Onions can be planted almost any time of year but your location and timing are important factors to consider when you are considering planting onions in your home garden.
When it comes to climate, onions are typically hardy plants that can grow in nearly any condition. When to plant onions really depends on what climate you live in, and what variety of onion plants you have selected.
Keep reading for more information about when to plant onions in your home garden, including timing information about the variety and climate.
Onion plants are hardy crops, meaning they grow well during cold weather, as long as temperatures don’t drop low enough for a hard freeze.
These plants can survive cold temperatures down to around 28 degrees Fahrenheit, so the best time to plant onions will vary based on your location.
Onions are a long crop, which means you’ll want to start your plants as soon as possible for the earliest harvest. These plants require around 100 to 120 days from seed to harvest a fully-grown onion bulb.
If you prefer to use transplanted onions or sets you can expect to harvest around 60 to 80 days later.
If you want to harvest green onions from your plants, you can begin doing so as soon as the plants are large enough to use. The best time to plant onions for green onions varies by location as well, but green onions will be ready for harvest around 2 to 4 weeks after planting.
The size and number of green onion leaves on your plants will give you a good idea of how big your finished onion bulbs will grow.
Since you want as many green onion leaves as possible before the signal for onions to bulb starts in your area, the best time to plant onions is as early into the season as you can.
When to Plant Onions
For most areas, the best time to plant onions is in early spring for an early summer harvest or in the late summer or early fall for an over-winter spring harvest.
For onions to form bulbs they need a certain number of hours of daylight each day during their growing season.
The most important thing to remember when trying to figure out the best time to plant onions is the day length for bulbing.
Best Time to Plant Short-Day Onions
In areas closer to the equator where day lengths get shorter during the summer, you will want to plant short-day onions.
The shorter day length requires specific day-length plants to thrive in these areas. Some examples of short-day onions are Texas Early White, Texas Grano, Merlin, Red Rock, and Cipollini Yellow varieties.
Short-day onion varieties need at least 10 to 12 hours of daylight to thrive. These varieties are best suited for US zones 7 and warmer, where the day length doesn’t vary all that much between summer and winter.
The best time to plant short-day onions is in the fall so they will be ready to harvest in the spring. Short-day varieties can grow over the winter, forming plenty of top growth for bulbs to form underground for harvest during the spring.
These varieties are generally ready to harvest in around 110 days.
Keep in mind that planting short-day onions in the north won’t produce full-sized bulbs no matter when onions are planted. This is because these varieties will most likely develop early, but they will still produce small bulbs.
Best Time to Plant Long-Day Onions
In areas closer to the pole where day lengths are longer during summer, you will want to plant long-day onions.
Long-day onion varieties need at least 12 to 14 hours of daylight to thrive. These varieties are best suited for US zones 6 and colder, where summer days are long.
The best time to plant long-day onions is in late winter or early spring so they will be ready to harvest in mid-to-late summer. Long-day varieties are ready for harvest anywhere from 90 to 110 days later.
Keep in mind that planting long-day onions in the south won’t result in any bulbs developing underground no matter when onions are planted, because they won’t get enough light. But these varieties will still produce plenty of green growth, perfect for green onions.
Best Time to Plant Intermediate-Day Onions
In areas that are conveniently located in the middle, intermediate-day onions are probably your best bet, but you can also experiment with either short-day or long-day varieties.
Some examples of intermediate-day onion varieties are Early Yellow Globe, Superstar, Candy, Red Stockton, Sweet Red, and Cimarron.
Intermediate-day onion varieties need at least 14 to 16 hours of sunlight per day to thrive. These varieties can grow nearly anywhere but are best suited for US zones 5 and 6.
The best time to plant intermediate-day onions depends on how mild your winters are. Your plants will mature around 100 days after being planted either way.
If you live in an area with a mild winter, plant your intermediate-day onions in the fall. If you live in a more frigid area with colder winters, plant your onion plants in early spring.
When experimenting with short-day and long-day varieties in these areas you should remember that the leaves, roots, and bulbs of onions develop best in temperatures between 55 degrees Fahrenheit and 75 degrees Fahrenheit.
Once your onion plants have established themselves in the ground, they can survive in temperatures above 75 degrees.
When to Plant Onions Indoors
The best time to plant onion plants indoors from seed is during early spring. Make sure to plant them in containers with well-draining fertile soil, like Miracle-Gro Potting Mix.
You should start your seeds around 8 to 10 weeks before you plan to transplant them into the ground.
Remember the soil needs to be at least 50 degrees Fahrenheit to transplant onion plants into the ground.
When to Plant Onions Outdoors
The best time to plant onion plants outdoors from seed is as soon as the soil is workable, usually between late March and early April. Plant onions into raised beds or directly into the ground soil, whichever you prefer!
Don’t plant onions outdoors until the threat of a hard freeze is over after the threat of temperatures dropping below 28 degrees Fahrenheit has passed.
Frequently Asked Questions
How late can I plant onions?
Onions can be planted nearly anytime since they are pretty hardy plants even in colder temperatures.
If you want your harvest as quickly as possible, the best time to plant onions is as early in the season as possible.
The later you plant your onions the smaller the bulbs will be because the plants don’t have as much time to mature before the bulbing stage begins. But if you’re not worried about the bulb size or are growing the plants for green onions it doesn’t matter when you plant onions.
Do onions grow in the sun or shade?
Onions need full sunlight to grow properly. Full sunlight is a requirement because it signals the bulbing process. If you live in an area that is mostly overcast for a large amount of time your plants may delay bulb formation, resulting in smaller onion bulbs at harvest.
How should I plant onions – using seeds, sets, or transplants?
As with other aspects of planting onions, whether you use seeds, sets, or transplants depends on your timing.
If you’re starting onion plants from seeds, you will need to keep in mind seeds are slow-growing and typically need around 12 to 16 weeks from sowing the seed until you can transplant the seeds into the ground. Onions are easy to plant from seed, with seeds being the cheapest way to plant the vegetables. You will also have access to a bigger selection of onion varieties when using seeds.
Starting with onion sets makes the process easier because they are easy to work with and start growing quickly. Sets are affordable but you won’t have much of a variety to choose from.
Starting with transplants is the easiest and fastest of the three ways but it also tends to be the most expensive. Transplants are recommended if you are running behind on starting your garden for the season. You will run into the same issue of availability as with sets. There won’t be as much variety to choose from with transplants.
How do I know when my onions are ready to be harvested?
Onions are ready to be harvested when the bulbs are large and the tops of the bulbs begin to dry out, turn yellow, and fall over.
Wrapping Up When to Plant Onions
No matter where you live, onions can be planted nearly any time of year, depending on the variety. From short-day and long-day to intermediate-day onions, there is an onion variety perfect for planting in every zone in the United States.
For more information about onions, including different varieties and how to grow them, check out the onions section of our site.