Onion is a must-have vegetable for everyone and one of the easiest vegetables to grow. If you are a novice gardener, you should learn how to grow onions- The reward will be worth it.
You can plant onions using different methods, including seeds, transplants, and bulbs called sets. As onion plants mature, they develop bulbs in response to temperature and day length variations. Therefore, the local climate and latitude determine which varieties will successfully produce bulbs in a given region and the optimal timing and methods for planting onions.
What’s the Best Way to Grow Onions?
There are multiple methods you can use to grow onions. Most gardeners use seeds and sets for onion cultivation. If you are a beginner wondering how to grow onions, you should definitely grow them from sets. It’s quicker and easier to handle
Onion sets are small, immature onions that mature in about 14 weeks. They tolerate light freezes and generally have a higher success rate than seeds or transplants. Sets are available at gardening stores and grow into full-size onions once they mature. For best results, select sets with bulbs about 3/4 inch in diameter, as larger bulbs tend to form stiff necks and go to seed prematurely.
While starting onions from seed is possible, it’s often necessary in colder regions (Zone 5 and below). Seeds require soil temperatures of at least 50°F to germinate, so they should be started indoors about six weeks before transplanting outdoors.
Remember to practice crop rotation with onions. Avoid planting them in the same spot year after year to prevent spreading diseases that affect the crop.
When to Plant Onions
You can plant onion sets outdoors as soon as the soil is workable, typically in late March or April when temperatures are unlikely to drop below 28°F (-2°C).
To grow onions from seed, start them indoors about six weeks before transplanting. Make sure the soil temperature is at least 50°F before moving them outside.
If you want to plant onions in the fall, ensure they have 4 to 6 weeks of warm weather to establish themselves in the soil. During the cooler months, they will go dormant and resume growth in early spring as the temperatures and soil warm up again.
How to Plant Onions
When learning how to grow onions, select a location with direct sunlight because the more energy they get from the sun, the larger their bulbs can grow. When planting, mix a nitrogen-rich fertilizer into the soil. Organic gardeners often add compost to the bottom of each row before planting. Alternatively, dig a trench about 2 inches deep and 3 inches wide, then fill it with an inch of compost.
Planting onion sets 2 to 6 inches apart is best; pressing them into 1 to 2 inches deep soil. Use closer spacing if you plan to harvest some as scallions. For transplants, space them 4 to 5 inches apart, with rows 12 to 18 inches apart. Be sure to set the bulbs with the pointed end facing up, and don’t bury them more than 2 inches deep, as planting too deeply can affect bulb formation.
To retain moisture and suppress weeds, mulch the rows with straw.
How to Grow Onions and Care for Them
Follow these best practices to successfully grow onion bulbs and care for your plants in the garden.
Sunlight
Onions need full sun and require 10 to 16 hours of light daily (depending on the variety) during bulb formation. If you’re growing onions indoors year-round and don’t receive enough natural sunlight, a grow light can provide the necessary light.
Soil and Fertilizer
Onions thrive in fertile, moist soil enriched with compost and high in nitrogen, essential for healthy growth. A macro-nutrient-rich fertilizer can help in nutrient absorption and water intake. You should apply fertilizer before planting and every 4 to 6 weeks throughout the growing season.
Watering
Onion seedlings should be kept consistently moist. Once they mature, they only need about an inch of water per week. “If the leaves start to turn yellow, it could be a sign of overwatering, which can lead to disease and cause the onions to rot. At the same time, be careful not to underwater, as onions have shallow roots, and dry soil can harm the plants.
Yellowing or wilting can also indicate a pest infestation, such as onion maggots, which attack the plant stems.
How to Harvest Onions
Remove any onions that develop flower stalks because this means that the bulb stops growing. These onions won’t store well but can be used in recipes within a few days.
Spring-planted onions are typically ready for harvest by mid-summer. When they mature, the tops will turn yellow and fall over. You can bend the tops or step on them at this stage to speed up the ripening process. You can loosen the soil around the bulbs so they dry.
Harvest onions by late summer, ideally during dry weather, as wet onions don’t cure well and may rot in storage. Once the tops have turned brown, gently pull the onions from the ground. Handle them with care, as even minor bruising can lead to rot. Trim the roots and cut the tops down to 1 or 2 inches unless you plan to braid the onions for storage.
Storing
- Cure onions by placing them on dry ground for a few days or in a sheltered area like a garage or barn if the weather is unfavourable.
- Once cured, store onions by:
- Hanging them in mesh bags or nylon stockings
- Spreading them up to two layers deep in a box
- Braiding and hanging them in a cool, dry, well-ventilated area
- Ideal storage temperature: 40 to 60°F (4 to 15°C); avoid storing in a refrigerator due to excess humidity.
- Regularly check for sprouting or rotting onions and remove affected ones.
- Avoid storing onions with apples or pears, as the ethylene gas from these fruits can disrupt onion dormancy, and onions can spoil the fruits’ flavour.
- Pungent onions store longer than sweet varieties, which have higher water content. Eat sweet onions first and save pungent ones for later.
- To prevent bruising, store onions without touching them, such as by placing them in old pantyhose with knots tied between each one and hanging them in a cool, dry place.
Common Problems When Growing Onions
While onions are super easy to grow, learning how to grow onions can still present some common problems you might face
Pests
Onion maggots can be a problem for this crop, but you can prevent infestations by following a three- to four-year crop rotation plan. Crop rotation is crucial because onion maggots overwinter in the soil, and the adults emerge early to mid-spring. If onions are planted in the same spot yearly, the emerging pests will find their favourite food waiting. Rotate onion family crops to different areas yearly and cover newly planted beds with lightweight row covers in early spring to prevent infestation.
Mildew
The downy mildew disease causes onion leaves to turn yellow or develop brown patches, eventually leading to leaf collapse. While this disease may not kill the plants, it does affect bulb size and yield. To minimize the risk of downy mildew, practice crop rotation and space onions properly to ensure good airflow.
