How to Grow Onions in Containers - Backyard Boss
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How to Grow Onions in Containers

Onions are a staple food in nearly every pantry. Along with garlic, these vegetables are the perfect way to boost flavor in your dishes and add a nutritious punch. In fact, planting onion crops not only grants you a large supply of a hearty vegetable, but it also helps to repel pests and protect other plants in your garden.

When people think of onions, they likely think of bulbs growing in the ground, where they’ll have plenty of space to settle their roots into the soil. However, the best part about growing onions is their adaptability to diverse conditions. The bulbs themselves may need space to grow, but onions can often do very well in small spaces – namely, a potting container. 

Fortunately, homeowners with a minimalist garden area can easily grow onions efficiently in a small space. If you are looking to start growing onions in containers, here’s a list of steps to follow to ensure you have a bountiful harvest.

When Should You Plant Your Onions?

onion growing in dirt
Image credits: MabelAmber via Pixabay

Since onions are a cool-weather crop, the preferred time to plant onions is in early spring. This ensures that the onions are planted while temperatures are slightly cool to be grown throughout the warm weather.

If you are growing onions from sets – which are essentially small onion bulbs – you’ll want to plant these outdoors around late March or April, when temperatures are more likely to rise above 28 degrees Fahrenheit. As for growing onions from seed, start the seeds indoors in the spring, about six weeks before transplanting them to the soil that reaches at least 50 degrees Fahrenheit.

Keep in mind that onion crops that are planted in the fall will need at least 4 to 6 weeks to become settled into the ground. They become dormant in the colder seasons, only to come back to life when temperatures are warm again in the spring. Ideally, spring-planted onions will be harvested just in time to make a hearty side dish for a mid-summer potluck that same year, but fall-planted onions should be ready to harvest in early to mid-summer the following year.

Now that you know the ins and outs of generally planting onions, it’s time to take a look at how they thrive in containers!

How to Plant Onions in Containers

When you begin growing onions in containers, you’ll notice that the process is largely akin to growing onions in the ground – there’s just less space to work with. If you are looking to start a home garden with minimal room, here are some simple steps to growing onions in pots.

Step 1: Choose an Appropriate Location

Spring onions in pot
Image credits: Studio_Loona via Shutterstock

Before planting your onions, it’s essential to place your containers in an area that receives up to 12 hours of sunlight each day. This will ensure your onions grow to their maximum size and receive enough energy to form bulbs. Ideally, this would entail placing your containers outside where they have full access to the sun, or on a windowsill indoors.

However, in the case that you are growing onions indoors and sunlight does not reach your garden, it is possible to induce photosynthesis by placing fluorescent bulbs close to the top of the onions. An easy way to do this is by attaching a shop light on an adjustable chain and hanging it over your planting containers.

Step 2: Plant Onion Bulbs in Containers

young onions growing in a box on the windowsill, close-up
Image credits: Bonsales via Shutterstock

Before planting your onions, it’s essential to create a nutrient-rich bed of soil. Do this by adding nitrogen fertilizer at planting time or digging a trench into the soil – about 2 inches deep and 3 inches wide – and fill with compost. Then, bury your onion sets 2 to 6 inches apart and press them about an inch deep into the soil.

You might also choose to make your own potting mix at home. This can be made with equal parts of coir, sand, and compost/manure. Add fertilizer on top of this to boost the amount of nutrients your onion plants are taking in. Ensure that your homemade mix has a pH between six and seven, as onions won’t take well to acidic soil.

Step 3: Care For Your Onion Plants

Person Planting Onion Herbs at Home in a Pot
Image credits: troyanphotos via Canva

Once the onion bulbs are snug in their containers, it’s time to maintain them until harvest. You can start by covering your immature bulbs with a light mulch to keep them protected and retain moisture. Water your crops sparingly; about 1 inch of water per square foot, including rainwater, should do well for your onion plants.

Moreover, it’s best to fertilize your onion plants with nitrogen once every few weeks. Once you see that the onions have emerged from the soil, stop fertilizing immediately. Do not cover the onions with soil again; this means the bulb process has started and your onion plants are growing properly. Onion sets will mature within 14 weeks.

Step 4: Harvest Your Container-Grown Onions

freshly harvested onions with roots
Image credits: Zoe Schaeffer via Unsplash

When the time comes to harvest your onions, it’s important to know the difference between a ripe onion and an onion that has stopped growing. An onion plant that has halted the growing process will start sending up flower stalks. Pull these onions whenever you see them; they won’t store as well as ripe onions, which means you’ll need to use them in recipes within a few days’ time.

On the other hand, you’ll know your onions have fully ripened when the bulbs are large and the stalks begin to turn yellow or fall to the side. At this point, you can speed up the final ripening process by stepping on the stalks to bend them. 

Harvest your onions in late summer when tops are fully brown. Make sure that you are pulling your onions in dry weather, as onions harvested on a rainy day will cure poorly and likely rot in storage. Unless you plan to braid the onions together, cut the roots and trim the tops for easier storage.

Get Your Onion Crops Ready

Onions may be an easy vegetable to grow, but having a tiny yard can make it difficult for homeowners to fit them into their gardens. If you would like to plant onions but don’t have enough acreage to do so, planting them in containers is an efficient way to grow onions with the least space possible. Simply fertilize regularly, water sparingly, and pull when stalks have browned to ensure a healthy harvest.

Have you attempted growing onions in containers? Share your tips and experiences in the comments below!