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Short Day vs Long Day Onions: Choosing the Right Variety

  • 3 min read

Do you know which type of onion is best for your garden? When you’re deciding what to plant in your garden, you’ll probably see different varieties referred to as “long day” or “short day” onions. This refers to the lighting conditions required for optimum growth and development of a specific variety. Let’s look at each type, the differences, and a few examples.

Long Day Onions

Long Day Onion

Long day onions need at least 14-16 hours of daylight to fully form bulbs. These onions thrive in northern latitudes where summer days are longer and nights are shorter. If you live in USDA Hardiness Zone 6 or colder, you’re in the sweet spot for growing long day onions. These onions are typically planted in spring after the soil has warmed up and the threat of frost has passed. They grow during the warm months and are harvested in late summer to early fall after bulbs have reached maturity and leaves begin to yellow.

The thin skin of long day onions allows for better air circulation and prevents mold and rot. Long day onions have more sulfur content, which makes them more pungent and also helps to inhibit bacteria growth. As a result, these varieties are the best for long-term storage, and can often be stored for 10-12 months. Ideal storage temperatures are between 32°F to 40°F (0°C to 4.4°C).

One of the best examples of a long day onion is the Walla Walla onion, the state vegetable of Washington. These long day onions have a mild, sweet flavor and are often eaten raw in salads or sandwiches. They can be planted in fall and overwintered for larger bulbs or planted in early spring for smaller bulbs with a sweeter flavor.

Short Day Onions

If you only get 10-12 hours of daylight in the summer, short day onions are a better choice for your garden. This means USDA Hardiness Zone 7 and south. Some gardeners in Zones 5 and 6 can also have success with short day onions if they plant in late winter. Short day onions can be planted in fall to overwinter, especially in mild regions. Otherwise, they can be started early in spring. Cool weather helps these onions form bulbs, but they also need some protection from frost.

Short Day Onion

Short day onions tend to be juicier, with higher water and sugar content. They tend to also have less sulfur than long day onions, which means they are less pungent tasting. They have thicker skins, too. All of these factors add up to a sweeter onion that doesn’t store much longer than a couple of months.

White Grano is a short day onion that produces mild bulbs that get up to 3” in diameter. This is a neutral-flavored onion, so it can be used both raw and cooked.

Red Burgundy is another wonderful short day onion that produces 4” red bulbs. These onions are delicious fresh, so slice some up and add them to your sandwich or salad. They are also exceptionally good pickled!

Intermediate Day Onions

There’s one more type of onion to discuss, the intermediate day onion. You’ve probably already guessed how much daylight they need: 12-14 hours. Growers in the short and long day zones can usually have some success with these onions, too.

Intermediate Day Onion

We’ve currently got one variety of intermediate day onions: Tokyo Long White Bunching Onion. This is a tasty green onion that doesn’t form round bulbs. It thrives in containers and will produce continuously throughout the year. Since this onion isn’t typically grown for its bulb, almost anyone can successfully grow this easy bunching onion, regardless of their day length.

What Happens If I Grow the Wrong Type of Onion?

If you happen to buy the wrong sort of onion for your growing zone, your seeds will still grow, but they probably will not form full-sized bulbs. If you grow long day onions in an environment that is too hot, your plants will probably bolt early and go to seed before they form bulbs. Longer daylight hours cause short day onions to delay bulb formation. If you have a greenhouse, you may be able to regulate the light exposure and temperature enough to get results.

What should you do if you make a mistake and start the wrong type of onion? You can throw them out and start over or you can this as a learning experience and experiment! After all, when you’re growing a survival garden, you learn to make the best of every situation and waste as little as possible. Your onions still may produce small bulbs with a little extra attention, and you can still enjoy the green tops of these onions and add them to your dishes.

Onions in the garden

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