How to Grow Onions: A Comprehensive Guide

Posted on Categories:"How To Grow", Edible Plant Growing Information
How to Grow Onions

How to Grow Onions

Onions are a kitchen staple, and growing your own ensures a fresh supply at your fingertips. These versatile vegetables come in various types, including red, yellow, and white, and can be used in an array of dishes. In this comprehensive guide, we’ll take you through the step-by-step process of how to grow onions successfully, whether you have a garden, a balcony, or a small indoor space.

Note: MEG offers onions exclusively through the CSA program. Click here for more information!

1. Choosing Onion Varieties

Before you start your onion-growing journey, it’s essential to choose the right onion varieties that suit your climate and culinary preferences. Here are some common onion types:

  • Short-Day Onions: These onions are best suited for southern regions with mild winters and shorter daylight hours. They typically mature in about 110-130 days. Varieties include ‘Texas 1015Y,’ ‘Yellow Granex,’ and ‘Red Creole.’
  • Intermediate-Day Onions: These onions are well-suited for regions with moderate winter climates and intermediate day lengths. They take around 130-150 days to mature. Examples include ‘Superstar,’ ‘Candy,’ and ‘Red Candy Apple.’
  • Long-Day Onions: These onions thrive in northern regions with long, cool growing seasons. They typically mature in about 150-170 days. Varieties include ‘Walla Walla,’ ‘Yellow Spanish,’ and ‘Red Zeppelin.’

2. Starting Onion Seeds or Sets

Onions can be grown from seeds, sets, or transplants. Starting from seeds offers the most options, while sets and transplants provide a head start. Here’s how to start onions from seeds:

  • Starting Indoors: Onions are typically started indoors 8-10 weeks before the last expected frost. Use seed trays or pots and a good-quality seed starting mix. Sow the seeds about ¼ inch deep and keep the soil consistently moist. Transplant seedlings into the garden when they’re around 4-6 inches tall.
  • Starting Outdoors: In mild winter regions, onions can be directly sown in the garden in the fall. In regions with cold winters, sow the seeds outdoors in early spring as soon as the soil can be worked.
  • Using Sets: Onion sets are small, dormant onion bulbs. Plant them directly in the garden in early spring. They mature earlier than onions grown from seeds but have a greater chance of bolting (producing flowers and seeds).

3. Site Selection and Soil Preparation

Onions thrive in full sun, so select a planting location that receives at least 6-8 hours of sunlight daily. Here are the steps for site selection and soil preparation:

  • Well-Draining Soil: Onions prefer well-draining soil with good fertility. Work the soil to a depth of at least 6 inches and remove any rocks, debris, or weeds.
  • Soil pH: Onions do well in slightly acidic to neutral soil with a pH level between 6.0 and 7.0. You can adjust the pH if necessary using lime or sulfur.
  • Fertilization: Onions are moderate feeders, and they benefit from a balanced fertilizer. Incorporate organic matter, such as compost or well-rotted manure, into the soil to improve fertility.

4. Planting Onions

The timing and method of planting onions may vary based on your location and the onion type. Here’s a general guideline for planting onions:

  • Spacing: Space onion sets or transplants about 4-6 inches apart in rows. Space rows 12-18 inches apart. If you’re planting from seed, thin the seedlings to the desired spacing.
  • Planting Depth: Plant onion sets about 1 inch deep with the pointy end facing up. For transplants, set them at the same depth they were grown in the nursery.
  • Regular Irrigation: Onions need consistent moisture, so water them thoroughly and keep the soil evenly moist throughout the growing season.

5. Care and Maintenance

Proper care and maintenance are crucial for growing healthy and productive onion plants. Here’s what you need to do:

  • Weed Control: Keep the onion bed free of weeds, as onions are sensitive to competition for nutrients and water.
  • Thinning: If you’ve planted onions from seed, thin them when they reach about 4 inches in height. Leave 2-3 inches between each plant.
  • Fertilization: Onions benefit from a side-dressing of nitrogen-rich fertilizer when they are around 6 inches tall. Apply a balanced fertilizer as recommended on the product label.
  • Pest and Disease Management: Keep an eye out for common onion pests, such as onion thrips and onion maggots. Use organic pest control methods as needed.

6. Harvesting Onions

The timing of onion harvest depends on the type and your intended use. Here’s how to know when your onions are ready for harvest:

  • Green Onions: These can be harvested when they are 6-8 inches tall. Snip the tops as needed.
  • Mature Onions: For bulb onions, wait until the tops have fallen over and turned yellow or brown. This indicates that the onions have reached maturity. You can bend the tops over to speed up this process.
  • Storage Onions: To store onions, lift them from the soil and let them cure for a few days in a dry, well-ventilated area. After curing, trim the roots and tops, leaving about 1 inch of the top intact.
  • Sweet Onions: These are ready for harvest when they are still relatively small and the tops have fallen over.
  • Shallots: Harvest shallots when the bulbs have reached a good size, usually when the tops have fallen over.

7. Storing Onions

Proper storage is essential to keep your onions fresh for an extended period. Here are some tips for storing onions:

  • Curing: Before storing, allow onions to cure for about 2-3 weeks in a warm, dry, and well-ventilated area. This helps to toughen the skins and prolong their shelf life.
  • Storage Location: Store onions in a cool, dark, and dry place. A basement, garage, or cellar with good air circulation is ideal. Ensure that the storage area maintains temperatures between 32-40°F (0-4°C) and relatively high humidity.
  • Storage Methods: You can store onions in mesh bags, old pantyhose, or slatted wooden crates. Keep them away from potatoes, as they release moisture and gases that can affect onions.


Growing onions is a rewarding experience that provides you with a steady supply of these versatile vegetables. By selecting the right onion varieties, preparing the soil, providing proper care, and safeguarding your plants against pests and diseases, you can look forward to a bountiful harvest. Whether you have a large garden or just a small balcony, onions can be successfully grown in a variety of settings. Homegrown onions not only offer freshness and flavor but also the satisfaction of cultivating your own vegetables. So, roll up your sleeves, put on your gardening gloves, and start growing your very own onions.