Growing Onions in Containers: A Complete Guide

Onions are an important part of almost every kitchen because they are the base for many savory dishes around the world. You can easily grow these alliums at home, and it will cost you even less than buying them on the store.

You can grow onions in pots on your porch, patio, or fire escape even if you don’t have a garden or land. You can grow red, yellow, or white onions in planter pots. Make sure the spot where you’ll keep the pot gets full sun, preferably from the south, before you plant onions in it.

Alexandra Jones is a certified master gardener in Philadelphia. Jones writes about gardening, climate, urban farming, and sustainability, and he grows plants both inside and outside.

Onions are one of the most versatile vegetables to grow in your garden. Their pungent flavor adds depth and aroma to soups, stews, salads and more. The good news is that you don’t need a large garden plot to grow onions – you can easily grow them in containers right on your patio or balcony.

Container gardening makes it possible to grow onions even if you only have a small space. With the right techniques, you can harvest abundant crops of onions from pots on your deck or windowsill. Follow this simple guide for successfully growing onions in containers all season long.

Choosing the Right Container

The most important factor is ensuring that your onions have enough room to grow. Onion containers should be at least 10 inches deep. The diameter can be any size as long as each onion has 3 to 4 inches of room to grow.

Good container options include

5 gallon buckets
Planter boxes

Sturdy pots
Window boxes
Half whiskey barrels

Make sure your container has drainage holes in the bottom so excess water can escape, This prevents the onion roots from getting waterlogged,

Selecting the Best Onion Variety

There are three main types of onions:

Long-day onions: Require 14-16 hours of sunlight per day. Best for northern regions. Examples: Copra, Patterson, Red Wing
Short-day onions: Only need 10-12 hours of sun daily. Best for southern regions. Examples: Granex, Texas Early White, Candy

Day-neutral onions: Need 12-14 sunlight hours per day. Best for central regions. Example: Super Day, Wadenswil

Choose an onion variety that matches your region’s daylight hours for optimal growth and bulb formation. Check seed packets or with local garden centers to find ones suited for your area.

When to Plant Onions in Pots

Onions can be grown from seeds, sets, or transplants. If planting seeds, start them indoors 6-8 weeks before your last spring frost date.

The best times for planting onions sets or transplants are:

Spring planting: When daytime temperatures reach 60°F

Fall planting: 6-8 weeks before first autumn frost

Onions require soil temperatures above 50°F to grow well.

How to Plant Onions in Containers

Step 1: Fill container with potting mix

Use a high-quality organic potting mix with compost or manure added. Onions prefer soil with a neutral pH between 6.0-6.8.

Step 2: Plant onions

Plant onion sets 1-2 inches deep, with 3-4 inches between each one. Pat soil gently around each onion set.

For seeds or transplants, plant 1⁄2 inch deep in rows 4 inches apart. Cover with soil and water after planting.

Step 3: Water and fertilize

Water thoroughly after planting. Let the soil dry out between waterings. Fertilize every 2-3 weeks with a balanced organic fertilizer.

Step 4: Monitor growth

Place in full sun. Rotate the container occasionally for even growth. Apply mulch around the onions to retain moisture.

Step 5: Harvest onions

Onions are ready to harvest when their tops turn brown and fall over. Loosen the soil with a fork and gently pull the bulbs. Allow them to dry out of direct sunlight for 1-2 weeks before storing.

Tips for Growing Onions in Containers

Give each onion adequate space to reach maturity. Overcrowding leads to smaller bulbs.
Weed weekly to prevent competition for nutrients.

Use good drainage and aerate soil periodically.
Water when top inch of soil is dry. Too much moisture causes disease.
Harvest promptly once the tops fall over. This prevents rotting.

Cure harvested onions before storage by allowing them to dry out of sunlight.

Common Problems Growing Onions in Pots

Leggy seedlings – Onions started from seed may get long, weak stems. Ensure they get enough sunlight.

Poor bulbing – Insufficient sunlight, overcrowding, or incorrect variety can inhibit bulb growth.

Root rot – Excess moisture leads to fungal diseases. Allow soil to dry out between waterings.

Bolting – Onions that flower prematurely often bolt when exposed to temperature swings. Maintain consistent conditions.

Pests – Onion thrips and onion maggots bore into bulbs. Keep area weed-free and use row covers if needed.

Storing Onion Harvests

Cured onion bulbs will keep for 2-3 months in a cool, dry, dark place with ample air circulation. Avoid humidity and moisture. Check regularly and remove any bulbs showing signs of rotting.

With the right care, onions are extremely rewarding to grow in pots. Even gardeners with limited space can produce bumper crops by following these simple guidelines. Get your containers ready this season for a patio or balcony overflowing with homegrown onions!

Choose the Right Onions

Before planting, youll want to choose the variety of onion thats best suited to your growing zone. Onions are picky about how much light they get every day, and they won’t start making bulbs until those conditions are met.

Walla Walla onions and other long-day onions need 14 to 16 hours of sunlight every day and were specifically bred to grow in the northern United States. On the other hand, short-day onions like White Bermuda only need 10 to 12 hours of light a day and grow best in the south of the country.

There are day-neutral onion types, like Candy, that are in the middle. They were bred to do best with 12 to 14 hours of sunlight a day. Plant these if you live in the central part of the country, around growing zones 5 or 6.

Step 3: Care for Your Onion Plants

Water the soil well so that it is wet all the way through and water flows out of the holes in the bottom of the pot. Place the containers in a spot outdoors with full sun.

Keep an eye on how wet the soil is in the pots and water the plants when the top inch or so of soil is dry to keep the roots from rotting. 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.

How to Grow Onions from Seed in Containers and Garden Beds| Easy Planting Guide

FAQ

Do onions grow well in containers?

For onions you plan to harvest as scallions or spring green onions, an 8-inch (or larger) pot works fine. To raise bulb onions, you’ll need a container wide enough so that each onion has about 3 inches of space around it. Many gardeners choose to grow onions in plastic tubs or half whiskey barrels.

How many onions can you grow in a 5 gallon bucket?

A 5-‐gallon bucket works fine for growing 6 or 8 onions. A large planter box works great, or even a plastic tub. Be sure your container has good drainage holes and try to elevate it a little bit off the ground.

What month do you plant onions?

When to Plant Onions. In spring, plant onion sets outdoors as soon as the ground can be worked, usually in late March or April, when temperatures are no longer likely to dip below 28°F (-2°C). In spring, start onion seeds indoors for about 6 weeks before transplanting to the ground (once the soil is at least 50°F).

How many onions grow from one bulb?

One small onion set grows into one larger onion. Plant these in autumn or spring, 10-15cm apart in well-prepared, moisture-retentive, fertile soil in full sun. Keep the area weed free and water in dry periods. Harvest the onions when they’re big enough to eat or the foliage has turned brown and started to wither.

How do you grow onions in a container?

The first step is to choose the right container for your onion sets. Onions need a container that is at least 12 inches deep and 8 inches wide. The container should also have drainage holes to prevent the roots from rotting. You can use a variety of containers for growing onions, including pots, grow bags, and even old buckets.

How much water do onions need to grow in a container garden?

Water is important to growing onions in container gardens because your container onions will have little access to naturally stored rainfall from surrounding soil like onions grown in the ground do. Onions grown in containers will need at least 2 to 3 inches (5-8 cm.) of water a week, perhaps even more in hot weather.

What size container do onions need?

Onions need a container that is at least 12 inches deep and 8 inches wide. The container should also have drainage holes to prevent the roots from rotting. You can use a variety of containers for growing onions, including pots, grow bags, and even old buckets. If you’re using a pot, make sure it has a drainage hole in the bottom.

How much space do you need to grow onions?

So don’t let space limit your ability to grow your food. Container size is important for growing onions. A pot with a depth of at least six inches and a width proportionate to the height will work well. The onion tops should not touch each other when growing but should be separated by two inches or more.