Guide to Growing Onions

Did you know that onions are one of the top-selling vegetables in the United States, coming in just after tomatoes and potatoes? If you’re like our family and you have meals made with onions 3 or 4 times a week, that’s probably not too shocking. If you do eat onions regularly, it can be well worth the time it takes to grow them in your own garden. Depending on the variety of onion, it can take between 3 and 5 months before they’re ready to eat or to be cured and stored. With onions, though, you have a few options for how to grow them. Here’s a look at the choices you have and what to know before you start growing onions in your garden.

Onion Seeds, Sets, and Plants

There are 3 ways to start growing onions. You can start them from their tiny black seeds, plant sets, which are small, dry, immature bulbs, or plant partially grown live plants that you can purchase from garden retailers and some online suppliers.

There are advantages and disadvantages to each of these methods. Growing onions from seeds gives you access to the most varieties, and onion seeds cost less than sets or plants (ex. $3–4 for a packet of 300 seeds vs. $12.50 for a bunch of plants, which is approximately 50 onion plants). However, in most climates, onion seeds need to be started indoors because the soil temperature needs to be above 50 degrees F to germinate, and that means you’ll need a seed starting medium, a container, and grow lights, and you’ll be putting in more time to care for the seedlings. Onion sets and plants on the other hand, while more expensive and limited in terms of choice, can be directly planted in the garden and will produce onions that are ready to harvest earlier in the season.

Long-Day, Short-Day, and Day-Neutral Onions

Onions start to form their bulbs when the number of daylight hours reaches a certain point, and different onion varieties require different daylight hours. Onions are categorized into 3 groups, which makes it easier to choose onion varieties for your specific growing zone.

Long-day onions require the longest day lengths, typically 14 to 15 hours, which happens in Northern regions around the summer solstice. Long-day onions typically grow well in Zone 6 and colder. Long-day onions include varieties such as Walla Walla, White Sweet Spanish, Yellow Sweet Spanish, Ailsa Craig, and Ruby Red.

Short-day onions will start to form bulbs when the day length hits 10 hours per day. These onions grow best in Southern regions where daylight hours do not reach 14 hours per day. Planting these onions in the fall gives them enough time to produce the top growth necessary to form large bulbs when the daylight reaches 10 hours per day. Short-day onion varieties include Georgia Sweet, Texas Super Sweet, Red Burgundy, and more.

Day-neutral (or intermediate) onions require around 12 hours of light per day. These onions will grow in most regions, but may not be the best fit for the most Northern or Southern regions of the United States. Sierra Blanca, Candy, and Cabernet are examples of day-neutral onions.

For detailed information regarding the right zones for each onion category, I suggest going to Johnny’s Selected Seeds to view their map.

Choosing the Right Onion Variety

Once you’ve determined the type of onion that grows best in your climate, you’ll want to consider other factors, such as flavor and storage length. Some onions are sweeter than others, while some are more pungent. There are some onions that store well for 6 months or more, and there are others that are best when eaten fresh. Sweet onions tend to not store well because they have high moisture content.

One thing to note is that if you’re planning on growing from sets, you may not have that many options to consider. Many suppliers simply offer red, white, and yellow sets without giving information on the variety. If you’re considering specific varieties, you’ll find them as seeds or possibly as bunches of plants.

Basic Requirements for Growing Onions

  • Onions like well-drained, nutrient-rich soil with a slightly acidic to neutral pH (6.0 to 7.0).

Starting Onions from Seeds

If you’ve weighed your options for starting onions, and you’ve decided you want to start them from seeds, here’s how to do it.

  • When do you start onion seeds indoors? This depends on where you live and how long your growing season is. In the South, you start them so they’ll be ready for planting in the fall. In the North, you start them so they’ll be ready for planting 2 to 4 weeks prior to your last frost date or whenever the ground can be worked up. In general, they should be started so they spend at least 8 to 10 weeks growing indoors.
  • You may want to add a light layer of vermiculite on top of your growing medium to help prevent damping off. Damping off is when seedlings die from a soil-borne disease that’s most commonly caused by fungi.

When and How to Harvest Onions

You can harvest onions to eat fresh whenever you’re satisfied with the bulb size, but to store onions, you should wait until the tops turn yellow and fall over. You don’t have to wait for them to all do this on their own, though. Once they start turning yellow, you can bend over the tops to stop bulb formation so that all of the onions can be harvested together.

If storing the onions, you’ll need to cure them. To cure them, pull the onions out of the ground and gently brush off the dirt. Lay or hang the onions in the sun until the greens dry and the skin of the bulb toughens. You’ll need to protect them from rain while they cure. Once your onions are cured, you can braid them together and hang them in a cool (40 to 60 degrees F), dry place. You can also remove the dried green tops and hang them in a mesh bag.

The Onion Growing Experience

Growing onions is a unique experience compared to other well-known vegetables that you can grow in your backyard garden. They’re not the easiest plants to grow from seeds (I’d give that award to tomatoes), but they’re not hard to grow either. If you’re growing onions for the first time, let me know how it goes in the comments section. I’d love to hear about it, whether it goes really well or you run into trouble and don’t know what went wrong.

Originally published at on January 27, 2021.

Homesteading and gardening blogger and chief homestead officer at Cedar Swamp Homestead |

Homesteading and gardening blogger and chief homestead officer at Cedar Swamp Homestead |