Harvesting and storing

Lodging and Drying of Leaves (Foliage)

This is the most important and reliable sign. When bulb formation is complete, the flow of nutrients from the leaves to the bulb ceases, and the leaves begin to die off naturally. First, they lose turgor and lodge (the false stem softens, and the foliage falls to the ground), then they dry out and turn yellow (Balashev and Zeman, 1981; Rubatzky and Yamaguchi, 1997).

How it works: Lodging is a signal that the bulb no longer needs the green mass for photosynthesis and is fully prepared for the dormancy period. Its neck (the transition point from leaves to bulb) becomes soft and thin, allowing the leaves to fall.

Practical advice: Begin harvesting when 50-80% of the foliage in the bed has lodged (Gubb and MacTavish, 2002). If you wait for 100%, there is a risk that some bulbs' roots will start growing again or diseases will develop, sharply reducing their storage ability (Böttcher, 1999). For sweet, thin-skinned varieties (e.g., 'GranO' or 'Granex' types), it is recommended to start harvesting earlier—at 20-50% lodging—to preserve as many protective scales as possible (Sargent et al., 2001).

Drying and Softening of the Bulb Neck

This sign is linked to the first and is its logical continuation. During maturation, the false stem at the base of the bulb, the so-called "neck," gradually loses moisture, becomes soft, thin, and begins to dry out (Rubatzky and Yamaguchi, 1997; Swiader, 1992).

How it works: A thin, dry neck is a natural "lock" that closes off the interior of the bulb to pathogens and prevents further moisture loss. A thick, succulent neck is a sign that the onion is still growing.

Practical advice: A few days before the intended harvest, you can selectively check a few bulbs. If the neck at the base is dry and twists easily (not breaks, but actually twists), the onion is ready.

Change in Color and Condition of the Outer Scales

As the onion matures, the outer protective scales (the tunic) lose moisture, become dense, dry, and acquire the color characteristic of the variety—golden, yellow, brown, or red (Balashev and Zeman, 1981; Gubb and MacTavish, 2002).

How it works: This is the final stage in forming the protective barrier. A dry, dense, colored tunic protects the bulb from mechanical damage and excessive moisture evaporation, which is critically important for long-term storage. In sweet, poor-storing varieties, the outer scales are often thin and easily damaged.

Practical advice: Try removing the tunic from a few bulbs. If it separates easily and rustles, the onion is ripe. If the scales adhere tightly and feel moist, it is worth waiting.

Important note: In rainy weather, these processes may be delayed, and the signs of maturity become less noticeable. In such cases, do not wait for perfect weather; harvest the onions at the initial lodging stage, otherwise, they may begin to grow again.

Methods for Accelerating Maturation

There are several proven agronomic techniques that can be applied in your garden. Most of them are aimed at stopping the supply of moisture and nutrients to the plant.

1. Stopping Irrigation

The simplest and most effective method. As soon as foliage lodging begins, irrigation must be completely stopped.

How it works: Moisture is the main growth stimulator. Stopping irrigation signals to the plant that the growing season is ending and accelerates the flow of nutrients into the bulb. It also dries the top layer of soil, making subsequent harvesting easier and reducing the risk of rot infection.

Practical advice: Irrigation is usually stopped 20-30 days before the intended harvest (Balashev and Zeman, 1981; Swiader, 1992). In a rainy summer, this method will not work, and then the following methods come to the rescue.

2. Undercutting (Root Pruning)

1-2 weeks before harvest, you can gently cut the onion roots at a depth of 5-10 cm below the base using a sharp spade or hoe (Balashev and Zeman, 1981).

How it works: Damage to the root system sharply restricts the supply of moisture and nutrients to the leaves. This triggers a stress maturation mechanism: the plant, "sensing" the threat, accelerates the translocation of reserves from the leaves to the bulb and begins to form protective scales.

Practical advice: This method is especially effective for accelerating maturation in conditions of a wet, drawn-out autumn. It is important to perform the undercutting very carefully to avoid damaging the bulb itself.

3. Forced Lodging (Rolling or Breaking the Foliage)

If the leaves do not lodge naturally, the process can be artificially accelerated. Two methods are used:

• Rolling: A light roller or even a board is used to press the leaves to the ground. This causes softening and lodging of the neck.
• Breaking (or "snapping" the tops): Previously, breaking or pressing the foliage by hand was practiced, but this labor-intensive method can injure the bulb neck, opening the door to infection.

How it works: Forced lodging disrupts the structure of the false stem, causing softening and blocking of the vascular system. As a result, the flow of substances into the bulb accelerates (Balashev and Zeman, 1981). However, this method is considered outdated and potentially dangerous.

Important caveat: Modern research shows that rolling or breaking the leaves can damage the neck and increase the risk of neck rot caused by Botrytis allii during storage (Gubb and MacTavish, 2002). Therefore, if possible, it is better to resort to undercutting or stopping irrigation.

4. Desiccant Treatment (for Large Farms)

In commercial vegetable growing, chemical desiccants, for example based on diquat or glyphosate, are used to accelerate maturation and facilitate mechanized harvesting (Rubatzky and Yamaguchi, 1997). For home gardeners, this method is not recommended, as it requires strict adherence to dosages and waiting periods.

Conclusion: In most cases, stopping irrigation and allowing the onions to mature naturally is sufficient. If the weather is unfavorable, the safest and most effective technique for the gardener is careful root pruning. Forced lodging of foliage should be used cautiously to avoid injuring the bulb neck.

Choosing the Right Time and Weather

The best time for harvesting is a dry, sunny day, preferably in the afternoon, when morning dew has evaporated and the bulbs are warmed by the sun (Balashev and Zeman, 1981; Swiader, 1992).

Why this is important: Wet bulbs harvested in rain or dew dry much less well and are more often affected by fungal and bacterial diseases during storage. Sunny weather allows you to immediately begin the natural drying process in the field, which is the best start for long-term storage.

Practical advice: If possible, plan harvesting for a period of stable dry weather. If rain is forecast and the onions are already ripe, it is better to harvest them slightly early than to risk leaving them in wet soil.

Extraction Technique: Digging, Not Pulling

Pulling onions out of the ground by the tops is the most common and most harmful mistake. This method inevitably leads to damage to the base and neck of the bulb.

How to do it correctly: Bulbs should be carefully dug up with a garden fork or spade, stepping back 5-7 cm from the row, and then lifted from the soil while holding them by the neck (Balashev and Zeman, 1981; Swiader, 1992).

Why this works:

• Preservation of the base: Jerking often tears off part of the roots or damages the base, which breaks the natural protective barrier and accelerates moisture loss.
• Preservation of protective scales: Careful digging helps preserve the dry outer scales, which are the bulb's main defense.
• Assessment of root condition: By digging, you can assess the condition of the root system and the degree of maturity.

Practical advice: On light, sandy soils, you can carefully pull the onions, but only if the soil is dry and crumbly. On heavy, clay soils, digging is mandatory. Never shake off soil by hitting the bulbs against a shovel or each other—this causes micro-cracks and bruises that will later lead to rot (Gubb and MacTavish, 2002).

Handling Onions During and After Harvest

The greatest danger to freshly harvested onions is mechanical damage. Research shows that even a drop from a height of 10 cm onto a hard surface can cause internal bruising that is not visible externally but significantly accelerates respiration and promotes rapid spoilage (Herold et al., 1998; Gubb and MacTavish, 2002).

What you should do:

• Avoid impacts and drops: Carefully place the lifted bulbs into shallow boxes or buckets. Do not throw or pour them from a great height.
• Do not cut leaves immediately: Immediately after harvesting, do not cut off the leaves and roots. Leave them for 3-5 days for primary drying in the field. This allows the plastic substances from the leaves to complete their transfer to the bulb, and the cut wounds to dry (Balashev and Zeman, 1981; Rubatzky and Yamaguchi, 1997).
• Protection from sun: In very hot weather (above 30°C), freshly dug onions may suffer sunburn, especially thin-skinned varieties. Therefore, it is better to move them immediately under cover or cover them with the foliage (Rubatzky and Yamaguchi, 1997; Swiader, 1992).

Practical advice: Lay the onions out to dry in a single layer (or two or three) directly on the bed, with the foliage covering the bulbs. Ensure good air circulation.

Primary Drying in the Field

After harvesting, the onions should be left on the bed for primary drying for 3-7 days (depending on the weather) (Balashev and Zeman, 1981; Rubatzky and Yamaguchi, 1997). If the weather is rainy, move the bulbs under cover or into a well-ventilated area.

Why this is important: During this period, final maturation and drying of the protective scales occur. The neck becomes dry and firm, and the outer scales gain strength and characteristic color. This is critical for the onion to enter dormancy with maximum protection.

How to know the onion is ready for the next stage: When the foliage becomes dry and brittle, and the protective scales begin to separate easily and rustle, you can proceed to trimming and sorting.

Conclusion of the chapter: The main principle of harvesting is careful handling, minimizing damage, and ensuring good primary drying. Onions harvested at the right time and with all rules observed are half the success of storing them.

Two Stages of Drying: Field and Final

The drying process can be conditionally divided into two stages.

Stage 1: Field Drying (3–7 days)

Immediately after harvest, the onions are left directly on the bed for primary drying (Balashev and Zeman, 1981; Rubatzky and Yamaguchi, 1997).

How to organize it properly:

• Spread the onions in one or two layers so that the foliage covers the bulbs from the scorching sun.
• Ensure good air circulation.
• Turn the onions daily so they dry evenly.
• At night or in case of rain, it is better to cover the bulbs or move them under cover.

How to know this stage is complete: The foliage becomes dry and brittle, and the outer scales begin to separate easily and produce a characteristic "rustling" sound.

Stage 2: Final Drying (2–4 weeks)

After the onions have dried in the field, they are moved for final drying to a dry, well-ventilated area: under cover, in a shed, in an attic, or in a garage (Balashev and Zeman, 1981; Swiader, 1992). In commercial production, special dryers with forced ventilation and heated air are used for this purpose.

Optimal conditions for final drying:

• Temperature: 25–30°C in the first few days, then gradually reduced to 20–25°C (Gubb and MacTavish, 2002; Rubatzky and Yamaguchi, 1997). Higher temperatures (above 35°C) can cause discoloration and even damage to the inner scales.
• Relative Humidity: 60–75%. Air that is too dry (below 50%) makes the skin brittle, causing it to crack, and the bulbs lose marketable quality (Gubb and MacTavish, 2002). Air that is too humid (above 80%) promotes mold and rot development.
• Ventilation: Very important for removing moisture released by the bulbs during respiration. Good air circulation is the key to even drying and disease prevention.

Practical advice for home conditions: The ideal place for drying onions is an attic with good ventilation or a warm, dry shed. If such a space is unavailable, onions can be spread in a thin layer on the floor in a room or on a veranda. The main thing is to ensure a constant supply of fresh air. A fan can be used to enhance circulation.

How to Determine If the Onions Are Dry Enough?

Readiness for storage is determined by three main signs (Rubatzky and Yamaguchi, 1997; Swiader, 1992):

1. The neck is completely dry and thin: When squeezed between fingers, the neck should be firm, dry, and easily crumble. If the neck is moist or soft, the onion is not ready for storage.

2. The outer scales are dense and rustling: The outer scales should be dry, strong, easily separated from the bulb, and produce a rustling sound when touched.

3. The foliage is completely dry and brittle: The leaves should be completely dried and snap easily, rather than bending.

Important: Do not rush! It is better to over-dry the onions than to leave them moist. Even a small amount of moisture in the neck can cause neck rot caused by Botrytis allii during storage (Gubb and MacTavish, 2002). This pathogen is the most common cause of storage losses.

Signs of insufficient drying:

• The neck remains soft and moist.
• The protective scales feel damp to the touch.
• When cut, the bulb shows succulent, immature tissue.
• Mold appears on the bulbs, or roots begin to sprout.

Practical advice: If you are unsure whether the onions are ready, check several bulbs from different parts of the batch. It is better to give the onions an extra week to dry than to risk the entire crop.

Trimming Leaves and Roots

Trimming is not just a cosmetic procedure. It performs an important protective function and facilitates subsequent storage.

When to start trimming: Only after the onions are completely dry. If you trim earlier, the open wounds can become entry points for infection. Signs of readiness: a dry, thin neck and completely dry, brittle foliage (Rubatzky and Yamaguchi, 1997; Swiader, 1992).

How to trim leaves correctly:

There are two main ways to trim the foliage:

1. For long-term storage (cutting "at the neck"): The leaves are cut, leaving a "tail" of 2–5 cm (Balashev and Zeman, 1981; Rubatzky and Yamaguchi, 1997). This keeps the neck tight and protected, and the cut area dries quickly. Cutting lower (flush with the bulb) damages the neck and increases the risk of neck rot (Balashev and Zeman, 1981; Gubb and MacTavish, 2002).

Why this works: The remaining "tail" creates an additional barrier that prevents pathogens from entering the bulb through the neck. This is especially important for long-term storage (more than 4-6 months).

2. For braiding (cutting "for a braid"): If you plan to store the onions in braids, the leaves are not cut at all or left 15–20 cm long. This traditional storage method provides good ventilation and is convenient for hanging.

Practical advice: Onions with long, strong foliage are best for braiding. Before weaving, it is recommended to keep them under cover for a few days to make the foliage more flexible and less prone to breaking.

How to trim roots correctly:

The roots are cut, leaving a stump of 0.5–1 cm (Balashev and Zeman, 1981; Rubatzky and Yamaguchi, 1997).

Why this is important: Completely removing the roots (cutting "flush to the base") can compromise the integrity of the base and open the way for pathogens. A small stump prevents this, preserving the protective barrier. The base must remain dry and firm. If you see moist, succulent tissue when trimming, the onions are not fully dried and need more drying.

Tools: Trimming is done with sharp secateurs or scissors. A blunt tool will crush the tissues rather than cut them, increasing the risk of damage.

Sorting: Selecting the Best

Sorting is just as important as trimming. It allows you to select bulbs that are guaranteed to store well and use first those that will not last.

Principle: Use non-standard bulbs first for food, and leave only the highest quality, well-matured specimens for long-term storage.

Onion categories for sorting:

1. Bulbs for long-term storage (marketable):

• Appearance: Bulbs must be firm, undamaged, with intact and dry protective scales of the color characteristic of the variety. The neck must be thin and dry.
• Size: Medium-sized bulbs are best for long-term storage. Very large bulbs (especially sweet varieties) often store less well, while small ones may become overly dry (Gubb and MacTavish, 2002).
• Maturity: Fully matured, with well-formed protective scales.

2. Bulbs for "immediate" consumption or processing (unmarketable):

This includes all bulbs that are not suitable for long-term storage.

• Immature bulbs: With a thick, succulent neck. They will not store and will quickly rot or sprout. Use them first.
• Damaged bulbs: With mechanical damage (cuts, cracks, dents). Even minor damage is an entry point for infection.
• Sprouted bulbs: Those with roots starting to grow or green shoots appearing.
• Diseased or rotting bulbs: With signs of mold, rot, or spots.
• "Doubles" (conjoined bulbs): Such bulbs have a deformed shape and often store poorly, especially if moisture and dirt get trapped between them.

3. Bulbs for seed or sets (planting material):

If you are growing onions not only for food but also for producing seeds or for planting the following year for greens, be sure to select several of the best bulbs for these purposes. They should be stored separately and under special conditions.

Practical sorting tips:

• Sort onions on a dry, clear day.
• Inspect each bulb carefully. Do not hesitate to discard questionable specimens—better to lose one bulb now than several dozen during storage.
• Separate onions by size. Large, medium, and small onions store better separately. This simplifies use and allows you to monitor the storage of each fraction (Swiader, 1992).
• Immediately after trimming and sorting, the onions cannot be placed into permanent storage! They need another 1-2 days to lie in a dry, ventilated place so that the cut areas dry completely.

Conclusion: Proper trimming and thorough sorting are the final stage of preparing onions for storage. Selecting only the highest quality, healthy, and well-matured bulbs, along with competent trimming, is the guarantee that the harvest will last until spring, delighting you with its taste and firmness.

Why Onions Need Special Storage Conditions

The bulb is a natural storehouse of nutrients created by nature to survive an unfavorable period. In the dormant state, important physiological processes occur within:

1. Respiration: Even in dormancy, the onion respires, consuming oxygen and releasing carbon dioxide, water, and heat. The intensity of respiration determines how quickly the bulb will "age" and deplete its reserves (Brewster, 2008).

2. Moisture evaporation: Onions lose moisture through the skin. The drier the air, the faster the evaporation, but too dry air makes the skin brittle, causing it to crack and lose moisture even faster (Gubb and MacTavish, 2002).

3. Sprouting: This is the main enemy of long-term storage. As soon as the dormancy period ends and favorable conditions (temperature around 10–15°C and humidity) are created, the bulb begins to sprout, using its reserves for growth.

Understanding these processes allows us to manage storage conditions to slow them down as much as possible.

Optimal Storage Parameters

There are two main approaches to storing onions: cold (for temperate climates) and warm (for tropics and subtropics). The choice depends on your capabilities and region.

Practical Recommendations for Choosing a Storage Location

Practical advice: If you do not have a specialized storage facility, follow the principle "the drier and cooler, the better." Even in an urban apartment, you can find a place to store a few kilograms of onions, for example, in a dry, dark cupboard or pantry, but always in breathable containers.

Monitoring the Condition of Onions in Storage

Even under ideal conditions, you must regularly inspect stored onions. Every 2–3 weeks, sort through them, removing bulbs showing signs of spoilage—soft, moldy, sprouted, or discolored (Gubb and MacTavish, 2002). One rotting bulb can "infect" neighboring ones, especially at high humidity.

Conclusion of the chapter: Long-term onion storage is maintaining a balance between three factors: low (or high) temperature, moderate humidity, and constant ventilation. Understanding the physiological processes occurring in the bulbs will help you create optimal conditions and preserve the harvest until spring.

Basic Requirements for Containers and Storage Methods

Regardless of the chosen method, any container for storing onions must meet three key requirements:

1. Air permeability: The walls must allow air to pass through to remove excess moisture and carbon dioxide.

2. Prevention of condensation: The material should not create a "greenhouse effect."

3. Protection from mechanical damage: Bulbs should not press heavily against each other.

Now let's examine the most common and proven methods in more detail.

Onion Storage Methods

What to Avoid

1. Plastic bags and airtight containers: This is the most common mistake. High humidity quickly builds up in them, and the onions begin to rot and become moldy. Studies show that within just 2–3 weeks of storage in a plastic bag, onion quality declines sharply (Gubb and MacTavish, 2002).

2. Too deep a pile: A thick layer of onions (more than 30–40 cm) creates excessive pressure on the bottom bulbs, damaging them and hindering ventilation. Additionally, carbon dioxide may accumulate in the depths, causing internal tissue damage (Solberg, 1997).

3. Storing next to potatoes: Onions and potatoes should not be stored together. Onions release substances that accelerate potato sprouting, while potatoes release moisture that can trigger onion rot.

4. Direct sunlight: Light stimulates bud awakening and onion sprouting, especially if dormancy is already weakened.

Choosing a Storage Method: What Is Best?

The choice of method depends on your conditions and the volume of the harvest:

Conclusion of the Chapter

A correctly chosen storage method is the finishing touch to your work. The main rule: the onion must "breathe." If you ensure good ventilation, moderate humidity, and protection from light, your harvest will delight you until spring, retaining its firmness, aroma, and beneficial properties.

1. Sprouting

Sprouting is a natural biological process signaling that the bulb is emerging from dormancy.

Why it happens:

• End of dormancy period: The length of natural dormancy varies among different varieties. Short-day sweet varieties (like 'GranO' and 'Granex') have a short dormancy period—only 1–2 months. Sharp, long-day varieties may have a dormancy period of 5–7 months or more (Miedema, 1994a; Brewster, 2008).
• Unsuitable storage temperature: The most dangerous temperature for storing onions is from +5 to +15°C. In this range, sprouting processes are most actively triggered (Abdalla and Mann, 1963; Brewster, 2008).
• High humidity: High air humidity (above 80%) stimulates root awakening, which accelerates emergence from dormancy and subsequent sprouting (Tanaka et al., 1985; Brewster, 2008).
• Mechanical damage: Any damage to the base or neck accelerates sprouting. This is linked to the release of "wound hormones" that stimulate growth (Boswell, 1924; Miedema, 1994c).
• Disruption of harvest timing: Harvesting too early or too late shortens the natural dormancy period (Gubb and MacTavish, 2002).

How to prevent it:

• Choose varieties with a long dormancy period, especially if you plan long-term storage.
• Strictly observe the temperature regime: either below +2°C or above +18°C.
• Maintain humidity within 65–75%.
• Avoid mechanical damage during harvesting and storage preparation.
• Do not store onions near apples and potatoes—they release ethylene gas, which stimulates sprouting.

2. Fungal Diseases

Fungal infections are the main cause of storage losses, especially in conditions of high humidity. Fungal spores may be present on the bulbs at harvest time or enter through wounds and damage (Maude, 1990; Gubb and MacTavish, 2002).

3. Bacterial Rots

Bacterial infections usually develop on the background of mechanical damage or already initiated fungal infection.

Main pathogens: bacteria of the genera Pseudomonas, Erwinia, Burkholderia.

Causes:

• Mechanical damage during harvesting, sorting, or transportation.
• Storage at high humidity and temperature.
• Moisture entering the bulb (e.g., through a damaged neck).

Prevention:

• Handle onions carefully at all stages to avoid damage.
• Ensure good ventilation and avoid over-humidification.
• Promptly remove affected bulbs.

4. Physiological Disorders

These are abnormalities not caused by fungi or bacteria but by improper growing or storage conditions.

5. Natural Dehydration (Shrinkage)

Even under ideal storage, onions gradually lose moisture, becoming less succulent, and the protective scales thin.

Causes:

• Natural processes of respiration and evaporation.
• Air that is too dry (below 50%).
• Long storage period.

Prevention:

• Maintain optimal humidity (65–75%).
• Do not keep onions in storage longer than recommended for the variety.
• Use varieties with high storage ability (high dry matter content) for long-term storage (Brewster, 2008).

Summary Table: Causes of Onion Spoilage and Prevention

Conclusion of the Chapter

Understanding the reasons why onions spoil is the main key to successful storage. The main enemies of your harvest are incorrect temperature (especially the "danger" zone of +5...+15°C), high humidity, poor ventilation, and mechanical damage. Fungal and bacterial infections are not accidents but consequences of mistakes made during cultivation, harvesting, or preparation for storage.

If you follow the recommendations from all the chapters of this article—from determining maturity to creating the right storage conditions—your onions will store well and delight you with their quality until spring.