While the world is struggling this March because of the pandemic outbreak of Covid-19, planning a summer garden makes even more sense. Planting onions is often the first thing I do in the spring to ensure that I have fresh produce in the summer for my family and friends.
Onions are day-length sensitive. What that means is that onions make big bulbs when they have certain lengths of the day. This article from 2010 explains the science behind what I know from experience. For example, in the summer, Alaska has 22 to 24 hours of sunlight each day, so onions grown there should be “long-day” onions. Here in Northern Arizona, our longest days are about 14 hours, so “intermediate day” or even “short-day” onions work best for us because they don’t need more than 12 hours of light per day to make bulbs. Several “old-timers” in town have complained for decades that locally-sold bulbs from big box stores don’t ever produce large bulbs, and this is often why.
What all this means, besides being careful to pick the proper day length of onion for the area, is that the plants need to be planted early enough in the spring that the days are not quite as long as they are going to be, but are getting enough sun each day to encourage the plants to send down roots and become established before the days do get long enough. For me in St. Johns at the 34th parallel, that means mid-March. By the Spring Equinox, the onions are going to try to start bulbing without having proper root growth and sometimes that means onion death by hateful wind and drought just as they should be trying to take off. I try to get planting before March 15.
Soil Preparation for Planting Onions in the Southwest
Onions need a loose soil that drains easily but is rich in nitrogen. Technically, onions are a leaf crop, and the bulb is a swollen part of the stem, not an actual root like a carrot. Because of that, they desperately need nitrogen frequently throughout the growing season. I use both well-composted manures and blood meal to make that happen in my personal garden.
Here’s how my planting day went this year.
First, I just raked it clean and turned it over with a broadfork to break up the clumps. Onions like soft, fluffy soil to send roots down, so I picked out large crazy roots. It took about 10 minutes to turn the above into this:
Planting Onions: Spacing and Depth
After the soil is prepared (I did have to lift up my dripline grid and then put it back down), I start planting. Many people plant onions way too deep, which causes them to split or never grow bulbs. I take the bottom of the onion between my thumb and forefinger, and insert it into the soil only to the depth of my first knuckle, which is about an inch or so.
Because I want large bulbs, and I buy very high-quality plants from Dixondale farms in the fall, I space my plants about 4 to 6 inches apart. My raised beds have an inside soil diameter of 4 feet by 8 feet, so I get about seven plants along each short side.
After I have all the onions planted, simply water deeply, and mulch if you expect winds, heavy precipitation, drought, or cold. Considering this is March in St. Johns, Ariz., we can expect all four in a single 24-hour period.
A properly-planted, properly-spaced, early spring onion bed can look like this and yield at least 120 delicious 4- to 6-inch onions in August.
Only Buy Onions Where Day Length is Listed
One final note: Onions purchased from a reputable source will always have day length information, as well as expected size and storage information. I tell all my gardening clients and students to stay away from any purchasing agent, whether big box store, feed store, or online shopping option if they don’t state the day length of the onions they are selling. There is nothing more frustrating than buying “onion sets” or “onion plants” that look beautiful but won’t bulb in the particular area they are going to be planted in because the seller doesn’t actually know anything about how to get big beautiful bulbs!
Here’s some I grew a couple years ago, as large as softballs. They were delicious, as well, and stored for about 5 months.
Regina Hitchock is a high school biology teacher in St. Johns, Arizona, where she co-founded the Gardeners with Altitude organic garden club and brings gardening, aquaponics, aeroponics, hydroponics, and seed starting into her classrooms. She serves as Secretary for White Mountain Community Cooperative to promote food- and economically secure self-sufficiency in Arizona. Connect with Regina on Facebook, and read all of her MOTHER EARTH NEWS posts here.
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