Harvesting and storing

Biological Maturity

Biological (or physiological) maturity is the stage at which the seeds inside the pit are fully mature and capable of producing a new plant. Externally, this manifests as the pit becoming hard and its shell turning dark brown. However, the fruit at this moment may still be hard and inedible.

Why should a gardener know this? Biological maturity is a guide for determining the onset of removable maturity. For most plum varieties, it occurs 1–2 weeks before the fruits become fit for eating (Westwood, 1993).

Removable (Technical) Maturity

Removable maturity is the stage when the fruits are sufficiently developed to be picked from the tree for storage, transportation, or processing. At this time, they reach the size and shape characteristic of the variety, but do not yet have full flavor and aroma.

The main signs of removable maturity are:

• The fruit separates easily from the stalk with a slight twist.
• The skin acquires the varietal color (for dark varieties — blue-purple, for light ones — yellow-green).
• The flesh remains firm but loses excessive hardness.

For most plum varieties, removable maturity occurs 3–5 days before consumer maturity (Agustí, 2010). It is at this stage that fruits intended for long-term storage and long-distance transportation are harvested.

Consumer Maturity

This is the stage when the fruits are fully ready to eat: they have acquired the characteristic taste, aroma, juiciness, and optimal softness of the variety. Unlike apples and pears, plums are non-climacteric fruits. This means that after harvest, they practically do not increase sugar content or become sweeter (Westwood, 1993).

Important! Plums picked too early will not ripen to full flavor during storage — they will remain hard and sour. They can only be used for processing (compotes, jams).

If you plan to eat plums right away, wait for full consumer maturity. For local sale and processing, fruits are harvested at this stage or 1–2 days before it (Тарасов, 1981).

In practice, different maturity stages are used for different purposes:

Signs of Ripeness

In practice, a combination of several simple signs is used to determine the removable maturity of plums. Relying on only one of them is not advisable — weather conditions and variety characteristics can distort the picture.

1. Skin Color (Ground Color)

In most plum varieties, the ground color of the skin changes as they ripen. In dark-colored varieties (e.g., 'Hungarian', 'Stanley'), the green background changes to purple, blue, or dark red. In varieties with yellow or green skin ('Greengage', 'Mirabelle'), the background becomes golden or yellowish-green.

Important: in some varieties, full color may appear before the fruit reaches removable maturity, so color is only one of the guidelines (Westwood, 1993).

2. Ease of Detachment from the Branch

The most reliable practical test: take the fruit in your hand, slightly lift it and turn it 90°. If the plum easily separates from the stalk without significant effort — it has reached removable maturity. If the fruit sits tightly and does not separate — it is too early. This sign is universal for all varieties and is considered primary (Тарасов, 1981).

3. Flesh Consistency

At removable maturity, the flesh becomes firm but no longer hard. When lightly pressed with a finger, it yields slightly but does not indent. Overripe fruits have soft flesh and are no longer suitable for storage (Agustí, 2010).

4. Taste and Sugar Content

For consumer maturity, taste is the guide: the fruits should be sweet, with the characteristic aroma of the variety. For removable maturity, a portable refractometer can be used — for most good-quality plum varieties, the soluble solids (sugars) content is at least 12–14% (Crisosto & Kader, 2000; Gull et al., 2023). If you don't have a device, simply taste the fruit: at removable maturity, it is no longer astringent, but may not yet be fully sweet.

5. Iodine-Starch Test

This method is well known to experienced gardeners. Make a fresh cut on the fruit and drop a weak iodine solution (1–2%) onto it. If the cut turns blue — there is a lot of starch in the fruit, they are underripe. If the staining is weak or absent — the starch has turned into sugars, the fruit is ripe. For removable maturity, most plum varieties show a 2–3-point color reaction on a five-point scale (Тарасов, 1981). This method provides additional information but is not mandatory for the home gardener.

Characteristics of Different Plum Groups

Ripening times and signs of maturity differ among different botanical groups, which is important to consider when planning harvest.

European Plums (Prunus domestica)

This group includes most common garden varieties — 'Hungarian', 'Greengage', 'Stanley', 'Victoria'. They usually ripen later (August–September) and have an extended harvest period of 2–3 weeks. Fruits on a single tree do not ripen simultaneously, so harvesting is done in 2–3 passes (Westwood, 1993). These varieties are most often used for drying (prunes) and long-term storage.

Japanese Plums (Prunus salicina)

Varieties in this group ('Shiro', 'Santa Rosa', 'Black Amber') are distinguished by earlier ripening (July–August) and, as a rule, more delicate flesh. Their consumer maturity arrives quickly, and the harvest period is very short — 5–7 days. The fruits easily overripen on the tree, becoming soft and unsuitable for storage (Gull et al., 2023). Therefore, it is especially important for them to be harvested on time, at the removable maturity stage, if you plan to store or transport them.

Cherry Plums and Myrobalan Plums (Prunus cerasifera)

These crops ripen early (in southern regions — in June–July), with small but very dense fruits. Their removable maturity occurs when the skin acquires yellow, pink, or red coloration, and the flesh becomes slightly soft. Cherry plum fruits can hang on the tree for a long time without falling, but it is better to rely on color and taste for harvesting (Трунов, 2012).

Hybrid Varieties (Pluots, Apriums)

These modern hybrids between plums and apricots combine characteristics of both parents. Their removable maturity is determined in the same way as for Japanese plums — by color and easy separation, but ripening times can vary greatly (Buckingham, 2010).

Influence of Weather Conditions

The weather during the ripening period has a strong influence on both the harvest time and fruit quality. Here are the main factors to consider:

Heat and Sunny Days

In hot and dry summers, ripening accelerates by 5–10 days compared to long-term average dates. In such a situation, it is important not to miss the moment of removable maturity — inspect trees daily. High temperatures also increase sugar content, but can lead to overripening and softening of fruits (Westwood, 1993).

Rainy Weather Before Harvest

Heavy rainfall during the ripening period is a risk factor. Water hitting the fruit can cause skin cracking. Cracks are entry points for infections (fungal rots), and such fruits do not store well. In addition, rain reduces sugar content and impairs taste (Gull et al., 2023). If rain is forecast, harvest a little earlier, at an earlier stage of removable maturity — this will reduce losses.

Frosts (Early Autumn)

If you grow late varieties, there is a risk of fruit damage from the first autumn frosts. Plums can tolerate short-term temperature drops to –2…–3 °C without serious consequences, but with stronger frosts, the flesh becomes watery, loses taste, and spoils quickly. In such cases, the crop is harvested before frost sets in (Agustí, 2010).

Wind and Hail

Strong winds can cause premature fruit drop, especially overripe ones. Hail causes mechanical damage, after which the fruits are no longer suitable for storage — they should be sent for processing immediately.

Practical Recommendations for Determining Harvest Time

1. Keep a calendar. Record flowering and harvest dates for each variety in your garden. By comparing data over several years, you will learn to predict ripening times to within 3–5 days.

2. Inspect trees regularly. During ripening, check fruits every 2–3 days. Start with the parts of the canopy that receive more sunlight — fruits there ripen faster (Westwood, 1993).

3. Perform the detachment test on several fruits from different sides of the tree. If most fruits detach easily — it's time to harvest.

4. Consider the purpose. For long-term storage, pick fruits a little earlier, at the beginning of removable maturity. For immediate consumption and local sale — let them ripen to consumer maturity (Тарасов, 1981).

5. Do not delay. In warm weather, a delay of 2–3 days can lead to massive overripening and fruit drop. It is better to start harvesting a little earlier than to be late.

Harvesting Technique: How to Pick Fruits Correctly

Proper plum picking is not just pulling the fruit from the branch. It is a precise movement that preserves the integrity of the fruit and its protective properties.

The main rule: separate the fruit with its stalk

The most reliable method is to take the fruit in your palm, slightly lift it, and simultaneously twist it along its axis by 90–180 degrees (Westwood, 1993; Тарасов, 1981). In doing so, the stalk separates from the branch exactly along the natural abscission layer — without damage. The fruit remains with the stalk, which is extremely important:

• The stalk closes the "entry point" for rot pathogens (Agustí, 2010).
• Fruit with a stalk loses moisture more slowly (Тарасов, 1981).
• Such fruits withstand transportation and packing better.

What not to do:

• Do not pull the fruit down, away from the branch — this often leads to the stalk tearing off or part of the flesh being pulled out.
• Do not squeeze the fruit with your fingers — remaining dents quickly darken and become sites of damage.

If the fruit does not separate with a gentle twist — it is not yet ripe. Do not use force.

Organizing the Harvest: Order and Tools

Timing and Frequency of Harvest

Plums on one tree do not ripen simultaneously. Usually, fruits on the well-lit southern and southwestern sides of the canopy ripen first, then in the middle part, and lastly in the lower and shaded areas (Westwood, 1993; Тарасов, 1981). Therefore, harvesting is done in 2–3 passes with an interval of 3–5 days. This approach allows each batch to be picked at the optimal removable maturity stage and minimizes losses from overripening and drop.

Tools and Containers

• For harvesting from low trees, hands and lightweight containers (baskets, shallow buckets) are sufficient. The bottom of the container should preferably be lined with soft material (cloth, paper) (Buckingham, 2010).
• For tall trees, use garden stepladders that are stable on loose soil. Pick fruits from the upper tiers using fruit-picking bags (Тарасов, 1981).
• Containers should have a capacity of no more than 8–10 kg: in overly deep containers, the bottom fruits are damaged by the pressure of the top ones (Gull et al., 2023).
• Boxes and baskets must be clean, dry, free of burrs and sharp edges. Use soft pads between layers.

Sequence of Actions During Harvest

1. Start with the peripheral, better-lit branches. Move from the upper part of the canopy to the lower.

2. Pick only those fruits that separate easily. Leave unripe ones for the next pass.

3. Immediately discard fruits with signs of disease, cracks, or damage — they will not go into storage.

4. Carefully place fruits in the container, avoiding throwing. Each fruit should lie freely, without pressure from neighbors (Тарасов, 1981).

Time of Day for Harvest

The best time is early morning, after the dew has dried, or evening, when the heat subsides. In hot weather, fruits become softer and more sensitive to damage. In addition, fruits picked in the heat have a higher temperature, which accelerates respiration and reduces their shelf life (Agustí, 2010). If possible, harvest during cooler hours.

Preventing Damage

Damage during harvesting and transportation is the main cause of losses during storage. The main types of damage and how to avoid them:

Mechanical Damage (Bruises, Punctures, Scratches)

• Cause: careless handling, throwing fruits, using rigid containers, overfilling containers.
• Consequences: at the site of damage, respiratory processes are activated, the tissue darkens, creating conditions for fungal infection (Agustí, 2010).
• How to avoid: pick fruits gently, pack them carefully, prevent impacts and friction.

Damage from Stalks of Adjacent Fruits

When packing in containers, stalks can scratch and puncture the skin of neighboring fruits. To prevent this, fruits are placed with stalks down or sideways, and soft paper is laid between layers (Тарасов, 1981). For long-term storage, wrapping each fruit in thin paper is also practiced.

Impact from Falling

An accidental fall of a fruit to the ground or the bottom of a container from a height of more than 30 cm almost guarantees an internal bruise, which is not immediately visible but will manifest during storage. Use soft mats under containers and do not overload them (Buckingham, 2010).

Sunburn

If fruits are left in the sun for a long time after harvest, their skin can get burned — yellowish-brown spots appear, and tissues become loose. This is especially dangerous for light-yellow and green varieties. Move harvested fruits to the shade immediately (Westwood, 1993).

Typical Harvesting Mistakes

Based on many years of gardener experience and scientific recommendations, here are the most common mistakes:

1. Delaying the start of harvesting. Waiting for "full ripening" of all fruits leads to the first batches overripening and dropping. Harvesting should begin with the first signs of removable maturity and be done selectively.

2. Picking unripe fruits hoping they will ripen during storage. This technique does not work for plums: if a fruit is picked too early, it will not accumulate enough sugar and will remain sour and hard (Westwood, 1993). For storage, pick only at the removable maturity stage, but not earlier.

3. Harvesting during the hot part of the day. The elevated temperature of the fruit accelerates respiration and aging, reducing shelf life. Whenever possible, harvest in the morning or evening.

4. Using dirty or wet containers. Dirt is a source of microorganisms; moisture promotes rot development. All containers must be clean and dry before use.

5. Damaging fruits when picking (tearing without stalk, pressing on the fruit). This sharply reduces resistance to storage diseases.

6. Mixing fruits of different maturity stages in one container. Riper fruits release more ethylene, stimulating overripening of earlier ones. Sort them during the harvesting process (Gull et al., 2023).

Following these simple rules will allow you to harvest with minimal losses and prepare it for long-term storage.

Why Sorting is Necessary

Sorting solves three main tasks:

1. Selecting fruits for long-term storage — only the best, without damage and at the correct maturity stage.

2. Setting aside fruits for processing — those not suitable for storage but still usable.

3. Removing diseased and damaged fruits — they should not come into contact with quality fruits.

Sorting also allows calibrating fruits by size, which improves their appearance and allows more rational use of packaging and storage space (Тарасов, 1981).

Selecting Fruits for Long-Term Storage

Only fruits meeting the following requirements are suitable for storage:

Maturity Stage. Only removable maturity. Fruits must be sufficiently dense and firm, but not hard. They already have the characteristic color of the variety, but are not yet fully soft. Overripe fruits are unsuitable for storage (Westwood, 1993; Gull et al., 2023).

Skin Integrity. The skin must have no cracks, punctures, scratches, or bruises. Any breach of integrity is an entry point for fungal infection. Even small scratches from the stalks of neighboring fruits can cause rotting during storage (Agustí, 2010).

Presence of Stalk. For long-term storage, it is advisable to select fruits with the stalk intact. The stalk prevents moisture loss and closes the channel for pathogen entry. Fruits without a stalk lose moisture faster and are more susceptible to rot (Тарасов, 1981).

No Signs of Diseases or Pests. Carefully inspect each fruit: are there any suspicious spots (brown, black), traces of insects (wormholes, punctures), growths, or mold? Even one infected fruit can cause the spread of infection (Buckingham, 2010).

Caliber (Size). For storage, it is better to select fruits of the same size (caliber). This facilitates packing and allows for more uniform air circulation if the fruits are packed in boxes. Fruits of different sizes are packed in different batches.

Fruits for Processing (Not for Storage)

Not all plums can be stored long-term. However, this does not mean they are wasted. Many are excellent for processing. This category includes:

• Fruits with minor surface defects — small scratches, light bruises, hail marks, if the damage does not penetrate the flesh. Such fruits can be used for jam, preserves, compotes, juice (Gull et al., 2023).
• Fruits at full consumer maturity, which are already too soft for storage but still good-tasting. They are best eaten immediately, processed, or frozen.
• Small fruits that lack commercial appearance but taste as good as larger ones. They are suitable for canning, making thick jam, or fruit leather.
• Underripe fruits (picked too early) — they will not become sweeter during storage, but they can be used for compotes, marinades, as well as for making plum vinegar or sauces (Westwood, 1993).

Damaged and Diseased Fruits

This is a category that requires immediate attention. Diseased and severely damaged fruits:

• Cannot be stored — they will quickly rot and infect neighboring ones.
• Cannot be placed together with quality fruits even for a short time.
• Should be removed from the bulk immediately during harvest or right after it (Agustí, 2010).

This category includes:

• Fruits with signs of fungal diseases (brown rot, fruit rot — see Chapter 6).
• Fruits with deep cracks, especially if the crack reaches the pit or the flesh has begun to darken.
• Fruits damaged by insects (e.g., plum moth) — with tunnels, excrement inside.
• Overripe fruits with softened, mushy flesh.
• Fruits with signs of physiological disorders (browning of flesh, glassiness, "watercore").

Such fruits are usually disposed of: buried in a compost pit (but not fresh, to avoid attracting pests), burned, or removed from the garden. In small farms, they can be used for animal feed (if there are no signs of toxicity), but more often they are simply destroyed (Buckingham, 2010).

Sorting Procedure: Practical Steps

1. Primary selection — right in the garden, during harvest. Discard obviously damaged and diseased fruits; do not put them in the common container (Тарасов, 1981).

2. Sorting at home (or on the packing table) — after delivering the harvest to a cool place. Sort the fruits into three categories:

• Category 1. For long-term storage. Only undamaged, with stalk, at removable maturity, same caliber.
• Category 2. For processing (immediate) and consumption. Slightly damaged, overripe, small, non-standard.
• Category 3. For disposal. Diseased, rotten, with deep damage, signs of pests.
• Additionally, if necessary, calibrate fruits by size (e.g., large, medium, small) — this facilitates packing in containers and may be important for sale.

Why Sorting is So Important for Storage

Scientific research confirms that even one fruit with an initial stage of brown rot in a box during storage can lead to the infection of 20–30% of neighboring fruits within 1–2 weeks (Agustí, 2010). Sorting is the simplest and most effective way to break the chain of infection spread and prevent massive losses.

Furthermore, separating by purpose allows optimal use of each part of the harvest. Fruits that do not pass the selection for storage are not thrown away but find use in processing or cooking. This increases the overall economic return from the garden and reduces food waste.

In the next chapter, we will move on to the most important stage — storage conditions: what temperature, humidity, and proper packaging are needed for the fruits to last for months.

Storage Temperature

Temperature is the main factor determining storage duration. Plums, like all living fruits, continue to respire after harvest, consuming stored substances and releasing heat. The higher the temperature, the more intense the respiration, the faster the fruits age, lose moisture, soften, and become vulnerable to diseases.

Optimal range: for most plum varieties, the recommended storage temperature is 0 to +1 °C (Agustí, 2010; Westwood, 1993; Hochmuth & Sideman, 2023). At this temperature, fruit respiration slows down about 3–4 times compared to room temperature (+20 °C), allowing quality to be maintained for 2–5 weeks or more.

However, there are important nuances:

• Sensitivity to low temperatures (chilling injury). Plum is a fruit sensitive to overcooling. Although the optimal temperature is 0 °C, long-term storage at temperatures below –1 °C can cause tissue damage (so-called "chilling injury"). Signs: flesh browning, loss of juiciness, appearance of watery areas, taste alteration (Gull et al., 2023). Therefore, do not allow fruit to freeze.
• Different varieties have different sensitivities. Some varieties (especially from the Japanese group, e.g., 'Santa Rosa') are more sensitive to cold, and a temperature no lower than +2…+3 °C is recommended for them (Gull et al., 2023). However, storage time is reduced at this temperature. European varieties ('Hungarian', 'Stanley') are usually more robust and store well at 0 °C.
• Gradual cooling (pre-cooling). After harvest, fruits have field temperature (often 20–25 °C). Placing them abruptly in a cold storage can cause moisture condensation on the surface and tissue stress. It is recommended to cool fruits gradually: first at +10 °C for 6–12 hours, then at +2…+3 °C, and only then bring to 0 °C (Agustí, 2010). At home, this means that you should not immediately put warm fruits on the coldest shelf in the refrigerator — it's better to let them cool in a cool room (e.g., in the basement) overnight.

Air Humidity

Humidity is the second most important parameter. Plums contain a lot of water (about 85%), and during storage, they constantly lose moisture through evaporation. If the air is too dry, the fruits shrivel, the skin becomes flabby, and the fruits lose their visual appeal and taste. If humidity is too high (above 95%), conditions are created for the development of mold fungi and rots.

Optimal relative humidity range: 85–95% (Hochmuth & Sideman, 2023; Westwood, 1993). At this humidity, evaporation from the fruit surface is minimal, which prevents wilting, but does not create excessive moisture that promotes the development of pathogens.

How to maintain the required humidity at home:

• In a cellar or basement, you can use containers of water, wet burlap, or regular floor spraying to increase humidity. However, make sure that water does not come into contact with the fruits.
• In a refrigerator (domestic), humidity is usually below optimal (about 65–75%). To increase it, you can place fruits in closed containers with ventilation holes or use special vegetable containers with humidity regulation. Packaging in perforated polyethylene bags also helps — they create a microclimate with increased humidity.
• Avoid condensation — water droplets on the fruit surface. This provokes rot development. If you notice condensation, provide additional ventilation or slightly open the packaging.

Ventilation

Plums continue to respire, absorbing oxygen and releasing carbon dioxide and ethylene. Ethylene is a gaseous hormone that stimulates ripening and aging. If excess ethylene and carbon dioxide accumulate in the storage, it accelerates overripening and degrades quality. Therefore, air circulation is necessary.

Practical recommendations for ventilation:

• In stationary storages (cellars, basements), there should be natural or forced ventilation, providing fresh air inflow and removal of excess heat and gases. Optimally, air exchange occurs 1–2 times a day (Hochmuth & Sideman, 2023).
• In refrigerators and home cellars, try not to pack boxes too tightly. There should be space between boxes and from walls for air circulation.
• Do not put plums in airtight plastic bags without holes — carbon dioxide quickly accumulates in them, leading to off-flavors and spoilage. Use perforated bags or open containers with lids but with air gaps.
• Regularly (every 1–2 weeks) check the condition of the fruits and ventilate the storage if you smell musty air.

Packaging

Proper packaging performs several functions: protects fruits from mechanical damage, regulates gas exchange, maintains optimal humidity, and prevents cross-infection by diseases.

For long-term storage at home, the following options are recommended:

1. Boxes (wooden or plastic) with ventilation gaps. This is a traditional method. Fruits are laid in rows, interlayered with soft paper (e.g., kraft paper) or wood shavings (clean, without odor) (Тарасов, 1981). A layer of paper between rows prevents contact, reduces mechanical friction, and absorbs excess moisture. Boxes should have holes for air circulation.

2. Polyethylene liners (liner bags) for boxes. This is a modern approach that allows creating a modified atmosphere inside the package with reduced oxygen and elevated carbon dioxide, further inhibiting ripening (Gull et al., 2023). The liners must have small perforation holes (5–10 mm diameter) to prevent the accumulation of excess CO₂ and condensation. At home, you can use ordinary plastic bags, but always with several punctures.

3. Wrapping each fruit in paper. Labor-intensive but reliable, especially for valuable varieties. Each fruit is wrapped in thin, dry paper (tissue or kraft) and placed in a single layer in a box. This completely eliminates contact between fruits, preventing infection transfer and reducing losses from bruising (Тарасов, 1981). For large harvests, this method is not always practical, but for small quantities it gives the best results.

4. Containers with lids (for the refrigerator). For storage in a domestic refrigerator, plastic containers with lids with small holes are convenient. Place a layer of paper towels on the bottom of the container to absorb excess moisture, and cover the fruits with another layer to prevent evaporation. This method is suitable for storing 2–3 weeks.

Important packaging rules:

• Before packing, make sure the fruits are completely dry. Wet fruits rot faster (Agustí, 2010).
• Do not stack more than 2–3 layers of fruits in a box to avoid pressure on the bottom ones.
• Do not mix different varieties and different batches in one package — they may have different storage durations and different disease sensitivities.
• Label the boxes (variety, harvest date) — this will help monitor storage times.

Storage Duration Depending on Variety and Conditions

Under optimal conditions (0 °C, 90–95% humidity), most European plum varieties (e.g., 'Hungarian', 'Stanley', 'Greengage') can be stored from 2 to 5 weeks, with some late varieties lasting up to 8 weeks (Hochmuth & Sideman, 2023; Westwood, 1993). Japanese varieties generally store less well — no more than 2–3 weeks.

At higher temperatures (+5 °C), storage time decreases to 1–2 weeks. At room temperature (+20 °C), plums retain freshness for no more than 3–5 days.

Signs that the storage time is coming to an end:

• Fruits become too soft (easily indented with a finger).
• The skin loses its gloss, becomes dull, and wrinkles appear.
• Dark spots appear — signs of the beginning of fungal infection.
• Fruits begin to exude juice or become watery.

Additional Techniques to Extend Storage

Modern research recommends some additional methods accessible to home gardeners:

• 1-Methylcyclopropene (1-MCP) treatment. This is a gaseous ethylene receptor inhibitor that significantly slows ripening and extends the shelf life of plums (Gull et al., 2023). In industry, it is applied in specialized chambers, but for amateurs, small sachets can be placed in packaging with fruits (available in garden stores). Application significantly increases storage time, especially for Japanese group varieties.
• Modified Atmosphere (MA). At home, you can create an MA effect using thick plastic bags with small holes (perforation). Over time, a reduced oxygen content (2–3%) and elevated carbon dioxide content (up to 5–8%) are established inside, inhibiting respiration and ripening (Hochmuth & Sideman, 2023). However, be careful: if the holes are too small, an anaerobic environment can form, causing alcoholic fermentation and off-odors.
• Regular inspection. Even under ideal conditions, some fruits may spoil. Once a week, go through the stored plums and remove suspicious specimens. This significantly increases the overall storage time of the remaining fruits.

Following all these conditions will allow you to extend the enjoyment of fresh plums for several weeks, and sometimes months, which is especially valuable for late varieties that can be stored up to winter.

Storage Diseases

The main cause of losses during plum storage is fungal infections. Pathogens enter the fruit through micro-cracks, wounds, the stalk attachment point, or through intact skin in the case of some aggressive species. In a storage facility with high humidity and moderate temperature, fungi develop rapidly, moving from one fruit to another.

Physiological Disorders

These disorders are not related to infection — they arise from metabolic disturbances within the fruit, often due to varietal characteristics, growing conditions, or storage errors.

Violation of Storage Conditions as a Cause of Losses

In addition to diseases and physiological disorders, a significant portion of losses is caused by basic errors in organizing storage:

• Too high temperature — accelerates respiration, leads to rapid overripening, softening, moisture loss, and creates favorable conditions for fungi.
• Low humidity — causes wilting (see above).
• Too high humidity or condensation — promotes the development of molds and rots, especially gray mold.
• Insufficient ventilation — accumulation of ethylene and carbon dioxide accelerates aging, can cause physiological disorders, and also promotes the growth of aerobic fungi in oxygen deficiency.
• Improper packaging — airtight packaging without perforation leads to anaerobic respiration, alcohol formation, and off-flavors. Too dense packaging without gaps between fruits promotes infection spread upon contact.
• Mixing different batches — mixing fruits of different maturity stages (riper ones release ethylene and accelerate ripening of less ripe ones, leading to their quick spoilage) (Gull et al., 2023).

Practical Recommendations for Minimizing Losses

1. Start with proper harvesting (see Chapter 3) — this is the foundation.

2. Sort carefully (Chapter 4) — remove even slightly damaged fruits.

3. Ensure rapid cooling — the faster the fruits reach 0 °C, the longer they will keep.

4. Maintain stable conditions — do not allow sharp fluctuations in temperature and humidity.

5. Inspect regularly — every 1–2 weeks, examine the fruits, remove those on which spots have appeared or softening has begun. This prevents mass infection.

6. Use separate packaging for different varieties and batches.

7. Keep the storage clean — before storing the crop, treat walls and boxes with a solution of potassium permanganate or bleach.

When Losses are Inevitable

Even with all precautions, a small portion of fruits inevitably spoils. Usually, home storage losses do not exceed 10–15% over 2–3 months with good organization, but can reach 30–50% with serious violations. It is important not to get upset, but to analyze the reasons: what went wrong? Perhaps the variety is not intended for long-term storage, or there were unfavorable weather conditions this year that affected fruit quality.

In any case, even if some fruits spoiled, the remaining ones — those that are storing well — you can still use and enjoy your harvest.

Congratulations! You have gone through all the stages: from understanding the ripening processes to organizing storage and dealing with losses. Now you know how to harvest, sort, and store plums so that they bring you joy for as long as possible. May your harvest be plentiful and your storage successful!