Everything you need to know to grow onions

Potted Egyptian walking onion

Friday, April 12, 2024

The onions we cultivate in our gardens today likely originated from a wild Asian onion, but has been grown so long, the road back to the original is lost. Two thousand years ago, there were many varieties that we would recognize today. There were round onions, white onions, red onions, flat onions, long onions, keeper onions, sweet onions, spicy onions. 

Onions have been important for their perceived health benefits in times gone past and proven health benefits today as well as the fabulous taste they add to an array of dishes.  For the nutritional rundown, onion nutritional info

Onions are easy to grow, have little to no pest problems and are a perennial to boot!  They will hang out in the garden until you pull them.  Some will even multiply underground and produce "seeds" above ground.

Onions have shallow roots, like to be moist, but can’t stand being waterlogged. Continuously wet soil causes them to rot.  You should enrich the soil with plenty of organic matter before planting. As common sense would tell us, they also like loose soil that allows their bulb to expand without restriction. Organic matter helps this along. Onions can be grown in the ground or in pots. My perennial Egyptian walking onion has been growing in its pot for 10+ years.

In the Midwest, seeds can be started indoors as early as February and transplanted outdoors in March. Transplanting should be done 4-6 weeks before the last spring freeze for spring planting.  Planting later than this is also fine.

Since onions are perennials you can also plant in the fall, October for our Zone 6/7 garden. For multiplier type onions, fall planting will provide a bigger harvest next spring and summer.  

Egyptian walking onions propagate underground and through their bulblet tops they put on at least twice a year.  In our area, Our Egyptian walking onions put on their bulblets in May or June.  As soon as the bulblets turn reddish brown and have filled out, they are ready to plant.  

The more popular method of starting onions is planting “sets” that are young onions that can be put out in early spring as soon as the soil can be worked, just as the daffodils begin to fade for full size onions.  You can plant later and still get scallions or smaller bulbs.  Or leave in the ground overwinter for a bigger harvest the following year.

Bulbing onion flowering in late spring

You can place them close together and pull for scallions until the bulbing onions are 5-6” apart. As the bulb reaches full size, you can pull the soil away from the top of the onion to help the bulb and neck cure for harvest.

You can also plant the bottoms of store bought onions. If you get enough of the bottom, the onion will take root and give you an onion next season.

Onions tell you when they are ready to harvest, when half of their tops fall over. What can be easier than that? Like garlic, they should be lifted rather than pulled from the ground and leave them in shade for about a week to harden. I use a trowel to dig under the bulb and pop them out. You don’t want to knick them or they will not store well. If you do, keep them in the fridge and use them first.

Onions and garlic ready for harvesting

So, how do you choose which onions to plant? The best bet is to talk to your local nursery to see which grow the best in your area for the ones that thrive in your climate.

There are 3 types of bulbing onions-short day, intermediate day, and long day onions. Intermediate and long day varieties have been around for a long time. Short day onions are relatively newcomers.

Onions are sensitive to daylight hours. They start forming bulbs when daylight hours hit a minimum. For long day onions, it is 15 hours. For intermediate, it is 12-13 hours. Short day onions are 9-10 hours.

I would have thought long day onions would be for further south, but this is wrong. The north gets the really long summer days (think of Alaska in June with no darkness). Long day onions should be planted in states north of the Oklahoma/Kansas border (approximately 36 degrees latitude).

Long day onions are planted in states in the northern part of the US, intermediate in the middle and short in the South.

Short day onions are planted in the fall and form bulbs in the spring. Intermediate and long day onions are typically planted in the spring as sets, not seeds. Seeds require sprouting indoors and transplanting.

So, if you want a sweet onion and live in the Midwest, Vidalias are not the best bet since it is a short day type. A better choice is a Walla Walla or a Sweet Spanish.

Close up of onion flower

The other thing to keep in mind is that, like wine, onions pick up the terroir they are grown in. You can grow the exact same onion as you buy in the store or at a farmers market but have a different taste because of the differences in your soil.

There are many fun onions to grow besides the round ones. There are the flat disk like Borrettana Cipollini or the Red Baron onion that is a red scallion type onion. Of course, there is the onion made famous in French cooking, the shallot-French, Gray or Sante are well known varieties.

Then, there are onions for keeping over the winter like Rossa Di Milano, Early Yellow Globe, Sweet Sandwich, and Granex Yellow.

Onions will also keep over another year in the ground. When onions I planted last spring did not get to decent size, I left them over the winter. They gave nice bulbs the next summer.

Another type of onion is the Egyptian walking onion (pictured above in a pot). It is a perennial that you can pull year round. They do not form bulbs. They are about the size of a large scallion or leek, getting an inch or two wide and 3” long bulb. They also grow great in a pot. When they get their bulblets, they remind me of Medusa. Really cool.  You just snap off the bulblets, separate them and plant for scallions this year or more onions next year.  They also multiple underground year on year.  For more on Egyptian walking onions:  Egyptian walking onions

They are one of my must haves in the garden since they can be harvested year round. Their bulb is great as a cooking onion and their greens as a chive.

Onions are a great addition to the garden. They are perennials, easy to grow and have little to no pest problems. I really like the perennial type onions, the Egyptian walking onions and multiplier onions like potato onions. The Egyptian you can just leave in place and harvest from year round. The multiplier potato onion has a very long shelf life indoors for a storage onion. When you harvest it, just leave behind the smaller onions and they will multiply again for next year’s harvest.

Garlic on the left, newly planted onion sets on the right

This spring my Egyptian walking onions are doing great.  I planted some onion seed several weeks ago in my mini greenhouse outdoors, but am not seeing a lot of action there yet and I bought intermediate day bulbs with white, sweet and red onion sets.  These I planted a few weeks ago and are doing just fine.