Planting Onions in Northern Arizona

| 3/20/2020 9:52:00 AM

Large bulbing onions 

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. 

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