Growing Onions

Colorado State Univ. Field DayDo you grow onions? They’re not the most popular crop for the home veggie garden, which is a shame because they’re incredibly easy to grow. Sure, you can go to the store and buy a bag for a pittance, but that’s true for most vegetables we grow. And the flavor of home-grown onions isn’t that different from the ones at the market.  The primary advantage of growing your own onions is that you know exactly what you sprayed them with—or didn’t.

In general, growing onions is as easy as sticking a few sets into the ground in early spring. You can start them from seed, but they take forever to reach transplant size. That’s why many garden centers and mail order seed companies sell bunches of transplants and onion sets.

Transplants are just that—bunches of onions that were grown to a certain size, then pulled and bundled for sale. Sets are simply baby onions. They both make onion growing much easier. However, while you might think that larger is better, don’t buy transplants thicker than a pencil. Sets should be no larger around than a dime.

Onions are biennials, and plants that are too large will be primed to make a flower, not a bulb. (Extreme fluctuations in springtime temperatures—typical for Colorado—can also “fool” an onion into thinking that an extra winter has come and gone, and it’s time to flower.) If your plants do flower, don’t try to store them; that stem rising through the center of the bulb will soon decay. Maybe it’s time to make some French onion soup?

Onions are considered “heavy feeders” so it pays to make sure your soil is in top shape with plenty of nitrogen (but not too much!). As usual, I recommend a soil test so that you aren’t applying too much or too little fertilizer.

Onions_DBG_LAH_4522Both sets and transplants are small and it’s tempting to crowd them, but remember the plants need room to expand, so space them about four inches apart. I usually plant them twice that densely, then thin every other one to use as scallions. Plants for scallions can be planted a bit deeper, too, so you’ll have a longer blanched stem at the base. Those you intend to leave until mature should be about one inch deep. A two- to three-inch layer of mulch will help suppress weeds that would otherwise compete for nutrients and water.

I used to get pretty confused about which variety to grow. Did I want a “short day” or a “long day” cultivar? Colorado is kind of in the middle!* Happily, breeders have come up with “day neutral” varieties, solving my dilemma. (If all you want are green onions, day length doesn’t matter in the slightest.)

I’ve read plenty of articles advising the gardener to pinch off the flower stalk and/or seed head if the onion bolts. The idea was that the plant should be putting its energy into increasing the size of the bulb, rather than making offspring. Well, it doesn’t work that way. Rather, the size of the onion is directly related to how many leaves are on the plant. Each leaf is connected to one layer of onion—and the biggest leaves have the biggest rings. Plus, according to the experts at Texas A&M, “if you pinch the seed pod off immediately it will keep the center core of the onion from growing and the end result is a smaller onion that will not store well.”

In areas with short growing seasons, such as we have here in Colorado, we’re often advised to knock the tops of the onions over, so the bulbs will “finish up” more quickly. It’s true that you’ll stop the bulbing process in its tracks. The problem is that those plants still have the urge to grow, and they’ll do it in storage.  It’s better to look for an early cultivar, and let it proceed according to its normal timetable.

At some point, the tops will die back naturally, much like any other bulb (think daffodils and crocuses). Once the tops fall over, pull the bulbs and allow them to dry (perhaps in a garage, if afternoon thunderstorms continue). Trim off the roots and tops, leaving an inch of leaves. Then keep them in a cool, dry place. They’ll keep longer if they don’t touch one another.

Onions aren’t the most popular crop for the home veggie gardener (that honor goes to tomatoes).  But when you consider how little effort it takes to grow them, how little space they take up in the garden, and how indispensible they are in the kitchen, they’re certainly worth a try. And when you serve those grilled onions on your next steak (or burger), you can proudly announce that “I grew them myself!”

* Another quote from the Texas A&M site: “Onions are characterized by day length; “long-day” onion varieties will quit forming tops and begin to form bulbs when the daylength reaches 14 to 16 hours while “short-day” onions will start making bulbs much earlier in the year when there are only 10 to 12 hours of daylight. A general rule of them is that ‘long-day’ onions do better in northern states (north of 36th parallel) while “short-day” onions do better in states south of that line.” Colorado Springs happens to be at 38 degrees north, so technically we’re in the “long day” category.

2 thoughts on “Growing Onions

  1. My onions are doing great this year. I read about cutting the leaves down to use as gren onions and they will grow back. I am trying that out by only harvesting one or two leaves per plant occasionally. (I don?t see why they couldn’t be grown in deck containers….just made sure to keep them evenly watered)

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