Onions have always been the kick-off to my gardening season as they take quite some time to mature. They are a much-needed reminder in February that summer will again return here in frosty northern Minnesota. Onions are a staple in many kitchens, adding flavor and depth to a wide range of dishes. Whether you’re an experienced gardener or just starting out, onions are a great crop to try! They are relatively easy to grow and can be stored for months after harvest. Let’s take a closer look at how to grow onions, from sowing seeds to curing and storage.
Seeds vs. Sets
In the past, I grew onions from sets but last year I started from the majority from seed but I grew a few sets alongside just to compare. I love a good gardening experiment. Same soil, same conditions, same planting time. You can grow delicious onions either way but wow, what a difference! Onions grown from seed are typically larger, sweeter, and more “perfect” in shape, and store quite a bit longer. They also tend to be less prone to going to flowers than onion sets.
Types of Onion Seeds
Onion seeds come in Short Day, Long Day, and Day Neutral (or intermediate) varieties. Which is best for your area depends on how many hours of daylight you have.
Short Day: Best for Southern growers who have 10-12 hours of sunlight.
Long Day: Best for Northern growers who have 14 hours of sunlight.
Day Neutral: These can grow well in most climates that receive 12-14 hours of sunlight.
Starting Seeds
Start your onion seeds 10-12 weeks before your last expected frost date. While most seeds do not like to be crowded, onions on the other hand, are perfectly fine being pulled apart to be transplanted into the ground come spring. Keep the soil moist and warm on a heat mat or in a warm space in your home. Expect them to germinate within 10-12 days.
As the onions grow, you will need to trim them back. They become tall and heavy while reaching toward the light and will topple over, reducing airflow. Simply give the greens a haircut with clean scissors to keep them around 3-4 inches high. This tells the seedling to send its energy back to its roots, helping the greens become sturdier and thicker.
Transplanting
As with all other seedlings started indoors, be sure to harden off your onions for a week or two before transplanting them into the ground. Onions are fairly cold tolerant but the little transplants will have a difficult time surviving overnight frost so plant outdoors after your last predicted frost date.
If possible, avoid planting in low-lying areas where rainwater tends to collect. I suggest mulching around your onions for moisture and temperature control and to keep weeds at bay. Weed fabric is also an option but I prefer to use organic material when possible. Plant the seedlings 2 inches deep and spaced 4 to 6 inches apart and water them in.
Care
Onions can be heavy “feeders” meaning they pull a lot of nutrients from the soil. Use an organic, balanced fertilizer such as Fish Emulsion every few weeks throughout the growing season. They will require about one inch of water per week.
Another thing to look out for with onions in the height of the summer is going to flower. When the temps really start to get up there, onions will want to send up their flowers which essentially stops their bulb growth. If you know you are going to have an especially hot day, I suggest giving them a good watering in the morning to help keep the soil cooler during the day. Onions will not continue to grow in size once they have flowered, so feel free to pick that onion and throw it in your dinner tonight, all is not lost!
Harvesting
Most onions take between 90-120 days to reach full maturity. Late in the growing season, your green onion tops will begin to flop over. Once this happens it is a sign to wait a week or two before harvesting. It is ideal to harvest onions when the soil is dry so keep an eye on your forecast and pick a day when the soil has had some time to dry. But keep in mind- You can harvest and use your onions at any point during the growing season. If you harvest any of the “younger” onions the green tops are also delicious and not as tough as the mature onions.
Curing
This step is crucial to ensure a long storage life. The curing process can vary depending on the conditions, but typically takes around 14 days. It’s essential to cure them in a dry and well-ventilated area to allow for proper airflow around each onion. Consider a covered porch, deck, breezeway, basement, or garage. Cure your onions upside-down to promote a more even drying process and mold prevention. There are many creative ways to achieve this, such as suspending them from scrap wood or cattle panels. In the past, I have cured them by laying 2x4s across sawhorses under our 2nd story deck. You will know the onions are done curing when the greens have turned brown and brittle. Cut the stems off after curing and move them to storage.
Storage
Many onion varieties can be stored for several months if cured properly. They prefer to be stored in a cool dark environment, for me this was our basement laundry room in a wire basket. Each variety of onion stores differently, so check your seed packet or seed supplier site for their suggestions but most can last for 4-6 months. Check them periodically to see if any need to be used up before they go bad. If one begins to rot it can affect the others that they are stored with.
Preservation Methods:
Dehydrating
Freezing
Pressure Canned (salsas and sauces)
Happy Growing!
