How To Grow Onions: Which Types are Best For Your Area?

Perhaps you’ve wondered why certain types of onions grew huge bulbs in your vegetable garden and why others just sort of sat there doing a whole lot of nothing. The reason could be that you grew a short-day onion when you live in an area where you need to grow a long-day onion. Yep, all onions are not created equally.

Onions are rather finicky about which area of North America they’re grown in. This isn’t a problem when you grow sets from a garden center, as they’re (at least I hope they are) the right onion for your area of the country. But if you order onion seeds from a catalog, check the day length of that cultivar first. Look up your USDA Hardiness Zone before buying onions.

Types of onions

Bulb onions are specifically adapted to respond to certain lengths of days and nights. This determines when and even if they’ll form bulbs, flowers, and set seed. All onions fall into one of these categories:

Long-Day onions

Long-Day onions need the light of long summer days – at least 14 hours of daylight – to grow properly. That happens in Zone 6 or parts farther North. These types of onions are available in sweet or storage varieties and can be stored for up to 8 months if dried properly.

Long-Day onions should be started from seed indoors in late winter for a mid to late-summer harvest. They can also be planted from seed in the fall for a spring harvest. Bulbs begin to form after the summer equinox in most northern areas, and they typically mature in 90-110 days.

The best choices for Long-Day onions are:

• Yellow Globe Danvers
• Walla Walla
• Red Cipollini
• Southport Red Globe
• Southport White Globe
• White Sweet Spanish
• Yellow Sweet Spanish
• Yellow Flat Grant
• Yellow Rynsburg
• Zittan Yellow

Day-Neutral onions

Also known as Intermediate onions, day-neutral varieties are the most versatile onions and tend to be very sweet. They’ll grow in any zone (except far south Florida or south Texas) but will do best in zones 5 or 6. Day-Neutral onions require 12-14 hours of daylight to start forming bulbs and will mature in roughly 110 days. Seeds can be planted in fall for a spring harvest, or in early spring for a mid-late summer harvest.

The best choices for Day-Neutral (Intermediate) onions are:

• Candy Onion
• Early Yellow Globe
• Australian Brown
• White Portugal
• Southport Yellow Globe
• Super Star
• Italian Red Madiera

Short-Day onions

Short-day onions are for use in warm climates – Zone 7 or farther south. Bulbs begin to form when day length reaches 10-12 hours, and they mature in roughly 110 days. Short-day onions can be grown north of zone 7, but they may or may not perform well.  These onions tend to be very sweet and should be planted in the fall for a late spring harvest.

The best choices for Short-Day onions are:

• Ebenezer
• Georgia Sweet
• Candy Onion
• Early Strasberg
• Red Creole
• Sweet Red, Texas Super Sweet
• Texas Sweet White
• White Bermuda
• Texas Early White
• Texas Legend
• California Early Red

See an onion day-length map from Dixondale Farms

 Buy on Amazon: Jiffy Professional Greenhouse Seed Starting Kits 

How to start onions from seed indoors

Starting onions from seeds indoors is easy. The simplest method is to seed them in a flat, also known as a seed tray. Just fill the flat with starter medium, broadcast the seeds, cover with about 1/4″ more starter medium (or whatever the seed packet directions indicate), and water in (but take it easy on the water – don’t saturate it).

When the seeds germinate and the first leaves emerge, place the flat under grow lights and thin the seedlings as needed. After 6 weeks they’ll be ready to transplant into your garden bed. By the way, don’t bother holding onion seed for more than one year, as it’s rarely viable after the first season unless perfect storage conditions are met. If you have leftover seed, broadcast it in your garden bed in the fall.

When to plant onions

Planting onions in your organic garden at the proper time of year is key, as the onion must establish significant top growth to support bulb formation. Onion sets and transplants can be planted as soon as the garden soil is workable in spring, but only after nighttime temps are consistently above 28 degrees (F).  Plant sets one inch deep and allow 4-5 inches between each, depending on the mature size of the bulb. Sets should never be planted deeper than one inch, as you want to let the “shoulders” of the maturing bulb push above the garden soil as it matures. Don’t cover the shoulders, as this may contribute to a fungal infection. If the bulb is planted too deeply, its growth may be restricted.

If planting onions from seed at any time of year, soil temperatures should be between 65-85 degrees F for the best chance at germination. That’s why it’s best to start seeds indoors or plant them in the garden in the fall.

How to grow onions

Few crops are as easy to grow as onions. They’re not too particular about where they grow in your garden, as long as they have enough light and a modest amount of water. The key to big bulb growth is to make sure the foliage has grown sufficiently before it’s time for the bulbs to form. That’s why lots of light is critical in the early stages of onion growth, and sufficient nitrogen in your garden soil to stimulate foliage growth. When you notice that the tops are no longer growing taller, that’s when the bulb is forming.

Onions like lots of organic material in the soil so that it drains quickly. Waterlogged or persistently damp bulbs tend to rot and develop fungal diseases. Work plenty of compost into the onion bed the season before planting, so the nitrogen, phosphorous, potassium, and micronutrients are available to the plant after seeding or transplanting. Side-dress onions with compost monthly until 30 days before harvest.

Don’t saturate onions with water during the growing season, as they only need about one inch a week, including rainfall. If you cover the soil with a mulch after planting, they should do just fine, assuming you have normal rainfall. A mulch will also help with weed control.

When to harvest onions

Onions are one of those garden vegetables that can be harvested at any stage of their development. The tops are excellent to lend a mild onion flavor to salads, stir-fries, stews, and soups. Onion bulbs of any size can be used, although the flavor will change significantly as the bulb matures. Early in its growth, the bulb will have a very light flavor. It’s “onion-ess” will become stronger and sweeter as it gets closer to full maturity.

If any of your garden onions send up a flower stalk, it’s time to pull them up, as they’ve “bolted”. This is a response to warm weather and the onion is attempting to set seed. No further bulb growth will occur after this point. If they aren’t fully mature, they won’t store well, so use them as quickly as possible.

When the onion tops start to yellow and droop, the bulb is reaching full maturity. At this point, fold the tops down (but don’t remove them) to funnel all of the plant’s remaining energy into bulb growth. Make sure the soil is loose to encourage drying.

When the tops are fully brown, pull the onions from the garden and allow them to dry on top of the soil, or on a porch, deck, or patio. Allow them to dry for about three weeks – any less, and they won’t store well. I can tell you that there’s nothing worse than a bin full of rotten onions in November after all of your hard work.

We garden in Pennsylvania, United States, zone 6B. Much of the info we share is based on gardening in our temperate area. But many of the flowers, vegetables, and fruit we write about can be grown in soil other than ours (clay) and significantly different weather conditions and elevations. You might need to choose specific varieties for your region, modify your garden, add soil amendments, or adjust the soil pH to match our results. Please check your local university extension website for specifics for your area.