The Iowa Gardener: Growing your own onions is easy

Why grow onions? Sure, they are cheap and plentiful in the grocery stores, but if you've never grown onions before, they're an easy, fun crop. You can even braid them into ropes for a beautiful and practical kitchen decoration that you can pull from throughout the winter.

Overall, growing onions is easy. Just plant baby onions — called sets — in the ground in full sun in April or so and let them grow. It's only when you want to grow big, baseball-sized onions that they will need a little more attention.

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You can start onions indoors from seeds in winter, but the easiest way is to buy those onion sets at the garden center. They look like little baby onions bundled together. Choose ones that are relatively fresh with plenty of still-green foliage. Bigger is not better; the smaller ones are less likely to flower prematurely (called bolting), which diverts energy from bulb development. These onion sets should be less than a nickel size in diameter.

If you want to grow big onions, find a variety that boasts large mature size. Those include “Ailsa Craig,” “Walla Walla,” “Yellow Sweet Spanish,” “Mammoth Red” and “Stuttgarter.“

How to plant

Onion sets should be planted in spring once the soil thaws thoroughly and warms up slightly, which is around mid-April in the Cedar Rapids area.

They do best in rich, loose, well-drained soil. Ideally, in the fall prior to planting, you would have worked in lots of compost from your compost pile or worked in manure, and then allowed it to age over the winter to break down so it doesn't "burn" plants the way fresh manure can.

If you want only large, mature onions, plant the sets 1 to 1 1/2 inches deep and 2-3 inches apart. Rows should be 12-15 inches apart.

If you would also like green onions (also called scallions), plant the sets 1-2 inches apart. After two to six weeks, when the onions are still slender and the green tops are perhaps 6 or so inches high, then harvest every other one to enjoy as green onions.

Leave the others in the ground to get large and round for harvest later in the summer. Depending on the type of onion you planted, that can be 90 to 120 days after planting, which translates into a harvest starting possibly as early as July and as late as September.

Watering and fertilization

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Onions like water, and they like nitrogen-rich fertilizer. As best you can, provide consistent moisture, avoiding dry spells followed by soaking the ground. The ideal is about 1 inch of water a week. Onions will not get large if they are too dry, and they will rot if they are waterlogged.

Fertilize with the nitrogen-rich fertilizer of your choice at planting time and then again three to four weeks after planting. The goal is to promote good leaf development, which in turn supports good bulb growth.

An inch or so of mulch is helpful to both conserve moisture and suppress weeds.

Onions are bothered by few pests and diseases, especially if you plant them in a different spot from year to year.

Harvesting

Harvest onions when approximately half of the tops have fallen over. ​ Pull or dig them up gently. Brush or rub off the dirt. Do not wash the onions. They need to "cure," that is, the outside skin gets papery and the "neck" where the bulb meets the foliage to get tight and dry so the onions store well.

If you are going to braid the onions to hang, do that now and hang them in a warm, dry (not extremely humid), well-ventilated area not in direct sunlight and sheltered from rain and dew.

If you are not going to braid the onions, trim off the foliage at the top of the onion. Then lay them out on newspaper, cardboard, or screening in a similarly dry and well-ventilated spot.

Store the onions in a cool, dry place that does not freeze. Properly cured and stored onions will last for several months.

Growing onions might not save you money, but it's a fun way to grow edible plants in your garden and savor the fruits of your summer labor well into winter, for months to come.

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Veronica Lorson Fowler is co-publisher of the Iowa Gardener website at www.theiowagardener.com.