How to Harvest, Cure, and Store Onions

Congratulations on making it this far! I assume most of you have onions almost ready in the garden if you’re reading this. Before you learn how to store onions, you’ll also need to know how to harvest at the right time and cure the onions.

This is Part 2 of Growing Onions. You can find Part 1 HERE. 

How to Know When to Harvest Onion Bulbs

Onions are wonderful because they give an easy sign that they are ready for harvest. The tops will start to yellow and flop over. Not just a little bit but entirely over at the neck of the onion plant.  The image below shows onions that are not ready to be harvested yet.

There is an old practice to wait until at least ½ of onion tops fall over and then push down the rest on purpose so they are all ready to harvest at once. The manual bending of the onion leaves hastens the ripening process of onions which aren’t quite mature yet.

However, as a home gardener it’s not really necessary to follow such practices. The low numbers makes it so you can harvest as they become ready and wait for the tops to fall naturally. Barbara Damarosch explains this well in her book, “The Garden Primer”. She says:

“A common practice is to bend over the onion tops manually to hasten ripening, but it is not a necessity, and you can harm the plants if you do not do it carefully. Better to let them fall naturally unless you are trying to hasten maturation for a special reason such as imminent frost or wet soil that you fear might rot the bulb.”

All that said, I personally have found that on occasion, I’ll have a few stragglers that just don’t want to fall over for some reason or another.

The first year this happened I waited and waited and waited but they never flopped over just sat in the soil and almost started to rot. However, they did show signs of yellowing in the leaves and that is what you can pay attention to in this case.

In my own garden, as soon as the first few onions of a specific variety start to flop over, I write down the date. I pull up the mature onions and then let them dry on a screen under a covered porch. During the next week as onions continue to mature, I harvest them.

If the rest of the onions leaves of the same variety haven’t fallen down naturally within a week or two, I pull them out of the soil and dry them without bending over the leaves. I will usually use these onions fresh in my canning or summer eating and not for storage.

How to Cure Onions

Curing is essential to extend the storage life of an onion. As I mentioned above, my curing process involves moving them under a covered area outdoors and setting them on a screen for maximum ventilation around the bulb.

However, if you live in a dry climate and/or there is no rain in your forecast, you can also harvest onions by pulling them out of the ground and leaving them on the soil to dry.

Some say you can cure entirely out in the sun for a few weeks but I wouldn’t go more than a day or two, especially if they are exposed. The fear in this case is too much sun resulting in sun-scald on the bulb.

This can happen when there isn’t sufficient tough papery outer skins around the bulb and under full sun exposure.

A solution to this is you can lay the stems so they criss cross over the bulbs giving some protection from the harsh sun. I’ve never tried this because we’ve always had too much moisture to dry in the field or garden so I can’t tell you for certain whether or not its successful.

You can read more about this process called “shingling”and see photos HERE.

Whether you choose cure out in the field or under cover, don’t wash the onions after you harvest. I brush off the extra dirt with my hands.

To cut tops or not to cut tops- that is the question!

Here again, we come to another fork in the road, where some people will tell you to chop the green tops to one inch above the neck and others will tell you to leave them on while they dry.

From my experience leaving the green tops of the onions on throughout the entire drying and curing time is the best practice. I notice I have a longer onion storage time post curing and I’m also able to braid the onions later if I choose.

Since I leave the tops on, I wait at least a full two weeks for the onions to cure. Some varieties take a little longer than others. The stems should be completely dry and brown with no moisture remaining.

The most important part is to be sure the neck of the onion is dry. To do this pinch your fingers together at the neck of the onion. It should feel like there is almost nothing there, thin, dry, and papery. If the onion is not fully cured the neck of the onion will feel thick, moist, and slippery.

How to Store Onions

At this point, now that the onions are fully dried and cured, if you do want to cut down the onion tops you can. Leave at least and inch above the top of the onion. If you find there is still green in there let them cure longer outdoors.

And just to be clear, I’ll restate this again:

• cutting off green tops before drying = bad for storage
• cutting off tops after drying = good for storage
• no cutting at all even after drying= good for storage

I’ve done both braiding and cutting back to an inch on the top after curing. I actually really like both methods and haven’t found one to be superior over the other it’s more of a matter of preference.

They do look really pretty when braided though! And I’ve had questions about whether or not braiding them makes them rot at the neck. The answer is no, as long as the onion is fully dry it won’t rot at the neck or cause them to spoil earlier.

Here is my favorite video for braiding onions and it’s not done by me. This guy is far more entertaining to listen to:

Storage Conditions for Onions

Once the onions are completely dry, its time to move them indoors. The goal is to adjust them to the lower temperature difference slowly to avoid  condensation on the bulbs.

In my own root cellar this happens quite naturally. After curing outdoors they come in to an inside temperature that is 10-20ºF colder than outside. This unheated room slowly drops its temperature with the weather.

Eventually the goal would be to get it to ideal storage conditions. The ideal conditions for long term storage of onions are 32ºF or 0ºC.  Humidity for onion storage should be at 65-75%.

If you have too much humidity it promotes root growth, while high temperature promotes sprouting. Combining both high temperatures and high humidity increases  rotting and decreases quality.  Source found HERE.

My root cellar is just in the basement an it gets to about 50-60ºF with 60-70% relative humidity.  It’s perfect for winter squash and sweet potatoes but not onions. Because they have a higher temperature they do occasionally sprout.

The goal is to get your storage area as close as possible to the ideal conditions. In the home setting, it can be difficult to get it just the right conditions for every vegetable or fruit. Get creative and try new storage methods if one area doesn’t work out very well.

Oh and one little tip. Keep your storage onions in a dark place. Light makes storage vegetables spoil faster.

One last thing to consider with onion storage is how long the variety will last under optimal storage conditions.

Sweet onions only last 1-3 months and storage onions usually last anywhere from 3-9 months.

There are many different varieties under the category of “storage onions” but mainly these are long day onion types.  You can also check on your seed packet description it will usually say the number of months the onion can be stored or that it stores moderately well or very well.

Due to my location, I grow intermediate day varieties and have found “Rossa Di Milano” and “Valencia” to be the longest lasting of all the onions I’ve trialed so far.