How to grow healthier onions! Part 1

How to grow healthier onions! Part 1

Last week I was at a growers conference and a friend asked me a bunch of questions about growing onions.  Then on Friday, I received an email from a customer asking more questions about-- you guessed it-- growing onions! So here are my top tips on how to grow healthier onions! 

We grow all of our Dakota Tears onions from seed-- not onion sets. Onions grown from seed do better than onions grown from sets. Why? They are less likely to get diseased, will not bolt and try to produce seed, size up their bulbs faster, and store better-- all helping to ensure your gardening success!The past few years we've been experimenting with direct seeding onions, in addition to starting transplant seedlings early in the spring. Our results have been promising!


Maybe you have a serious need to scratch that gardening itch by starting onions from seeds early in the season—onions can be started earlier than most anything else for your gardening pleasure.  Maybe you also like easy! The more simple, the better!  You could direct seed some of your onions. We recommend caution and that you hedge your bets, growing some starts AND trying your hand at direct seeding. You choose! Have fun with it!


Direct Seeding

We are located about 25 miles north of the ND/SD border on the 46th latitude. We direct seed Dakota Tears onions at the end of April or the first week of May, depending on the season.  If you live further south than we do, you would want to plant Dakota Tears onions earlier than that; further north, a little later.  

The advantage of direct seeding is no transplanting and no transplant shock!  The onions have the luxury of growing right where they are planted and they will take off!

To direct seed, prepare your seed bed and lightly firm the soil to a nice even level.  This will help to ensure an even planting depth. Onions are finicky; you don't want to get them planted too deep.

We plant a double row of onions in one garden row, about 7-8 inches apart. Plant spacing should be about 10 seeds per foot. Onion bulbs will push each other aside and still produce nice onions. You can thin some out if necessary. Just use the ones you thin for fresh eating, leaving the rest with ample space to size up for storage onions. 

Growing Transplant Seedlings

When we grow seedlings for transplant, we start our Dakota Tears onions the last few days of March to the first days of April. This gives us 4-6 weeks to grow good-sized onions before transplanting early to mid May, as the season warrants. Onions can be transplanted into the garden 2-3 weeks before you would transplant more cold-sensitive crops, like tomatoes. 

As always, pay attention to weather forecasts!  Onions are cold tolerant and can withstand some frost but there are limits.


Let’s start with the soil. This soil mix is based on the mix used by the Rodale Center.

  • 4 parts screened compost
  • 1 part perlite
  • 1 part vermiculite
  • (optional: for added moisture retention) 2 parts coir (ground up coconut husks) 
    Why coir and not peat?  Coir’s pH is near neutral and it retains more water than peat.  In addition, it is much more sustainable than mining peat bogs, which releases carbon into the atmosphere.

This mix will help with retaining moisture and with drainage, keys to starting healthy seedlings. It’s easy for the soil to stay too wet, and that can lead to damping-off, a fungal disease that causes newly germinated seedlings to rot at the soil line and die.


We plant the seeds in propagation trays with 72 round cells per tray.  Fill your tray with your starter mix and screed the excess dirt off the top with a straight edge so each cell is level full. Use another filled tray to place on top of the newly filled cells, pressing down to GENTLY firm (not pack) the soil to an even level in each of the cells at once. This method helps to ensure you do not OVER-fill the cells; you want the soil level to end up just a little below the top of the cell so that water has the opportunity soak in instead of running off the top.

Inspect the cells for uniform soil depth and make any adjustments needed. Onions are sensitive to planting depth, so take the time to get it right.

Place your onion seed in each cell and cover with 1/8 inch of your soil mixture.  Now water thoroughly and evenly. As you do so, notice the water settles the soil in each cell. Make sure to tag your tray with the variety name and date planted.

We have had the most success growing onion seedlings much like wheat grass, planting them in a milk carton tipped on its side with the top side panel cut out and the carton spout/peak firmly stapled.  Prior to cutting the top panel, use a sharp awl to poke about 2-3 dozen holes in the bottom side for drainage. Fill 2/3-3/4 of the carton with your soil mix and gently firm the soil. Sprinkle approximately 150-200 seeds evenly over the surface of the soil. Cover the seed with an 1/8 inch layer of soil mix.  Water thoroughly and evenly, and label your carton with the variety name and date planted. 


Place the flats or cartons in a warm place for fast germination-- preferably about 70 degrees F. Onions take about a week to germinate.

Cover the flats with a piece of clear plastic to keep the environment moist and humid. However, keep the trays out of direct sunlight to avoid getting them too warm. Watch the trays carefully for sprouting; when you see the first hint of plant emergence, remove the plastic!


At the FIRST signs of sprouting, make sure the containers are in a bright spot—a sunny window, a greenhouse, or beneath grow lights. If using grow lights, suspend the lights just above the plants and gradually raise them as the seedlings grow taller. Watch and adjust as needed! Plants will become weak and spindly if they have to stretch or lean toward the light.

Turn the lights on and off at the same time each day, mimicking the natural day length. Hooking them up to an electric timer is highly desirable and the most foolproof strategy!

Stay tuned! Next time we'll talk about onion transplanting tips! Here's to the best onion crop ever!

Click here to go to: How to Grow Healthier Onions! Part 2