How to Grow Onions at Home: Easy Guide for Beginners

Written by: Gloria RamirezPosted in: Gardening
grow onions

Growing your own onions might sound a little daunting at first, but once you get started, you’ll see just how easy and fun it can be! Even if you’re just starting out, you can grow all kinds of onions—red, white, or yellow—right in your own space.

In this guide, I’ll walk you through everything you need to know—from selecting the right onion variety to planting, watering, harvesting, and even storing them for later use.

Let’s get started!

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Understanding Onion Types

Onions come in different types, each suited for specific climates and daylight hours. Knowing which type fits your area helps you grow healthy, flavorful bulbs.

Short-Day Onions

Short-day onions need 10 to 12 hours of sunlight per day to form bulbs. They thrive best in warm areas, such as USDA zones 7 and above. These onions are ideal for planting in the fall, especially if you live in the southern U.S., as they grow through winter.

If soil temperatures reach at least 50°F, it’s time to plant them.

They mature faster than long-day types, making them great for early harvests. Sweet varieties, such as Texas Sweet, are popular choices among gardeners. Avoid growing these in cold climates since they may not form bulbs properly.

Aim for rich, well-drained soils to give them a strong start!

Long-Day Onions

Long-day onions need at least 14 hours of daylight to start forming bulbs. These onions thrive in cooler areas, like USDA zones 6 and below. Plant them early in the spring, about 45–60 days before your area’s last frost date.

Popular types include Walla Walla, known for its sweet flavor.

They mature by midsummer if planted on time. Long-day varieties store well, lasting up to four or five months when appropriately cured. They grow better with peak summer sunlight but don’t do well in southern gardens where daylight is shorter.

Focus on choosing these onions if you want a longer storage option and live in a northern region.

Intermediate-Day Onions

Intermediate-day onions need 12 to 14 hours of daylight to grow bulbs. They do best in areas with moderate climates, where long-day or short-day onions may struggle. These types are also known as day-neutral onions, providing flexibility if your region experiences variable weather.

You can find intermediate varieties at local garden centers or online nurseries. Plant them based on the last frost date and the length of your growing season. Storage life depends on the specific type you choose, so check labels for details before buying onion sets or seeds.

Choosing How to Grow Onions

You have several options for starting to grow onions, depending on your available resources and time. Each method offers unique benefits—choose the one that fits your garden best!

Growing from Seeds

Start onion seeds indoors about 6 to 8 weeks before the last frost. For example, in Nashville, it begins around January 1st. Use shallow containers filled with damp seed starting mix. Plant seeds 1/4 to 1/2 inch deep and space them in a 2-inch wide band.

Rows should be about 12–18 inches apart.

Keep the soil moist until seeds sprout, which takes roughly 7–14 days. Once seedlings emerge, provide grow lights for at least 12 hours daily. After germination, thin seedlings to leave about 3–4 inches of space between each plant.

This helps prevent overcrowding and gives bulbs room to grow properly over time.

Growing from Sets

Onion sets are small bulbs from the previous season. They are easy to plant and save you time compared to seeds. Plant each set with the pointy end up, about 2 inches deep in soil.

Space them 3–4 inches apart, with rows 12–16 inches apart for proper growth.

Sets can tolerate mild frosts, making them great for early spring planting. The soil should be at least 50°F before planting. They mature fast, usually in about 14 weeks, and are hardier than other options.

You can also grow sets to save money on future onions or share extras with neighbors!

Growing from Transplants

Transplants are small onion plants with green tops, sold in bunches. These are great for growing mature bulbs quickly. You can find them at nurseries or garden centers. Trim the roots to about 2 inches and the tops to 4 inches before planting.

This helps them establish better in the soil.

If you need to delay planting, keep bundles stored upright in 2 inches of moist soil. Place them in a cool, bright spot until ready. Transplants don’t need thinning and often grow more successful bulbs than sets.

They start growing within days after planting, giving you a head start in your veggie patch!

When and Where to Plant

Plant onions early in the spring or fall, depending on your type, and ensure they receive full sun. Keep reading to plan the perfect spot!

Best Time to Plant (by Onion Type & Climate)

Short-day onions thrive in warm zones (7+). Plant these in the fall so they can grow over the winter. In cold climates like Minnesota (zone 4b), sets and transplants work best if planted by April or early May.

Aim for 45–60 days before the last expected frost date.

Intermediate-day onions are suitable for planting in late winter or early spring. For long-day onions, wait until the soil temperature reaches 50°F. Spring-planted onions usually finish growing by midsummer, providing you with fresh bulbs to harvest then.

Ideal Sunlight and Temperature Conditions

Onions thrive with 6–12 hours of direct sunlight each day. Full sun helps them develop larger, healthier bulbs. Avoid planting in shaded areas, as this can reduce yield and bulb size.

Place containers or rows in areas that remain bright throughout the day. Extended daylight, ranging from 12 to 14 hours, depending on the type, is key for bulbing.

The best temperature range for onions is between 45°F and 80°F. They can withstand frost, making early spring an ideal time to plant them. Raised beds or mounded rows help warm the soil faster during cool weather.

This setup also ensures good drainage for strong root systems. Warm conditions, paired with ample sunlight, result in better growth and more productive harvests.

Choosing Between Ground or Container

Grow onions in the ground if you have space. Flat, well-drained soil works best. Heavy clay can hold too much water, so improve it by adding compost or organic material. Use raised beds or mounded rows with a 3-inch layer of compost mixed into the top 6 inches of soil for improved drainage.

If space is limited, use containers at least 10 inches deep and wide. Choose sandy loam or potting soil with added compost for healthier onion bulbs. Make sure your container has good drainage to prevent root rot.

Container gardening provides the flexibility to grow on patios or reposition plants for more sunlight during the day.

Preparing the Soil

Healthy soil is the base for strong onion growth. Use organic matter, such as compost or manure, to enhance nutrient availability and improve drainage.

Soil Type and Texture

Choose loose, well-drained soil for onions. Sandy loam works best, especially in containers. Avoid compacted or heavy clay soils, as onion roots are shallow and need air. For gardens with dense or clay-heavy soil, use raised beds or mounded rows to improve drainage.

Amend the soil with compost or organic matter, such as grass clippings, before planting. This boosts fertility and creates a more favorable environment for growing bulbs. Level and loosen the ground to avoid waterlogging, which can cause bulb rot.

With proper care, your onions will thrive in the right type of soil and texture.

pH Level and Nutrient Needs

Onions grow best in soil with a pH of 6.0 to 7.0, which is slightly acidic. Test your soil before planting by using a basic soil test kit available at a nursery or gardening store. If the pH is too low, add lime to raise it.

Use sulfur if you need to lower it.

Onions require moderate levels of phosphorus and potassium, but many soils already have sufficient amounts for growth. Nitrogen is key for healthy tops; however, excessive amounts can delay bulb maturity and lead to poor storage later on.

Apply urea (45-0-0) at 0.25–0.5 pounds per 25 feet of row during the growing season, once or twice only as needed. Always spread fertilizers six inches away from plants and gently scratch them into the ground to avoid burning the roots.

Improving Drainage and Fertility

Add a 3-inch layer of compost to the top 6 inches of soil. This boosts nutrients and helps onions grow strong. Avoid using fresh manure, as it can introduce weeds or harmful bacteria. Use well-rotted materials, such as aged manure, for safe fertility improvement.

For better drainage, work organic matter into the soil before planting. Raised beds or containers with holes also help avoid water pooling near roots. Mulch using straw, weed-free grass clippings, or pine shavings to lock in moisture and slightly increase soil acidity.

How to Plant Onions

Planting onions takes simple steps but needs care. Follow the proper spacing and depth to give them room to grow strong.

Spacing Guidelines

  1. Place onions 3–4 inches apart in each row. This helps bulbs grow larger and healthier. Keep rows spaced 12–18 inches apart for good airflow and easier weeding. In containers, leave at least 4–6 inches between seedlings or sets. Thin crowded seedlings to maintain 3–4 inches of space.

    Avoid overcrowding, as it leads to smaller, misshapen bulbs and increases the risk of diseases like rot or downy mildew.

    For scallions or green onions, tighter spacing works fine, as they don’t require much room to grow fully.

Planting Depth for Seeds, Sets, and Transplants

  1. Sow seeds 1/4 to 1/2 inch deep into the soil. Keep them shallow for easier sprouting and healthy growth. If planting onion sets, place them 2 inches deep with the pointed tip facing up.
    This helps bulbs expand properly.

    For transplants, cover only the roots with about an inch of soil. Ensure that you do not bury their necks, as this may stunt their development. In containers, leave at least 1 inch of soil above the roots for stability and moisture retention. Proper depth ensures strong bulb formation without exposure or drying out.

Row Layout and Garden Planning

  1. Space rows 12–18 inches apart. This makes weeding, watering, and mulching easier. Leave enough room to move between rows for maintenance. Use raised beds or mounded rows in heavy soils to improve drainage.
  2. Arrange rows north-south for better sunlight exposure. Add companion plants, such as lettuce or carrots, nearby to maximize space efficiency. Avoid low areas where water collects. Plan by leaving space for straw or grass clippings as mulch to retain moisture and reduce weeds.

Onion Plant Care Tips

Caring for onions involves watering correctly, fertilizing the soil, and controlling weeds—learn how to grow healthy bulbs!

Watering Frequency and Techniques

  • Water onions deeply once a week. This keeps the shallow roots moist. If you have sandy soil, increase watering since it drains faster. During bulb formation, steady moisture is crucial for producing larger bulbs.
  • Check the soil often and water when the top inch feels dry.
  • Use drip irrigation to prevent wetting leaves and reduce disease risks, such as downy mildew or rot. Stop watering altogether when the green tops start to fall over. Overwatering near harvest can lead to rotting bulbs, so keep an eye on signs of maturity.

Fertilizing at Key Growth Stages

  • Feed onions once or twice during their growing season for the best results. Use urea fertilizer, like 45-0-0, at a rate of 0.25–0.5 pounds per 25 feet of row. Place it six inches away from the plants and scratch it into the soil to avoid direct contact with roots.
  • Too much nitrogen can delay bulb maturity and reduce storage quality. A continuous-release plant food ensures steady nutrients without overloading. For raised beds or containers, Miracle-Gro Performance Organics Edibles Plant Nutrition Granules are a suitable option.
  • Follow soil test recommendations for phosphorus and potassium needs to support healthy growth stages without harming your vegetables. Avoid fertilizers labeled “Weed and Feed” as they can damage nearby onions, such as shallots or garlic, in your garden setup.

Mulching for Moisture and Weed Control

  • Use a 3–4 inch layer of mulch, such as straw, pine shavings, or grass clippings, to keep the soil moist and block weeds. Pine shavings work well if your soil needs more acidity for healthy onion growth.
  • Spread mulch only after seedlings are growing strong and rows are weed-free.
  • Mulch also stabilizes the temperature around the roots. In containers, use light mulches to prevent the soil from drying too quickly. Remove mulch when onions start bulbing to prevent neck rot.
  • Replace it as needed throughout the season for best results.

Thinning Crowded Seedlings

  • Thin seedlings early, within a few weeks of sprouting. Leave 3 to 4 inches between plants for proper bulb growth. Crowded onions compete for nutrients and water, leading to small or oddly shaped bulbs.
  • Removing weaker plants helps your stronger ones thrive.
  • Trimmed seedlings can be used as green onions or scallions in salsas or dishes like burgers and salads. Be gentle while thinning to avoid disturbing nearby roots. Improved spacing boosts airflow, reduces disease risks, and supports healthier onion development.

Companion Planting with Onions

Onions pair well with certain vegetables and herbs, enhancing both health and flavor. Avoid planting them with crops that compete for nutrients or attract pests.

Best Companion Plants

Lettuce grows well next to onions. Onions repel aphids, protecting the lettuce leaves. Tomatoes and strawberries also benefit from this pairing, as the strong onion smell scares off Japanese beetles and aphids.

Broccoli, kale, kohlrabi, and Brussels sprouts also thrive when paired with onions. These vegetables suffer less from cabbage worms because of onions’ natural pest-fighting abilities.

Carrots, beets, dill, and peppers are also great partners. Planting any of these near your onions improves garden health while reducing the need for chemical treatments.

Plants to Avoid

Keep onions away from peas and beans. These crops can be affected by flavor contamination when grown near onions. Onions also inhibit the growth of some legumes, which affects their health and yield.

Avoid planting onions near asparagus, as they can have a negative interaction. Do not plant them close to other alliums like leeks or shallots to limit onion maggot infestations. Keep at least 12–18 inches between these incompatible plants for healthier growth and larger bulb sizes.

Growing Onions in Containers

Growing onions in containers is excellent if you have limited space. Choose the right pot, and you’ll enjoy fresh bulbs at home!

Choosing the Right Container Size

Choose containers or grow bags at least 10 inches deep and wide for each onion plant. This depth allows roots to expand properly, supporting healthier bulbs. Deeper containers also hold more soil, which helps retain moisture for a longer period.

Small pots may dry out fast and limit bulb size due to cramped root space.

Use large planters with enough room to group onions while maintaining proper spacing between plants. Wide openings make planting and maintenance easier as well. Opting for larger containers reduces the risk of stunted growth caused by crowded roots or poor drainage.

Soil Mix and Drainage Tips

Fill your container with sandy loam or a quality potting mix. Blend it with compost for added nutrients. Loose soil is key to onion growth, so avoid heavy clay-based mixes.

Use pots with multiple drainage holes to prevent waterlogging. Onion roots need air and proper moisture levels to thrive. Add mulch lightly to the surface to retain moisture, but remove it as the bulbs begin to expand.

Refresh the soil yearly to keep it fertile and disease-free.

Positioning and Watering Considerations

Place your onion containers in a spot with 6–12 hours of daily sunlight. Rotate the pots occasionally to ensure even light hits all sides. Protect them from excessive rain, which can cause waterlogging and damage the bulbs.

Water onions when the top inch of soil feels dry to the touch. Use a watering can or drip irrigation to avoid wetting leaves, as this helps prevent diseases. During hot days, you may need to water every day, as containers dry out more quickly than garden beds.

Consistent moisture is key to healthy growth.

Identifying Onion Growth Stages

Watch your onions grow—from tiny sprouts to plump bulbs—and adjust care at every step for the best harvest.

From Sprouting to Bulbing

Onion seeds germinate in 7 to 14 days under optimal conditions. Once sprouted, you’ll notice green shoots starting to grow. During this stage, the plants focus on leafy growth.

They need steady moisture and weed management for healthy development. If seedlings look crowded, thin them out to give each plant room.

Bulbing begins when the day length meets your onion type’s needs, usually requiring 10–14 hours of daylight or more. The base of the plant will swell as bulbs form and push slightly above the soil line.

Reduce fertilizer during this phase since the energy shifts from leaf production to bulb expansion. Regular care ensures a strong harvest later!

What to Expect at Each Stage

Green shoots emerge within 7–14 days after sowing. During this sprouting stage, onions need even moisture and no competition from weeds. Leaves proliferate after this, reaching several inches tall.

This is the early vegetative phase when consistent watering matters most.

Bulbs start swelling at the base as daylight increases in spring or summer. Pay attention during this time, as bulb growth speeds up just before the bulb matures. Tops begin to yellow and fall over, signaling readiness for harvesting by late summer or early fall.

If left too long, flowering stalks may appear, which can reduce bulb quality.

Adjusting Care Based on Growth Phase

Increase watering during the bulbing phase to support proper growth. Reduce water as the onions near maturity, especially after the tops fall over. This helps them start curing.

Stop using nitrogen fertilizers once the bulbs begin to form. Too much nitrogen at this stage can hinder their development. Remove mulch around expanding bulbs to prevent rot and improve air circulation.

Stay alert for pests or diseases at every stage, and treat issues promptly with natural or chemical remedies as needed.

Harvesting Onions

Onions are ready to pull when their tops fall over and dry out. Gently lift the bulbs from the soil to prevent bruising.

Signs Onions Are Ready to Harvest

The tops of onions will yellow, dry out, and naturally fall over. The necks become soft and easy to bend. These are key signs your bulbs are ready to pull.

Bulbs push above the soil surface as they reach full size. Skins turn papery and begin to dry out. Flower stalks appearing mean you should harvest right away before the quality drops.

How to Properly Harvest Bulbs

Use a garden fork or shovel to gently loosen the soil around the bulbs. Lift them carefully by the base, not pulling on their tops. Harvest on a dry, sunny day to keep moisture off the bulbs and reduce rot risks.

Shake off extra soil, but avoid washing them before curing. Leave tops attached for proper drying. Lay the bulbs in a single layer in a well-ventilated spot to initiate the drying process. Handle each bulb with care to prevent bruising, as this can shorten its storage life.

Curing and Storing Onions

Dry your onions in a warm, airy spot to toughen their skins. Store them in a dark, cool area to maintain freshness for months.

How to Cure Onions for Long-Term Storage

Lay onions in a sunny spot for one to two days after harvesting. This dries the roots, making them easier to handle. Move the onions to a shady area afterward. Shade prevents sunburn while the curing process continues.

Curing takes two to three weeks. Wait until the tops and roots are dry and wiry before storing. Store cured onions in a cool, dark, and dry place with good airflow. Ideal locations include bins or braids hung off the ground to avoid moisture buildup.

Storage Conditions: Temperature, Humidity, and Light

Store onions in a cool, dry place between 45°F and 80°F. This helps maintain their freshness for a longer period. Keep them away from wet areas; excessive moisture can cause the material to rot. Proper airflow is key, so don’t crowd them together.

Avoid placing onions near fruits like apples or bananas that produce ethylene gas. The gas can make your onions sprout early. After curing for two to three weeks, sweet varieties store well when wrapped in paper towels or newspaper and stored in the refrigerator.

Braiding and Binning for Airflow

Braiding onion tops helps airflow between the bulbs. This method helps keep onions fresh longer and reduces the risk of rot. Cut the roots and tops to approximately 1-2 inches in length before braiding for better results.

Hang the braided onions in a cool, dry spot to cure them properly.

Use a mesh bag or bin for storage if you don’t braid them. These allow air circulation, which prevents moisture buildup that can lead to spoilage. Keep your cured onions away from fruits like apples or bananas as they make onions sprout faster due to ethylene gas release.

Common Onion Growing Problems

Pests and diseases can hurt your onions if you’re not careful. Discover how to identify problems promptly and maintain your plants’ health.

Pests: Onion Maggots, Thrips, etc.

Onion maggots can destroy roots and bulbs. These pests thrive near other alliums, such as chives, garlic, or shallots. Rotate crops each season to stop their spread. Use lightweight row covers to keep adult flies from laying eggs on your plants.

Thrips feed by sucking sap from leaves, which weakens growth. Inspect your onion leaves for silvery spots or curling edges. Spray plants with insecticidal soap or use neem oil to control thrips naturally.

Companion planting also helps; grow onions near radishes or marigolds to deter these pests and others, such as aphids.

Diseases: Downy Mildew, Rot, etc.

Downy mildew spreads fast in wet conditions. It causes yellow patches on leaves and weakens plants. Keep the soil well-drained to prevent it. Avoid overhead watering, as wet leaves encourage this disease.

Rot often harms onions after harvest. Overly moist soil increases its risk. Store bulbs for two to three weeks in a dry, airy space after curing for the same period. Control weeds around your crop to reduce the risk of infections such as botrytis rot or fungal issues.

Yellowing Leaves and Other Growth Issues

Yellowing leaves often indicate that your onions lack nitrogen, have too much, or are not receiving enough water. Check if the soil drains well, as standing water can harm growth and cause yellowing. Maintain steady watering; letting the soil dry out, then overwatering, stresses plants.

Poor pH levels also hurt onion health. Aim for a soil pH between 6.0 and 7.0 to ensure proper nutrient uptake. Test your soil regularly and add compost if needed for healthy growth.

Plant companions, such as carrots or lettuce, nearby to repel pests that might stunt or damage your onions further.

Prevention and Treatment Strategies

Control pests like onion thrips and root maggots early to prevent damage to your crops. Use sticky traps or insect-proof netting to reduce infestations. For diseases like downy mildew, plant in well-drained soil and avoid wet conditions.

Rotate your crops yearly to prevent the buildup of pathogens.

Hoe between rows often to manage weeds, but don’t dig too deep near onion roots. Apply a balanced fertilizer, such as urea (0.25-0.5 pounds per 25 feet of row), to promote healthy growth without delaying maturity.

Harvest onions on dry days to lower the risk of rot during curing and storage.

Conclusion

Growing onions is a rewarding and relatively easy process. With the right type, good soil, and proper care, you can enjoy fresh bulbs at home. Watch for signs of maturity and take time to cure them well.

These steps ensure a plentiful harvest and long storage life! Start planting now, and soon you’ll savor the results in your meals.

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