How to Grow Onions

Onions are one of the most popular vegetables in the world, and growing onions is a snap in the home garden when you know how to grow onions properly. Onions can be sliced, diced, chopped, and quartered for use in just about every recipe.

Onions are not usually eaten on their own, but used as a side dish or in the preparation of the main meal. Onion flavor varies from sharp and spicy to tangy and powerful to sweet and mild depending on the variety.

One of the first crops ever cultivated, Onions (Allium cepa) are found the world over and available in a variety of forms. Spanning many cultures around the globe, the humble onion has been a staple food for thousands of years and is one of the most versatile and popular ingredients used in cooking today.

First cultivated in ancient Egypt and revered as a sacred food, the onion is an amazing plant that is still a commonly found vegetable planted in many home gardens.

In addition to the edible uses of the onion, there are many medicinal uses. Onions are known to increase circulation, lower blood pressure, and prevent blood clotting. Onions also have been shown to benefit women in menopause fight off the effects of osteoporosis.

The onion is a wonderful vegetable to grow in the home garden and they are easy to plant, care for, harvest, and when stored properly last for months.

Onion Types

Gardeners tend to grow onions for a variety of reasons: winter storage vegetables, delicate summer flavour, and even giant vegetable contests. Each of these uses calls for a different type of onion. Luckily, there are plenty of onion varieties to meet every gardener’s needs.

Onions are members of the Allium family, which also includes leeks, garlic, scallions, and shallots. Onions form their distinctive bulbs in response to day length.

There are 2 major types of onions: short-day and long-day. Short-day onions will start making bulbs early in the year when day length is only 10-12 hours. They are often mild and soft-fleshed making them unsuitable for storage.

The more pungent long-day onions will bulb up much later in the year, when day length reaches 14-16 hours. As a general rule, long-day onions are planted north of the 36th parallel, in the northern states and Canada. Short-day onions do better in southern states.

Choosing a Variety

Although onions can be started from sets, seed will give gardeners access to a wider variety of onion cultivars. Choosing the right variety depends very much on what you prefer in your onions.

Giant onions, grown for exhibition or competition, start with the right variety. Ailsa Craig, Beacon, and Lancastrian are just some of the recommended varieties. Although they don’t store well in the kitchen, their size and mild flavour are nonetheless prized.

For mild-flavored, normal-size onions, choose varieties like Walla Walla, Vidalia, or Sweet Spanish. These onions have a high sugar and water content which makes them excellent fresh-eating onions. However, these same attributes make them poor storage onions so eat them soon after harvesting.

Good storage onions require thick skins and high sulphur content. Sulphur is nutrient that gives onions their particular pungency (The capacity to make you cry is caused by this sulphur content as well). The sulphur prevents pests like fungus and insects from damaging the bulbs in storage. Varieties recommended for their storage capacity include Copra, Buffalo, and New York Early.

How to Grow Onions

Plant onion sets about one inch deep and spaced four inches between each plant in full sun and well-drained soil. To harvest green onions, space each onion plant two inches apart, and then pull every other onion as the bulbs start forming. Onions are hardy down to twenty degrees Fahrenheit and should be planted four to six weeks before the last frost.

A lot will depend on where you are in the world and the type of soil conditions you have but growing in early Spring just as the frost is fading away is a great time to get started with your onion growing plans. For people in the US or the UK, seeding your onions around February time is ideal, although January could be suitable if your climate is not too harsh, and this should see them blooming at a great time of year.

Sowing the onions too early will leave them at risk of a cold snap and sowing them too late could see them fail to grow to their full size by the time you would be looking to harvest. A lot will also depend on when you are hoping to be able to enjoy the onions but a good rule of thumb is after the coldest part of Spring.

Even though knowing when to plant onions is important, it is also vital to move into action before this date. Before you plant onions, there is a need to prepare the soil to ensure that the onions are placed in the right conditions to boost their growth.

Onions do not grow as well in heavy soils as they do in lighter soils so spending some time to prepare your land with this in mind is likely to bring about positive results. It is also important to remember that onions do not like fresh manure soil, so bear this in mind when preparing your onion plot.

Onions are heavy feeders preferring a regular application of nitrogen rich compost that is incorporated into the soil before planting, and then applied every three weeks until approximately four weeks before harvest.

Once the base of the neck of the onion shoot is sift do not apply any more fertilizer. Be sure to water after every compost application and generously apply water thorough out the growing season. The closer to harvest, the more water the onion needs to form the bulb. Cultivate around each plant to control weeds, and loosen soil, taking care not to damage the onion plant or bulb.

Onions are categorized by the day length needed to form bulbs. Varieties are traditionally long day and short day, with newer hybrids being considered mid day. Long day onions will start to form bulbs when the days offer fifteen hours of sunlight. Short day onions will make bulbs when the average daylight is nine to ten hours. Long day varieties are recommended for northern climates and can be set out early in the spring.

Onions are ready to be harvested when the top shoots fall over. Grab each onion near the bulb and pull from the ground, loosening surrounding soil as needed. After pulling from the ground allow the onion to dry, clip the roots and cut the tops back to one inch.

For long term storage success, be sure to keep the onions in a cool, dry place, arranged so that the onions are not touching each other. Wrapped separately and stored in the refrigerator, onions can last up to a year.

When storing onions the rule of thumb is, the sweeter the onion the higher the water content and therefore a shorter shelf life. A more pungent onion will keep longer than sweet varieties, so eat sweet varieties first and save less sweet varieties for long term storage.

Plant onions near broccoli, cabbage, carrots, peppers, tomatoes, strawberries, and lettuce for greater yields. Chamomile and summer savory improve onion growth and flavor. Onions stunt the growth of beans and peas so avoid planting nearby.

How to Grow Onions from Seed

Many people will tell you that growing onions from sets is the easiest way to have some great onions but there is nothing too difficult in growing onions from seeds. It is a slightly more involving process than growing from sets but there are benefits to this process and it can be a lot more rewarding for someone who really enjoys the gardening process.

One of the first benefits of growing onions from seed is the fact that it is cheaper than growing from a set. In these tough economic times, many people are turning towards being self sufficient in order to save money so it makes sense that people will look for the more cost efficient way of growing onions. If this is the case for you, growing onions from seed should definitely be your number one choice.

Another major benefit in growing onions from seed comes with the fact that there is a far greater level of variety in the onions that you can grow. To the untrained eye, an onion may be an onion but there are many different varieties, all of which have their own tastes and nuances.

If you like a particular onion or you know that a certain type will go perfect with a dish you are hoping to make, growing onions from seed will give you a better opportunity of growing the onions that you want.

A disadvantage of growing onions from a set is the fact that they tend to bolt more so if you are looking for a successful batch, it is often better to grow onions from seed.

Starting Seed

Onion seeds do need to be bought fresh each year. Their germination rates do not last more than one year so don’t plan all of your harvest around last years’ seed. Growing your own transplants requires at least 7 weeks so time your sowing date so that you transplant after your last hard frost.

Onion seeds do require some warmth to germinate so start them indoors at this time of the year. Choose either a sterile seed mix or make your own seed starting mix with compost, sand, and peat or coir.

Seeds should be sown about 1/4″ deep either in individual cells or 6-8 seeds per 2-inch cell in the larger seed trays. Since the seed is so shallow, the soil needs to be kept moist so either cover the seed tray with a dome, saran wrap, or enclose in a plastic bag. Germination should occur in 7-14 days.

As the seedlings grow, provide supplemental light to keep the leaves healthy and short. Begin feeding the onions with dilute fish fertilizer every 2 weeks. Do not thin the onions or else you might disturb their shallow root system. However, to promote thicker stems, cut back to leaves to 3″ every couple of weeks.

Transplanting

By mid-April, begin hardening-off the seedlings by moving them to a cold frame or gently exposing them to outdoor temperatures for a few hours each day. Before transplanting, prune the leaves once more to help reduce stress on the root system.

Onions prefer growing in full sun in rich soil that has been amended to pH 6.0-6.5. Although they are heavy feeders, over fertilization with too much nitrogen can decrease their storage capacity and will also attract more pests as the onions are growing. Compost or well-rotted manure will provide the full range of nutrients that onions will need to grow properly.

Pests

The only pests that I have found when starting onions from seed are fungus gnats. Part of the problem when growing onions from seed is trying to balance adequate watering with good drainage. Onions have shallow root systems so their rooting medium shouldn’t be allowed to dry out. However, this is a great environment for fungus gnats.

If you do begin to see these black, flying insects, don’t panic. Set out some yellow sticky traps and cut your watering down by about 25%. You should see a decrease in the problem without having to resort to any sprays. If the problem persists, predatory nematodes can be watered into all of your starting trays to control fungus gnat larvae.