Plants

When to Harvest Onions

Published on November 27, 2022

Whether you’re growing a variety of onions for the spring or fall harvest, knowing when to harvest them can be critical to ensuring a fresh, ripe crop. When you harvest onions, you’ll want to keep them from spoiling by storing them properly, curing them, and preparing them for cooking.

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Short-Day vs Long-Day Varieties

Depending on your climate, you might be wondering which type of onions you should grow. There are three main types: short day, long day, and day-neutral. Each type is more suited to a particular region. You’ll want to check with your local extension agents to find out which type is best for you.

Generally, short-day onions will grow well in the southern half of the country, while long-day onions are more appropriate for the northern half. The difference in daylight hours is more pronounced as you get farther away from the equator.

For example, a short-day onion will bulb when it receives 10 to 12 hours of daylight. In contrast, a long-day variety will bulb when it receives 14 to 16 hours of daylight. Typically, the long-day variety is best for growing in the upper Midwest states.

The short-day onion may be the easiest type to grow, but it’s not the only onion that’s capable of bulbing. Long-day onions have a better chance of producing large tops, which can be used to fuel bulb formation.

Mature vs Spring Onions

Whether you are growing spring onions, scallions, or other alliums, you need to know when to harvest. While you can grow onions all year, the spring and summer season is the most popular time for the alliums. The leaves are green for most of the year, but turn yellow when the bulbs reach their peak maturity.

You can harvest spring onions when they are at least four inches tall and the bulb has begun to develop. You can keep them in an open zip-top bag in the fridge to prolong their shelf life.

You can harvest scallions after the bulb has swollen. These onions are ready to eat when they are six to eight inches tall. However, they are harder to substitute for spring onions. Spring onions are sweeter, have a thinner bulb, and have a more intense flavor. You can also add scallions to a variety of dishes, including soups, stews, and frittatas.

The difference between spring onions and scallions is that the scallions are green. The green tops of the onions don’t caramelize like the bulbs.

Curing

Whether you are harvesting onions in the field or picking them off a tree, curing them for storage is a necessary step. Curing onions properly protects them from damage and rot and helps them last longer during storage.

Curing onions naturally involves leaving them in a warm, dry location for at least a month. Depending on the growing region, a variety of curing techniques are used. For optimal curing, consider using wooden crates and bulk pallets.

For long-term storage, onions should be cured at temperatures of 32-40 degrees Fahrenheit. For optimal curing, a relative humidity of 65-70 percent is preferred.

Onions can be stored in a basement, an unheated garage, or even a cellar. Storage areas should be temperature-controlled, and onions should be stored in a crate or mesh bag.

If you are harvesting onions in the fall, curing them for storage is important. If you harvest your onions early enough, they will stay fresh for many months. However, if you harvest onions later in the fall, they may get damaged by freezing temperatures.

Storage

Ideally, onions should be stored in a cool, dry place at 32-45 degrees F with 65-70 percent relative humidity. When storage temperatures are too high, they can be prone to mildew and mould. A good storage location for onions is in a basement, in a root cellar, or in a cold store.

Storage conditions will depend on the variety of onions you are storing. Onions can be stored for months when properly cured. But, they will not last as long if they are stored in a damp or humid environment. Whether you store them in the garage, in a cold room, or in a root cellar, it is important to make sure they are dry and that they are placed in an area with good ventilation.

To store onions, you can use a net bag or a purpose-sold vegetable storage net. You can also store onions in a wicker basket. But, the wicker basket will limit air circulation around the bulbs.

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Emma Gomez

Content Strategist at Plumber Marketing Company

A mother and lover of all things practical. My blog covers about motherhood by exploring all areas of life. Our tips and tricks help large community to do more in less time so they can spend time enjoying happy, healthy families.