How Much Sun Do Onions Need

Onions are pretty easy to grow, although they require more fertilizer than many other vegetables. You may also be wondering how much sun do onions need. The answer depends on the variety you have.

Short-day onion varieties require 11 to 12 hours of sunlight, intermediate-day varieties 12 to 14 hours, and long-day varieties at least 14 hours. Fortunately, it’s not really possible for onions to receive too much sunlight.

If your garden receives a limited amount of sunlight, you are better off with green onions or a short-day variety. Green onions can grow with as little as seven hours of direct sunlight! Also, you should know that onion plants can be more prone to disease if they grow in partial shade.

How Much Sun Do Onions Need

How Much Sun Do Onions Need

The short answer is that onions need a decent amount of sun, at least 11 hours of full sun a day.

Short-day varieties include Georgia Sweet, White Bermuda, and Sweet Red.

Overall, onions require a minimum of 11 to 16 hours of sun a day, depending on the variety. Short-day varieties include Georgia Sweet, White Bermuda, and Sweet Red. They need about 11 to 12 hours. Long-day varieties such as Vaquero need 14 to 16 hours of sun.

Intermediate-day onion varieties are also called medium-day.

Examples are white Superstar and Sweet Red.

Whether onions are a short, medium, or long-day type depends on the latitude they do best in.

Long-day onions are best suited for northern latitudes, while medium-day onions do great in the central parts of the United States.

Short-day onions thrive in the southern states.

So, basically, you are better off picking a variety that does well in your location and giving it that minimum necessary amount of sunlight.

FInd out the 2 growth stages of onions, & why they’re important for gardeners.

Do Onions Need Full Sun

Do Onions Need Full Sun

Onions definitely grow best in full sun, but it is possible to grow them in less than. If you do that, choose green onions or a short-day variety, also called a day-neutral variety. Keep your expectations about growth on the low side until you have more experience.

Ideally, onions would grow in areas with full sun and top-notch drainage.

Onions form bulbs depending on the amount of daylight they receive

Onions form bulbs depending on the amount of daylight they receive, so you’d choose day-neutral onions for partial shade conditions.

These plants form bulbs starting at 10 hours of daylight per day.

Onions are photoperiodic vegetables, meaning that length of daylight affects their growth.

If you’re not familiar with the U.S. Department of Agriculture Plant Hardiness Zone Map, take a look here. 

You’ll see 11 zones and the best type of onion for each zone.

If you live in Zone 11, which includes most of Florida and some of southern California, you should plant short day onions.

Check out our complete guide to planting onion sets.

Can Onions Grow in the Shade?

Can Onions Grow in the Shade?

Onions love the sun and need at least 10 hours of daylight.

Many varieties need more than that 10-hour minimum.

However, yes, onions can grow in the shade as long as they are a variety that requires only about 10 to 11 hours of sunlight or less. The shade also should not be too “shady.” Give your onions as much sunlight as possible.

Green onions, also called scallions, may be your best bet, as they sometimes grow in spots that get only six to eight hours of full sun a day.

Ideally, the onions you grow in the shade would still be in full sun for close to 10 hours a day. 

Examples of short-day or day-neutral onion varieties are Red Creole, White Bermuda, and Yellow Granex.

They perform best in the southern part of the United States in USDA hardiness zones 7 and warmer.

These zones are split according to average low temperature, but, fortunately, short-day onions grow OK anywhere.

If you plant a long-day onion in the shade, you are probably out of luck.

Go with a day-neutral variety instead and follow best practices such as giving your onions plenty of fertile, well-drained soil with a pH of 6.0 to 6.8.

Also, check your “shade” onion plants often for signs of disease or fungi.

Onions that grow in partial shade are more susceptible to issues.

Can Onions Get Too Much Sun?

Can Onions Get Too Much Sun?

Onions need plenty of sun, but is there such a thing as them getting too much sun? No, not really!

Onions cannot get too much sun, especially when they are early in their growth.

Onions cannot get too much sun, especially when they are early in their growth. That said, a major potential problem is soil becoming too dry and fertilizer becoming less effective. So, you will be fine as long as you have plans to prevent against dry soil and neutralized fertilizer.

In anticipation of these issues, ensure you check soil moisture/fertilizer about three weeks after planting and infuse with regular applications every two to three weeks.

You can stop with the fertilizer once the neck of the onion begins to feel soft.

The closer onions are to harvesting, the more water they require.

The closer onions are to harvesting, the more water they require.

Onions that do not get enough sun are susceptible to fungal diseases such as downy mildew.

It covers onions with a purplish mold that is hard to get rid of.

Leaves are likely to develop yellow, white, or gray spots, particularly in humid or cloudy weather.

With a lack of sunlight, you can also expect an absence of bulbs or too-small bulbs.

How Much Sun Do Green Onions Need

How Much Sun Do Green Onions Need

Green onions differ from other onion varieties in that they can grow OK in lesser amounts of sun.

Green onions need about 6-7 hours of sun a day, although a grow light for that amount of time should do fine, too. Just remember to keep the soil moist, and you should be good to go. Of course, if your green onions get more sunlight, they may grow a bit bigger and better.

However, don’t worry if you can’t give your green onions more light than six or seven hours a day.

You can even make a tiny greenhouse for your home or apartment. 

See our complete guide to making an indoor greenhouse. 

Consider including are scallions/green onions, green beans, carrots, and strawberries.

How Much Sun Do Spring Onions Need

How Much Sun Do Spring Onions Need

Spring onions are often used as another name for scallions, green onions, and bunching onions.

Full sun exposure for spring onions is ideal for at least 6-7 hours a day. More sun or grow light exposure than that will not hurt as long as you keep the soil moist and fertilized. Onions have high nitrogen requirements with the majority of the need after the plant begins to bulb.

Spring onions are fun to grow at home, whether indoors or outdoors, alongside other plants.

The flexible direct sunlight requirements make them versatile.

They take about eight weeks to grow and can be a good filler crop in between vegetables that grow more slowly.

Throw them in salads and stir frys, and you have some delicious meals coming up.

Don’t underwater or overwater your spring onions, though.

Cover the bottom area only, and new growth should occur above the water.

Find out whether onions are fruits or vegetables.

About the author

Greg Volente

Greg Volente holds a Naturalist Certificate from the Morton Arboretum, worked for The Nature Conservancy leading environmental education programs and doing natural areas restoration, and worked in the soil science research & testing lab at Michigan State University. Besides gardening, he's an avid wildflower enthusiast, and loves botanizing, hiking, and backpacking.