Horticulture Magazine

How To Harvest And Store Onions

rows of onion plants in a field ready for harvest

Learning how to harvest and store onions in the right way is essential for home growers.

Onions are a popular and useful garden crop, but it is important to make as much as you can of your onion yield.

This involves making sure that you know how to harvest and store your onions correctly.

You do not want to invest all the hard work involved in growing onions, only to waste those onions when it is time to take them from the ground.

In this article, we will help you make sure that you correctly harvest and store the onions you grow.

We will talk through a range of topics: from choosing the right onions in the first place, to preserving your crop for as long as possible.

We’ll help you avoid waste and make the most of your homegrown produce.

Choosing Onions Which Store Well

onion bulbs in the ground

First things first, it is important to remember that not all onions will store well.

When choosing which onions to grow, you should always think about how you like to use them, and how long you would like them to remain in-store.

Some onions might be grown and used up right away. While others can be stored to allow you to eat your own onions right through the winter months, and maybe even longer.

In this article, we will focus on traditional bulbing onions.

Spring onions or scallions are treated in different ways, and there are obviously also different considerations when it comes to perennial allium varieties.

Bulb onions are generally either mild or pungent. This refers to their flavour.

But whether an onion is mild or pungent can also give you a clue about how well they will store.

If you are not sure which type you are growing, cut into them – if the onions make you cry when you cut them, they are high in sulphurous compounds. [source]

The compounds that make us cry also inhibit rot.

So these are pungent onions and they will tend to store better, and can be stored for longer than mild onion types.

Typically, the milder the onion, the more quickly they must be used.

Set aside milder types to use up more quickly, and set your most pungent onions aside for traditional storage.

How and When To Harvest Your Onions

Another important thing to remember is that it is important to harvest onions at the right time, and in the right way.

Even the most pungent onions will not store as well if they are harvested too early.

Onions will store best if they are fully mature.

However, leaving the harvest too late can also be a problem – if you leave onions in the ground too long they may be more likely to succumb to pests or diseases.

To harvest healthy onions:

  • Add potassium around June to help bulbs to mature.
  • One bulbs have plumped up around midsummer, halt watering and feeding.
  • Avoid fertilisation (especially nitrogen feeds) for the last 6 weeks of growth.
  • Wait for stems to turn yellow and begin to flop over.
  • As soon as at least 1/3 of your crop is yellowing and flopping, it is time to harvest.

Onions will also store less well if they are damaged when you harvest.

You need to harvest your onions carefully to make sure they are unblemished and in tip-top quality for storage.

Ease your onions from the ground with a fork or other gardening implement, rather than trying to tug them out of the ground manually.

Lay them down gently, and do not throw them around.

As you harvest, check each onion over carefully.

Brush the dirt gently off the bulbs, and look for any signs of damage or any other problems.

Set any damaged bulbs aside to use up more quickly, since they will not store successfully for as long.

Curing Your Onions

onions curing outside

To make sure you can traditionally store onions for as long as possible, there is another stage to go through before your harvested onions are ready to store.

Bulb onions should be cured before they are stored.

Curing your onions simply means removing moisture, and allowing the outer layers of skin and stem to dry out.

The dry layers provide a protective barrier around your onion bulbs, helping to keep them fresher for a longer period of time.

As the stem point dries out, this seals off the insides.

Ideally, onions should be cured at 25-30°C. They should be placed somewhere that is warm and dry, with relatively good ventilation.

You can hang up the onions, or place them on a rack or shelf.

If you have a greenhouse or polytunnel, this can be a good place to put them to cure. A sunny porch or veranda can also be a good place.

At the very least, keep them covered, and up and out of the dew, in a sunny spot.

Leave your onions to cure until their necks have become taut, stems are dry, and the outer skins are papery and tight around the bulbs.

Once your onions have cured, you can then think about moving them to a position suitable for storage.

Where To Store Onions

onions hung to dry out

Onions should ideally be stored:

  • In a location with temperatures between around 1 and 5°C and at least below 10°C.
  • Where relative humidity can be kept between 55 and 65%.
  • In a dark environment.
  • Somewhere with some ventilation (but not too much). Ventilation is essential to avoid an increase of CO2 levels, and to dissipate heat generated by the onions as they slowly continue to respire. However, too draughty a spot can cause onions to respire more and lose too much weight. [source]
  • Not too close to other produce such as apples or potatoes, for example.

The ideal spot to store onions is in an old-fashioned root cellar or cold store/ pantry.

Of course, we do not all have access to such a space – so if you do not have a root cellar or a pantry – then regular cellars, garages or sheds, or even a cool spare room in your home can also be fine.

As well as thinking about the general environmental conditions for storing onions, you should also think about storage solutions.

Storage solutions for onions that can work well include:

  • Braiding.
  • Hanging them in mesh bags or tights.
  • Placing them in cardboard boxes.
  • Putting them in wicker baskets.

Braiding onions involves weaving the stems together just as you would braid hair.

If you have difficulty doing this, or the stems are too short or too brittle then there is also another method to try –

Make a loop of string or twine long enough to accommodate your onions, then take an onion and, at the base of the loop, wind it in and out between the two sides of the loop in a figure of eight pattern – then repeat until all your onions are attached to the twine or string.

Preserving Onions

If you do not have a suitable spot for traditional onion storage, there are a few other ways to preserve your onions so you can keep and use them over a longer period of time.

These other methods can also be better for milder onions which will not last as long as the storage methods mentioned above.

Freeze Onions

Your first option is to freeze some of your onions.

This can be a good choice, especially, for milder onion types where you have some freezer space available.

The best and easiest way to freeze your onions is simply to slice them.

Then you can seal the un-blanched, raw, sliced pieces in jars or other freezer-proof containers.

In order to prevent the frozen pieces from sticking together, and for easier retrieval, you can freeze pieces first on a tray.

Once frozen, these pieces can then be transferred to containers.

This makes things easier because you can tip out only as much you need for a meal without having to defrost all the onions.

Of course, you can also cook up your onions and freeze them in a range of recipes to enjoy later in the year.

Dehydrate Onions

dehydrated onions in a bowl and on a spoon

If freezer space is limited, another traditional way to store onions is by dehydrating them.

Drying onions is another good way to make sure they will last as long as possible.

You can dry onions in an electric or solar dehydrator, or dry them in your oven on a low heat.

Fully dehydrated onions can be kept in sealed jars, to use as needed.

Or they can be powdered and turned into an onion powder, which can be very useful in your store cupboard.

Canning Onions

onion jam in a glass jar on a wooden table

Finally, one other way to store onions long term is to can them.

Canning onion chutneys, onion jams and other preserves, for example, can be a great way to make sure you do not waste any of your onions, and can make use of your harvest over as long a period as you can.

Just make sure that you follow a canning recipe from a trusted authority to make sure it is as safe as possible.

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