If you’re looking for a low-maintenance crop that won’t take up much space, onions are a great choice. There are many onion varieties to choose from, and you can grow them from seeds, sets, or transplants! But before you begin planting, there are a few things to consider.
Known as the common or bulb onion, onions (Allium cepa) are a biennial crop, but are often grown as an annual. This means that even though they can live for two years, we typically harvest them after the first growing season. Onions are part of the same family as garlic, leeks, and chives.
Let’s take a look at how to grow these versatile vegetables!
Choosing the Right Onion Variety
Onions come in many different shapes, sizes, and colors. From red, yellow, and white onions to scallions and green onions, the options are endless.
However, common onions can be further broken down into three main types: short-day, intermediate-day, and long-day. This classification is based on the number of daylight hours (not direct sunlight) they need to form bulbs. Here’s a quick overview of each type:
- Short-day onions: This variety needs 10-12 hours of daylight to form bulbs and is best suited for warmer regions with a longer growing season. Crystal White Bermuda onion, Southern Belle, and Red Creole are all short-day onions.
- Intermediate-day onions: These onions require 12-14 hours of daylight to form bulbs. They are also known as day-neutral onions. Early Yellow Globe, Cabernet, and Cipollini are examples of intermediate-day onions.
- Long-day onions: As the name suggests, these are more daylight than the other varieties – at least 14 hours. They are best suited for cooler regions with shorter growing seasons. Walla Walla, Spanish Sweet, and Copra onions are some popular long-day varieties.
So, besides choosing an onion based on flavor and growing requirements, consider the day length needed for bulb formation. This will ensure a successful harvest!
When Should You Plant Onions?
The best time to plant onions depends on your chosen variety and region’s climate.
Generally, onions are a cool-weather crop and are often planted in the spring when the last frost date has passed. You can also plant them in the fall if your area only experiences mild winters. They’ll go dormant over the winter and start growing in the spring.
What Are the Best Growing Conditions for Onions?
Aside from the time of year, there are a few key factors to consider when growing onions:
Onions love loose soil with lots of organic matter. It should also be well-draining, as they don’t like sitting in too much water. The pH should be neutral to slightly acidic, around 6.0-7.0.
Onions don’t like heavy clay soils or soils full of rocks – these conditions are too compact for the onion bulbs to grow.
Full sun is essential for growing onions. They need at least six hours of direct sunlight daily to form bulbs. Avoid planting them in shady areas or near large trees that may block the sun.
While onions don’t need a ton of room to grow, it’s essential to give them enough space for good air circulation. Planting them too close together can lead to disease and pest problems. Onions should be planted around 6 inches apart in rows, with 12-18 inches between rows.
Onions can be planted with other members of the Allium family, such as garlic or shallots, but they may spread diseases or pests to one another. Good companion plants for onions include beets, carrots, lettuce, broccoli, and tomatoes.
Temperature and Humidity
The best temperature range for onions is 68-77°F (20-25°C). They can handle slightly warmer temperatures, but this may stunt their growth. Anything over 86°F (30°C) can cause the bulbs to bolt and go to seed – not ideal when growing onions for their bulbs.
Humidity isn’t a huge factor for onions, but they do prefer moderate humidity levels. Too much moisture in the air can lead to fungal diseases.
Can You Grow Onions in Pots?
Growing onions in pots is more commonly done with green onions or scallions, which are harvested before the bulb fully forms. However, it is possible to grow full-sized onions in pots as well! This is ideal for those with limited garden space or have less than ideal soil conditions.
Choose a 10-12-inch container and make sure it has good drainage holes. Use a well-drained soil mix and ensure there is enough space between the onions (4-6 inches) for proper air circulation. Any plants grown in a pot will require more frequent watering. Keep the soil consistently moist but not waterlogged.
How to Grow Onions
There are several methods for growing onions, including from sets, seeds, or transplants. Which method you choose will depend on your preferences and growing conditions.
Growing Onions from Sets
Sets are the most common way to grow onions. They are small bulbs that are already partially grown. This is a good option for beginners, but they can be more prone to bolting than other methods. Consider buying heat-treated sets to reduce the risk of bolting.
Here’s how to grow onions from sets:
- Choose a sunny spot with good drainage in your garden.
- Prepare the soil by loosening it and adding organic matter. Remove any debris or weeds.
- Lightly press the sets into the soil, about 4 inches apart. Their tops should be just above the soil surface.
- Don’t hill up the soil around them – they will naturally push themselves up more as they grow.
- Water as needed and keep the area weed-free.
- Onion sets can store well for months if kept in a cool, dry place. This means you don’t need to plant them all at once. In fact, staggering your planting can give a longer harvest window.
Growing Onions from Seeds
Growing onions from seeds allows for a wider variety of onion types to choose from, but it requires more patience and attention.
Here’s how to grow onions from seeds indoors:
- Start seeds indoors 6 weeks before the last expected frost date for a spring planting. For a fall planting, start seeds indoors in the late summer.
- Use a good quality seed starting mix and fill trays or individual pots
- Sow seeds about a quarter inch deep and lightly cover with soil. The more seeds you sow per container, the smaller the resulting onions will be. You can always thin out the onion seedlings later.
- Keep the soil consistently moist but not soggy. Place in a warm spot or use a heat mat/propagator.
- Once seedlings have emerged, provide them with as much light as possible by using a grow light or placing them in a sunny window.
- Harden off seedlings by gradually exposing them to outdoor conditions for a few hours each day for a week.
- Transplant the seedlings into your garden once hardened. They should be planted about 4-6 inches apart.
How to grow onions from seeds outdoors:
- Remove any weeds or debris to prepare the soil for planting. Add some organic matter if using.
- Sprinkle seeds onto the prepared soil in rows, which should be about 12 inches apart.
- Push the seeds down about 1cm and cover lightly with soil.
- Keep the soil consistently moist but not soggy until seedlings emerge.
- Thin out seedlings when they are about 1/4 inch tall, leaving about 4-6 inches between each plant. You can use the young plants you remove in salads.
Growing Onions from Transplants
Transplants are young plants that have already been started from seeds and are ready to be transplanted into the garden. This is a good option if you want a quick and easy way to grow onions.
Here’s how to grow onions from transplants:
- Purchase healthy onion transplants from reputable nurseries or garden centers.
- Prepare the garden bed by removing weeds and debris and adding organic matter if needed.
- Dig small holes about 4-6 inches apart in rows. Each hole should be around 1 inch deep.
- Gently remove the transplants from their containers and place them in the holes. If the roots look tangled, carefully loosen them before planting.
- Fill in the holes with soil and gently firm it around the transplants. Don’t cover any leaves of the transplants.
- Water the transplants after planting.
6 Tips for Growing Onions
Your new onion plants will need some care and attention to grow successfully. Here are some tips to help you along the way:
Onions must be watered regularly to help them grow and produce large bulbs. Water deeply once a week – around 1 inch of water is enough. It’s best to water in the morning to avoid evaporation during the day’s heat.
Onions are heavy feeders, meaning they need many nutrients to grow well. Fertilize them regularly with a balanced fertilizer or one high in nitrogen to help promote leafy growth.
Space Them Out
If you limit the amount of space between your plants, you’ll also limit how big your onion bulbs can grow. Planting in rows is best for outdoor growing. Rows should be around 12-18 inches apart, and the plants within them should be spaced around 4-6 inches apart.
Container-grown onions should be planted in a large enough pot and not overcrowded.
Add Some Mulch
Mulching around your onion plants can help to retain moisture, suppress weeds, and regulate soil temperature. A layer of organic mulch like straw, coco coir chips, or grass cuttings can work well.
Keep an Eye on Pests and Diseases
Onions can be susceptible to pests and diseases. Leafminers, thrips, and onion maggots are common pests to watch out for. Some possible diseases are basal rot, downy mildew, and purple blotch. Regularly inspect your plants and treat any issues quickly to prevent them from spreading.
Remove Any Flowers
Onions usually flower in their second year, which isn’t a problem for those who grow them as annuals. However, onions can bolt in their first year if they experience stress or extreme weather changes. Remove any flower stems as they form to stop the plant from using energy for seed production instead of bulb growth.
Any bolted onions should be used fresh as they won’t store well.
How to Harvest Onions
You’ll know when your onions are ready for harvest because the tops will begin to turn yellow and start falling over. Once approximately 50% of the plants have fallen over, it’s time to harvest.
But remember, you can harvest onions at any time! You don’t have to wait for them to be fully mature – not unless you specifically want large onion bulbs.
Gently dig around each onion bulb, but don’t completely uproot it. Allow the onions to dry on the soil in the sun for a few days. Then, carefully dig up each onion (rather than pull) and remove any remaining soil. Trim off the roots and tops, leaving 1-2 inches of each.
Move them to a well-ventilated, covered space if the weather is wet to leave them on the soil.
How to Store Onions
If you want to store your onions for a prolonged period, you’ll need to cure them. Curing helps to dry out the onion skins and preserve them for longer.
Brush off any remaining soil from the onions and lay them in a single layer in a warm, dry place with good air circulation. A garage or shed is ideal for this. The onions will need to be cured for 2-3 weeks to dry out the outer skins completely.
Store your cured onions in a cool, dry, dark place. A mesh bag hung up somewhere is perfect as it allows good air circulation. You can also store them in a paper bag or basket. They can last up to a year if cured and stored correctly!
Here are some other storage options:
- Store whole, unpeeled fresh onion in the crisper drawer for 2-3 months.
- Cut or sliced onions can be stored in an airtight container for up to 7 days.
- Chop or dice raw onions and freeze them in an airtight bag or container. They’ll keep for 6-8 months and can be used directly from the freezer.
- Slice onions into thin rings and dehydrate them in a food or herb dehydrator until they are completely dry. Store in an airtight container or bag. They can last from 6 months to 2 years if stored correctly!
- Pickling is a great way to preserve onions. You can pickle them in vinegar and store them in airtight jars for up to 2 years.
How to Use Onions in Cooking
There aren’t many dishes that don’t call for onions! They’re the perfect addition to soups, stews, casseroles, and more. Here are some of my favorite recipes to use onions in:
- Canned green beans with bacon and onion
- Crockpot hashbrown casserole
- Chicken bone broth
- Pan fried cube steak
- Crockpot cabbage
- Slow cooker chicken pot pie
- Zucchini pasta
- Homemade chicken and dumplings
- Sheet pan sausage and veggies
- Instant Pot beef stroganoff
And if you’re curious about how to cut an onion like a pro, check out my complete guide on how to cut an onion properly!
Yes! This is essentially what an onion set is – a small onion bulb that can be planted to grow into a full-size onion. It’s a great way to get a head start on your onion crop and bypass the long growing process from seed.
Yes, you can grow onions in containers! Use a pot that is at least 10-12 inches deep and has good drainage. It should also be placed somewhere with access to plenty of sunlight.
Onions contain a sulfur compound that is released when they are cut or crushed. This chemical irritates the eyes and makes them water. Yellow, white, and red onions are the biggest culprits for making you tear up, as they have the highest sulfur content! Try chilling your onions in the fridge for 30 minutes before cutting to lessen the effects.
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