile, delicious, and rewarding crop to grow.