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Yellow onions in a basket

Steps For Growing Onions From Seed To Harvest Including Storage

Food For Life Garden
Start onions from seed to get the biggest bulbs. It is so rewarding and the cheapest way to grow lots of big onions. Follow this step-by-step guide from Seed to Harvest with instructions on how to cure and store your onions.
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Equipment

  • Planting containers
  • Waterproof tray
  • Seed Starting Soil
  • Fish Emulsion
  • Grow Lights
  • Onion Seeds
  • vermiculite (optional)

Instructions
 

  • Start your onion seeds 8-12 weeks before your last frost date.
  • Fill your planting container with a moistened seed starting soil mix and place the containers in a waterproof tray.
  • Sow 10-20 onion seeds in each container.
  • Label your container with the variety of onions.
  • Cover with ¼ inch of soil or vermiculite.
  • Lay a sheet of plastic wrap over your containers or put the whole operation into a large clear plastic bag to make a "greenhouse". This will keep the soil moist for better germination.
  • Keep the soil temperature above 50 degrees for germination.
  • Mist the surface to keep it moist if necessary.
  • Once seedlings emerge, remove the plastic wrap and put the trays under lights.
  • Keep the lights on the plants for 16 hours a day and off for 8 hours.
  • Water with a light fish emulsion solution once a week.
  • Start hardening the plants off about 4 weeks before your last frost date and transplant a week later.
  • On transplanting day, soak the pots in a solution of fish emulsion and optional EM-1 or LABs for an hour or so before transplanting.
  • Transplant seedlings into the garden 3 weeks before the last frost date.
  • Add compost into the planting hole and as a side dressing.
  • Mulch lightly for moisture retention, to keep weeds from growing, and to keep the soil cool in hot weather.
  • Water with fish emulsion about once every two or three weeks and keep the soil moist throughout the growing season.
  • Onions: Pull the dirt away from your onions as they start bulbing up.
  • Leeks: Push the dirt or mulch up around your leeks to keep the stems blanched.
  • Harvest onions after the tops have fallen over, are starting to brown, and the neck, where it is bent, has almost dried up. The soil should be dry on harvest day (a few days without rain if possible). This assures best chances for long storage.
  • Leave your onions in the field to dry for a day or two if the weather is dry.
  • Move your onions to a dry, airy, shady area to cure for 4 weeks. This will dry their outer skin and make them suitable for long storage.
  • Cut the roots off and the tops, leaving about 2 inches on the onion. If you are going to braid them, don't cut those tops.
  • Remove any bruised, questionable onions for immediate use. Also any that still have green tops.
  • Store in net bags, burlap or wooden crates in a cool, dark, airy and dry spot, away from potatoes or apples. Remove any onions that are showing signs of spoilage immediately to prevent infecting the rest.

Notes

How to choose your onion variety

I recommend you check out my onion varieties primer for selecting onions that will work for you.
Here are the most important things to pay attention to when you go to select seeds and before you order. 

Consider the right day length: 

Based on the area you live in, you'll need to choose from either long-day, short-day or day-neutral (intermediate) day onion varieties. So north of the Mason-Dixon line you'll be choosing long-day varieties. South of this line, choose a short-day. If you're in one of the states just on either side of the line, you can use any variety. 
Intermediate-day or day-neutral onion varieties will work just about anywhere except in Southern Florida or Texas or the far north.
In the south at zone 7 and above, onions are planted in the fall while it is still warm out for about 4-6 weeks to get the onions established. Short day onions can work in the north too, but they would be planted in spring and they won't yield big bulbs at all. You might be very disappointed planting these except if you desire to grow pearl onions. 

Consider the uses:

Now you'll be choosing whether you want Storage onions or the milder sweet varieties that don't store well. Or are you looking to grow leeks or green bunching onions? Perennial onions?
For bulbing onions, the more pungent, the longer they store. The sulfur content in the onions is what makes them pungent and gives them a longer shelf life. 
Sweet onions generally are juicier and milder and so they will store for just a few weeks to a few months. Those are the ones you use for fried onion rings and burger toppings.
Storage onions on the other hand are very hard, tightly wrapped and are going to make you cry when cutting. The harder you cry, the longer they will store. 

My strategy is this: 

  1. I plant a bunch of fast growing green onions to get some onions in my food quickly. And if you don't pull them, they'll keep regrowing greens all season long and even into the winter if it's not too cold. 
  2. Then I grow bulbing onions, about half of them sweet onions. I'll use the sweet onions first during the fall and early winter and if I don't use them all, I ferment them for fresh use or chop and freeze them for cooking. They can also be dried for onion powder.
  3. The other half of bulbing onions I plant for storage. After harvesting and curing them, I store them away till I run out of the Sweet onions. They will get me through the winter until the green onions are growing and ready to eat and so the cycle continues.