When to Harvest Onions in the UK – Complete Harvesting and Storage Guide

Growing your own onions is one of the most satisfying parts of having a vegetable garden or allotment. After months of planting, weeding, watering and watching them develop, there is nothing quite like lifting your own homegrown onions from the soil.

But one of the biggest questions UK gardeners ask is when to harvest onions in the UK.

Should you wait until every leaf has turned yellow? Do onions have to fall over before they’re ready? Can you harvest them early? And what is the best way to dry onions so they last for months in storage?

Getting the timing right is important, especially if you want to store your onions throughout autumn and winter.

Here at Gardening with Ben, I’ve been growing vegetables on the allotment for many years, and harvesting onions is always one of the jobs I look forward to.

In this complete guide, I’ll explain when to harvest autumn and spring-planted onions, the signs that your onions are ready, how to lift them without damage, and how to dry, cure and store them successfully.

When Do You Harvest Onions in the UK?

In the UK, the onion harvesting season generally runs from June through to October, depending on the variety, planting date and growing conditions.

The biggest difference is whether you’ve planted your onion sets in autumn or spring.

Autumn-planted onions establish themselves before winter and normally mature earlier than spring-planted onions.

Spring-planted onions develop during the warmer months and are generally harvested later in summer or early autumn.

UK Onion Harvesting Calendar

Month	Onion harvesting advice
January	No normal bulb onion harvest
February	Overwintered onions continue developing
March	Autumn onions resume stronger growth
April	Bulbs begin developing on established crops
May	Some early onions can be used fresh
June	Many autumn-planted onions become ready
July	Main autumn onion harvest; some early spring onions
August	Main harvest for many spring-planted sets
September	Later spring and seed-grown onions
October	Some late-maturing varieties may still be harvested
November	Main harvest generally finished
December	Use previously dried and stored onions

These are approximate dates for typical UK conditions. Onion varieties, weather and regional growing conditions will affect harvesting times.

The important thing is to look at your onions rather than relying entirely on the calendar.

Five Signs Your Onions Are Ready to Harvest

Knowing when your onions are ready is one of the most important parts of successful onion growing.

There are several signs to look for.

1. The Leaves Start Turning Yellow

One of the first signs of onion maturity is the foliage beginning to turn yellow.

During active growth, onion leaves should generally be green and healthy.

As the bulb reaches maturity, the plant naturally begins to slow down.

The foliage starts losing its green colour and gradually dries.

However, yellow leaves aren’t always a sign that onions are ready to harvest.

If the plants are still small and it’s early in the growing season, yellowing could indicate disease, poor drainage, nutrient deficiency or another growing problem.

Always consider the stage of development.

2. Onion Leaves Fall Over Naturally

This is one of the clearest signs that onions are approaching harvest.

As the plants mature, their necks soften and the green foliage begins falling over.

You might notice that several onions in the same bed start leaning over within a few days of each other.

You don’t need every single plant to fall over at exactly the same time.

Once a substantial proportion of the crop has naturally toppled and the bulbs look mature, start preparing for harvest.

Gardening with Ben tip: Let your onion tops fall over naturally. There is no need to force them down.

3. The Bulbs Have Reached a Good Size

Mature onions should have developed bulbs appropriate for their variety.

Some varieties naturally produce larger bulbs than others.

A smaller onion doesn’t necessarily mean something has gone wrong.

If the foliage is yellowing and collapsing and the bulb has reached its natural mature size, it may be ready to harvest.

You can also lift smaller onions earlier if you plan to use them fresh rather than store them.

4. The Neck Starts Softening

The neck is the area where the leaves meet the onion bulb.

As onions mature, this part of the plant gradually softens and loses moisture.

The foliage begins drying, and the neck will eventually become dry during curing.

A thick, green and actively growing neck suggests the onion hasn’t fully matured.

A soft, wet or rotten neck is different and could indicate disease.

5. The Outer Skins Begin Drying

As onion bulbs mature, their outer layers begin developing the dry protective skins associated with storage onions.

Different varieties produce different skin colours.

Yellow onions normally develop golden or brown skins, while red onions develop reddish-purple outer layers.

The skins become properly dry and papery during the curing process after harvest.

When to Harvest Autumn-Planted Onions

Autumn onion sets are normally planted from September to November.

Popular overwintering varieties include Radar, Senshyu Yellow and Electric.

These onions establish their roots during autumn and survive winter before making stronger growth in spring.

Because they’re already established when the weather improves, autumn onions usually mature earlier than spring-planted crops.

Harvesting Autumn Onions in June

Many autumn-planted onions become ready during June.

Look for yellowing foliage, naturally falling leaves and well-developed bulbs.

If the crop is mature and the weather is reasonably dry, you can begin harvesting.

Harvesting Autumn Onions in July

Other overwintering varieties may continue maturing into July.

Cool spring weather or differences between varieties can delay harvesting.

Don’t worry if your onions aren’t ready at the beginning of June.

Give the plants time to mature naturally.

Do Autumn Onions Store Well?

Some autumn-planted varieties store reasonably well, but many don’t keep as long as good storage varieties planted in spring.

Autumn onions are particularly useful for providing fresh onions earlier in the year.

Always check the variety information for its expected storage performance.

When to Harvest Spring-Planted Onions

Spring onion sets are typically planted between February and April, depending on weather conditions.

Unlike autumn sets, they complete most of their growth during spring and summer.

Spring-planted onions are generally ready between July and October.

July Harvest

Some early varieties may mature during July, particularly after a favourable growing season.

Check whether their tops are beginning to fall over and whether the bulbs have developed sufficiently.

August Harvest

August is an important harvesting month for many spring-planted onions.

As the plants mature, you’ll often notice a large proportion of the foliage turning yellow and collapsing.

This is usually a good opportunity to harvest during a spell of settled weather.

September and October Harvest

Later varieties and seed-grown onions may take longer to mature.

Some crops remain in the ground into September or even October.

However, avoid leaving mature onions in increasingly wet autumn soil unnecessarily.

Prolonged damp conditions can make harvesting and curing more difficult.

How to Harvest Onions Without Damaging Them

Once your onions are ready, it’s time for one of the most enjoyable jobs on the allotment.

Harvesting onions isn’t particularly difficult, but it’s worth taking care.

Damaged onions are more vulnerable to storage problems.

Step 1: Choose a Suitable Day

Where possible, choose a dry day for harvesting.

Dry weather makes it easier to lift the onions and begin curing them.

If the weather is wet for a prolonged period and the bulbs are already mature, don’t leave them indefinitely. Instead, lift them carefully and dry them somewhere sheltered and ventilated.

Step 2: Loosen the Soil

Use a garden fork or hand fork to loosen the soil around the bulbs.

Insert the fork a little distance away from the onions to avoid stabbing or cutting them.

Gently lift the soil beneath the bulbs.

Step 3: Lift the Onions

Once the soil has been loosened, carefully lift the bulbs.

Avoid pulling hard on the leaves, especially if the necks are already soft and drying.

Step 4: Remove Loose Soil

Gently remove loose soil from the outside of the bulbs.

Don’t knock the onions against each other to remove dirt.

Bruising and damaging their protective skins can affect storage quality.

Step 5: Inspect Your Harvest

Check each onion for signs of damage or disease.

Separate onions that have been cut, bruised, damaged or have unusually thick or soft necks.

Healthy, undamaged bulbs are generally the best candidates for long-term storage.

Should You Bend Onion Leaves Over Before Harvesting?

This is a gardening question that often causes debate.

Traditionally, some gardeners would manually bend onion tops over in the belief that it encouraged the bulbs to mature.

However, forcing the foliage down is no longer recommended.

Damaging the leaves or necks can interfere with natural maturation and increase the risk of problems.

Instead, allow the plants to complete their growing cycle.

Once the leaves begin yellowing and falling naturally, the onions are approaching harvest.

There’s also no need to deliberately break the roots to force maturity.

Can You Harvest Onions Too Early?

Yes, although harvesting early isn’t necessarily a problem if you intend to use the onions immediately.

Young bulb onions are edible and can be used fresh in cooking.

However, onions harvested before they mature may not have fully developed protective skins or properly dried necks.

These onions usually won’t store as well as fully mature bulbs.

If your aim is to grow onions for winter storage, it’s best to let the crop mature naturally.

Can You Leave Onions in the Ground Too Long?

Yes.

Once onions have matured, leaving them in wet soil for an extended period can increase the risk of rotting and other problems.

In some situations, mature bulbs may begin producing new roots or shoots when moisture and temperatures encourage renewed growth.

This can reduce their suitability for storage.

Keep an eye on your onion bed as the foliage begins dying back.

Harvest mature bulbs before the leaves have completely disappeared and before prolonged wet conditions cause problems.

How to Dry Onions After Harvesting

Once you’ve lifted your onions, the next important job is drying them.

This process is commonly called curing.

Curing allows moisture to leave the necks and outer skins, helping prepare suitable onions for storage.

Drying Onions Outside

If the weather is warm and dry, you can begin curing your onions outside.

Place them on a suitable rack, mesh shelf or other dry surface that allows air to circulate.

Avoid piling onions deeply on top of one another.

Ideally, spread them in a single layer.

A little sunshine can help drying, but protect onions from prolonged intense heat, which can damage exposed bulbs.

Never leave harvested onions outside during persistent rain.

Drying Onions in a Greenhouse

A greenhouse can be useful when the British weather is unpredictable.

Place onions on shelves or mesh racks where air can circulate around them.

Keep the greenhouse well ventilated and avoid excessively hot, humid conditions.

A shaded or well-ventilated position is preferable if direct sunlight would overheat the bulbs.

Drying Onions in a Shed

A dry, well-ventilated shed is another excellent option.

Lay the onions out on slatted shelving, mesh racks or suitable trays.

Make sure there is enough space for air movement.

An enclosed, damp shed without ventilation isn’t suitable because moisture can build up around the crop.

How Long Do Onions Take to Dry?

Onions commonly need approximately two weeks to cure under suitable warm, dry and ventilated conditions.

In cooler or more humid weather, drying may take longer.

Don’t rely entirely on a fixed number of days.

Check whether the bulbs have genuinely dried.

Properly cured onions usually have:

• Dry, papery outer skins.
• Dry, shrivelled roots.
• Dry foliage.
• A firm bulb.
• A neck that has thoroughly dried.

If the neck is still green or moist, allow more time.

Bulbs that remain thick-necked or fail to cure properly should be used sooner rather than put into long-term storage.

Should You Cut Onion Leaves Off Straight After Harvest?

If you’re planning to store onions, it’s usually best to leave the foliage attached while they cure.

This allows the necks to dry naturally.

Once the foliage is completely dry and papery, you can trim it if you wish.

Leave a short length of dry neck above the bulb rather than cutting directly into the top.

You can also leave the dry foliage attached if you want to plait the onions together for hanging.

Don’t cut into the bulb itself because this creates an entry point for decay.

Best Ways to Store Homegrown Onions

Once your onions have dried properly, it’s time to put them into storage.

Good storage conditions are just as important as successful growing and harvesting.

Onions need a cool, dry and well-ventilated environment.

Avoid locations that experience excessive moisture or condensation.

1. Store Onions in Mesh Bags

Mesh or net bags are one of the simplest options.

They allow air to circulate around the onions and are convenient to hang.

Don’t overload the bags, and inspect them regularly.

2. Store Onions in Wooden Crates

Wooden crates with gaps between the slats can work particularly well.

Arrange onions in a shallow layer so that air can move around the bulbs.

Avoid creating deep piles.

3. Store Onions in Slatted Trays

Slatted trays are ideal if you have shelving available in a suitable shed or storeroom.

They make checking onions straightforward.

4. Plait Your Onions

Plaiting onions is a traditional way of storing them.

Once the foliage is suitably dry but still workable, it can be braided into strings.

Hang the finished plaits somewhere cool, dry and well ventilated.

This can be a useful way to save storage space.

Where Should You Store Onions?

Choose somewhere with stable, cool conditions and good airflow.

A suitable frost-free shed, pantry or ventilated storeroom may work well.

Avoid placing onions next to heaters or in damp corners.

Don’t store them in sealed plastic bags, which can trap moisture.

Inspect your onions regularly so that any bulbs beginning to deteriorate can be removed promptly.

How Long Do Homegrown Onions Last?

The storage life of onions depends on the variety, how well they’ve matured, curing conditions and storage environment.

Some autumn-planted varieties are best used within a few months of harvesting.

Suitable spring-planted storage varieties may last through winter and into the following spring when properly cured and stored.

Sweet or mild onions often have shorter storage lives than varieties specifically bred for keeping.

When choosing onion sets or seeds, check whether the variety is described as having good storage qualities.

Why Are My Stored Onions Going Soft?

Soft onions are a common storage problem.

Several things may be responsible.

Poor Curing

If onions are stored before their necks and skins have dried properly, they’re more vulnerable to decay.

Excessive Moisture

Damp storage conditions can encourage rotting.

Bruising or Damage

Bulbs damaged during harvesting may develop soft areas later.

Disease

Certain bacterial and fungal diseases can cause stored onions to deteriorate.

Unsuitable Variety

Some onions simply aren’t designed for long-term storage.

Gardening with Ben tip: Check your stored onions regularly. Remove any that are soft, leaking, mouldy or visibly rotting. Don’t eat onions showing signs of rot.

What Should You Do With Onions That Have Bolted?

Bolting happens when an onion plant begins producing a flower stalk.

It’s often triggered by environmental stress or temperature fluctuations.

When an onion bolts, the developing flower stalk can affect bulb quality and storage potential.

If you notice a flower stalk, remove it and plan to use the onion sooner rather than putting it into long-term storage.

Bolted onions can still be useful in cooking if they’re sound and healthy.

However, they may contain a hard central stem, and their storage life is usually reduced.

Can You Harvest Onions After Heavy Rain?

You can harvest onions after rain if necessary, but dry conditions are preferable.

Wet soil sticks more readily to bulbs and makes curing more challenging.

If your onions are mature and prolonged rain is forecast, it may be better to harvest them and move them into a sheltered, airy location.

Don’t put wet onions straight into storage.

Allow them to dry thoroughly first.

Can You Harvest Red and White Onions at the Same Time?

Red, white and yellow onions all show similar general signs of maturity.

Their harvesting dates depend more on the variety and planting time than on their colour.

Some varieties mature earlier than others.

Watch the foliage and bulbs rather than assuming every onion in the garden will be ready on the same date.

Different varieties can also have different storage characteristics.

Common Onion Harvesting Mistakes

There are several mistakes that gardeners should try to avoid.

1. Harvesting too early for storage: Immature bulbs may not have developed suitable protective skins.
2. Leaving mature onions in wet soil: Prolonged damp conditions can affect bulb quality.
3. Forcing the foliage to fall over: Allow onion tops to collapse naturally.
4. Damaging bulbs with a fork: Bruised or cut onions are less suitable for keeping.
5. Storing onions before curing: Damp necks and skins increase storage problems.
6. Using sealed plastic bags: Poor ventilation encourages moisture to accumulate.
7. Keeping damaged onions with healthy ones: Sort your harvest carefully.
8. Forgetting to check stored onions: Regular inspection helps prevent losses.

Frequently Asked Questions About Harvesting Onions

What month do you harvest onions in the UK?

Autumn-planted onion sets are generally harvested during June and July. Spring-planted onions are commonly harvested from July to September, with some later varieties continuing into October.

How do I know when my onions are ready to harvest?

Look for yellowing foliage, naturally falling leaves, mature bulbs and softening necks. These are common signs that onions are approaching maturity.

Should onion leaves be completely brown before harvesting?

No. Onions can be lifted once their foliage has yellowed and naturally toppled. It’s generally better to harvest before all the foliage has completely disappeared.

Do onions have to fall over before harvesting?

If you want fully mature storage onions, naturally falling foliage is a useful indicator. However, onions can be harvested earlier for immediate use.

Can I eat onions straight after harvesting?

Yes. Freshly harvested onions can be used in cooking. Curing is particularly important when you want to store them for longer periods.

How long should I leave onions to dry?

Approximately two weeks is common, although cool or humid conditions can make the process take longer. Check that the skins and necks are thoroughly dry.

Can I dry onions in a greenhouse?

Yes. A greenhouse can be suitable if it’s dry and well ventilated. Avoid excessive heat and humidity.

Can I store onions in a cardboard box?

A ventilated cardboard box in a cool, dry place may work for a small quantity, but mesh bags, slatted trays and suitable crates generally provide better airflow.

Why are my onions sprouting in storage?

Sprouting can be encouraged by unsuitable storage temperatures, moisture, variety characteristics or the length of time they’ve been stored.

Can onions survive frost after harvesting?

Stored onions should be protected from freezing temperatures. Choose a cool but frost-free storage location.

Final Thoughts: Harvesting Your Homegrown Onions

Knowing when to harvest onions in the UK is an important part of getting the most from your vegetable garden or allotment.

Whether you’re growing autumn-planted onions for an early summer harvest or spring-planted onions for storing through winter, timing makes a considerable difference.

Watch for yellowing leaves, naturally falling foliage and mature bulbs.

Harvest carefully, avoid unnecessary damage and give your onions enough time to dry properly before storage.

Remember that not every variety will mature at exactly the same time, so let the plants guide you.

There is something incredibly satisfying about harvesting a fantastic crop of homegrown onions and knowing that, with a little care, you can enjoy them in your cooking for months afterwards.

I hope this complete onion harvesting guide helps you achieve a wonderful crop on your own allotment or in your garden.

Thank you for joining me here at Gardening with Ben.

Keep smiling, keep shining, keep gardening with Ben!