Full disclosure, I struggled with growing onions for years before I learned what I was doing wrong. It was only when I sat down and did some serious research that I learned my mistakes. Hopefully by sharing my mistakes I can prevent you from making the same ones.
Three Common Mistakes Made When Growing Onions
Mistake #1 - Grow the right type of onion for your area.
Did you know there are short-day, intermediate-day and long-day onions? Onions are photothermic, meaning hours of light and heat affect how they grow.
Short-day onions are meant to be grown in areas close to the equator, where the hours of daylight don’t vary vastly from summer to winter. Intermediate-day onions are great for growing in the in between area. They do best with 12 to 14 hours of sunlight a day. Intermediate day onions can also be grown with success in both shorter and longer day areas. Long-day onions, on the other hand, are the best type for growing if you are getting closer to the northern or southern pole than you are to the equator. Long-day onions grow well in areas that experience 14+ hours of sunlight during their longest days.
Mistake # 2 - Know when to plant onions outdoors.
Because daylight affects onion growth, it is beneficial to get onions outdoors into natural light as soon as possible. Onions tolerate mild frost well. Consider planting your onions outdoors two to four weeks before your last frost. This allows you to make the most out of those days with long hours of daylight. If you expect night temperature to dip below 20F (-6C) consider covering your onions.
Mistake # 3 - Planting too deep.
For some reason, I used to have it in my head that the deeper I planted my onions the bigger they would grow. This probably came from a misunderstanding of what part of the plant the onion bulb actually is. I thought it was part of the root - and I was wrong. The bulb part of an onion plant is neither part of the root or the stem but is called a ‘tunicated bulb’. This part of the plant is meant to grow at least half-way out of the soil. In fact, if 2/3rds of the onion is on top of the soil as it becomes close to maturity, that is a good thing. There is less restriction for the bulb to develop that way
Seed or Set?
When deciding if you would like to grow onions from seed or sets, take into consideration the fact that onions are biennial. An issue with growing onions from sets is that the set is in its second year of life. Often it will try to form a seed head. If that begins to happen, the plant will put most of its energy into reproduction by maturing the seeds and little energy to onion bulb growth. If you are growing onions from sets and this begins to happen, cut off the forming flower.
Growing onions from seed takes much longer and in cool climates the seeds need to be started indoors months prior to planting the seedlings outdoors. I have found I end up with larger onion bulbs by harvest time when I grow onions from seed. One nice thing about growing onions from seed is that they can be sown in a relatively small container, close together. Onion roots are strong and separate fairly easily when it comes time to transplant them. Keep the tops of the onions trimmed to around 3 inches while they are indoors to prevent the tops from falling over and breaking.
Harvesting, Curing and Storing Onions
Harvest and use onions as you need them for cooking throughout the summer. Onion greens can be cut and used in recipes as a substitute for green onions. Instead of trimming all the tops from one onion, take one from each until you have enough.
Harvest all your onions around 2 weeks after the tops begin to fall over or before your last frost; whatever comes first. Avoid watering your onions for 3 days prior to harvesting them and do not wash onions after harvesting. Also avoid harvesting following rainfall. The lower the moisture content in the onions at harvest time, the less likely they are to rot or mold in storage.
Cure onions in a cool dark place, preferably with good ventilation, until the tops have completely dried and turned brown. Some (including me) like to use a mesh wire rack for hanging onions upsidedown to cure them. Spacing onions in wire mesh allows for good airflow around each onion.
If you wish to braid and hang your onions you will need to do that before the tops are completely dry and brittle. This is best done on days 3 to 7 of curing your onions.
If you do not plan to braid your onions, trim to one inch and trim off roots once the tops are thoroughly dry and dead. Gently rub off any onion skin covered in soil. At this time onions can then be transferred into cloth mesh bags and hung for long-term storage.
Written by Krista Green www.zone3vegetablegardening.com
Krista Green is a Canadian gardener, author and mother of 3. She and her husband live on a 4 acre homestead in southern Alberta. She is passionate, not only about growing food for her
family, but about teaching others to grow their own food as well. Krista runs the website www.zone3vegetablegardening.com which is full of tips on gardening in northern climates. As well she actively shares gardening tips on Instagram. You can find her under @zone3vegetablegardening