Onions are a hardy, cool season crop that you can grow in your home garden. They are pretty easy to grow, but a few important tips will help you to successfully harvest large bulbs for eating and storage.
If you’ve only ever bought onions at the store, you might be surprised by the flavor and variety options that are out there. You can grow white, yellow, or red (sometimes called purple) varieties with flavor ranging from mild to potent.
Planting a good storage variety will keep you eating your harvest through the winter and may cut down on your grocery bill!
If you’re ready to get started, here’s how to grow onions, plus care, harvest, and storage tips.
All About Onions
Onions are a cool season, biennial crop belonging to the Allium family and closely related to garlic, leeks, chives, scallions, and shallots. They grow shoots and bulbs their first year and will flower in the second year, although most are harvested before this happens.
Most gardeners treat onions like annuals: You plant them new each year and harvest them at the end of their season. However, if you’re interested in collecting seeds, you can let a few plants hang around for a second growing season.
Onions can be grown in almost any USDA hardiness zone, but you’ll need to choose the right variety for the region you live in.
Most people buy onions at the store, but it’s not hard to grow your own at home. You can fit a large crop into a small space and will be rewarded with bulbs that can last for months.
Choosing the Right Type
The biggest factor when selecting the right type of onion for your garden isn’t temperature or precipitation levels. It’s daylength.
There are three main types of onions and each one will form a bulb only if it gets the right amount of sunlight each day during the growing season. Latitude is the most important factor in deciding which type to grow.
- Long Day Onions– Long day varieties need about 14-16 hours of daylight to start forming bulbs. They grow best in northern regions where daylength gets long in the summer. If you look at a map, this type grows best from 37-47° latitude. Long day varieties include sweet, storage, and specialty onions.
- Short Day Onions– Short day varieties will start forming bulbs when days reach 10-12 hours of sunlight. This type is mostly grown in the south from 25-35° latitude. Planting is usually in the fall for a spring harvest. Onions are mainly best for fresh use but some storage options are available.
- Day Neutral or Intermediate Day– A third type of onion is referred to as either day neutral or intermediate day. These varieties fall in between the other two and can be grown in a wide region that overlaps the other two: 32-42° latitude. They start forming bulbs with a daylength of 12-14 hours.
If you aren’t sure which type to choose based on your location, this daylength and latitude map will help.
After you figure out which type to plant, you have a few more choices to make. Onion varieties are usually labeled as either fresh or storage onions, although a few can be used as either.
You may not know it because just a few main varieties are sold at the grocery store, but there’s a wide range of flavor and intensity when it comes to onions. Growing your own gives you the chance to try new options.
You also get to pick from white, yellow, or red varieties that each have a different flavor. Yellow options tend to be sweeter and milder than the others, but you’ll have to experiment to find which taste you like the best!
Here are some of the top varieties to try based on type:
Long Day Varieties
- ‘Walla Walla’ or ‘Ailsa Craig’– Both of these are large and sweet yellow onions. Best used fresh, but Ailsa Craig can be stored short term.
- ‘Patterson’ or ‘Cortland’– Both of these are large, yellow storage onions. Great flavor and will store for months.
- ‘Red Carpet’ or ‘Redwing’– Two good red storage varieties. Redwing takes slightly longer to mature and Red Carpet is slightly smaller.
- ‘Rossi di Milano’– Huge red storage onion. Bulbs have beautiful bronze-purple skin and last 6+ months in storage.
- ‘New York Early’– Large and yellow onion that matures quickly. Good fresh or for medium term storage.
- ‘Blush’– Specialty onion with brown-pink skin and light purple rings inside. Bulbs get large and can be stored.
Short Day Varieties
- ‘White Bermuda’ or ‘White Castle’– Two white varieties with mild, somewhat sweet flavor. White Castle produces larger bulbs and takes longer to mature. It can be stored 3-4 months and White Bermuda for about a month.
- ‘Yellow Granex’– A jumbo yellow variety with mild, sweet flavor. Great for fresh eating, not good for storage.
- ‘Red Rock’ or ‘Red Burgundy’– Two of the best red short-day varieties. Red Rock gets bigger but matures more slowly. Both have great flavor and can store for about 3 months.
Red onions typically have their own distinct flavor. They tend to have more of a bite than sweet, yellow onion and also add color when you cook with them or use them raw.
- ‘1015Y Texas Supersweet’– One of the best large, sweet onions for planting in southern regions. ‘1015’ stands for the traditional planting date of October 15th, and the ‘Y’ stands for yellow.
Day Neutral/Intermediate Day Varieties
- ‘Candy’– This is a jumbo yellow variety similar to the popular Walla Walla variety but can be grown further south.
- ‘Sierra Blanca’– Large white variety with mild flavor. Can be grown almost anywhere in North America. Best fresh but can be stored for short periods.
- ‘Cabernet’– Medium to large red variety that matures early. Can be stored 4-6 months.
- ‘Monastrell’– Another good red variety that gets larger and matures later than Cabernet. Will store 3-5 months.
- ‘Scout’– An early maturing, Spanish type variety that has good disease resistance. Bulbs get very large and store 3-4 months.
How to Grow Onions
There are three different ways to grow onions, each with its own pros and cons. You can try each one to see what works best or pick a method and stick with it.
There are three different methods for getting your onions started: by seed, by sets, or by plants. Which one you choose will depend on how much work you want to put into it and how much choice you want to have for variety.
Growing from Seed
Onion seeds shouldn’t be planted directly in the ground since they won’t have near enough time to grow and mature before the season is over (unless you have a very long growing season).
You can start them indoors 10-12 weeks before your last average frost date for spring planting. Southern gardeners can start seeds 8-10 weeks before planting in late fall for a spring/summer harvest.
The biggest benefit of starting onions from seed is variety. You’ll have tons of options available that aren’t sold in garden centers, and you can pick out exactly what suits your needs. Another benefit is that onions won’t flower or go to seed their first year of growing.
Once your seeding trays are ready, sow 2-3 seeds per cell. Onions can sprout and grow up close together, and you’ll be able to easily separate them before planting. Water your seeds and cover the trays with plastic domes if you have them.
Once seedlings start sprouting, remove the plastic domes and place the trays under grow lights. You can use fluorescent lights, keeping them a few inches above your seedlings as they grow. Give them at least 10-12 hours of light a day.
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As your seedlings grow, you’ll need to give them a haircut every so often. If you notice them getting long and flopping over, trim them with sharp scissors back to 3-4 inches tall.
Cutting your onion seedlings regularly make the greens stronger and thicker and forces them to focus on growing strong roots. You can harden off your plants a few weeks before the last frost by taking them outside during the day.
Growing from Sets
Onion sets are probably the most popular way to plant onions. They are basically tiny onion bulbs that were started the previous year.
The upside to planting sets is that a lot of the work is already done for you. You can just plant the bulbs in your garden in early spring and let them grow.
The downside is that onion sets are likely to flower and go to seed since this is technically their second year of growth. This prevents the bulbs from getting very big. Also, you have little choice when it comes to variety, and most sets aren’t even labeled beyond ‘red’, ‘white’, or ‘yellow.’
Still, if you are short on time or a beginner gardener, onion sets take a lot of guesswork out of the process. You can simply buy them at a garden center and plant when it’s time.
Growing from Plants
This option is sort of a combination of the previous two. Onion plants or transplants are started by farmers or greenhouse owners by seed a few months before they go up for sale.
Growing onions from sets means your plants are more likely to flower, which stops the bulbs from getting large and lessens their storage ability. Plants and seeds avoid this but take a little more work.
Essentially, you get to work with onions that have just been started and won’t flower or go to seed without actually doing the work of seeding them yourself. They are more likely to produce larger bulbs that onion sets, and all you have to do is buy and plant.
The biggest downside is that onion plants can be harder to find. Most garden centers and home improvement stores carry onion sets, but you may have to search to find a nursery that has transplants.
Another good option is to order from online, reputable companies that will ship onion plants in spring or fall. You won’t get as much variety as if you grew by seed, but there will be more choices than if you went with onion sets.
Planting Your Onions
When to Plant
The planting time for your onions depends on what region you live in. Most northern gardeners plant in early spring as soon as the ground can be worked. This is usually sometime right before your last average frost date.
The best time in northern areas with cold winters is usually late March or April.
Your best planting and harvest time depends on what region you live in. If you get very cold winters, you should plant in spring. If you have very mild winters, you can plant in late fall.
Southern gardeners and those in the pacific northwest who have milder climates can plant in late fall or winter to harvest the following spring/summer. In this case, the onions will be dormant for a while without being killed until longer and milder days come.
Growing Conditions and Soil Prep
Onions need full sun to grow and shouldn’t be planted where they’ll get shaded out by other plants.
It’s always a good idea to practice crop rotation, which means you shouldn’t plant onions in the same spot multiple years in a row. You should also avoid planting them where other allium crops like garlic or chives were last year.
The best soil to grow onions in is well-drained and loose soil. If your soil is heavy clay or has a lot of rocks, the bulbs will have a hard time growing to full size. Poor drainage is an invitation for rot and disease.
If your soil is less than ideal, you can amend with compost and other organic material. This adds nutrients to your soil, lightens it, and helps with drainage. Sand can also help amend clay soil.
Use a rake to break up the top few inches of soil before planting if the ground is hard. Onion plants are heavy feeders, especially of nitrogen, so add in some compost, aged manure, or nitrogen fertilizer.
It’s a good idea to add some compost or a nitrogen fertilizer to your soil before planting. This will give plants the nutrients they need to get off to a good start and produce large bulbs.
Make sure your planting area is also weed free so that your transplants don’t have to compete for water or nutrients.
How to Plant Onions
One of the biggest considerations to keep in mind as you start planting is spacing. Most varieties should be spaced out by 6 inches on all sides, although some of the smaller ones can be spaced 3-4 inches apart.
You can use a hoe or small hand trowel to make trenches and drop your onions in 6 inches apart. Or you can dig individual holes for each onion.
Plant onions one inch deep. If you have transplants with green tops, these should stay sticking out of the ground. You can trim the tops back to 3-4 inches before or after planting if you haven’t done so already.
Water your new transplants and make sure the soil is firm around all of them.
Caring for Your Onion Crop
One of the biggest needs onions have is regular water. They have short root systems and will need supplemental water during dry periods. Especially make sure you water new transplants every few days until they get established.
Onions need consistent water in order to form large, juicy bulbs. You won’t be able to tell from the plants themselves when they need watered, so make it a point to water during long dry spells.
Using a light mulch like straw or hay is a great way to help keep moisture in the soil and weeds down. Wait a couple weeks before mulching until your little seedlings start getting bigger and the cold, wet part of the season is over (if you’re planting in the spring).
Fertilizing isn’t necessary, but giving your onion plants a nitrogen heavy fertilizer every few weeks can really help your crop. Stop fertilizing when you see the plants forming bulbs.
Pests and Problems
The strong scent of onions deters big pests like deer and rabbits as well as most insects. Thrips and onion maggots are the two most common potential pests.
You can use an insecticidal soap to get rid of thrips if your plants get infested. Onion maggots are usually only a problem in damp conditions and during rainy periods. The best prevention is crop rotation and not mulching until the weather dries out.
Onions can be susceptible to some fungal diseases if conditions are damp and/or humid. For prevention, you can buy disease resistant varieties, practice crop rotation, space plants properly, and avoid using mulch during wet weather.
Harvesting Your Onions
When to Harvest
One of the biggest questions gardeners often have is when to harvest their onions.
You can harvest onions any time after they start forming bulbs and even earlier for green onions. However, if you are growing onions to store, you should let them get to full size before harvesting.
If you planted in the spring, you’ll notice the onion tops start to yellow and flop over in June or July. This is actually a good sign and means that it’s just about time to harvest your crop.
Some gardeners and farmers will bend the tops over at this point and step on them to help the ripening process. You can do this or just leave your plants be.
When the tops are mostly brown, it’s time to harvest. You can also pull onions for fresh eating early because they are edible at any size. However, make sure you leave storage onions in the ground until they’re completely ready.
If you planted onion sets and see that your plants are flowering, pull them out of the ground immediately. They will be good to eat but won’t store very well.
How to Harvest
The easiest way to harvest onions is to loosen the soil around plants with a garden fork or shovel. Just take care that you don’t accidentally stab any of your onion bulbs.
If you stab or bruise any onions when you’re pulling them up, eat them right away since they won’t last very long. Undamaged ones can be cured and stored.
You can then go through and pull the bulbs out of the loosened soil. If your soil is already pretty loose, you may be able to just go down the rows and pull up each bulb by hand. Handle them gently, especially those you want to store long term.
How to Store Onions
Once you’ve successfully harvested your crop, the next step is to make sure your onions will last for months to come. Of course, you’ll need to have grown good storage varieties to start with.
Curing your onions is an important step to make sure they’ll last for the longest possible time in storage. Any you plan to eat fresh don’t need to be cured.
You can either leave the green tops on or cut them back to an inch or two. Clip off the roots without cutting into the bulbs.
The best curing temperature for onions is between 80-90°F, which is usually what the temperature is when they are harvested. Lay the bulbs out in a sheltered and warm place that preferably has low humidity and good airflow.
If your weather is humid, you can still cure your onions, it just may take them a little longer. Put them on wire racks or something similar so they can get circulation on all sides.
Curing onions allows them to dry out and to develop thicker skins that will help them keep longer in storage. Don’t skip this step if you’re hoping to store the bulbs long-term.
Let the bulbs cure for a few weeks. When the outer skin and neck are both dry and crispy, you’ll know they’ve been cured long enough.
After curing them, onions are best stored somewhere cool and dry at a temperature range of 40-50°F. Keep them in mesh bags or braid the stems together to make bundles and store in your basement or a root cellar.
Make sure you separate onions from apples, pears, and potatoes. It’s a good idea to keep them in their own section so their strong flavor doesn’t get into anything else you’re storing.
The length of storage time depends on the variety and storage conditions. Some will store for a few months and others will last 6 months or more.
As a general rule, eat the smaller and sweeter onions first. Larger and stronger onions tend to last longer. Check through them regularly and remove any that are going bad.
Enjoying Your Onion Harvest
Onions can be an extremely rewarding crop to grow, especially if you love to cook with them. They are very hardy plants and can be grown in almost any region. You can use them fresh or keep them in storage for months.
After you’re done harvesting your onions, you might want to think about planting some garlic in the fall to harvest next year!
Jen is a master gardener, interior designer and home improvement expert. She has completed many home improvement, decor and remodeling projects with her family over the past 10 years on their 4,500 sf Victorian house. She is also a passionate farmer who keeps goats, chickens, turkeys cows and pigs on her farm, and an instructor for her community’s Organic and Sustainable Farming project.