A little bit sweet, a little bit spicy, onions are delicious any way you slice them! Homegrown onions fresh from the garden taste even better.
If you’ve been wondering how to grow onions, this article is for you. You’ll learn when and how to plant onions and find out what varieties grow best in your zone. Learn how to fertilize and water properly, get harvest and storage tips, and even see some tasty onion recipes to try.
Types of Onions to Grow
From big fat bulbs to long skinny scallions, there is a surprising number of onion varieties out there!
Bulb Onions
Large bulb onions like red, yellow, and white onions grow very well in home gardens. Choose a sweet variety like the Sweet Spanish Utah Onion or an antioxidant-rich red variety like Sofire.
Shallots are a smaller variety of bulb onion that is also very delicious!
Other Types of Onions
Other types of onions like scallions, spring onions, and leeks are grown more for their stems than the bulbs. In fact, some varieties (like scallions) don’t grow bulbs at all.
Tadorna Leeks have beautiful dark green leaves and are delicious in soups or salads. Warrior Bunching Onions are a fast-growing green onion variety that’s delicious either raw or cooked.
How to Choose the Right Variety
For many gardeners, flavor is the top consideration when it comes to choosing what plants to grow. For others, how easy the variety is to work with is more important.
When it comes to growing onions, you need to choose a variety that’s well suited to the climate where you live.
Onions develop bulbs based on how many daylight hours the plants are exposed to. If you choose the wrong variety, the bulbs won’t develop properly. Even if you do everything else right!
Thankfully, there are delicious varieties that grow well in every zone, so you won’t have a hard time finding something that works for you.
Long-Day Onions
Long-day onions need 14-16 daylight hours to form bulbs. These types of onions grow best in northern areas. Here are some long-day varieties to try.
Intermediate-Day Onions
Intermediate-day onions need 12-14 hours of daylight. These grow best in central areas of the United States, including USDA hardiness zones 5-7. Check out some of these intermediate-day varieties.
Short-Day Onions
Short-day onions only need 10-12 hours of daylight to bulb. These types of onions grow best in southern areas with mild winters.
Check out this video from Dixondale Farms to learn more about onion day length and find out which type is best for your zone.
The Best Time to Grow Onions
The best time to start growing onions is when the weather is cool.
Depending on your zone and the variety you’re planting, most onions are grown between fall and spring. They’re ready to harvest by mid-summer.
In southern areas, onions are planted in the fall and harvested by early spring. In northern areas, it may be late summer or early fall before onions are ready to harvest.
Check your seed packet or look at the label on your onion starts to see when the best time to plant your particular variety is.
What Onions Need to Grow
Once you’ve chosen a variety and decided when to plant, it’s time to get started prepping the garden!
Successfully growing onions starts with providing the right conditions. Here’s what you’ll need.
Sunlight
Choose a bright, sunny location for planting onions. They need full sun which means at least 6-8 hours of direct sunlight per day.
Sunlight is essential for onions to develop healthy bulbs. Without enough sun, the bulbs won’t be able to develop.
For other types of onions like scallions and leeks, you can do partial shade if that’s all you have, but full sun is better.
Soil
Onions need well-draining soil that’s loose and rich. If your soil is very compacted, loosen it up by adding some organic matter like compost or well-aged manure.
A soil pH between 6.0 and 6.8 is best.
Planting Location
Onions can be grown in the ground, in raised beds, or in containers.
Small varieties like scallions are very happy in containers. All you need is a small pot that’s at least 6-8 inches around.
Large bulb onions can also be grown in containers. Just make sure there’s adequate space. Crowded onions won’t develop very big bulbs so you want to give the onions enough room to grow.
The size pot you need will depend on how many onions you want to grow in it. Aim for about three inches between each onion on all sides.
How to Grow Onions
You can grow onions from seed or start with onion sets from the store.
Onion seeds are inexpensive, easy to find, and give you the ultimate choice when it comes to varieties. Online stores like Hoss Tools carry a wide selection of onion seed varieties in all different sizes, shapes, and colors.
Onion sets are faster and easier, but they’re harder to find and are a lot more expensive. You can find them pretty easily in garden centers and nurseries, but there won’t be as many varieties to choose from.
There are pros and cons to each method of planting onions so choose the one that’s right for you!
Starting Onions From Seed
Starting onions from seed does take more time, but it’s a great way to save some money. Especially if you already have some basic seed starting supplies.
If you need some seed starting tools, here are some recommendations to get you started.
- Heat Mat
- Grow Lights
- Seed Starting Mix
- Potting Soil
- Seed Starting Trays with Humidity Domes
- Small Containers
- Gardening Gloves
- Gardening Shovel
- Spray Bottle
- Watering Can
- Garden Labels
You don’t necessarily need everything on this list to start growing onions, but having a good setup can save you a lot of time and money in the long run.
If you plan on starting more plants from seed, it’s well worth the investment to get some high-quality equipment.
Starting Onion Seeds Indoors
Starting onions indoors is a great way to get a headstart on the growing season.
Gather your equipment and set it up in a place that’s convenient but out of the way.
Fill a seed tray or shallow container with seed starting mix. Sprinkle onion seeds over the soil and cover to a depth of ¼ inch. Moisten thoroughly using a spray bottle so you don’t disturb the seeds.
Keep the seeds warm by placing the tray on a heat mat. Make sure the seed starting mix stays moist, but not overly saturated. Onion seeds can take a couple of weeks to germinate so be patient!
As soon as sprouts emerge, put the tray under a grow light or in front of a large sunny window.
Transfer your onion starts into the garden in early-mid spring.
Direct Sowing Onions
Onion seeds can be planted outdoors as soon as the soil has warmed up to around 35 degrees. Onion plants can handle chilly weather and some light frost so there’s no need to wait until after the last frost.
After preparing the soil, plant onion seeds in rows 12-18 inches apart. Seeds should be planted ¼ inch deep. Water thoroughly and keep the area moist while seeds are germinating.
After sprouts have reached 2-3 inches, thin the plants to 3-4 inches apart for large onions and 1-2 inches for smaller varieties like scallions.
Planting Onion Starts
Whether you started them yourself or purchased starts from a store, eventually those little plants need to get moved into the garden.
Plant onion starts in rows 12-18 inches apart. Space the plants 1-4 inches apart depending on the size of the variety.
Caring for Onions as They Grow
Learning how to plant onions is just the beginning. Here’s how to care for the plants as they grow
Water
Onions have shallow roots so it’s important not to let the soil dry out too much. Add water any time the top inch of the soil feels dry.
When onions are fully grown, stop watering 1-2 weeks before harvest. This reduces the chance of the onions rotting.
Fertilizer
For the best bulb development, onions need a lot of nitrogen. Fertilize your plants regularly using a nitrogen-rich fertilizer like ammonium sulfate or calcium nitrate.
Apply the first dose of fertilizer about three weeks after planting onions. Continue adding fertilizer every 2-3 weeks throughout the growing season.
Non-bulb onions like leeks and scallions benefit from additional nitrogen as well. That’s because nitrogen promotes green leafy growth.
Weeding
Onions don’t like to compete with weeds, so keep the garden bed free from weeds as best as you can.
Check on your onion plants regularly and pull up any weeds as soon as you see them. Pulling large weeds can disturb the onions so it’s best to pull them when they’re small.
When to Harvest Onions
Onions are ready to harvest about 100-125 days after planting, depending on the variety. Onion starts are usually ready after about 60 days.
You can tell onions are ready to harvest when the leaves start to bend over and die back.
Another sign is when the onion plants start flowering. There’s no need to trim off flowers, just bend the stems back to prepare for harvest.
How to Harvest Onions
Gently loosen the soil around the bulbs and then pull them up from the stem. Try not to break the stem of the onion. Keeping the stems intact during the curing process reduces the risk of rot.
Curing Onions
After harvesting, bulb onions need to be cured before storing. Brush off any large clumps of dirt but don’t worry about cleaning them just yet.
Spread the onions out in a single layer using a cardboard box, basket, or shallow tray. Proper air circulation is important, so avoid stacking or bunching the onions. Put the trays in a cool, dry place like a cellar or garage.
Curing takes a few weeks, depending on the temperature and humidity of the storage location.
You can tell onions have finished curing when the stems and skins are completely dry. At this point, you can trim away the extra stems and roots and clean off excess dirt.
Storing Onions
Bulb Onions
When stored properly, bulb onions last for months at a time. Long-day onions can keep for six months or even more. Short-day onions don’t keep quite as long, but you can still get a good 2-3 months out of them after curing.
Other Onions
Green onions, leeks, and other types of onions are best stored in the fridge.
After harvesting, rinse the onions and pat them dry. Wrap them in a lightly damp paper towel and place them in a sealable plastic bag. Keep the bag in the crisper drawer of your fridge.
Onions stored this way will stay fresh for 1-2 weeks.
Freezing Onions
To freeze onions, dice them up or cut them into strips then place them in a freezer bag. Squeeze as much air out of the bag as you can and store it in the freezer until needed.
Thawed onions don’t have quite the same texture as fresh so they’re not ideal for eating raw. However, once they’re cooked, you can’t tell the difference between fresh and frozen onions!
Pre-chopped frozen onions are super convenient. They’re perfect for use in cooked recipes like soups, stews, sauces, crockpot or Instapot recipes, and more.
Onion Recipes
Speaking of recipes, any of these would be absolutely delicious with some tasty homegrown onions!
Tips for Cooking Onions
Wrapping up How to Grow Onions
Once you learn how to grow onions you won’t want to go back to buying them at the store. Are you ready to start planting onions?
To learn more about different varieties of onions, check out our onion page. For more planting guides, head to the seed starting page. There you’ll find tips and tricks, plus helpful guides for how to plant all kinds of vegetables, fruit, flowers, and herbs. There’s something for everyone!