Mainstay Vegetables: Onions

Wendy S. Delmater
By Wendy S. Delmater on Wed, Aug 14, 2013 - 12:56pm

Onions are a vegetable that I use in almost every meal. Chopped into soups or omelets, fried as rings, boiled in stews or raw on salads, onions are truly a mainstay vegetable. And luckily for me (and you), they are incredibly easy to grow.  But what kind should you put in your garden?

Onion varieties are classified as either Long-Day, best in the North, or Short-Day, best for the South. Yellow Spanish onions are long-day. ‘Stuttgarter’ is a comperable short-day variety with slightly flat shape and both should be grown from sets, if possible. But the easiest to start with are bunching or pencil onions from seed. These are the green ones you see chopped on Chinese food, and both the slim bulbs and the green tops are flavorful but mild. As their name implies they grow in bunches. I have no trouble whatsoever raising pencil onions that look like they were bought in the supermarket, in six-inch-deep raised beds. You can grow them or any other type of onion in as little as 4" of soil as long as it's not compacted - all onions need loose soil and full sun in USDA zones 3-9.  Just remember to plant them no more than an inch deep.

I've grown the yellow and white onions you see in the store from sets, but found that--for me, at least--they did not get as large as supermarket onions. That makes sense since I needed to add nitrogen! I later discovered that onions are heavy feeders and need nitrogen to make big bulbs. But while mine never get as large as store-bought, and they tasted great. Note, my white and yellow onions did not overwinter well, even under six inches of pine straw mulch. 

What I have had sucess with are perenial walking onions (a.k.a. potato onions). They grow very quickly and like pencil onions the green tops are great chopped, at least until the plant gets old. The smallish dry bulbs store well, and they overwinter in my garden beds better than yellow or white onions since they are closely related to cold-hardy leeks. But then, I am in Zone 8.

What a lot of people don't realize is that onions are a cold-season crop, and while easy to grow in cool weather because of their hardiness they--like many other plants--stop producing much in the hottest part of the summer, especially in warmer climates. I've taken to starting new walking onions indoors from the prolific bulbs they drop and replanting those outside once the fierce, midsummer heat is past. I get two harvests: one in early August and one in late October.


  • Seeding? Onion seeds are short-lived. If planting seeds indoors, start with fresh seeds each year. Start seeds indoors about 6 weeks before transplanting. Move transplants into the garden as soon as the ground can be worked. Plant the transplants about 4 inches apart.
  • Sets? Plant sets directly outdoors 4 weeks before last spring frost. Make sure temperature doesn’t go below 20 degrees F.
  • Set 5 inches apart from each other in a row and in rows 12 inches apart. (Biointensively, in raised beds I have planted them as little as 2 or 3 inches apart, based on onion type. Those that will make big bulbs go 3" apart.)
  • Think of onions as a leaf crop, not a root crop. When planting onion sets, don’t bury them more than one inch under the soil; if more than the bottom third of the bulb is underground, bulb growth can be restricted.
  • Practice crop rotation with onions. (Remember, they are heavy feeders)
  • Fertilize every few weeks with nitrogen to get big bulbs. Cease fertilizing when the onions push the soil away and the bulbing process has started. Do not put the soil back around the onions; the bulb needs to emerge above the soil.
  • Generally, onions do not need consistent watering if mulch is used. About one inch of water per week (including rain water) is sufficient. If you want sweeter onions, water more.
  • Onions will look healthy even if they are bone dry, be sure to water during drought conditions. Once the tops dry out, it's too late.
  • Make sure soil is well-drained. Mulch will help retain moisture and stifle weeds.
  • Cut or pull any onions that send up flower stalks; this means that the onions have "bolted" and are done.  - Source, Old Farmer's Almanac Planting Guide

When onions start to mature in late summer, their tops start turning yellow and begin to fall over. At that point, you should bend the tops down. Leave the onions in the ground to finish ripening. Hand-rake the mulch off and loosen the soil to encourage the bulbs to dry.  Experts suggest that you then pull them and let your onions cure on dry ground, but our climate is so humid I cure mine indoors. You have to handle them very carefully—the slightest bruise will encourage rot to set in. If you have a root cellar store your dry onion bulbs at 40 to 50 degrees F (4 to 10 degrees C) in braids or with the stems broken off. DO NOT store them with apples or potatoes due to offgassing problems.

A few word about pests. I have never, ever had a problem with any insects or diseases on my onions, but in case you do here is more info from the Old Farmer's Almanac Planting Guide

  • To control thrips—tiny insects about as fat as a sewing needle—take a dark piece of paper into the garden and knock the onion tops against it; if thrips are present, you will spot their tan-colored bodies on the paper. A couple of treatments with insecticidal soap kills them. Follow the package directions. Spray the plants twice, three days apart, and the thrips should disappear.
  • Onion Maggots: Cover your emerging onion crop with a fine mesh netting. Seal it by mounding soil around the edges. The onion maggot likes to lay its eggs at the base of plants, so the netting should prevent that. You should also keep mulch away because the insects like decaying organic matter, and make sure you completely harvest your onions as the season progresses. Onion maggots are usually a problem in very rainy periods, so these precautions may be unnecessary if you have a dry season.


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