Onions grow very well in many different climate zones and soil conditions. They are more than just a tasty food crop – onions also help gardens by repelling insects and deterring herbivores. Gardeners grow onions for their bulbs or for tender greens. Some species of onion don’t even form bulbs – those are perfect for growing onion greens.
Overview of Growing Onions
If you’ve never raised onions, here’s a quick overview. Onions are biennial plants (which means that they can survive winter and grow for 2 years) but they can be harvested annually. Onions grow best in temperate climates without extremes of heat or cold. The time of year when onions are planted affects when they form bulbs.
If you plant your onions too late in the season, they may not form bulbs properly. Onions come in two different classes: long-day and short-day onions. Long-day onions are more appropriate for northern states because they are adapted to longer days. Southern states should use short-day varieties of onions. When you go to your nursery, long-day onions are often marked with an “L” and short-day onions are labeled with an “S”.
Onions are sometimes called Scallions, but Shallots are a different vegetable. Shallots are also in the onion family and many of these tips will help when raising French shallots (grey shallots), red shallots, echalion shallots, and Dutch yellow shallots.
There are many varieties of onion. The broad categories include white onions, yellow onions, and red onions. In general, white onions such as the Bermuda and Portugal White have the strongest flavor, but do not keep very well in storage. They should be eaten quickly for the best taste.
For longer shelf times, pick yellow onions, such as the Yellow Globe, Copra, and Sweet Sandwich. Red onions have a milder, sweet flavor, which is good if you want the health benefits with less bitterness. Red varieties include the Red Burgundy and Red Wethersfield. Sometimes, yellow and white onions are referred to as ‘sweet onions’.
These varieties include the Vidalia, Sweet Spanish, Bermuda, and Walla Walla onions. These onions are often hybridized to produce disease resistance – a few examples include the Texas Grano 1015Y and the mildly flavored White Crystal Wax Onion. Some onion species are best suited for raising onion greens. These include White Portugal onions, White Spear, Ebenezer, and Tokyo Long White.
Bunching onions such as the Beltsville Bunching and Japanese Bunching are a good pick for colder climates and late fall to winter harvests. They will not form bulbs and indeed the entire plant with the root structure can be harvested and used. For Winter onions that produce bulbs, check out Egyptian, Hill and Walking Onions.
Diseases and Pests That Affect Onions
Several different diseases and pests may affect your onions. Pink Root, Rot, Purple Blotch, and Tip die off can all be controlled by choosing disease resistant varieties in combination with an organic fungicide.
Here’s some in-depth information about onion diseases. Common insect pests include thrips and onion maggots. Organic pest killers are effective at controlling thrips, while Nematodes are the best natural tool against root maggots. Another way to repel root maggots is to plant marjoram and oregano next to your onions. Before planting onions, it’s important to prepare the soil.
Caring For Your Onion Crop
Onions require good drainage, plenty of organic material, and an absence of weeds. It’s important to till the soil and add compost until you get the pH between 6.2 and 6.8. If time permits, grow a crop of corn, beans, potatoes, or cowpeas in the area where you plan to use before planting onions there. Onions have shallow roots and require a bit of help to get established. They have shallow roots and are vulnerable to competition from weeds, so weed regularly. Onions can be grown from transplants, small dry bulbs (also known as sets), or seeds.
If growing onions from seed, make sure to rake the soil after heavy rains so that the onion stalks can break through, and water the soil regularly in the morning. Once your onions become established, horticultural corn meal is a great way to keep weed seeds from germinating.
Mulch will also help because it boosts the soils water capacity and mulch can help regulate the temperature to prevent onions from bolting (onions stop growing their bulb and start growing a flower stalk when temperature extremes occur). Established onions don’t require much water, and will typically need to be irrigated only every 5 to 7 days.
When growing onions, fertilizers aren’t really necessary. Blending compost into the ground is usually more than sufficient. But, if your soil is particularly poor in nutrients, organic fertilizers are better than chemical fertilizers because they don’t leave harmful residue in the soil. There are also organic products that allow plants to get more nutrients out of the soil, such as Mycorrhizal Fungi Root Builder.
Onions can be grown very close together, and a row of onions will produce plenty of bulbs. The optimal density is between 8 and 10 onions per foot, but many onions can die off between planting and maturity. So, the best time to thin onions is after stalks start to drop, and that’s also a good time to harvest onion greens.
A 10 foot long row of onions will produce about 10-15 pounds of onions. When 25-50% of the stalks droop, that’s the right time to pull up the bulbs. For more information on harvesting onions, here’s a guide to gathering and storing onion bulbs.