Growing from sets to turnips

1.1. Fraction (Size) — The Main Criterion

Set size directly affects final bulb size, maturity timing, and tendency to bolt (produce flower stalks). Sets are typically calibrated by diameter.

• Optimal size for a large bulb: 15–22 mm. This is the second group (fraction) according to standards used in Belarus and Russia (Autko et al., 2012). This size is considered best for a two-year crop, as it produces uniform germination, active growth, and minimal bolting.
• Large sets (22–30 mm and above): Using this material without special preparation (prolonged heating) is extremely risky. Larger bulbs are more likely to transition to the reproductive phase and bolt, especially if storage conditions were poor (Nonnecke, 1989). They are often used for green onion production (scallions) or very early harvests, but are not suitable for producing high-quality, storable bulbs.
• Small sets (10–15 mm): This is the first group. Such sets almost never bolt and store well, but they generally produce small to medium bulbs. They are ideal for growing pickling onions or green onions, but not for large commercial bulbs (Kemble, 2022).

Practical tip: When purchasing, choose uniform-sized sets. This ensures plants develop synchronously, simplifying care and harvesting.

1.2. Appearance and Condition

Healthy sets are your primary asset. When selecting, pay attention to the following:

• Firmness: Bulbs should be firm and springy to the touch. Soft, limp specimens indicate rot or improper storage.
• Skin: Dry outer scales should be dry, intact, and have the characteristic color of the variety (golden-yellow, white, or purple). Missing or damaged scales make the bulb vulnerable to disease.
• Neck: In quality sets, the neck should be thin, dry, and tightly closed. A thick, loose neck or signs of rot on it is a serious defect (Brewster, 2008).
• Basal plate: Examine the base (where roots attach). It should be dry, without signs of mold or blackened roots. A healthy base ensures rapid rooting.
• No mechanical damage: Avoid bulbs with cracks, dents, or bruises, as these are entry points for infections.

1.3. Variety and Regional Adaptation

This factor is as important as size. Success in onion cultivation depends on matching the variety to the day length and temperature of your region (Brewster, 2008; Nonnecke, 1989).

• Choose varieties listed in the official registries of your region. They have already been tested and proven productive under local conditions.
• Keep in mind: varieties intended for two-year culture (growing from sets) differ from those grown from seed in an annual crop. For sets, choose regionalized winter or spring varieties adapted to your climate. In Autko et al. (2012), varieties such as 'Vetraz st.', 'Stuttgarter Riesen', and 'Strigunovsky local' are recommended for two-year cultivation in Belarus. In northern regions, prefer more cold-hardy, pungent varieties; in southern regions, opt for sweet and semi-sweet varieties.

1.4. Storage Conditions Before Planting

This is a critical factor that many gardeners overlook. The fate of your harvest is largely determined by how the sets were stored. The main goal of storage is to prevent the bulbs from transitioning to generative development (bolting).

Optimal regime: The best way to store sets for a bulb harvest is the cold-warm method. In autumn and spring, keep them at +18...20°C, and in mid-winter (January-February) at –1...–3°C (Autko et al., 2012). Relative humidity should not exceed 70%. This delays the onset of growth processes and prevents bolting.

"Warm" storage: If sets were stored at a constantly high temperature (around +18...20°C) — this stimulates early sprouting and may lead to bolting after planting, as the process of vernalization (preparation for flowering) in many varieties occurs precisely in the range of low positive temperatures (Brewster, 2008). Therefore, such sets require mandatory warming before planting.

"Cold" storage: Storing at constantly low positive temperatures (around 0...5°C), on the other hand, can cause vernalization and provoke mass bolting. Such bulbs require pre-planting treatment with high temperatures to "awaken" vegetative buds and suppress generative ones.

Important note: If you buy sets in spring and do not know how they were stored, be sure to apply a warming procedure before planting (see Chapter 4).

Chapter summary: Choosing sets is a choice between a future harvest and disappointment. Choose firm, medium-sized bulbs (15–22 mm) with a dry neck and intact scales, suited to your region. Consider how the planting material was stored and be prepared for pre-planting preparation. Investing time in the right choice at the start lays the foundation for a generous and high-quality harvest of large onions.

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2.1. The Physiological Meaning of Calibration

The size of a set bulb is not just an indicator of its "age" or nutrient reserves. It determines the plant's physiological state.

• Nutrient reserves: Large sets have significantly more stored sugars and minerals, giving them a head start in growth. They root faster and form a more powerful leaf apparatus. However, as noted in the first chapter, larger size increases the risk of bolting because such bulbs have already progressed partway toward generative development (Brewster, 2008).
• Growth rates: Plants from different fractions will develop at different speeds. The first group (small) will produce later, weaker shoots, while the third group (large) will produce early, vigorous ones. If planted together, large bulbs will shade and suppress small ones. Ultimately, you won't get quality large onions from the large sets (they may bolt or produce coarse-necked bulbs), nor a full harvest from the small ones (Nonnecke, 1989).

Conclusion: By sorting sets, we aren't just separating by size; we are creating groups of plants with the same biological potential. This allows us to apply specific planting and care strategies for each group to maximize their potential.

2.2. Standard Set Fractions

In professional vegetable and seed production, a clear classification by bulb diameter is used. Following standards described in reference works (Autko et al., 2012), sets are divided into the following main groups:

Important! Depending on the region and variety, fraction boundaries may vary slightly. For multi-nest varieties (which form several bulbs from one), the second group may start at 15 mm, while for single-nest varieties, it may start at 10 mm (Autko et al., 2012). Always check recommendations for your specific variety.

2.3. What to Do with "Off-Grade" Material?

During calibration, damaged, diseased, or too-small bulbs (<10 mm) inevitably appear. They shouldn't be planted in the main bed for large bulbs.

• Very small sets (ovsyuzhka): Bulbs smaller than 10 mm are excellent for autumn (winter) planting. They don't bolt and produce an early harvest the following year.
• Damaged sets: Bulbs with rot, mechanical damage, or signs of disease should be discarded to avoid contaminating the soil and healthy plants. If such bulbs are few and still have a healthy portion, they can be used for forcing greens indoors.

2.4. Practical Calibration Tips

1. Start with visual inspection: Spread the sets on a table or clean surface. First, remove all suspicious bulbs: those with mold, soft spots, or damage.

2. Use a calibration sieve: The fastest and most accurate method. You can use a standard wire mesh with cells of the required diameter (10 mm, 15 mm, 22 mm). Passing bulbs through different-sized cells gives you clean fractions quickly.

3. Calibrate by hand: If you don't have a sieve, take the time to sort the sets "by eye." It won't take long, but it will be very beneficial. Keep templates handy, like a coin of a specific diameter.

4. Plant by groups: Be sure to plant each fraction separately. This allows you to precisely adjust planting density and depth, and predict harvest timing. Small sets can be planted more densely, large ones more sparsely.

5. Start with small sets: In field planting, it's recommended to plant small sets first, then medium, and large last (Autko et al., 2012). This is because small sets have a slightly longer growing season and tend to dry out faster in the air.

Chapter summary: Calibration is not tedious sorting, but creating "comfortable conditions" for each group of bulbs. By separating sets by size, you can accurately calculate planting rates, ensure uniform plant development, and ultimately achieve an even, high-quality, and well-stored onion harvest. Remember: planting different fractions together will only result in large bulbs suppressing small ones.

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3.1. Sorting and Final Inspection

Before starting active procedures, go through the sets again. After storage and transport, new damaged or rotting bulbs may have appeared. Remove any specimens with mold, softness, or mechanical damage. Remember: one diseased bulb can become a source of infection for the entire bed (Brewster, 2008).

3.2. Warming: The Key to Preventing Bolting

This is perhaps the most important preparation step if you are unsure of the sets' storage conditions. The bolting process (flower stalk formation) is triggered in many onion varieties by exposure to low positive temperatures (+2...+10°C) for a specific period. This is called vernalization (Brewster, 2008; Nonnecke, 1989). If sets were stored at such temperatures and then planted in the ground, they will likely bolt, and you won't get a large bulb.

Why warm them? High temperatures (+30...+40°C) suppress the vernalization process and switch the bulb's physiological processes toward vegetative growth (leaf and bulb formation) rather than generative growth (flowering). It's a kind of "reset" for the plant (Autko et al., 2012).

Warming methods:

1. Traditional (long-term): The simplest and most reliable method for home use. 2–3 weeks before planting, spread the sets in a thin layer (no more than 5–10 cm) in a dry, warm room at +20...+25°C. Place them near a radiator or in another warm spot. Periodically stir the bulbs for even warming. This method gradually "awakens" the buds and prepares them for active growth (Nonnecke, 1989).

2. Quick (emergency): If time before planting is short, you can use a more intensive method. 10–15 days before planting, heat the sets at +35...+40°C for 8–10 hours (Autko et al., 2012). This can be done in a drying cabinet, oven (with the door slightly open at minimal heat), or on a warm floor. Important: temperature must not exceed +40°C, otherwise the bulbs may "cook" and lose viability.

Important note: Warming is especially critical for large sets (22–30 mm) and for sets bought in spring from an unknown seller, as you don't know how they were stored.

3.3. Disinfection: Protection from Disease

Warming stimulates growth but does not protect against disease. The next mandatory step is disinfection of the planting material. Bulbs can carry spores of fungal and bacterial infections (e.g., downy mildew, neck rot, fusarium). Disinfection destroys pathogens on the scale surface and reduces the risk of field infection (Brewster, 2008; Kasynkina and Kudin, 2018).

Disinfection methods:

1. Soaking in copper sulfate solution: A classic and very effective method. Prepare a 1% copper sulfate solution (10 g per 1 liter of water). Soak the sets for 15–30 minutes. Afterward, rinse the bulbs with clean water and dry.

2. Soaking in potassium permanganate solution: A gentler but also effective method. Prepare a dark pink solution (1–1.5 g per 1 liter of water). Soak the sets for 30–40 minutes. Then rinse thoroughly and dry.

3. Thermal disinfection: An alternative to chemical methods, widely used in commercial production (Autko et al., 2012). Sets are heated for 8 hours at +40...+42°C or 10–12 hours in a warm air stream at +45...+47°C. At home, a vegetable dryer or oven with minimal heat and the door slightly open can be used. Strict temperature control is essential to avoid overheating.

Tip: After warming (either long or quick), the effectiveness of disinfection increases because the bulbs become more receptive to disinfectant solutions.

3.4. Growth Stimulation (Optional)

To accelerate germination and increase yields, some gardeners soak the sets in growth stimulant solutions (e.g., "Epin," "Zircon," "Humate") after disinfection. This is not mandatory but beneficial, helping plants adapt faster to stressful conditions after planting. Follow the instructions on the chosen product.

3.5. Final Step: Drying

After any water treatments (soaking in solutions), the sets must be thoroughly dried. Spread them in a single layer in a warm, well-ventilated area. Drying prevents basal rot and stimulates the formation of a protective film on the scale surface. The bulbs should feel dry to the touch and only then are they ready for planting.

Chapter summary: Proper set preparation is a set of measures aimed at "awakening" the plant, suppressing its tendency to flower, and protecting against disease. Warm the sets to neutralize the effects of cold storage and prevent bolting. Disinfect them to destroy surface pathogens. And don't forget to dry them before planting. By paying attention to these simple but crucial steps, you give your onions an excellent start and significantly increase your chances of a large, healthy harvest.

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4.1. Physiology of the Process: Why Do Onions Bolt?

Bolting (flower stalk formation) is a natural reproductive process for onions. However, for the gardener, it's a disaster: the plant channels all its energy into flowering and seed production, while the bulb either doesn't form at all or grows small, with a coarse, thick neck, and stores poorly (Nonnecke, 1989).

The key factor in triggering this process is vernalization — the effect of low positive temperatures (+2...+10°C) over a specific period (Brewster, 2008; Nonnecke, 1989). Sets stored under such conditions (e.g., in a basement or root cellar) undergo vernalization. By planting time, they are already "programmed" to flower. Once they enter warm soil, this mechanism is triggered.

The goal of warming is to disrupt this mechanism. High temperatures (above +20°C) block the effect of vernalization. They shift the bulb's physiological processes from the generative pathway (flowering) to the vegetative pathway (leaf growth and bulb formation). Simply put, we "trick" the plant into thinking winter is over and it's time to grow green mass, not waste energy on reproduction (Autko et al., 2012).

4.2. Who Needs Warming Most Urgently?

• Large sets (22–30 mm): They are most prone to bolting, so warming is essential.
• Sets bought in spring: You don't know their storage history. If stored at low temperatures, they will almost certainly bolt. Warming is your only insurance.
• Sets stored in a refrigerator or basement: If you stored sets at +1...+10°C, be sure to warm them before planting.

Exception: Small sets (ovsyuzhka, 1st fraction) almost never bolt, so warming is optional, though not harmful. They are often planted before winter without any preparation.

4.3. Warming Methods: From "Slow" to "Fast"

The choice of method depends on the time available before planting.

A. Long-term (natural) warming (3–4 weeks)

• Essence: 2–4 weeks before planting, spread the sets in a dry room at +20...+25°C.
• How to organize: Scatter the sets in a layer no more than 5–10 cm on shelves, on the floor, in boxes, or on nets. Ensure good ventilation to avoid sweating. Periodically stir the bulbs for even warming.
• Why it works: Gradual, gentle temperature increase awakens the apical bud and activates growth enzymes without sudden stress. It mimics the natural arrival of spring (Nonnecke, 1989).
• Ideal for: Home conditions and gardeners who have a warm room and time.

B. Quick (intensive) warming (8–12 hours)

• Essence: 10–15 days before planting, the sets are warmed at a higher temperature (+35...+42°C) for 8–12 hours (Autko et al., 2012).
• How to organize: At home, this can be done in an oven (at minimum heat with the door slightly open), in a vegetable dryer, or in a special heating cabinet. Use a thermometer to monitor temperature. After heating, bulbs should be cooled slowly.
• Why it works: Short exposure to higher temperatures provides a powerful "push" to awaken growth buds and reliably blocks the vernalization effect.
• Ideal for: "Emergency" cases when you bought the sets shortly before planting.

C. Contrast warming (combined method)

Some experienced gardeners use a technique combining both approaches. First, the sets are warmed at +35...+40°C for 8 hours, then at +20...+25°C for another 2–3 days. This gives maximum effect but requires more time and attention.

4.4. Common Warming Mistakes

1. Temperature too high (> +45°C): At this temperature, protein denaturation occurs inside the bulb cells. The sets may "cook" and lose viability. Even if they sprout, the shoots will be weak and deformed.

2. Insufficient warming time: If warming is too short (less than 6–8 hours at +35...+40°C), bolting may not be fully suppressed, and some plants will still bolt.

3. Warming wet sets: Do not warm bulbs immediately after soaking in water or solutions. This can cause steaming and mold growth. Warm only dry sets (Brewster, 2008).

4. Ignoring warming: The most common mistake. Many gardeners think it's unnecessary hassle. But by planting unwarmed sets, they often get not a harvest of bulbs, but a field of flowering stalks.

4.5. What If You Didn't Have Time to Warm?

If time is lost and planting is near, you can try to reduce the bolting risk by other means:

• Plant later: Wait until the soil warms to +15...+18°C. In warm soil, the bolting process slows down.
• Water with cold water: Right after planting, water the bed with cold well water. This creates a temperature shock that may disrupt the vernalization program. This method is less reliable but sometimes works.

Chapter summary: Warming sets is not just a recommendation but a mandatory agricultural practice for obtaining large, healthy, storable onions. It blocks the vernalization process that causes plants to bolt. Choose a convenient method—long or quick—and allocate time for this procedure. Investing just a few hours in warming will save you months of disappointment and reward you with a bountiful harvest.

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5.1. Why Is Disinfection Necessary?

• Protection during the critical period: Young roots and seedlings are most vulnerable to infections. Disinfected sets root faster and more easily, forming a strong root system.
• Disease prevention in the field: Treated sets are less affected by fungal and bacterial diseases throughout the growing season.
• Improved storability: Bulbs grown from disinfected sets store better over winter because they lack internal sources of infection.
• Saving effort: It's much easier and cheaper to treat sets before planting than to try to save diseased plants in the field (Kasynkina and Kudin, 2018).

5.2. Disinfection Methods: Choosing Your Method

There are several effective and accessible methods, each with its own advantages. Choose the one that suits you best.

5.3. Method Comparison: What to Choose?

5.4. Practical Tips and Warnings

1. Don't mix: Do not mix several chemical preparations in one solution unnecessarily. Use one method.

2. Observe timing: Do not over-soak sets in aggressive solutions (especially copper sulfate), as this can damage the base and delay germination.

3. Treat before planting: Disinfection is best done 1–3 days before planting, not a month earlier. This gives plants time to adapt but doesn't allow pathogens to "recolonize."

4. Don't treat sprouted sets: If bulbs have already sprouted, avoid soaking in aggressive solutions to avoid damaging tender roots. In this case, use biopreparations or thermal treatment.

5. Drying is mandatory: After any water soaking, dry the sets thoroughly. Wet bulbs planted in cold soil may rot.

Chapter summary: Disinfecting sets is your main tool in the fight against diseases that can destroy your harvest. Choose the most convenient and safe method for you—whether soaking in copper sulfate, potassium permanganate, or treatment with a biological product. By spending just 15–30 minutes on this procedure, you protect your plants from rots and infections, laying the foundation for healthy, large, and storable bulbs.

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6.1. Why Is Planting Timing So Important?

Onions are long-day plants. This means bulb formation begins when the day length reaches a certain critical length (Brewster, 2008; Nonnecke, 1989). If you plant the sets too late, the plant won't have time to develop sufficient leaf mass by the time bulb formation starts. As a result, the bulb will be small, and its maturation will be delayed. Conversely, early planting gives the plant an advantage: it has time to form a powerful leaf apparatus before the summer heat arrives, ensuring good "filling" of a large bulb.

Additionally, planting timing affects the bolting percentage. If sets get into cold soil (below +5...+10°C) and remain there for several weeks, this can stimulate the vernalization process, causing plants to bolt (Brewster, 2008). Therefore, it's very important not to rush planting.

6.2. Guidelines for Determining Planting Time

The ideal planting time depends on the climate zone, but there are universal guidelines to follow:

1. Soil Temperature — The Main Indicator

The most reliable way to determine soil readiness is to measure its temperature.

• Optimal soil temperature for planting sets: When the soil at a depth of 5–10 cm warms to +10...+12°C (Autko et al., 2012; Kasynkina and Kudin, 2018).
• Minimum temperature: Sets can begin rooting at +2...+5°C, but in cold soil, this process is slow, and bulbs become vulnerable to rots and diseases.
• Maximum temperature: Planting in overheated soil (above +15...+18°C) is not recommended, especially if regular watering is not possible. In dry, warm soil, rooting is poorer.

2. Approximate Calendar Dates

Although exact dates vary greatly by region, general periods can be identified:

• Southern regions (e.g., southern US, Mediterranean, Central Asia): Planting is done from mid-October to late January, allowing onions to form bulbs before the onset of intense summer heat (Kemble, 2022).
• Temperate zone (Europe, northern US, southern Canada, central Russia): The optimal time is late April to early May, when the soil warms to +10...+12°C.
• Northern regions (Scandinavia, Canada, northern Russia): Planting shifts to late May to early June, when the threat of return frosts has passed.

3. Folk Signs and Indicators

For those without a thermometer, time-tested signs exist:

• Bird cherry blossom: In the temperate zone, people often use bird cherry blossom or birch leaf emergence as signals that the ground has warmed sufficiently (Nonnecke, 1989).
• Spring bulbs: Mass flowering of tulips and daffodils also indicates it's time to plant onions.
• Spring work: As the saying goes: "Plant onions when the ground has warmed up but hasn't dried out so much that a squeezed handful crumbles." This means the soil still retains spring moisture—ideal for rooting.

6.3. Winter Planting (Autumn Planting)

For some regions and small sets (ovsyuzhka), winter planting is practiced. This allows for a very early harvest the following year, as onions start growing immediately after snowmelt.

• Timing: 2–3 weeks before the onset of stable frosts, when soil temperature drops to +5...+8°C (usually October–November).
• Advantages: Sets have time to root but don't sprout until spring. This gives them a growth advantage and protects against bolting (small sets don't bolt).
• Risks: If autumn is too warm, onions may start growing and freeze in winter. Therefore, only small sets (ovsyuzhka) and frost-resistant varieties are used for winter planting (Kemble, 2022; Nonnecke, 1989).

6.4. Regional Features

6.5. Practical Tips

1. Don't rush: The most common mistake is planting too early in cold soil. Bulbs may stay dormant, rot, or bolt. It's better to wait a week or two for the soil to warm.

2. Watch the forecast: If frost is expected after planting, cover the bed with agrofiber or plastic film. This protects the rooting bulbs from stress.

3. Consider the variety: Short-season varieties can be planted slightly later, long-season varieties slightly earlier. Always follow recommendations for your specific variety (Autko et al., 2012; Kasynkina and Kudin, 2018).

4. Planting by fraction: Small sets can be planted one to two weeks earlier than large ones, as they are more cold-resistant and bolt less often.

5. Air temperature: No less important than soil temperature. The optimal air temperature for rooting sets is +15...+20°C. In cool weather (+10...+15°C), growth slows.

Chapter summary: Choosing the right planting time is the foundation of the future harvest. Plant onion sets when the soil warms to +10...+12°C. Don't rush and don't be late: too early planting leads to bolting and disease, too late leads to small and immature bulbs. Consider your region's climate and variety recommendations. Remember: it's better to wait an extra week than to lose the entire harvest due to haste.

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7.1. Why Is Planting Depth So Important?

The depth at which you plant sets affects several key processes:

1. Bulb neck formation: This is the most important factor. If you plant sets too deep, the transition point from bulb to leaves (the neck) forms below the soil surface. This results in a thick, loose neck that dries slowly after harvest. This is an ideal entry point for neck rot pathogens and other diseases during storage (Brewster, 2008; Nonnecke, 1989). Correct depth ensures a thin, well-sealed neck that dries quickly and reliably protects the bulb from infections.

2. Rooting and growth: If planted too shallow, the set may end up on or very near the surface. In this case, the root system develops poorly, and the bulb may be pushed out of the ground by growing roots (called "heaving"). Additionally, shallow planting increases the risk of the bulb drying out in hot weather (Autko et al., 2012).

3. Bulb shape: Planting depth also affects the shape of the bulb. Deep planting often results in more elongated bulbs, while shallow planting produces flatter, rounder bulbs.

4. Frost protection: Optimal depth protects the base and growing roots from temperature fluctuations and possible return frosts that can damage young roots (Nonnecke, 1989).

7.2. Optimal Planting Depth

The golden rule for planting sets for bulbs is:

Optimal depth is 4–6 cm (Autko et al., 2012; Kasynkina and Kudin, 2018).

But what does this mean in practice? It means that from the top of the bulb (shoulders) to the soil surface should be about 2 cm. That is, you plant the bulb so that there is about 2 cm of soil above its "shoulders."

Why exactly 2 cm?

• This is enough for the neck to form at soil level and dry properly.
• It ensures good contact of the base with moist soil for rapid rooting.
• It allows the bulb to develop normally without being "suffocated" by too thick a soil layer.

7.3. How to Determine Depth Correctly

1. Prepare furrows: Make furrows about 5–6 cm deep.

2. Place the sets: Carefully place the bulbs in the furrow. They should sit with the base down, not lying on their side.

3. Cover with soil: Cover the bulbs with soil so that there is 2 cm of loose soil above the "shoulders."

4. Check: After covering, you can lightly firm the soil over the furrow to ensure good contact with the base. But don't overdo it!

7.4. Influence of Soil Type and Region

• Light (sandy, sandy loam) soils: On such soils, you can plant slightly deeper — up to 6–7 cm, as they dry out quickly and bulbs won't suffocate (Autko et al., 2012).
• Heavy (clay) soils: On heavy, cold, and wet soils, reduce depth to 3–4 cm. This allows onions to warm up faster and start growing.
• Southern and arid regions: In hot climates, planting depth can be increased to 5–6 cm to protect the bulb from overheating and moisture loss (Kemble, 2022).
• Northern regions: In cooler climates, shallower planting (3–4 cm) is preferred so bulbs warm up faster and start growing.

7.5. Bulb Size and Depth

The general rule: the larger the set, the deeper you plant it. For small sets (1st fraction, 10–15 mm), optimal depth is 3–4 cm. For medium sets (2nd fraction, 15–22 mm) — 4–5 cm. For large sets (3rd fraction, 22–30 mm) — 5–6 cm (Autko et al., 2012). This is because larger bulbs have more powerful root systems and deplete nutrients from the upper soil layer faster.

7.6. Common Mistakes

1. Too deep planting: A common beginner mistake. The bulb is deep underground, making it hard to push through to the surface. The neck forms thick and loose, leading to poor storability. Additionally, the bulb may be deformed and yield reduced.

2. Too shallow planting: The bulb "sticks out" of the ground, roots develop poorly, it dries out quickly, and may "heave" to the surface. The neck forms low, also impairing storage.

3. Planting without regard to size: If all bulbs are planted at the same depth without sorting by size, small ones will be too deep, and large ones too shallow, leading to uneven plant development and reduced yields.

4. Planting in cold soil: Even at the correct depth, if you plant onions in un-warmed soil, they may rot or bolt (see Chapter 6).

Chapter summary: Planting depth is a key factor influencing the size, quality, and storability of future bulbs. Plant onions so that there is 2 cm of loose soil above the bulb's "shoulders" (total depth 4–6 cm). Consider soil type, set size, and your region's climate. Remember: correct depth ensures a thin neck that dries quickly and reliably protects the bulb from diseases during storage.

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8.1. Why Is Density So Important?

Onions respond sensitively to the area available for growth. The space you give each bulb affects:

• Bulb size: This is the main relationship. The sparser the planting, the more space bulbs have to gain mass, and the larger they grow (Brewster, 2008; Nonnecke, 1989).
• Maturity timing: Dense plantings mature faster. High competition for light and nutrients accelerates bulb formation and maturation. This can be useful in short-summer regions but may result in smaller yields (Autko et al., 2012).
• Uniformity: Too dense planting leads to some plants being suppressed by neighbors, resulting in an uneven harvest: a few large bulbs and many small ones.
• Storability: Moderate density promotes better maturation and the formation of a thin, tightly sealed neck, which is critical for long-term storage. In dense plantings, bulbs may be smaller and store worse.

8.2. What Is Optimal Density?

Optimal density depends on several factors: set size, variety, region, and growing goals. But there are proven recommendations.

Key concept — feeding area per plant. To obtain a large bulb, a medium set (15–22 mm) needs a feeding area of about 100–150 cm². This means spacing of 8–12 cm between plants in the row with row spacing of 45–60 cm.

Recommendations for different set fractions (per 1 m²):

These figures are based on research and recommended in reference literature (Autko et al., 2012; Kasynkina and Kudin, 2018; Kemble, 2022).

8.3. How to Calculate Density in Practice?

In practice, density is determined by two measurements:

1. Row spacing: Depends on your tool (hoe, cultivator, tractor). Common options: 45 cm, 50 cm, or 60 cm.

2. Spacing between plants in the row: This is what you can directly control during planting.

Calculation example:

Suppose you plan to plant onions with 45 cm row spacing. The optimal density for medium sets is 50 plants per 1 m². To calculate the in-row spacing, divide the area (1 m² = 100 cm × 100 cm) by the density and by the row width (in meters).

1 m² = 100 cm × 100 cm. Row width = 45 cm = 0.45 m.

In-row spacing (cm) = (100 cm × 100 cm) / (50 plants/m² × 45 cm) = 10000 / 2250 ≈ 4.4 cm.

This spacing seems very small. However, in practice, when growing for bulbs, medium-sized sets (15–22 mm) are planted 8–12 cm apart. The resulting density is 40–60 bulbs/m².

Why is that? Because onions planted too closely don't form large bulbs. Increasing spacing to 10 cm significantly increases bulb size without drastically reducing total yield per square meter (Nonnecke, 1989). For maximum large-bulb yield, use 10–12 cm in-row spacing (Autko et al., 2012).

Important: Not all bulbs will produce 100% emergence. So you can plant slightly denser (by 10–15%) and thin after emergence, leaving the strongest plants at the desired spacing.

8.4. Regional Features

• Southern regions (arid): In hot climates, planting density is often increased to reduce moisture evaporation from the soil surface and speed up maturation. However, this results in smaller onions (Kemble, 2022).
• Northern regions (short summer): Here, density is decreased to give plants more time and space to gain mass before cold weather (Nonnecke, 1989).
• On organic (muck) soils: On fertile, moist organic soils, planting density can be higher than on mineral soils because they contain more nutrients and moisture (Nonnecke, 1989).

8.5. Planting Patterns

Different planting patterns exist depending on equipment.

• Wide-row planting: Classic for hand planting and small plots. Rows are 45–60 cm apart. This provides easy access for weeding and cultivation.
• Narrow-profile bed planting: For commercial production, beds 1–1.5 m wide are often used, with 4–6 rows spaced 15–25 cm apart (Autko et al., 2012). This allows higher density and higher yield per unit area.
• Twin-row planting: Two rows are planted close together (10–15 cm), with a wide path (60–70 cm) left for cultivation. This is a compromise giving good yields.

8.6. Practical Tips

1. Consider the variety: For vigorous varieties with large leaf canopies (e.g., 'Stuttgarter Riesen'), increase in-row spacing to 12–15 cm. For more compact varieties, reduce to 8–10 cm.

2. Don't overcrowd: It's better to plant slightly sparser than too dense. Overcrowding is a major cause of small bulbs.

3. Use markers: For uniform planting, use a marker board or string with marked intervals.

4. Thin out: If you planted too densely, thin when plants reach 10–15 cm. Remove the weakest and smallest specimens.

5. Consider fertility: On very fertile soils, you can slightly increase density since plants will have more nutrients available. On poor soils, reduce density so each plant gets enough resources.

Chapter summary: Planting density is your tool for managing bulb size and total yield. For large, well-storing bulbs, use medium sets (15–22 mm) and plant them 10–12 cm apart in the row with 45–60 cm between rows. This provides optimal feeding area and allows each bulb to reach its full potential. Remember: it's better to plant slightly sparser than too dense — ultimately, you'll get a higher quality and more uniform harvest.

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9.1. Phase 1: Rooting and Leaf Growth (from Planting to 5–6 Leaves)

This period starts right after planting and lasts about 3–4 weeks. During this time, the bulb develops its root system and leaf apparatus.

Gardener's goal: Ensure rapid rooting and active green mass growth. This is when the potential of the future bulb is established: the more leaves the plant forms before bulb formation begins, the larger the bulb will be (Brewster, 2008; Nonnecke, 1989).

Main activities:

1. Watering:

• How to water: At this stage, onions especially need moisture. The root system is shallow and poorly developed, so it can't draw water from deep soil layers (Brewster, 2008). The soil should be consistently moist but without waterlogging.
• Rate: Water moderately but regularly, especially in dry, windy weather. Approximately 10–15 liters per 1 m² per week, depending on weather.
• Why: Moist soil promotes rapid rooting and leaf growth.

2. Cultivation and weeding:

• How to do: After each watering or rain, when the soil has dried slightly, do shallow cultivation (2–3 cm deep) to break the soil crust and allow oxygen to reach the roots.
• Why: Cultivation improves soil gas exchange, stimulating root growth. Weed control is critical because weeds are strong competitors for moisture and nutrients and can severely suppress young onion seedlings.

3. First feeding:

• When: 2–3 weeks after emergence, when plants have formed 2–3 true leaves (Autko et al., 2012; Kasynkina and Kudin, 2018).
• What to feed: Nitrogen fertilizers (ammonium nitrate, urea, manure or poultry manure infusion). For example, 15–20 g ammonium nitrate per 10 liters of water (rate: 10 liters per 1–2 m²).
• Why: Nitrogen stimulates leaf growth. The more green mass the plant accumulates before bulb formation starts, the larger the bulb will be.

Important: During this period, don't use phosphorus and potassium fertilizers — they are needed later when the bulb begins to form.

9.2. Phase 2: Bulb Formation and Filling (from 5–6 Leaves to Leaf Lodging)

This is the most important stage when the plant switches from leaf growth to forming a storage organ — the bulb. This period lasts 4–6 weeks.

Gardener's goal: Provide conditions for maximum bulb filling: change the feeding and watering regime to redirect the plant's energy from leaves to the bulb.

Main activities:

1. Watering:

• How to water: Watering remains important because the bulb is actively filling and needs moisture. But the watering rate can be slightly increased.
• Rate: 15–20 liters per 1 m² per week depending on weather.
• Why: Moisture is necessary for transporting nutrients from leaves to the bulb.
• Important: Avoid sharp fluctuations in moisture (drought then flood). This can cause bulb cracking.

2. Second feeding (main):

• When: 2–3 weeks after the first feeding, when bulb formation begins (usually late June to early July) (Autko et al., 2012; Kemble, 2022).
• What to feed: Phosphorus-potassium fertilizers. For example, 20–30 g superphosphate and 15–20 g potassium sulfate (or potassium salt) per 10 liters of water. You can use complex fertilizers labeled "autumn" or specialized onion fertilizers.
• Why: Phosphorus and potassium stimulate the movement of nutrients from leaves to the bulb, promote thickening, and improve storability. Nitrogen should be reduced or eliminated at this stage to prevent the plant from continuing to "fatten" and delaying maturation.

3. Cultivation and weeding:

• Continue regular cultivation and weed removal. Especially important to prevent soil crust formation.

4. Hilling (optional but beneficial):

• In some cases, to make bulbs rounder and better matured, you can lightly hill the plants, covering the bulb base with soil. However, many gardeners skip this as it may delay maturation. In commercial production, hilling is often not practiced (Nonnecke, 1989).

9.3. Phase 3: Maturation and Preparation for Harvest (Leaf Lodging)

This is the final stage when bulb growth slows and then stops. The sign of this phase is yellowing and lodging of leaves. This signals that onions are ready for harvest.

Gardener's goal: Speed up maturation and prepare bulbs for storage.

Main activities:

1. Stop watering:

• When: As soon as leaves begin to yellow and lodge (usually 2–3 weeks before harvest) (Autko et al., 2012).
• Why: Excess moisture at this stage delays maturation, promotes disease development, and impairs storability. The bulb neck must dry well to close tightly.

2. Fertilizing:

• No fertilizing is done at this stage. The plant should use nutrients stored in the leaves to complete bulb formation.

3. Accelerating maturation:

• Forced lodging: If leaves refuse to lie down, you can gently bend them to the ground to speed up nutrient transfer to the bulb.
• Root pruning: 1–2 weeks before harvest, some gardeners cut the roots with a shovel at 5–10 cm depth. This disrupts nutrient supply and accelerates maturation. However, this operation requires care to avoid damaging the bulb base.
• Bulb exposure: You can gently pull soil away from the bulb top so it warms better in the sun and matures faster.

9.4. General Care Principles Across All Phases

• Pest and disease control: Throughout the growing season, regularly inspect plants. At the first signs of disease or pests (onion fly, downy mildew, neck rot), take appropriate measures (Autko et al., 2012; Kemble, 2022).
• Proper watering: Water onions only at the base, avoiding wetting the leaves. This reduces the risk of fungal diseases.
• Mulching: Using mulch (straw, peat, compost) helps retain soil moisture, prevents weed growth, and protects bulbs from overheating.

9.5. Summary Table of Care by Phases

Chapter summary: Onion care changes with each growth phase. At the beginning, focus on nitrogen fertilizing and regular watering to build a powerful leaf canopy. During bulb formation, switch to phosphorus-potassium fertilizers and abundant watering to ensure bulb "filling." 2–3 weeks before harvest, stop watering so onions mature well. Regular cultivation, weeding, and pest/disease protection are mandatory throughout. By following these simple rules, you can grow large, healthy, storable onions.

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10.1. Why Do Onions Bolt? The Physiology

Bolting is a generative process — reproduction. For onions, it's a natural response to unfavorable conditions or a signal that it's time to leave offspring. The key factor triggering this mechanism is vernalization — exposure to low positive temperatures (Brewster, 2008; Nonnecke, 1989).

How it works:

1. During storage (autumn–winter), sets are exposed to low temperatures (usually in the range +2...+10°C).

2. If this exposure lasts long enough (from several weeks to several months, depending on the variety), the bulb "remembers" this cold.

3. When such sets are planted in spring in warm soil, they "think" they have survived winter and it's time for flowering and reproduction.

4. As a result, instead of forming a bulb, the plant directs energy to growing a flower stalk.

Thus, the key cause of bolting is improper storage temperature, specifically exposure to low positive temperatures during the critical period.

10.2. Factors Influencing Bolting

Several factors affect onion bolting tendency:

1. Set size: Large sets (22–30 mm and larger) are significantly more prone to bolting than small ones (10–15 mm). This is because large bulbs have greater nutrient reserves and pass through the vernalization stage faster. Small sets (ovsyuzhka) almost never bolt (Autko et al., 2012; Nonnecke, 1989).

2. Storage conditions: As mentioned, storage at +2...+10°C for a long period is the main bolting trigger. The period from January to March is especially critical, as generative buds are formed then.

3. Planting timing: Planting sets in too cold soil (below +5...+8°C) can trigger bolting, especially if the sets were already partially vernalized during storage (Nonnecke, 1989).

4. Variety predisposition: Some varieties are genetically more prone to bolting than others. For example, pungent varieties usually bolt more than sweet and semi-sweet ones (Autko et al., 2012). Choose varieties recommended for your region and resistant to bolting (e.g., 'Stuttgarter Riesen,' 'Strigunovsky Local,' 'Bessonovsky Local').

10.3. Comprehensive Measures to Prevent Bolting

Preventing bolting is a comprehensive task that starts with choosing sets and ends with proper planting. Here are key steps:

A. Choosing the Right Sets

• Prefer small sets: For large bulbs, use first and second group sets (10–22 mm). Third group sets (22–30 mm) should only be used for early green forcing.
• Buy certified sets: When purchasing, pay attention to variety and characteristics. Choose bolting-resistant varieties.

B. Proper Storage

• Cold-warm storage method: This is the best way to store sets to prevent bolting. In autumn and spring, store at +18...+20°C, and in winter (January–February) at –1...–3°C (Autko et al., 2012). This temperature change disorients the plant and blocks vernalization.
• Warm storage method: If you can't maintain a cold-warm regime, store sets at a constantly high temperature (+18...+20°C) and low humidity (no more than 70%). This also prevents vernalization, though it may cause some drying of bulbs (Brewster, 2008).
• Avoid refrigerator storage: Storing sets in a household refrigerator (at +4...+6°C) is almost a guaranteed path to bolting, as this temperature range promotes vernalization.

C. Pre-Planting Preparation (Warming)

• If you don't know how the sets were stored, or if they were stored at low temperatures, be sure to warm them before planting (see Chapter 4). Warming at +35...+40°C for 8–12 hours suppresses the vernalization effect and switches the plant to a vegetative development path (Autko et al., 2012).

D. Correct Planting Timing

• Plant sets when the soil warms to +10...+12°C (see Chapter 6). Planting in cold soil increases bolting risk.

E. Plant Care

• Provide balanced nutrition: Don't overfeed onions with nitrogen, especially early in the season. Excess nitrogen can stimulate bolting. Apply phosphorus-potassium fertilizers on time, which promote bulb formation rather than flowering (Nonnecke, 1989).
• Regular watering: Keep the soil moist, especially in early growth. Drought stress can also trigger bolting.

F. What to Do If Bolting Occurs?

If you notice some plants have bolted, don't despair.

1. Remove flower stalks as early as possible: Carefully break off the flower stalk at the base as soon as it appears. This won't save the bulb itself (it won't grow large), but it will preserve the mass already accumulated.

2. Use such plants for greens: Bolting plants won't produce good bulbs, but their leaves can still be eaten. They can also be used for seed production if needed.

3. Analyze mistakes: Think about what went wrong: improper storage, no warming, too early planting, or unsuitable variety. Learn for next season.

10.4. Summary Table: Bolting Causes and Control Methods

Chapter summary: Preventing bolting is not a single action but a set of measures, from choosing sets to proper care. The main goal is to prevent vernalization — exposure of sets to low positive temperatures. Use cold-warm storage, warm sets before planting, don't rush planting, and choose the right varieties. If bolting does occur, remove the stalks early. By understanding the physiology, you can effectively control bolting and each year harvest abundant yields of large, healthy onions that will delight you all winter.

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