Growing Onions in the Central Region

When I start talking about regions, things can get a bit gray. Since I have been a gardener, landscape designer, and horticulturalist for 2 decades in Kansas; I generally mean Kansas, Missouri, Nebraska, and all of Zone 5 when I say the Central Region.

Growing onions can be rewarding for those who love the taste of onions, as much as I do. There are 5 steps to growing great onions in this area:

  1. Site Selection
  2. Choose or amend your soil
  3. Pick a variety for your area
  4. Planting, hilling, and maintenance
  5. Harvest and Curing

Site Selection

When you are preparing your garden beds for vegetables, site selection is very important. For most vegetables, other than greens, you will want at least 8 or more hours of full sun. This is true for onions. They require lots of sun to produce big bulbs.

Onions growing in hills
Grow onions in hills for biggest bulbs!

You will also want your garden to be near a water source; if you have the ability to install drip irrigation or have a rain barrel nearby, those are good sources.

Soil Preparation

Once you have your spot picked out for planting, you should get your soil ready. I recommend getting a soil test done before planting, so you know how to fertilize and amend. Onions grow best in well-drained, loamy to sandy-loam soils. And they love nitrogen!

If your soil is heavy clay, DO NOT add sand to the soil; it will turn your soil into concrete. The best way to improve drainage of heavy clay soil is to add organic matter, slowly over the course of years.

After checking your soil test, amend your soil with compost instead of chemical fertilizers. Once the onions are planted, you should fertilize every other week with a nitrogen fertilizer. I like to use fertilome Fish Emulsion fertilizer that is 5 percent Nitrogen.

Copra onions
Copra is a Yellow Sweet Onion variety that grows quickly
Day-length map for onions

Choosing Onion Varieties

For most of Zone 5 and northward, you will want to choose a long-day or intermediate-day variety. Long day varieties grow best when there is 10-14 hours of sunlight per day. Intermediate varieties grow best in 10-12 hours of sunlight per day.

The varieties I like the best for my own garden are Copra, Candy, and Red Candy.

Copra is a Long-Day, yellow variety that produces 3-4″ bulbs in about 110 days after planting. They can store up to 12 months and are resistant to foliar diseases.

Candy and Red Candy are Intermediate-Day varieties. Candy is sweet yellow onion that takes 90-100 days until harvest, and can grow 6″ in size. Red Candy grows faster, 85-95 days until harvest, but only gets 3″ in size. Both Candy varieties are resistant to foliar diseases.

Everyone always asks how to plant onions- by seed, set, or plant? I ALWAYS recommend planting by plants if you are planting in spring. Plants are grown from seed and have not gone through a chilling process that forces the bulb to begin seed production. Sets have gone through vernalization that promotes seed production, and will not make big bulbs.

Planting, Hilling, and Onion Care

When you get your onion plants, remove the rubber band around the bunch and pull the plants apart gently. Do not let them dry out but store them in a cool, dry place, like the refrigerator or a dark garage.

Plant onions as soon as the soil can be worked and the nighttime temperatures do not drop below 28 degrees F. If planting in rows, mound up the soil into hills, 8-12 inches tall by 8 inches tall on top and gently sloping away. Make mounds 12-18 inches apart. Flatten the top of the mound gently with a garden rake.

Plant onion plants 4-6″ apart with just the tip of the bulb and the rootlets into the soil. Do not cover the whole bulb with soil if you want large bulbs. Water gently with a drip system or garden hose. You can mulch the hills with grass clippings, chopped leaves, or straw to prevent erosion and weeds.

Fertilize onions bi-weekly until the bulbs begin to swell and push the soil back. Once they begin bulb formation, stop fertilizing. Also, now is the time to pull the mulch away from the onions, so bulb formation is not disrupted.

While there are a variety of pests and diseases that onions can get, you will only have major issues if you do not rotate crops. Do not plant your onions in the same place year after year.

white onions
White onions ready for storage

Harvesting and Curing Onions

When the tops of the onion plants begin to yellow and fall over, it is time to harvest. Hopefully, most of the onions will have around 12-13 leaves. Pull the onions (whole plant) in the morning of a sunny day for best curing. I prefer to dry my onions on an old screen door set in a lean-to or open shed to prevent damage from rain.

Curing usually takes 3-5 days in this setup. The onion is dry when the neck where the bulb meets the leaves is dry and does not slip when squeezed. Cut the roots and the tops off the 1 inch above the bulb.

Store bulbs in mesh bags or wire bins a root cellar or cool, dry garage or basement. Sweet onions like Copra or Candy should be used first, as they do no last as long as pungent red onions like Red Candy or Redwing.

Come on out to the garden center at 2991 Goldfinch Road, Hiawatha, KS for your onions. Or check out the garden store online.

Happy planting!

One thought on “Growing Onions in the Central Region

  1. Hi, this is my first year planting onions. I have gardened for several years but onions intimidate me. I am in zone 6b in Missouri, about 45 minutes southwest of St. Louis, so I am growing three different intermediate day onions. I thought I had a good plan until I got on the internet today. I have three different trays ready to go. I have been trimming the green shoots and thought that I was about ready to put them out in the garden. By your recommendation, I think I am good to go, but I just read something else that said onions can’t go out if the weather is below 50 degrees. Can you clarify for me? I would greatly appreciate your help.

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