Growing onions from transplants have the added benefit of being earlier to harvest, and the product will be more uniform in size and stand. Seed waste is mitigated with onion transplants and it can help reduce pressure from pests and disease.
On the downside transplanting onions is a larger cost investment and requires specialized equipment to do at larger scales.
What to Do When You Get Your Onion Sets or Transplants
As soon as onion sets arrive you will want to remove them from the boxing. They will need to be placed in a well-ventilated area free from sunlight, soil or moisture. You want to keep them away from soil and water until you are ready to plant the sets/transplants.
For the optimal results with your onion sets, you will want to make sure your soil pH is between 6.2 and 6.8. Limestone is your go-to if the soil has too much acidity but you’ll want to use something like peat moss if alkalinity is your problem.
Where to Grow Onion Sets or Transplants
Site conditions are very important to successfully growing onion sets. Onions require full sun and won’t tolerate partial shade. While onions need a steady supply of water, they don’t like to be damp either. Exposure to the sun will help dry them off and keep diseases from being a problem. Onions will have to be watered immediately after transplanting and will require 1” of water per week.
Growing Healthy Onions
Onion spacing is very important and what your desired end goal is, will determine your spacing requirements. If you’re growing to harvest green onions then you will want them to be closer, 2” apart. However, if your plan is to harvest full-sized onions than you want to spread them out to 4”. If you wish to have both then pull ever other onion to harvest green and leave space for the rest to mature.
As far as the spacing between rows 16” should give your onions plenty of room to grow. If you want to fertilize your onions, it’s ideal to dig a companion ditch next to your onion row 6” away. The fertilizer trench should be 4” by 4” so you can spread .5 cup of fertilizer for every 10 feet of trench. After you’ve applied the fertilizer you can backfill with 2” of soil.
While the onions are growing you will want to continue fertilizing them. A light and balanced fertilizer will be ideal, but you could apply some compost as well if you prefer. Every 2 to 3 weeks should provide enough nutrients for your young onion plants. You’ll want to apply any soil amendments to your trench alongside your plants.
Eventually, as the onion plants begin to form bulbs the soil will crack, at this time fertilizing should stop.
Weeds & Insects
You may be surprised to hear that onions aren’t any different than most vegetables, they don’t care for weeds as they are growing. You should stay on top of weeding and can even perform shallow cultivation to keep the weed pressure down.
The biggest insect issues that you typically see with onions is Onion Thrips, so if you begin to see silvery blotches on your onions, you will want to apply Neem Oil as directed. Part of the reason why weeding is so important is that Thrips will overwinter in the weeds.
When It’s Time to Harvest Onions
Eventually, the top of your onion plant will begin to turn a brownish-yellow. When your onions are ready to be harvested pick a dry early morning to do the pulling. The onions will need to be dried out before they are ready for storage or you will risk them rotting away. The sun can help you dry your onions out, if you lay the onions in two rows and allow the tops of one row over the other this will prevent the onions from being scalded. If the weather isn’t cooperating and you need to get your onions out of the ground, curing indoors is possible but takes longer. If curing indoors be sure to choose an area with good ventilation and air movement.
After your onions are cured the neck of the onion to the skin will be dry and the entire skin will have a consistent texture to it. When your onions are dried enough you can cut the bottom roots off and braid the tops together. If you prefer not to braid the tops, you can snip those off as well, but be sure to leave 2-3” of the top on to allow the stems to dry and cure completely.
How to Store Onions
When you store onions the best results will be had when they are kept at NEAR freezing temperatures. After temperature, the humidity will be your biggest concern. The ideal humidity for onion storage is 65-70% in a bag or container that will allow air movement. You’ll want to keep an eye on your onion supply as decaying onions will need to be removed from any storage and discarded for the health of the other onions.