Growing Onions In Containers

Onion is a key ingredient in almost every dish you cook! No wonder it’s widely cultivated across the globe and easily available in almost every grocery store. Nevertheless, gardeners like growing their own in home gardens for the superior flavors and nutrients. 

Even if you have limited gardening space, onions are among the vegetables that won’t mind growing in pots! Growing onions in containers is easy and just as rewarding as growing them in garden beds. Continue reading, and you’ll learn all about growing onions before you can start your potted onion garden.

What To Start With : Seeds VS Bulbs

When planting onions, you have the option to start with seeds or bulbs. Many gardeners choose to plant sets since they are hardy, easy to care for, and quick to mature. However, since they are prone to forming a flowering stalk prematurely, try to choose small sized bulbs to plant, ideally ¾ inches in diameter. 

If you have more time, you can also start from seeds. Since they take up to four months to mature, you can only start them outdoors if you have a long, warm growing season. In cooler climates, start seeds indoors 6 to 8 weeks before the last spring frost. 

Container Size

Growing onions in containers is much the same as growing them in the ground. However, an added thing you need to care about is choosing the correct container size.

Since you’ll want to harvest at least a bunch of onions after putting in all the effort to grow them, choose a container that’s 10 inches deep and several feet wide to grow several plants in the same container. Window boxes or large tubs are good options for growing onions.  

Make sure there are drainage holes at the bottom. If there aren’t any, you’ll need to drill some before filling the pots with soil. 

Fill The Container

Choose a loamy, rich potting soil to fill the containers. Avoid using garden soil in your containers since they bring in diseases and weeds, and ask for additional care through the growing season to pull off a good crop. You can mix potting soil and compost in the ratio of 2:3 to fill the pots for best results. 

Planting Onions

Onions From Sets

Wait until the soil temperature is 60°F to plant sets. Plant them about 2 to 3 inches deep in soil and 2 to 3 inches apart if you just plan on harvesting the green tops. If you want to grow full-sized bulbs, however, space them at least 4 inches apart. Water the plants right after planting. 

Onions From Seeds

Fill a seedling tray with seed starting mix. Sow the seeds ½ inch deep in the soil and about 2 inches apart. You can space them further apart, 4 to 5 inches when you transplant them to a bigger container.

Germination is fastest when temperatures are between 68-77°F. You can place the tray over the refrigerator to provide warmth for germination. With the right conditions, seeds will take about 8 to 10 days to sprout. Once the seedlings have at least three leaves, you can transplant them to bigger containers.

Where To Place The Container For Maximum Onion Growth!

The best thing about growing onions in containers is that you can place them wherever there’s ample sunlight reaching. Onions grow best in full sun, with at least 6 to 8 hours of sunlight. A sunny balcony or south or west-facing windowsill is best for growing onions if you don’t have outdoor space. If onions aren’t getting ample natural light, supplement it with grow lights. 

Caring For Potted Onions

Temperature For Growing Onions

Though onions can adapt to a wide range of subtropical and tropical climatic conditions, bulbs develop best when temperatures are between 70 to 75°F.

Water Requirements For Growing Onions

Onions growing in pots will need more water than those growing in the ground since they don’t have access to the stored moisture in soil layers. They will solely depend on irrigation. Offer them 2 to 3 inches of water each week, possibly more in summers. Check the soil moisture daily, and water the plants if the soil feels dry to touch. 

Stop watering by the end of the growing season as soon as the tops fall over. Dry soil gives onions a chance to harden for better storage. 

Fertilize Onions In Containers

Onion plants are heavy feeders and will need regular feeding throughout the growing season. Offer a balanced liquid fertilizer every 3 to 4 weeks to help them grow their best. In the case of organic gardening, you can feed compost tea every few weeks to keep the plants nourished. For more details see my separate article on how to fertilize onions.

Harvesting

Green tops can be harvested once the shoots are 7 to 8 inches long. Fresh and tender shoots taste best. For harvesting the bulbs, you’ll need to wait between 100 to 175 days for them to reach maturity.

When the onion tops starting turning yellow and bend over, harvest time is near. Don’t water them beyond this point and wait until the tops are completely brown before harvesting the bulbs. Spread them out on a cool, dry surface to store them. When stored well, they can be used for over 10 months!