Growing Onions: From Type Selection To Harvesting

Types And Varieties Of Onions To Grow

Day length changes are the key to unlocking the bulb formation. So crop varieties are classified according to the relationship between the amount of daylight received and bulb initiation. Since day length varies with latitude, choose only varieties compatible with your growing region. You can find a large selection of onions to grow within each category:

• Short-day. Their bulbs form when the days are 10 to 12 hours long. These varieties grow well in southern climates (25–35 degree latitudes), allowing for a harvest before the summer heat sets in. Northern regions aren’t ideal for growing short-day varieties because they bulb too soon to yield a decent-sized bulb. Some examples of short-day varieties are Stuttgarter, White Bermuda, Georgia Sweet, Sweet Red, Red Burgundy, White Granex, Hybrid Yellow Granex, and Southern Belle.
• Intermediate-day (day-neutral). Plants in this category begin bulb formation when the days become 12 to 14 hours long. The ideal day-neutral onion growing conditions overlap with those of short- and long-day varieties (32–42 degree latitudes). They grow well across most of the US, except for the southernmost states. Day-neutral varieties include Candy, Sweet Red, Cimarron, Red Stockton, and Super Star.
• Long-day. These varieties initiate bulbs once the days are 14 to 16 hours long. That’s why growing them yields the most in northern regions (37–47 degrees latitudes). Some of the popular long-day varieties are White Sweet Spanish, Yellow Sweet Spanish, Walla Walla Sweet, Aisa Craig, Southport Red Globe, Rossa Di Milano, and Norstar.

Favorable Onion Growing Conditions

Onions don’t need much warmth to grow, but they will suffer if they don’t get enough sunshine. It is necessary to water this plant frequently and consistently because its shallow roots can’t absorb water well. In the following sections, we will explore these and other specific onion cultivation requirements.

What Is The Best Soil For Onions To Grow?

For onions, soil requirements include a pH range of 6.0 to 7.0 and good drainage. Plants prefer organic-rich loamy soils, but they can also grow in sandy or clay fields. To keep the sandy soil evenly moist, you’ll need to water and fertilize it more intensively. To improve clay and sandy soils’ structures, amend them with aged organic matter.

What Are Onion Temperature And Sun Requirements?

The crop is quite hardy and tolerates cold temperatures, including mild freezes. However, if the temperature is predicted to drop below 20°F (-6°C) or lower during a cold snap, make sure to cover beds with mulch or fabric. Although the crop can withstand freezing temperatures, seedlings will grow much slower in air temperatures below 40°F (4°C) and soil temperatures below 55°F (13°C).

EOSDA Crop Monitoring streamlines the process of tracking weather conditions for large-scale crop producers. We offer access to temperature data specifically for your fields:

• historical records going all the way back to 1979 will come in handy in pre-planting analysis to see if the area is suitable for growing onions;
• forecast for the next 14 days helps adjust field activities to upcoming weather and protect crops from adverse impacts of temperature and precipitation.

How Much Water Do Onions Need?

Crop water requirements vary depending on the crop growth stage, growing conditions, and irrigation methods. Because of their shallow roots, plants need consistent moisturizing to grow healthy, about 1 inch (25 mm) of water per week. To achieve high yields, it is particularly important to provide enough water during the vegetative stage, before bulb production starts. Plants that are just starting to grow and those growing in sandy soils need to be watered more frequently than once a week.

How To Plant Onions

Onions have some unique planting materials, especially because these biennial plants are grown as annuals for their bulbs. Being cold-tolerant, they are planted before most other crops. Let’s look at how and when to plant onions to achieve the desired yield.

Choosing Onion Planting Material

For growing the crop, you can use one of three planting materials:

• Seeds. This planting material offers the widest range of crop varieties at the lowest cost. Nevertheless, growing crops from seeds is also particularly challenging, as many farmers struggle with uneven germination. To encourage uniform crops, start your seeds indoors 10 to 12 weeks before you plan to transplant them. The best time to directly plant onion seeds is in the early spring, right after the soil becomes workable in colder growing regions, and in the late winter or even fall in warmer regions.
• Sets. Sets (small bulbs grown from the seed in the previous growing season) are another option for planting onions. While sets are easy to grow, they are bolting-prone, especially if their diameter exceeds 1 inch (2.5 cm). Sets have a much smaller variety selection and cost more than seeds.
• Transplants. Farmers typically buy transplants (pencil-thick dormant plants) from seed providers. When compared to sets, transplants offer a wider variety selection, experience less bolting, and yield more consistently. To plant either transplants or sets, wait until the soil temperature reaches 50˚F (10˚C), which is usually between four and six weeks before the last spring frost.

Preparing Soil For Planting Onions

You can prepare the soil for planting whenever it’s neither too wet nor frozen. Before planting, incorporate fertilizer with an NPK ratio of 10-10-10 into the soil along the designated beds. Also, add well-rotted organic matter and loosen the soil so that water and nutrients can easily reach young crops.

How Deep And Far Apart To Plant Onions

Recommended in-ground onion plant spacing is 6 to 10 inches (15 to 25 cm), and row spacing is 2 to 3 feet (0.6 to 0.9 m). Instead, the distances for growing in raised beds correspond to the lowest limits of in-ground spacing, which are 6 inches (15 cm) and 2 feet (0.6 m), respectively. Closer spacing leads to more bulbs and higher total yields, but smaller individual bulbs.

When deciding how deep to plant onions, aim for about an inch (2.5 cm) of depth. Plants are unable to bulb properly when planted too deeply in the soil, which results in smaller and misshapen bulbs. If you want your crops to grow and produce to their full potential, you need to plant them correctly and care for them along the way.

How To Care For Onions

The crop requires regular watering and abundant nitrogen fertilization to thrive. Furthermore, to grow healthy and productive onions, it is crucial to closely monitor the presence of weeds, diseases, and pests and manage them through a combination of integrated methods.

Consistent Irrigation

Plants require irrigation at transplanting, three days later, and then every 7–10 days (depending on soil moisture levels). Overirrigation can lead to bulb rot, while uneven irrigation or a dry spell followed by intense watering can result in bulb splitting and bolstering. Drip and micro-sprinkler systems significantly reduce water consumption and simultaneously improve harvest quality.

Keeping track of all your irrigation activities and other field operations is a breeze with the Field activity log in EOSDA Crop Monitoring. From a single screen, you can effortlessly handle activities across a few onion growing areas: add your scheduled and finished tasks to the interactive calendar and edit them whenever needed. The Field activity log goes beyond tracking your activities; it also allows you to effectively plan and analyze your farm-related expenses.

Sufficient Fertilizing

The growing crop, being a heavy feeder, requires plenty of nitrogen fertilizer. Fertilizer rates often fall within the following ranges, though this can vary depending on factors like crop variety and soil quality.

How to fertilize onion plants? 2–3 weeks after planting, spread nitrogen fertilizer at 6 inches (15 cm) from the plants, and water the plant afterward. If the soil is acidic, apply 15.5-0-0 calcium nitrate; if it is alkaline, apply 21-0-0 ammonium sulfate. Repeat the scheme of fertilizing onions after planting every 2–3 weeks until bulbs start developing.

If you’re looking for an informed way to manage the nitrogen fertilizer rates for your growing crops, try using vegetation maps in EOSDA Crop Monitoring. They visualize the field zones with varying degrees of vegetation using a color scheme ranging from rich green to red. In low-vegetation places (marked orange or red), crops may not grow as well because of the nutrient deficiencies that are common there. Therefore, applying extra fertilizer can help fill the nutritional gap and help crops grow better.

Integrated Disease, Pest, And Weed Control

Fungal and bacterial infections account for the vast majority of crop diseases, particularly during rainy growing seasons. Diseases, which typically start on the leaves, can hinder the bulb’s growth and decrease yield if not controlled. Infections later in the onion growing season can damage bulbs, resulting in storage losses ^{Grubinger, V. (2009, July). Onion Diseases - An Overview. The University of Vermont.}. To minimize damage and reduce chemical fungicide use, it is crucial to identify the diseases early on. The Disease risk and Scouting features of our crop monitoring solution can assist food producers with this.

Regular inspections will also help you detect pests before they cause any harm. Especially, watch for:

• Thrips. As a result of their feeding, damaged leaves develop a silvery hue and show visible specks. To avoid the spread of thrips — often overwintering in weeds and crop residue — clear the growing area from any debris.
• Onion maggots. Insects feed on bulbs, causing them to rot while stored. As the pest thrives on partially decomposed organic matter, you should only amend the soil with well-rotted materials.

Not only do weeds deprive your growing onions of water and other vital nutrients, but they also provide a home for various pests and diseases, making weed control an essential part of crop management. Farmers effectively eliminate weeds in the early stages of crop growth without harmful herbicides. For instance, you can use straw as a mulch between rows to keep the soil moist and prevent weeds from growing.

How Long Do Onions Take To Grow?

Although onions can be planted in either the fall or the spring, all of them are most commonly harvested from the late summer to the early fall, specifically from July to September. Spring-planted crops typically grow for four to six months, while fall-planted crops take about a year to grow.

How To Harvest And Store Onions

Harvesting onions is simple and follows the same procedure for all varieties. Curing the bulbs is a must before storing them. After that, store the bulbs in a controlled environment to prevent rot.

How To Harvest Onions

Upon ripening, the plants’ tops turn yellow and droop. You can hasten the last stage of ripening by bending the tops down or stomping on them. Before harvesting, loosen the soil around the plants to let the bulbs dry out; this will keep them from rotting while stored.

Pluck the bolting plants because their bulbs cease to grow. Keep these bulbs separate and use them quickly because they don’t last long in storage.

Farmers harvest onions using either manual or mechanical methods. Commercial-scale farming typically involves mechanized harvesting with tractors and other agricultural machinery such as grass toppers, swathers, and crop lifters. Be careful not to bruise the bulbs while harvesting and transportation, as this can cause them to rot.

How To Store Onions After Harvest

After harvest, curing onions is a must. To do this, spread out the bulbs on dry ground (if the weather allows) or in a covered area for a few days.

Then store your bulbs in a ventilated facility with a relative humidity of 50–60%. Be careful not to overventilate, which causes the bulbs to dry out too much. Onion storage temperature should fall within the range of 40 to 60°F (4 to 15°C), but it is equally important to maintain temperature stability. Regularly, look for and remove any sprouting or rotting bulbs. Onions grown from seed or planted in the spring can be stored into the following spring, bringing lasting financial rewards to farmers.