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The best time to plant and harvest onions depends entirely on your local climate and the type of onions you choose to grow.
If you’re wondering when to plant and harvest onions for a successful crop, the short answer is that you plant them in early spring or fall, and you harvest them in mid-to-late summer.
Getting the timing right for when to plant and harvest onions is the single most important factor for growing big, flavorful bulbs.
In this post, we’ll break down the perfect schedule for planting and harvesting onions, how to know when your onions are ready, and tips to make sure you harvest onions at their peak.
Let’s dig right in.
When to Plant Onions for the Best Results
Knowing when to plant onions is all about understanding their relationship with daylight and temperature.
Onions are photoperiodic, meaning they form bulbs based on the number of daylight hours, not just the calendar date.
So, when to plant onions depends on whether you have short-day, long-day, or intermediate-day varieties.
1. Plant Long-Day Onions in Early Spring
If you live in the northern United States or Canada, you should plant onions in early spring, as soon as the soil can be worked.
Long-day onions need 14 to 16 hours of daylight to trigger bulb formation, which naturally happens in the summer months up north.
Plant onion sets or transplants about 4 to 6 weeks before your last expected frost date.
This means you’ll typically plant onions in March or April, depending on your hardiness zone.
Soil temperatures should be at least 40°F, as onions will tolerate light frosts without any damage.
Planting onions too late in the season will result in lush tops but small, underdeveloped bulbs.
2. Plant Short-Day Onions in Fall
For gardeners in the southern United States, the best time to plant onions is in the fall.
Short-day onions need only 10 to 12 hours of daylight to start bulbing, which happens during the shorter days of late winter and early spring.
You’ll want to plant onions in September through November, giving them time to establish roots before winter.
These onions will go dormant during the coldest months, then resume growth in early spring.
Harvesting onions from fall planting happens in late spring, typically May or June, much earlier than their northern counterparts.
3. Intermediate-Day Onions Are the Flexible Option
If you live in a middle zone, like the central United States, intermediate-day onions are your best bet.
These varieties need 12 to 14 hours of daylight, making them perfect for regions with moderate latitudes.
You can plant onions in either early spring or fall, depending on your preference and your specific local climate.
In milder zones, fall planting is great, while in colder regions, early spring planting is more reliable.
The key is to plant onions early enough that they have ample time to grow large before the bulbing process begins.
When to Harvest Onions for Maximum Flavor
Once you’ve figured out when to plant onions, the next critical step is understanding when to harvest them.
Harvesting onions at the right time ensures they store well and have the best taste and texture.
Most onions are ready to harvest in 90 to 120 days from planting, but visual cues are much more reliable than a strict count.
1. Look for the Tops to Fall Over
The clearest sign that it’s time to harvest onions is when the green tops begin to flop over.
As onions mature, the neck softens and the leafy tops lose their rigidity and fall to the ground.
When about 50% to 75% of your onion tops have fallen over, you can start harvesting them.
Don’t wait too long after this happens, as leaving bulbs in the ground too long can cause them to split or rot.
2. Check the Bulb Size and Skin Color
Another reliable way to know when to harvest onions is to gently push back the soil around the bulb.
A mature onion will have a noticeably large bulb that has pushed the soil away naturally.
The outer skin should also begin to take on a papery, dry texture and develop its characteristic color, whether yellow, red, or white.
If the bulb still looks like a scallion with no bulb development, give it more time to grow.
3. Time Your Harvest for Dry Weather
Always aim to harvest onions on a dry, sunny day if possible.
Harvesting onions in wet conditions can introduce excess moisture, which leads to mold and poor storage quality.
If rain is in the forecast, it’s better to harvest slightly early than to risk the onions sitting in soggy soil.
Once you’ve pulled them from the ground, leave them in the garden to cure for a few hours of direct sunlight.
How to Cure Onions After Harvest
Curing is the final step that turns your freshly harvested onions into long-lasting pantry staples.
The curing process dries the outer layers and the neck, which prevents rot and extends storage life.
Proper curing is just as important as knowing when to plant and harvest onions.
1. Dry Them in a Warm, Airy Spot
Place your harvested onions in a single layer in a well-ventilated area, out of direct sunlight.
A garage, shed, or covered porch works perfectly for this step.
The ideal curing environment is warm (75–85°F) with low humidity and good airflow.
Leave them there for two to three weeks until the necks are completely dry and the skin is papery.
2. Trim and Store for Longevity
Once cured, you can cut off the dried roots and trim the tops down to about one inch above the bulb.
Then, store your onions in a cool, dark, and dry place, like a pantry or a mesh bag in a cellar.
Properly cured onions can last for months, though short-day varieties tend to store for less time than long-day ones.
Avoid storing onions near potatoes, as the gases they release can cause each other to spoil faster.
So, When Should You Plant and Harvest Onions?
When to plant and harvest onions is a simple matter of matching your variety to your climate and watching for visual maturity signs.
If you plant onions in early spring for long-day types or fall for short-day types, you’ll set yourself up for success.
And you’ll know it’s time to harvest onions when the tops fall over and the bulbs have reached a good size.
Just remember that gardeners who plant onions at the correct time and harvest them at the right moment get the sweetest, most flavorful bulbs.
So, take note of your zone, choose the right onion variety, and you’ll be enjoying homegrown onions in no time.