How to Properly Grow Onions in a Container

Onions are a staple ingredient in just about any kitchen, serving as the base for savory recipes across global cuisines. These members of the allium family are easy to grow at home—and it's even more affordable than buying them at the store.

Even without a garden or backyard, you can grow onions in containers on your porch, patio, or fire escape. You can grow red, yellow, or white onions in planter pots. Before planting onions in containers, ensure that the site where you'll keep the pot gets full sun, ideally with a southern exposure.

• Working time: 30 minutes
• Total time: One hour
• Skill level: Beginner
  

When to Plant Onions in Containers

The best time to plant onions in containers is in the springtime, or when soil temperature in your growing zone is at least 60 degrees. Note that in the southern portion of the country, where winters are mild, onions may be planted in the fall to harvest in early summer.

You can choose to plant onion sets, or baby onion bulbs, or grow your own onions from seed. However, onions grown from seed must be started indoors about eight weeks before your area's last frost date.

You can also plant organic onions from the grocery store or farmers' market that may have sprouted before you got a chance to eat them. Before planting a sprouted onion, peel away the outer layers until you get to the central sprouts (there may be one or more). Separate the sprouts, then plant them as you would onion sets.

Choose the Right Onions

Before planting, you'll want to choose the variety of onion that's best suited to your growing zone. Onions are sensitive to the amount of light they receive each day, and they won't start producing bulbs until those conditions are met.

Long-day onions like Walla Wallas require 14 to 16 hours of sunlight each day and have been bred to grow in the northern part of the United States. Conversely, short-day onions such as White Bermuda only need 10 to 12 hours per day and are best for planting in the southern part of the country.

Day-neutral onion varieties like Candy fall somewhere in the middle and have been bred to grow best with around 12 to 14 hours of sunlight per day. Plant these if you live in the central part of the country, around growing zones 5 or 6.

Tools and Supplies You Will Need

Onions can be grown in containers or in the ground, but you'll need a good-sized pot that's at least 10 inches deep to accommodate the roots. The pot should be about eight inches in diameter. If you're planting multiple onions in one pot, choose a pot that's three inches across for each onion you'd like to grow.

For example, a five-gallon container can accommodate between six and eight onion plants. You can also plant onions in window boxes or buckets with holes drilled in the bottom as long as they're deep enough.

Before you begin, gather the following materials:

• Onion sets, transplants, or prepared onion sprouts
• Plant pots with drainage holes in the bottom
• Potting soil
• Organic compost
• Trowel (optional)
• Gardening gloves (optional)

Step 1: Fill Containers With Soil

Add a mixture of two-thirds potting soil and one-third organic compost to the containers so that the soil surface is about an inch below the upper edge of the container.

Step 2: Plant Onions in Containers

Use a finger to make a small hole in the soil two to three inches deep for each onion you'd like to plant. Space them four to five inches apart. Place onion sets root end down in the holes, then gently pat the soil down around each one to keep it in place.

Step 3: Care for Your Onion Plants

Water the soil deeply so that it is well moistened and water comes out of the holes at the bottom of the container. Place the containers in a spot outdoors with full sun.

Monitor the soil moisture in the containers, and water the plants when the top inch or so of soil has dried out to prevent root rot. You can feed the plants with a low dose of organic fertilizer after a month or so. Remove any weeds that might grow in the containers.

Step 4: Harvest the Onions

Mature onions are typically ready to harvest three to four months after planting, typically in the late summer or early fall depending on your growing zone. Onions are ready to harvest when the leaves have begun to yellow and fall over. Carefully pull onions from the soil, leaving the plants intact, then gently shake the soil from the bulbs.

It's best to harvest onions early in the morning before it's too hot or sunny. Be sure to harvest onions before they bolt (grow flowers). Onions that have bolted should be used quickly because they won't store well.

Step 5: Cure and Store the Onions

You can store fresh onions in a plastic bag in the refrigerator to use right away. However, you must cure onions for longer storage out of the fridge.

Lay out the onions in a cool, dry, shady place like a shed or garage to dry for two to three weeks. Onions are cured when the tops are totally dry and the skin of the onions has started to become brittle. Store cured onions in a basket, crate, or other well-ventilated container in a cool, dark, dry place for up to three months.