Best Time for Planting Onions

best time to plant onions

The bulk of the best savory recipes in the world starts with some diced onions! Since onions are one of the most versatile cooking vegetables, planting onions in the garden is a great idea. The sweetness of homegrown onions is unmatched by store-bought onions; they are simple to grow and store well.

Onions (Allium cepa) are resilient plants that can grow practically year-round regardless of temperature. Most people plant them in the early spring for a harvest in the early summer or the late summer or early fall for a crop in the following spring.

Fixing the timing is the main factor in the onion’s success, and this article shows you everything you need to know to execute it correctly the first time. You will learn how to plant onions that are your favorites so you have them when you want them.

The day duration for bulbing is the most crucial factor to consider when determining the ideal planting time for onions. Onions require specific daylight hours per growing season to develop good bulbs.

This implies that even if your greenhouse is kept at a comfortable 80 degrees throughout the winter, you won’t be able to produce bulbing onions unless you add grow lights to replace daylight hours comparable to summer.

Onion Growing Tips

You can grow onions practically any time of year without worrying about day length if you aren’t worried about bulbing (also known as if you want to eat green onions).

Locate what the growing zone is for your area to help you pick the plants that will do well for you. Check here

Here is another way to see the growing zones 

There are three types of onions: intermediate-day onions, long-day onions, and short-day onions (AKA: day-neutral onions). The summer day lengths shorten as you approach closer to the equator, necessitating short-day onion cultivars, such as Texas Early White.

Here are some selections to get you started

Organic Onion Seeds – 7 Varieties

Red, Yellow, and Green Onions for Planting

8 Onion Seeds Variety Pack Heirloom

Walla Walla, Green Onion, Red Burgundy, White & Yellow Sweet Spanish Onions & More

Vidalia Sweet Onion Seeds Organic

If you are in a growing zone where the Vidalia onion will flourish, you will really like their sweet taste.

Since the summer days are longer and closer to the equator, long-day onions like Yellow Sweet Spanish and Walla Walla can be grown. You can experiment with both in the middle or try intermediate-day types, such as Early Yellow Globe.

Even if you are growing green onions, you can plant onions virtually any time of the year. Your timing will affect the quantity and timing of the crop. When the day duration in your location receives the appropriate amount of daylight hours for the variety, onions will receive the signal to create bulbs. This generally revolves around:

  • 10–12 hours of daylight for short-day onions (for Southern latitudes)
  • For intermediate-day varieties, there are 12–14 hours of daylight (in the middle)
  • 14 to 16 hours of daylight for long-day variants (for Northern latitudes)

The size and quantity of green onion leaves on the plant’s upper section directly affect the size of the completed onion bulb (those become the layers of your bulb onion). The objective is to have as many leaves as possible on an onion plant growing before your location receives the signal to begin bulbing.

This indicates that you should begin growing onions as soon as feasible. Some interpret this to mean planting starts (also known as transplants) or putting seeds in the ground in the early spring. Others might solve this as late summer or early fall by sowing seeds, seedlings, or sets in preparation for the winter.

How late into the year may onions be planted?

Onion plants will grow smaller when they start to bulb if you put off planting them in the spring for a longer period. The plants won’t have enough time to grow before bulbing starts if you wait too long.

For spring plantings, we advise putting onion starts (transplants) or sets in the ground a month before your final frost. You can sow seeds or seedlings for fall plantings for a spring harvest the following year in late summer (6-8 weeks before the first frost), early fall, or both (4-6 weeks before your first frost).

Do onions require direct sun?

Onions need full, direct sunshine to grow and indicate the beginning of the bulbing process. In the warmest of temperatures, onions may experience sunscald when exposed to direct sunlight. Sunscald is heat damage brought on by the intense summer sun, essentially roasting the onion.

Occasional sunscald can occur when growing in dark soils. However, it usually occurs after an onion has been harvested. Keep the soil moist to avoid this, and use a mulch to control soil temperatures, such as straw or pine shavings.

When planting onions, should I use sets, transplants, or seeds?

Your onion plants can be started in three ways, and they all work quite well! Choosing the best method for you when it comes to onions primarily hinges on timing:

Onion Seed: Although they grow extremely slowly and often take 12 to 16 weeks from sowing to transplanting, starting onions from seed is simple. Your perseverance will pay off, though, as seed onions allow you to cultivate a larger variety of onion varieties at a lower cost.

Sets of dried, young onion bulbs are comparable to those from your local supermarket. They usually are available at big-box retailers and garden centers, but you may also order sets online. These are simple to work with, begin to develop rather rapidly and are reasonably priced.

The problem with this is that your options are constrained; most supermarkets only carry one or two types of onion sets, and some aren’t even labeled with their precise variations, making it challenging to determine the ideal day length. All you need to know about the onions you purchase is that a nearby supermarket has enormous bulk bins with onion sets each year for red onions, white onions, and yellow onions.

Onion Starts or Transplants: also you can plant onion transplants that are already growing, either one you grew yourself or ones you bought. If you’re a little behind schedule with your planting, we advise planting these onions because they grow the quickest and simplest. The cost of the purchased three onion transplants is often the highest.

How long does it take onions to grow?

Growing onions takes 100–120 days from planting to harvesting a complete bulb. In 60 or 80 days, you can harvest from transplants or sets.

The green onion harvest can start as soon as the onion plants are big enough to use. That may be as quickly as 2-4 weeks after planting for sets and starts.

Are onion sets soaked before planting?

Onion sets can be soaked before planting; moisture tells the dried bulb when it’s ready to “wake up” and sprout. To speed up the growing process, soak the onion sets in compost tea or unchlorinated water overnight before planting. This moisture can also readily come through rain and soil moisture.

How deep should onions be planted?

Between 1 and 1 1/2 inches of soil should be used for onion sets and transplants. For successful germination, onion seeds only need to be sown 1/4″ below the soil’s surface.

How far apart should onions be planted?

If you are solely planting onions for bulbing, you should be spacing them 6 to 8 inches apart. Greater separation can result in a significant reduction in bulb size.

For green onions, however, we strongly advise planning your onions every 2-4 inches from the beginning. Harvesting every other one as the season progresses. You always have scallions available and enough space for your bulbing onions to spread out.

When to sow the onion seeds?

We advise starting your onion seeds 12 to 16 weeks before your last frost date for spring planting (for an early summer yield). Here in zone 6a/7b, onions are often the first plant we start from seed in January.

We advise direct sowing seeds outside six to eight weeks before your first frost for fall planting (for overwintering for an early spring crop). Here in zone 6a/7b, we sow our overwintered onion seeds in the middle of August.

Soil PH

An ideal soil pH for onions is between 6.0 and 6.8. They favor clay-free, loose, sandy-loamy soil.

Because onions have shallow roots and a high food requirement, fertilizing is crucial. Before planting, add a balanced organic fertilizer and roughly an inch of compost. After that, regularly provide compost tea or foliar fertilizers like fish emulsion and kelp.

Because onions are biennials, scapes (the shoots that eventually develop into flower stalks) may appear on your onions in the spring of the second year. The best course of action is to harvest the entire onion and consume it as a scallion or small bulb as an onion has finished directing energy to the bulb when it forms a scape.


Overwintering onions don’t store as well as their younger counterparts cultivated in the spring since they have completed their two-year lifetime. If you want storage onions, you should use the overwintered onions as soon as possible and plant another spring onion.

However, if you want to plant onion sets or seedlings for overwintering, it is best to plant 4-6 weeks before your first fall frost. We advise direct sowing seeds for overwintering.

You’ll have a successful onion crop if you have the time and choose the best variety for your latitude. You might never again purchase onions from the grocery store. Happy onion growing!

Wrap Up

We need to mention a few words about the types of onions from which you can harvest onion seeds. Many of the seeds or sets bought from major seed producers are hybrids, meaning they were created by crossing two parent varieties chosen for different traits. We get the best of both types when they are combined.

That’s fantastic, but there is a catch if you want to harvest onion seed from these hybrids. If the preserved seeds ever germinate, they will most likely produce onions that have the characteristics of either one parent or the other, but not both. So, rule number one: Don’t collect onion seeds from hybrids.


  • Marji

    My great-grandfather planted and maintained a large garden when I was a small child. He grew enough to feed many of our neighbors. His love of gardening is what sparked my lifelong interest in gardening. My grandparents continued his direction, as well as my parents. It was natural to have a garden of my own and continue the process, enjoy the results, and to share with others.

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