Harvesting and storage

Top Condition – The Main Visual Cue

The most reliable indicator is the natural wilting and yellowing of the tops. In early and mid-early varieties, leaves and stems usually dry completely by the end of the growing season. The process starts with the lower leaves and gradually moves upward (De Jong et al., 2011).

Why does this work? The dying back of the tops signals that the plant has completed its vegetative cycle. Nutrients from the leaves stop flowing to the tubers, and maturation processes begin: the skin thickens, growth ceases, and starch accumulates.

Ideally, harvesting should begin no earlier than two weeks after the tops have completely died back (De Jong et al., 2011). During this time, the skin becomes tough enough to withstand mechanical damage during digging, and the tubers enter a natural dormant state, which is critical for long-term storage.

Skin Firmness – The Maturity Test

The simplest and most reliable way to check maturity is the "thumb test." Take several tubers from different plants and rub the skin with your thumb. If it easily peels or rubs off, the potato is not yet mature (De Jong et al., 2011). In a mature tuber, the skin is firm, tough, and does not scrape off under light pressure.

Why is this important? A thick, strong skin is the tuber's main defense against moisture loss and the entry of pathogens. During storage, tubers with damaged skin lose water many times faster (Dean, 1993). In addition, rot pathogens easily enter through wounds, especially under high humidity conditions.

Tuber Size and Variety Characteristics

Don't rely solely on size: it depends heavily on variety, weather, and cultivation practices. However, by maturity, tubers reach the typical size for the variety. Much more important is variety type:

• Early varieties mature faster, and their tops die back earlier.
• Mid-season and late varieties stay green longer, and their harvest is best done closer to autumn, even if the tops are still partially green.

What to do if time is short but the tops are still green? If frosts are approaching and the potatoes are clearly not maturing, you can resort to forced defoliation (cutting the tops). More on this in the next chapter.

Practical takeaway: The main signs of maturity are dying tops and firm skin. Harvest potatoes 2–3 weeks after the tops have completely dried. Don't rush if the skin easily rubs off – let the tubers ripen in the ground.

Why Cut the Tops?

Removing the aboveground part of the plant before harvest serves three main purposes.

1. Accelerating skin maturation and wound healing

As long as the tops are green, they continue to supply nutrients to the tubers. After removal, this flow stops, and the plant "switches" to the final stage: the skin rapidly thickens and toughens. This is critical for protecting tubers from moisture loss and infection during harvest and storage.

Research shows that to achieve the best "healing" of micro-wounds and skin strengthening, tubers should remain in the ground for at least two weeks after the tops die or are removed (De Jong et al., 2011). During this time, a strong protective layer of periderm forms.

2. Reducing the risk of tuber infection

This is especially relevant if the tops show signs of late blight (brown spots, white mold on the underside of leaves) or other fungal infections. Spores of these pathogens are easily washed by rain or dew into the soil and can infect tubers. If you cut and remove diseased tops 10–14 days before harvest, the spores remaining on the soil surface lose viability, and the risk of tuber infection drops sharply (Czerko et al., 2023). Otherwise, infected tubers placed in storage quickly rot and become a source of contamination for the entire crop.

3. Making harvest easier

Dry, cut stems don't tangle in diggers and don't interfere with separating tubers from the soil. This speeds up work and reduces the number of damaged tubers.

When and How to Cut Tops Properly

• Timing: Ideally, 10–14 days before planned harvest (De Jong et al., 2011). This is enough time for the skin to strengthen and for minor wounds to heal.
• Technique: In small plots, tops can be carefully cut with a hoe or pruner, taking care not to damage the tops of the tubers. The cut should be as low as possible, without disturbing the soil.
• Important caveat: Don't destroy tops too aggressively (e.g., by pulling them out with roots). Abrupt, rough removal of green mass can stress the tubers, manifesting as darkening of the vascular ring (especially near the stem end). This not only harms appearance but may affect taste during cooking (De Jong et al., 2011). So cutting should be gentle.

Special Case: Late Blight

If the tops show signs of late blight, simple cutting is not enough. Diseased tops must not only be cut but also immediately removed from the plot and destroyed (burned or buried at least half a meter deep). Leaving them on the bed or nearby is not an option – they remain a source of infection for the tubers, especially in rainy weather (Kemble, 2022). After removing diseased tops, wait the same 10–14 days before harvesting.

Practical Takeaway

Cut the tops 10–14 days before harvest if:

• the tops are still green and time is running out (e.g., frost is approaching);
• the tops are affected by fungal diseases (in which case, definitely remove them from the plot).

This strengthens the skin, "heals" micro-wounds, and reduces the risk of rot during storage. Avoid rough, damaging removal – cut carefully to avoid harming the tubers.

☀️ Dry or Wet Weather?

The best time for harvesting is dry, clear days. The soil should be loose and dry enough so that tubers separate easily from the earth, don't get dirty, and aren't damaged during digging.

Why is this important?

• Wet soil sticks to tubers, making them harder to clean. But the main danger is the increased risk of bacterial and fungal infections. Wet tubers stored without thorough drying are almost guaranteed to rot, especially if the skin has micro-wounds (Czerko et al., 2023).
• Additionally, wet tubers are harder to separate from the soil, and mechanical harvesting causes more damage.

Practical advice: If there are prolonged rains and the potatoes are already ripe, try to choose at least 2–3 dry days before harvesting to allow the soil to dry. If that's not possible, after digging, dry the tubers in a dry, ventilated place (under shelter, in a shed) for several days before storing.

Air and Soil Temperature

The ideal air temperature for harvesting is 13–18°C (55–65°F) (De Jong et al., 2011). In this range, tubers are least vulnerable to mechanical damage, and the skin dries and strengthens faster.

What to avoid:

• Harvesting at temperatures below 7°C. Tubers become more brittle – increasing the risk of cracks, skin abrasions, and hidden bruises. This is especially critical for large, juicy tubers. Damaged areas are ideal entry points for rot pathogens (De Jong et al., 2011).

• Harvesting in extreme heat (above 27°C). If tubers are left in the sun after digging, even briefly, it can cause:
• Sunburn – the skin turns brown, and the flesh underneath softens.
• Greening – even short exposure to light triggers the synthesis of solanine (a toxic glycoalkaloid). Such potatoes are inedible (Dean, 1993).

Recommendation: If harvesting falls during a hot period, do it in the early morning or late evening and immediately move tubers to the shade. Don't leave them in the sun even for an hour.

What If Frost Is Expected?

If frost is forecast and the tops are still green and potatoes aren't mature, the best solution is to cut the tops 10–14 days before the expected frost. This allows the tubers to ripen in the ground and strengthen their skin, even if the aboveground part has already been killed by frost (De Jong et al., 2011).

What not to do:

• Dig potatoes in frozen ground. This will inevitably cause massive damage – tubers will break and crack. Such potatoes practically won't store.
• Leave frozen tubers in the ground for long. If the soil has frozen, tubers left in it lose turgor, become watery, and rot quickly upon thawing.

Harvesting After Rain: Special Considerations

Sometimes you have to harvest in wet weather despite all risks. In that case:

1. Try to wait at least 1–2 days after rain for the topsoil to dry.

2. Thoroughly dry the dug tubers in a dry, well-ventilated room at 12–15°C for 5–7 days. This helps dry the skin and prevent rot (Czerko et al., 2023).

3. Do not put wet tubers into long-term storage – let them dry and go through the curing period first.

Practical Takeaway

• Best time to harvest: dry, warm days with air temperatures of 13–18°C.
• Don't dig: in rain, when soil temperature is below 7°C, or in extreme heat (above 27°C) – this leads to damage, disease, and storage losses.
• If weather is unfavorable: either postpone harvest or arrange thorough drying and a curing period before storage.
• If frost threatens: cut the tops 2 weeks before frost so tubers have time to ripen in the ground.

Choosing Tools and Digging Technique

For small plots, the best tools are pitchforks (preferably with flat, wide tines) or a special potato hook (De Jong et al., 2011). A spade is less preferred because it often cuts tubers.

Proper pitchfork technique:

• Insert the fork vertically or at a slight angle to the side of the plant, about 10–15 cm from the center, to avoid piercing tubers.
• Gently lift the soil clod, slightly rocking the fork to shake off soil.
• Lift the nest from underneath so tubers don't scatter.
• Don't pull potatoes by the tops – stems may break, leaving tubers in the ground (especially in dense soil).

Important: Don't dig in dry, hard soil without pre-moistening – it leads to increased tuber damage. If soil is too dry, water moderately a day or two before harvesting (but don't overwater!).

Gentle Handling – The Key to Successful Storage

Tubers are very vulnerable after digging. Even a minor drop can cause hidden bruises that appear days later as black spots under the skin – the so-called "bruise" (Dean, 1993).

Rules for gentle handling:

• Immediately place dug tubers in containers with smooth edges (plastic crates, buckets, bags, but not rigid baskets with sharp edges). Use containers without burrs or sharp corners.
• Do not throw tubers from a height. The permissible drop height is no more than 15–20 cm (De Jong et al., 2011). Better to carefully hand-place them.
• When transporting and transferring, try to let tubers "roll" over each other rather than fall and hit hard surfaces.
• Avoid drops from vehicles – use soft padding (burlap, straw) when unloading.

Why is this critical? Even invisible damage breaks the skin's integrity, allowing bacteria and fungal spores to enter tuber tissues. In storage conditions (high humidity, temperature), they multiply rapidly and cause rot. Also, bruised areas lose moisture faster than healthy tissue, leading to shriveling (Czerko et al., 2023).

Sorting Immediately After Digging

This is one of the most important but often ignored steps. Sorting right in the field or immediately after harvest lets you:

1. Select seed material. The smoothest, healthiest, variety-typical medium-sized tubers (50–80 g) should be set aside immediately – they won't mix with table stock and won't accidentally be eaten. This is especially important if you plan to plant your own potatoes next year.

2. Remove diseased and damaged tubers. Even one rotten tuber in the bulk can become a source of infection and ruin the whole crop. So all tubers with signs of disease (rot, cracks, spots, growths) or mechanical damage should be immediately culled and used first (for food, feed) or destroyed.

3. Separate by size. For long-term storage, medium and large, smooth tubers are best. Small tubers lose moisture faster and store poorly; use them for processing or eat them first.

Important: If you wash potatoes before storage (not recommended), do so only after complete drying and with disinfectants (e.g., weak potassium permanganate solution). But most experts advise not washing potatoes intended for long-term storage, as water removes the protective layer and promotes rot.

Seed Selection – Special Attention

If you're saving part of the crop for planting, seed potato selection deserves special care:

• Select tubers only from the healthiest, most vigorous plants that showed no disease and produced a good yield.
• Tubers should be typical for the variety in shape and color, with no signs of degeneration.
• Size – 50–80 g (about the size of a chicken egg). Larger ones can be used but are less economical (more planting material needed), while very small ones produce weak sprouts (Dean, 1993).
• Never use for seed tubers with signs of disease, mechanical damage, greening, or even suspicious spots – they may carry viral and bacterial infections.
• Store seed potatoes separately from table stock, at a lower temperature (2–4°C) and, ideally, with access to diffuse light to suppress sprouting (Sowa-Niedzialkowska, 2004).

What Absolutely NOT to Do When Digging

• ❌ Throw tubers onto hard surfaces (ground, concrete, metal sheets) – this causes hidden bruises.
• ❌ Leave dug potatoes in the sun even for 1–2 hours – this causes greening, sunburn, and quality loss.
• ❌ Pack wet, dirty tubers into tight bags without drying – inside, ideal conditions for rot develop.
• ❌ Shake and tumble potatoes from heights, drop from vehicles – this causes massive micro-damage.

Practical Takeaway

• Dig carefully – use forks, lift the nest from the side, don't pull tops, avoid drops.
• Immediately after digging, do a rough sort: separate seed potatoes, discard diseased and damaged tubers, divide by size.
• For seed, select the healthiest, variety-typical medium-sized tubers (50–80 g) and store separately.
• Don't wash potatoes before storage (except in extreme necessity).
• Avoid prolonged exposure of tubers to sunlight – move them to shade or under cover immediately.

Why Is a Curing Period Needed?

During harvesting, sorting, and transport, tubers inevitably get micro-wounds: skin abrasions, scratches, light bruises, stolon breaks. These injuries are "gateways" for rot pathogens and channels for intense moisture loss.

Potatoes are capable of "healing" such wounds. This natural protective process is called suberization. Under the damaged skin, cells begin to divide, and a new protective layer forms over the wound. Cell walls become impregnated with suberin – a waterproof polymer similar to cork. Suberin effectively seals the damage, preventing infection and moisture loss (Bethke, 2020).

Without a curing period, wounds remain open. Moisture is lost, tubers dry out quickly, and bacteria and fungi enter freely, causing rot (Czerko et al., 2023).

What Conditions Are Needed for Healing?

The speed and completeness of suberization depend on three factors: temperature, humidity, and air access.

Temperature:

• Optimal range: 12–15°C. At this temperature, healing takes 10–14 days (Dean, 1993; Czerko et al., 2023).
• At 18°C, the process speeds up to 7–10 days, but the risk of disease is higher, so 12–15°C is considered a safe compromise.
• At 10°C, healing stretches to 3–4 weeks.
• At temperatures below 5°C, suberization almost stops (Czerko et al., 2023). If you put potatoes straight into a cold cellar, all micro-wounds remain unhealed for the entire storage period – and rot will develop with doubled intensity.

Air Humidity:

• Optimal relative humidity – 90–95% (Dean, 1993). At this humidity, tubers don't lose turgor, and wounds heal faster.
• If humidity is below 85%, tubers start losing water intensively, skin wrinkles, and healing slows.
• If humidity is above 95% and ventilation is inadequate – condensation forms on tuber surfaces, which can trigger bacterial rot.

Air Access (Ventilation):

During curing, tubers respire actively, releasing heat, carbon dioxide, and water vapor. In a closed, unventilated space, oxygen is quickly depleted and CO₂ accumulates. This can lead to suffocation of tubers – internal tissues darken (so-called "black heart"), and tubers become unfit for storage (Bethke, 2020).

What to do:

• Provide natural air circulation (don't seal the room).
• If storing in crates, don't place them tightly against each other or walls.
• For large volumes, you can periodically run a fan briefly (5–10 minutes a day) to refresh the air.

How to Organize Curing at Home

In practice, for a gardener this means:

1. Immediately after harvest and sorting, place potatoes in a dry, dark room with temperatures of 12–15°C and good ventilation. This could be a shed, garage, unheated veranda, or warm basement.

2. Spread tubers in a thin layer (no more than 3–4 layers deep in crates or on the floor) so air circulates freely between them. Don't use dense bags – they lack ventilation and tubers will "suffocate."

3. Maintain high humidity. In a dry room, place containers of water, hang wet burlap, or periodically spray floors and walls (but not the tubers themselves!). Avoid water getting on tuber surfaces – it can cause rot.

4. Hold for 10–14 days. During this time, the skin becomes firm, and scrapes and scratches heal. A sign that curing is complete – "wet" areas on damaged skin disappear, and the skin feels "tougher."

5. Gradually lower the temperature to optimal long-term storage levels (4–6°C for table potatoes, 2–4°C for seed). Lower gradually, over 1–2 weeks, at about 0.5°C per day, to avoid stressing tubers. Sudden cooling can trigger sugar accumulation.

What If You Skip the Curing Period?

If you skip curing and put potatoes straight into a cold cellar (5°C or below), wounds will remain unhealed. As a result:

• Moisture losses will be significantly higher.
• The risk of bacterial and fungal rot multiplies, especially with temperature fluctuations.
• Potatoes will store worse even if all other conditions are met.

Conversely, if you keep tubers in optimal conditions for at least 7–10 days, storability improves noticeably even for less ideal varieties.

Practical Takeaway

• Before storage, always do a curing period: 10–14 days at 12–15°C and 90–95% humidity, with good ventilation.
• Don't put wet or freshly dug potatoes straight into a cold cellar – this stops wound healing.
• Ensure air circulation: don't pack tightly, use slatted crates, don't seal the room.
• After curing, gradually (over 1–2 weeks) lower temperature to 4–6°C for long-term storage.
• Remember: 10–14 days of curing "heals" all harvest micro-wounds and builds a solid foundation for long storage. It's worth the time!

Storage Temperature

Temperature is the main control factor. However, it differs depending on the intended use.

Important warnings:

• Do not store potatoes at below 2°C – this causes cold sweetening (sugar accumulation) and also damages tuber tissues, making them watery and sweet-tasting.
• Sharp temperature fluctuations (more than ±1°C per day) cause condensation on tubers and promote rot. Try to maintain stable temperature.
• Above 8°C, sprouting and respiration accelerate sharply, leading to rapid weight loss and quality decline.

Air Humidity

Potatoes are 75–80% water. During storage, they inevitably lose moisture through the skin – this is called transpiration (Czerko et al., 2023). If storage humidity is low, water losses increase, and tubers become limp, wrinkled, and lighter. Every percent of moisture lost is a direct yield loss.

Optimal relative humidity – 90–95% (Dean, 1993; Bethke, 2020).

How it works: Air humidity is near 100%, so the difference in water vapor pressure between the tuber's internal environment (near 100% humidity) and the surrounding air is minimal, and water evaporates slowly. Below 85% humidity, evaporation sharply increases – mass losses can reach 1–2% per month.

However, there's a nuance: At humidity above 95% and insufficient ventilation, condensation can form on tuber surfaces (especially with temperature fluctuations). Drop moisture is an ideal medium for bacteria and mold. So it's important not only to maintain humidity but also to ensure air movement to equalize it and remove excess.

Ventilation

Ventilation during storage serves three critical functions:

1. Removing excess heat (respiratory heat)

Tubers constantly respire – a complex biochemical process where carbohydrates are oxidized, releasing heat, carbon dioxide, and water. Immediately after storage and at the end of the storage period (during sprouting), respiration is most intense. If heat is not removed, the temperature in the bulk can rise 2–3°C above the set point, accelerating all undesirable processes (Czerko et al., 2023).

2. Removing carbon dioxide (CO₂)

Respiration releases CO₂. In an unventilated store, its concentration can exceed 1–2%. This leads to:

• deterioration of chip and fry color (due to sugar accumulation),
• increased bacterial rot,
• development of so-called "suffocation" – darkening of internal tuber tissues (Bethke, 2020).

The recommended threshold is no more than 0.5–1% CO₂ in the store air (Czerko & Zgórska, 2006). For this, daily ventilation for 30–40 minutes is sufficient, especially in the first 2 months and before sale.

3. Equalizing humidity and temperature throughout the volume

Without air movement, different parts of the store may develop zones with different humidity and temperature – where it's warmer, rot develops faster; where it's colder, condensation forms. Ventilation helps distribute heat and moisture evenly.

Practical recommendations:

• For small stores (cellar, basement), natural ventilation (supply and exhaust pipes) is sufficient. In winter, open vents for 20–30 minutes daily, especially if outside temperature is lower than inside – this helps both cooling and CO₂ removal.
• In large stores, forced ventilation with automatic temperature and humidity control is used.
• Avoid direct drafts on tubers – this increases moisture evaporation. Air should circulate above the bulk, not through it (except for active ventilation systems).

Darkness – An Absolute Requirement

Potatoes must be stored in complete darkness. Even brief exposure to light (daylight, lamps) triggers photosynthesis in tubers, producing chlorophyll (skin turns green) and simultaneously accumulating solanine – a toxic glycoalkaloid that gives a bitter taste and can cause poisoning (Dean, 1993).

• Green areas should be cut off, but with heavy greening, the whole tuber becomes inedible.
• Solanine is not destroyed by boiling or frying.
• Therefore, the store must be completely shaded: use lightproof covers, don't leave lamps on in the potato room, put tubers in dark crates or bags.

Summary Table of Storage Conditions

Practical Takeaway

• Maintain stable temperature according to potato use. Avoid sharp fluctuations.
• Ensure humidity of 90–95%. In a dry store, place water containers, moisten floors and walls. In very humid stores, increase ventilation.
• Ventilate regularly – even 30 minutes a day is enough to remove excess CO₂ and heat.
• Store in complete darkness – use dark covers, don't turn on lights unnecessarily.
• Regularly (every 2–3 weeks) inspect tubers – remove rotten ones, check temperature and humidity.

Following these simple rules will keep your crop in excellent condition until spring.

Rots

Rot is the most serious and common storage problem. It can destroy 5 to 30% or more of the crop if not addressed in time. There are several types of rot, each caused by different pathogens and developing under different conditions.

Sprouting

Sprouting is a natural process that begins after the dormancy period ends. Different varieties have different dormancy periods – from 2 to 6 months after harvest (Zarzyńska, 2018).

Why is sprouting harmful?

• Sprouts consume nutrients from the tuber – it becomes flabby, loses weight and taste.
• Sprouts increase moisture evaporation – tubers shrivel faster.
• Sprouted potatoes are unsuitable for sale and for many processing types.

What affects sprouting timing?

• Variety: some have short dormancy (sprout within 2–3 months) and some long (up to 6–7 months) (Czerko, 2013).
• Storage temperature: the higher the temperature, the faster sprouting begins. At 3°C – sprouting usually starts in April, at 5°C – late February, at 8°C – already in January (Czerko et al., 2023).
• Weather during growing season: excess rain in July–September delays sprouting, drought accelerates it (Zarzyńska, 2018).

How to prevent sprouting:

• Store at low temperature (4°C for table, 2–4°C for seed).
• For seed potatoes: storage with access to diffuse light is acceptable – it slows sprout growth and makes them sturdy (but not for table potatoes!).
• Use varieties with long dormancy if planning long-term storage.
• For large volumes, sprout inhibitors have been used (e.g., CIPC – chlorpropham, 1,4-dimethylnaphthalene, peppermint oil), but for gardeners they are of limited availability (Czerko et al., 2023). For the home grower, proper temperature is key.

What if sprouting has already started?

• If sprouts appear but are still small (1–2 mm) – try to lower temperature by 1–2°C to slow growth.
• If sprouts are already long (>1 cm), it's best to break them off. But remember, they may regrow even more vigorously.
• Use sprouted potatoes first, don't put them into long-term storage.

Greening

Cause: exposure of tubers to light (even diffuse, indirect) triggers chlorophyll synthesis and simultaneous accumulation of solanine – a toxic substance (Dean, 1993).

How it looks: Green spots appear on the skin, which can eventually cover the whole tuber.

Danger: Solanine gives a bitter taste and in large amounts can cause nausea, vomiting, stomach upset. It is not destroyed by cooking. Green potatoes are absolutely inedible.

How to prevent:

• Store potatoes in complete darkness – use dark rooms, cover crates with heavy cloth or film, don't leave lamps on unnecessarily.
• Don't store potatoes in the light, even in mesh bags – light penetrates through the mesh.
• When sorting or packing, work under minimal lighting.

What if greening occurs? Such potatoes can only be used for animal feed (in small amounts) or for planting (green color doesn't affect germination, but solanine may suppress sprout growth). But for food – absolutely not.

Shriveling (Moisture Loss)

Cause: evaporation of water through the skin – so-called transpiration. This is a natural physical process, but its intensity depends heavily on storage conditions (Czerko et al., 2023).

How it looks: Tubers become limp, wrinkled, lose firmness. Weight decreases, skin peels off.

What increases shriveling?

• Low air humidity (below 85%) – moisture evaporates intensely into the dry atmosphere.
• Intensive ventilation – strong airflow speeds evaporation.
• Damaged skin – through abrasions and cracks, moisture escapes faster.
• High temperature – the warmer, the higher evaporation rate.

How to prevent:

• Maintain humidity of 90–95%. In a dry store, place water containers, hang wet cloth.
• Don't over-dry potatoes during the curing period.
• Minimize damage during harvest and storage.
• Lower temperature to optimal levels – colder means slower evaporation.

What if shriveling has already started? Restoring turgor is almost impossible, but you can slow down the process by increasing humidity. Weight loss is irreversible yield loss, so prevention is more important than cure.

Summary Table of Storage Problems and Prevention

Practical Takeaway

The main secret to successful storage is a comprehensive approach:

1. Quality potatoes – mature, healthy, with firm skin.

2. Careful harvesting – minimum damage.

3. Full curing period – 10–14 days at 12–15°C to heal wounds.

4. Stable storage conditions – temperature 4–6°C (2–4°C for seed), humidity 90–95%, darkness, regular ventilation.

5. Regular monitoring – every 2–3 weeks, sort through potatoes, remove diseased tubers, check temperature and humidity.

Remember: catching a problem early is much easier than fighting widespread infection. Regular inspection is the gardener's main tool for preserving the harvest.