Growing from seed

What Is a Mother Bulb?

A mother bulb is a bulb specially selected and stored over winter to produce seeds the following year. The entire seed production process revolves around this key element: it is the mother bulb that determines the variety, quality, and yield of the future progeny.

How Does Bolting Occur?

The transition from vegetative growth to generative (flowering) in onion is triggered by a complex set of factors. It is important to understand that bolting is not a deviation but a natural process built into the plant (Brewster, 2008). However, in some varieties and under some conditions it occurs easily, while in others it is difficult.

The bolting process goes through several key stages (Brewster, 2008; Nonnecke, 1989):

1. Vernalization (flowering induction). While in a dormant state, the mother bulb must receive a signal to switch to flowering. This signal is exposure to low temperatures. This stage is the most important and the most “breaking” point in home seed production. If the bulb does not receive the necessary cold stimulus, it will not produce a stalk the following year but will only produce new greenery and possibly daughter bulbs (Nonnecke, 1989).

2. Formation of the stalk primordium. After the bulb has been vernalized, a primordium of the future flower stalk begins to form inside it at the growing point (Brewster, 2008). At this time, the bulb shows no external changes.

3. Growth and emergence of the stalk. In spring, when growth resumes, the stalk primordium starts to grow actively and pushes through the neck of the bulb. A characteristic dense stem—the stalk—appears, which elongates and forms an umbel inflorescence at its tip.

Why Is It Important to Understand This Process?

Without understanding the biennial cycle and the role of vernalization, you will not succeed in growing your own seeds. The most common mistake among beginner seed growers is trying to get a stalk from a bulb that was stored in too warm conditions over winter. Such a bulb does not receive the cold signal and instead of bolting, it only produces leaves (Brewster, 2008).

Knowing the stages of the process allows you to control each of them: select bulbs correctly, create conditions for vernalization, plant them at the right time, and help strong stalks grow (Nonnecke, 1989).

Remember: producing onion seeds at home is a two‑season task. But the result—your own healthy planting material—is worth the effort.

Varietal Purity: Why It Matters

If you want to preserve varietal purity, keep only bulbs that are typical of the variety for propagation. Onion is a cross‑pollinated crop, and when different varieties are grown close together, cross‑pollination can occur (Nonnecke, 1989; Autko et al., 2012). However, for home seed production on a small plot, the main thing is to select bulbs that match your variety in shape, colour of dry scales, and firmness.

Mother bulbs should be:

• Typical of the variety in shape (round, flat, oval, etc.)
• Typical in colour of dry scales (yellow, white, purple)
• With the characteristic nest‑forming habit (number of growing points) of the variety

Bulbs with deviations—too elongated, with atypical colour, or with an abnormal number of growing points—are discarded (Autko et al., 2012; Balashev and Zeman, 1981).

What Bulb Size Is Optimal?

The size of the mother bulb directly affects the probability of bolting and the number of seeds. Bulbs that are too small often do not undergo vernalization and will not bolt the following year (Brewster, 2008). Bulbs that are too large may produce many stalks but are sometimes less resistant to diseases during storage.

Practical recommendations for the gardener:

• Optimum diameter of the mother bulb: 5–8 cm. These are fairly large but not giant specimens.
• For pungent varieties with a high number of growing points, bulbs of 4–6 cm in diameter can be left.
• For sweet and semi‑pungent varieties (which are usually single‑growing‑point types) — 6–8 cm (Autko et al., 2012; Balashev and Zeman, 1981).

Why this works: bulbs of a certain size have already formed enough leaf primordia to switch to generative development after vernalization. In very small bulbs, the vegetative buds have not yet reached the required level of development (Brewster, 2008).

Bulb Health: What to Look For

Diseased bulbs not only fail to produce quality seeds but can also become a source of infection for the entire plot. During autumn selection of mother bulbs, check each one:

Discard bulbs with signs of:

• Neck rot — softening and darkening of tissues in the neck area (Autko et al., 2012)
• Basal rot (Fusarium) — pink or white mould on the base, softening (Brewster, 2008; Autko et al., 2012)
• Mechanical damage — cuts, dents, cracks through which infections enter
• Signs of mould (black or green) on the dry scales
• Too thick, insufficiently dried neck — such bulbs store poorly and rot quickly (Balashev and Zeman, 1981)

Timing of Selection: Autumn and Spring

Experienced seed growers carry out selection in two stages (Autko et al., 2012; Balashev and Zeman, 1981):

1. Autumn selection — immediately after harvesting and drying the crop. At this stage, the most typical, healthy, well‑ripened bulbs of the required size are selected. They are put into winter storage.

2. Spring selection — 2–3 weeks before planting. Bulbs are sorted again, removing all that have rotted, sprouted prematurely, or show signs of disease. Only healthy specimens are kept.

Spring selection is extremely important: even perfectly selected bulbs in autumn can deteriorate over winter. Do not neglect this step.

How Many Bulbs to Leave?

For an amateur gardener, leaving 10–20 mother bulbs for seeds is sufficient. From one medium‑sized bulb with good care, you can obtain up to 5–10 g of seeds (nigella), which is enough for sowing several beds (Nonnecke, 1989). If you plan to sell seeds or supply several plots, increase the number of mother bulbs proportionally.

Practical Takeaway

When choosing mother bulbs, follow a simple rule: better five excellent ones than twenty doubtful ones. Concentrate your efforts on a small number of the healthiest and most variety‑typical specimens. This is the key to a good seed harvest without losses from rots and diseases.

Why Does Onion Flower at All? The Role of Vernalization

Onion switches to generative development (bolting) only after the bulb has been exposed to low temperatures for a certain period. This process is called vernalization (Brewster, 2008; Balashev and Zeman, 1981).

Vernalization is not just “cooling”. It is a complex physiological process during which, in the growing point (meristem), there is a switch from the programme of forming vegetative buds to the programme of forming a flower stalk primordium (Brewster, 2008). If the bulb does not receive the necessary cold stimulus, it remains vegetative and the following year will produce only green leaves and possibly daughter bulbs instead of a stalk.

Key conclusion: without properly organised winter storage, mother bulbs will not flower. This is the main reason for failures among beginner seed growers.

Optimal Temperature for Vernalization

For most onion varieties, the optimal temperature range for vernalization is +2…+10°C (Brewster, 2008; Nonnecke, 1989). However, the effectiveness of vernalization depends not only on temperature but also on its duration:

• At +9…+12°C vernalization proceeds faster than at +3…+5°C, but a longer period is required to consolidate the effect (Brewster, 2008).
• Some varieties (especially Japanese and intermediate‑day types) require more precise temperature regimes for bolting (Autko et al., 2012).
• At temperatures above +18°C, vernalization does not occur, and an already initiated process can be reversed (devernalization) (Brewster, 2008).

Practical recommendation for gardeners: store mother bulbs at +2…+6°C for at least 2–3 months. This regime ensures reliable vernalization for most varieties grown in temperate climates (Balashev and Zeman, 1981; Autko et al., 2012).

Humidity During Storage

Humidity is as important as temperature. Air that is too dry causes desiccation and weight loss of bulbs. Air that is too moist promotes the development of rots and premature sprouting.

Optimal relative air humidity for storing mother bulbs is 70–80% (Autko et al., 2012; Balashev and Zeman, 1981). At humidity above 80%, the risk of neck rot (Botrytis allii) and other fungal infections increases sharply (Brewster, 2008). At humidity below 60%, bulbs dehydrate heavily, lose viability, and undergo vernalization less effectively.

How to maintain proper humidity at home:

• Store bulbs in a dry, well‑ventilated place (cellar, basement, dry garage).
• Do not store them near vegetables that release a lot of moisture (potatoes, beetroot).
• Periodically check the condition of the bulbs and remove suspicious specimens.
• If the air is too dry (e.g., in a heated room), you can place a container of water to increase humidity, but avoid direct contact of bulbs with water.

How and Where to Store Mother Bulbs

Mother bulbs selected in autumn are stored in a well‑dried state. The moisture content of the bulbs before storage should be minimal—dry scales should rustle (Autko et al., 2012).

Storage methods for a small holding:

• In boxes or baskets — in a layer of no more than 2–3 bulbs to allow air circulation.
• In mesh bags — hung for better ventilation.
• On shelves — in a single layer.

Do not store bulbs in plastic bags or closed containers—this leads to condensation and rapid rotting (Balashev and Zeman, 1981).

Risks and How to Avoid Them

1. Rots (neck rot, basal rot). Prevention: thorough drying after harvest, selection of healthy bulbs, maintaining humidity not above 80%, regular inspection.

2. Premature sprouting. If storage temperature rises above +10°C, bulbs may start growing too early, weakening them for planting and reducing seed yield (Nonnecke, 1989).

3. Desiccation. If humidity falls below 60%, bulbs become flabby and lose viability. In that state, they root poorly after planting.

4. Mixing varieties. If you store several varieties, be sure to label each batch so you don’t mix them up in spring.

What Not to Do

• Store mother bulbs at room temperature (+18…+22°C) all winter—vernalization will not occur.
• Store them in a damp basement or cellar with constant humidity above 85%.
• Allow sharp temperature fluctuations, especially crossing 0°C—although onion tolerates short‑term frosts, prolonged freezing can damage tissues and cause rots.

The Bottom Line: Stability Is the Key

Bulbs do not require complex conditions, but they need stability. Sharp changes in temperature, dampness, and lack of ventilation all increase the risk of losing mother bulbs. Stable cold (+2…+6°C) and moderate humidity (70–80%) are all that is needed for successful vernalization and healthy bulbs by spring planting.

Warming Up: Awakening the Bulb After Cold

After long storage at low temperatures, bulbs are in a state of deep dormancy. To “wake” them and start growth processes, a gradual increase in temperature is needed. This is called warming up.

Why warm up:

• Warming stimulates the transition from dormancy to active vegetation (Brewster, 2008).
• It helps “fix” the vernalization effect and accelerates stalk emergence after planting (Nonnecke, 1989).
• During warming, the bulbs’ defence mechanisms are activated, increasing their resistance to field diseases (Autko et al., 2012).

How to warm up correctly:

• Start warming the mother bulbs 2–3 weeks before planting.
• Move them from cold storage to a room with a temperature of +18…+22°C.
• It is important that the temperature increase is gradual: do not move bulbs from cold to strong heat in one day—this causes stress and may provoke the development of rots (Balashev and Zeman, 1981).
• During warming, bulbs should be in a dry, well‑ventilated place, preferably in a single layer to allow air to circulate freely.

Additional thermal disinfection method:

Some gardeners, 10–15 days before planting, warm set (small bulbs) at +40…+42°C for 8 hours or in a stream of warm air at +45…+47°C for 10–12 hours (Autko et al., 2012). This method is also suitable for mother bulbs, but care must be taken not to overdry them. It helps destroy the agents of certain diseases (e.g., neck rot) and speeds up bud awakening.

Spring Sorting: Final Selection

Spring sorting is the last opportunity to discard bulbs that did not survive winter or are unsuitable for seed production. This is a mandatory step.

What to do:

• Carefully inspect each bulb.
• Remove all specimens with signs of rot, mould, or soft spots.
• Discard bulbs that have sprouted prematurely (produced green leaves) or, conversely, have dried out and become flabby.
• Keep only firm, healthy bulbs with well‑preserved dry scales, typical of the variety in shape and colour (Autko et al., 2012; Balashev and Zeman, 1981).

Important: even if a bulb seems healthy but has a very thick, insufficiently dried neck, it is better not to use it—it will store poorly and may rot after planting without producing a stalk (Balashev and Zeman, 1981).

Neck Trimming: Why and How

Trimming the upper part of the mother bulb is a common agronomic practice that offers several advantages.

Advantages of trimming (Balashev and Zeman, 1981; Nonnecke, 1989):

• Speeds up sprouting: trimming stimulates the buds to awaken, and stalks appear faster.
• Reveals hidden infection: if rot is starting inside the bulb, it will be visible on the cut (darkening, softening). Such bulbs can be discarded before planting.
• Facilitates access to the growing point: this promotes more uniform stalk emergence.

How to trim correctly:

• Trim 1–2 days before planting (Balashev and Zeman, 1981).
• Cut off the upper (“neck”) part of the bulb so as to slightly touch the tips of the inner closed fleshy scales, but without damaging the growing point itself, which is in the centre of the base.
• The cut should be smooth, without jagged edges. Usually about 1/4–1/3 of the bulb height is removed, but the exact depth depends on the variety (more is cut from bulbs with an elongated neck, less from flat ones).
• For some varieties (especially those with very firm bulbs), trimming may be omitted, but in practice it almost always gives a positive effect.

Alternative to trimming: you can simply make shallow cross‑cuts on the top of the bulb—this also stimulates bud awakening.

Disease Treatment

To protect mother bulbs from soil‑borne infections (fungi, bacteria) after planting, it is recommended to carry out pre‑planting dressing.

Recommended methods for the amateur gardener:

• Soaking in a fungicide solution. For example, in a 3% suspension of TMTD (8–10 ml per 1 kg of bulbs) for 15–20 minutes, followed by drying (Autko et al., 2012). Note: there are modern fungicides safe for home use; follow the instructions.
• Heating (described above) also has a disinfecting effect.
• Some sources recommend dusting with crushed charcoal or a mixture of charcoal and ash—this is a simple folk method that dries the surface and reduces the risk of rots.

Caution: if you use chemical products, strictly follow the dosage and safety measures indicated on the packaging. For a small number of bulbs, you can use milder agents, such as a solution of potassium permanganate (medium strength), in which bulbs are soaked for 20–30 minutes.

Final Checklist for Preparing Mother Bulbs

To avoid missing anything, here is a brief sequence of actions:

1. 2–3 weeks before planting — move mother bulbs to a warm room (+18…+22°C) for warming.

2. 10–15 days before planting (optional) — carry out thermal treatment for disinfection (if possible).

3. 1–2 days before planting — carry out spring sorting, removing all diseased, dried‑out, or sprouted bulbs.

4. On the same day (or the day before) — perform neck trimming to speed up sprouting and reveal hidden rots.

5. Immediately before planting — treat bulbs with a fungicide or potassium permanganate solution to protect against soil pathogens.

6. Dry the treated bulbs in the shade (not in the sun!) until planting.

Proper preparation of mother bulbs is an investment in your future seed harvest. It does not require much time but significantly increases the chances of obtaining strong, healthy stalks and abundant flowering.

Planting Timing: The Earlier, the Better

Mother onions are planted at the earliest possible date, as soon as the soil allows. This is one of the main rules of seed production.

Why it is so important to plant early:

• Onion roots actively grow at soil temperatures of +2…+4°C, while the above‑ground part begins to develop later. Early planting allows a powerful root system to form before summer heat sets in (Balashev and Zeman, 1981; Autko et al., 2012).
• Early rooting increases plant resistance to spring frosts and gives them a growth advantage (Nonnecke, 1989).
• The earlier the mother bulbs are planted, the sooner they start growing and the earlier they produce stalks. This is especially important in regions with short summers—so that seeds have time to ripen before autumn cold (Brewster, 2008).

When exactly to plant (guidelines for different regions):

For temperate climates (Europe, North America, Russia)

• Mother bulbs are planted as soon as the soil warms to +8…+10°C at a depth of 5–10 cm. In the middle belt, this is usually late April to the first decade of May (Autko et al., 2012; Nonnecke, 1989).
• Do not wait until all frosts have passed—mature bulbs withstand frosts down to –5…–7°C (Balashev and Zeman, 1981).

For southern regions (with mild winters)

• In Central Asia, southern Russia, and Mediterranean countries, mother bulbs are often planted in autumn (e.g., September–October) so that they root before winter and start growing early in spring. Autumn planting gives earlier flowering and a higher seed yield (Balashev and Zeman, 1981; Brewster, 2008).

For regions with severe winters (northern USA, Canada, Siberia)

• Autumn planting is not possible here. Mother bulbs are stored in storage and planted in spring as early as possible—late April to early May, as soon as the snow melts and the soil can be worked (Nonnecke, 1989).

Practical advice: in any region, try to plant mother bulbs within 1–2 weeks from the time the soil becomes workable. Delay reduces seed yield.

Planting Layout: How Much Space Does Each Plant Need?

Mother bulbs require more space than commercial onions because they have to produce a robust flower stalk, a branched inflorescence, and seeds. Overcrowding leads to reduced seed productivity and increased risk of diseases (especially downy mildew) due to poor ventilation (Brewster, 2008; Autko et al., 2012).

Optimal spacing for the amateur gardener:

Between rows: 50–70 cm. This provides easy access for care, watering, and seed collection (Autko et al., 2012; Balashev and Zeman, 1981).

Between plants in the row: 15–25 cm depending on the size of the mother bulb.

• For bulbs 4–6 cm in diameter — 15–20 cm.
• For bulbs 6–8 cm — 20–25 cm (Autko et al., 2012).

Why these distances:

• Each plant must receive enough light, water, and nutrients. With overcrowding, plants elongate, stalks become thinner, inflorescences smaller, and seeds smaller and less viable (Brewster, 2008).
• Wide row spacing makes weed control (cultivation, weeding) easier and allows the use of organic mulching materials.

Alternative layout for small plots:

• Mother bulbs can be planted in a staggered pattern, keeping a distance of 30×30 cm between bulb centres. This gives a feeding area of about 900 cm² per plant, which is sufficient for forming a large inflorescence.

Planting Depth: Slightly Deeper Than for Commercial Onions

Mother bulbs are planted deeper than onion sets or bulbs for food purposes.

Optimal depth:

• From the top of the bulb to the soil surface should be 4–6 cm (Autko et al., 2012; Balashev and Zeman, 1981). That is, the whole bulb is at a depth of about 5–8 cm (depending on its height).

Why such depth:

• Deep planting ensures better rooting and plant stability—they do not fall over in the wind when stalks grow to 1–1.5 m (Nonnecke, 1989).
• It helps protect the base of the stalk from damage and promotes the development of additional roots, which enhances plant nutrition.
• Too shallow planting (when the neck of the bulb sticks out above the ground) leads to rapid drying out, weakening, and low seed productivity (Brewster, 2008).

How to plant:

• Make furrows 6–8 cm deep.
• Place the bulbs with the base downwards, slightly pressing them into the bottom of the furrow.
• Cover with soil so that after settling, there is 4–5 cm of soil above the neck.
• Do not compact the soil heavily—onions need a loose, air‑permeable medium.

Isolation of Varieties: How to Maintain Purity

Onion is a cross‑pollinated plant. Pollen is carried by insects (bees, flies) over distances of up to 1–2 km (Brewster, 2008; Nonnecke, 1989). If other varieties or even related species (shallot, leek) are flowering nearby, cross‑pollination can occur, and the seeds will lose varietal purity.

How to ensure isolation on a small plot:

1. Spatial isolation — the most reliable method.

• To maintain variety purity, the distance between flowering different varieties should be at least 2 km in open terrain and at least 600 m in sheltered conditions (windbreaks, buildings) (Brewster, 2008; Autko et al., 2012). For the amateur gardener, this is often impossible.

2. Isolation by flowering time — if you have several varieties, plant them so that they flower at different times (e.g., an early and a late variety). Then cross‑pollination will be minimal (Nonnecke, 1989).

3. Artificial isolation — to obtain pure seeds from one variety on a small plot.

• Isolation with muslin bags: when the inflorescences begin to open, cover each umbel with a small bag made of fine mesh or muslin. This prevents insects from reaching the flowers (Brewster, 2008). In this case, pollination occurs through self‑pollination, as well as by wind and movement inside the bag.
• Hand pollination: you can gently shake the covered inflorescences to transfer pollen to the stigmas.
• Important: the isolation should be removed when seeds begin to ripen to ensure ventilation and prevent rotting.

4. Growing only one variety for seed — the simplest path for the gardener: if you preserve the purity of only one variety, do not plant other varieties for seed on the plot (or remove their flower stalks before flowering).

Important: if you do not plan to obtain pure varietal seeds but simply want to collect seeds for sowing (allowing natural cross‑pollination), isolation is not mandatory. However, in that case, the progeny may be heterogeneous, with loss of varietal traits.

Planting Technique: Step by Step

1. Prepare the bed: dig, remove weeds, level the surface.

2. Make furrows 6–8 cm deep with row spacing of 50–70 cm.

3. Place mother bulbs with the base downwards at 15–25 cm apart.

4. Cover with soil so that there is 4–5 cm of soil above the neck.

5. If the weather is dry, you can water after planting for better rooting (but do not overwater!).

6. If necessary, set up stakes and string to mark the rows, so you don’t damage the plants during care.

Summary

Early planting, sufficient feeding area, correct depth, and proper isolation of varieties—these are the four pillars of successful seed production. By spending time on these rules, you will obtain uniform stalk emergence, large inflorescences, and high‑quality seeds.

Nutrition: What and When to Fertilise

Seed onion plants consume more nutrients than onions grown for bulbs. They need to form not only the bulb (which gradually gives up its reserves) but also a powerful flower stalk up to 1–1.5 m tall, and then hundreds of seeds in each umbel (Brewster, 2008; Nonnecke, 1989).

Overall nutrient requirement (per 10 t of produce): N – 42.9 kg, P₂O₅ – 17 kg, K₂O – 45.7 kg (Autko et al., 2012). For a seed plot, these figures serve as a guide—your task is to provide the plants with a full set of macro‑ and micronutrients.

Fertilising schedule for mother onions (Autko et al., 2012; Balashev and Zeman, 1981):

1. First fertilisation (spring, growth‑stimulating). Applied 20–25 days after planting, when active leaf growth begins.

• Composition: nitrogen‑phosphorus‑potassium fertiliser in a ratio of about N₂₀P₂₀K₂₀ (e.g., 20 g of ammonium nitrate, 20 g of superphosphate, 20 g of potassium chloride per 10 L of water, application rate 5–10 L per 1 m²).
• Nitrogen is especially important at this stage because it stimulates the growth of vegetative mass and the formation of inflorescence primordia (Nonnecke, 1989).

2. Second fertilisation (before bolting). Applied during the phase of mass stalk emergence, when stalks reach 10–15 cm in height.

• Composition: phosphorus‑potassium fertiliser with a small amount of nitrogen (e.g., P₁₀K₁₅ or N₁₀P₁₅K₂₀).
• Phosphorus and potassium promote root system development, strengthen stalks (making them resistant to lodging), and improve seed quality (increase 1000‑seed weight, boost germination) (Brewster, 2008).

3. Third fertilisation (during flowering and seed maturation). Applied at the beginning of flowering.

• Composition: potassium‑phosphorus (e.g., P₁₅K₂₀), without nitrogen or with minimal content.
• Excess nitrogen at this stage delays seed ripening, prolongs vegetation, and reduces seed storage ability (Nonnecke, 1989; Autko et al., 2012).

How to apply fertilisers:

• Root applications: fertilisers are applied dry in furrows between rows, followed by incorporation and watering, or watered as a solution at the root. Distance from plants—at least 8–10 cm to avoid burning roots (Autko et al., 2012).
• Foliar applications (on leaves): during active leaf growth and at the start of flowering, you can spray plants with solutions of complex water‑soluble fertilisers (e.g., Ecolist “Standard” — 3 L/ha or similar). This helps quickly compensate for micronutrient deficiencies and increases stress resistance (Autko et al., 2012).

Important: do not overfeed with nitrogen! Excess nitrogen leads to “luxuriant growth”—excessive leaf development and weakened flowering, and also increases the risk of fungal diseases (Brewster, 2008).

Staking Stalks: Why and How

Onion stalks can grow up to 1–1.5 m or even higher, especially from large mother bulbs. Under the weight of the inflorescence and in gusts of wind, they easily lodge, break, or bend, reducing the quantity and quality of seeds (Brewster, 2008; Nonnecke, 1989).

When to stake:

• As soon as the stalk reaches a height of 30–40 cm, it should be tied to a support. Do not delay: staking later can injure an already lignified stem.

How to stake:

• Install individual stakes 1.2–1.5 m tall next to each stalk (or a single trellis for a row).
• Tie the stalk with soft twine or strips of cloth in 2–3 places (at the base, in the middle, near the inflorescence)—loosely, without constricting the tissues.
• For several stalks from one bulb, you can use a common stake and tie them in a bunch.

Alternative: if you have many mother bulbs and no time for individual stakes, you can stretch twine or netting between rows at heights of 60–80 cm and 100–120 cm, passing the stalks between the threads. This will keep them upright.

Watering: Regime for Seed Onions

The onion root system is weak and shallow (most roots are in the 5–20 cm layer), so it is very sensitive to moisture deficiency, especially during periods of active stalk growth and seed filling (Brewster, 2008; Balashev and Zeman, 1981).

Critical periods for watering (Autko et al., 2012; Balashev and Zeman, 1981):

1. After planting — rooting. If spring is dry, watering is needed for rapid regrowth.

2. Period of active stalk and leaf growth (May–June). At this time, the future seed yield is being set, and moisture deficit strongly reduces it.

3. Period of flowering and seed formation (June–July). Moisture is needed for full pollination and seed set.

Recommendations for the regime:

• Maintain soil moisture at 75–80% of field capacity throughout the period until seeds begin to ripen (Autko et al., 2012).
• In arid regions, carry out 3–4 waterings per season at a rate of 300–350 m³/ha (for the gardener—about 30–40 L per 1 m² per watering, aiming to wet the soil to a depth of 30–40 cm).
• Water regularly, but do not allow waterlogging—stagnant water around roots causes rotting and Fusarium infection (Nonnecke, 1989).
• Stop watering 2–3 weeks before seed harvest, when they begin to turn brown and ripen. Excess moisture delays ripening and promotes seed germination on the plant (Balashev and Zeman, 1981).

For small plots: use sprinkling or furrow irrigation. Drip irrigation is ideal because it does not wash off the waxy coating from leaves and does not create excessive air humidity, which promotes downy mildew (Autko et al., 2012).

Protection from Diseases and Pests

Seed onion plants are particularly vulnerable to diseases because they have a long growing period (up to 4–5 months). Infection of leaves and stalks reduces photosynthesis and, consequently, seed filling (Brewster, 2008).

Main diseases of seed onions (Autko et al., 2012; Nonnecke, 1989):

1. Downy mildew (peronosporosis, Peronospora destructor). The most dangerous disease for seed plants. Affects leaves and stalks, causing yellowing, deformation, and dieback. Develops in wet, cool weather and in dense plantings.

• Prevention: good ventilation (do not overcrowd!), weed removal, spraying with 1% Bordeaux mixture or modern fungicides (e.g., mancozeb‑based products) at the first signs (Autko et al., 2012; Brewster, 2008).

2. Neck rot (Botrytis allii). Affects tissues in the neck area, especially in weakened plants. Often occurs in rainy weather.

• Prevention: correct neck trimming before planting, fungicide treatment, timely harvesting (Nonnecke, 1989).

3. Fusarium basal rot (Fusarium spp.). Roots and base rot, and the plant wilts.

• Prevention: crop rotation (do not plant onion after onion), healthy planting material, well‑drained soil (Autko et al., 2012).

Main pests of seed plants:

• Onion fly (Delia antiqua). Larvae damage the bulb, weakening the plant.
• Onion weevil (Ceutorrhynchus jakovlevi). Feeds on leaf and stalk tissues.
• Thrips (Thrips tabaci). Suck sap from leaves, causing discoloration.

Control measures:

• Prevention: crop rotation, timely removal of plant residues, deep autumn ploughing (destroys fly pupae) (Nonnecke, 1989).
• In case of mass occurrence—apply approved insecticides (e.g., BI‑58 New, Decis) strictly according to instructions, observing the pre‑harvest interval (Autko et al., 2012).

For the amateur gardener: in a small holding, biological preparations and folk methods (infusions of garlic, tobacco, ash) can be used. But if diseases or pests develop strongly, chemical means cannot be avoided—act in time so as not to lose the seeds.

Additional Care Practices

• Cultivation between rows. After each watering or rain, when the soil dries out, carry out shallow cultivation (to 4–6 cm) to break the crust, conserve moisture, and destroy weeds. Over the season, 4–6 treatments are sufficient (Autko et al., 2012).
• Earthing up. During the phase of active stalk growth (height 30–40 cm), you can lightly earth up the bases of plants. This stimulates the formation of additional roots, improving stability and nutrition (Balashev and Zeman, 1981; Nonnecke, 1989).
• Removal of diseased plants. If any plant is clearly lagging in growth or affected by disease, remove it to prevent infection from spreading to neighbours.

Final Care Checklist

1. Fertilisation: 1st (after planting) — nitrogen‑phosphorus‑potassium; 2nd (before bolting) — phosphorus‑potassium; 3rd (start of flowering) — potassium‑phosphorus, without nitrogen.

2. Stalk staking — when they reach 30–40 cm in height.

3. Watering — regular (especially in dry weather) until seeds ripen, then stop.

4. Cultivation and weeding — systematically, 4–6 times per season.

5. Protection from diseases and pests — prevention + treatments as needed.

6. Removal of weak and diseased plants.

With good care, the plants reward your efforts with strong stalks, large umbels, and a high yield of seeds.

How Is the Onion Flower Structured?

Onion flowers are grouped into a spherical inflorescence—the umbel. One umbel can contain from 200 to 800 or even more flowers (Autko et al., 2012; Nonnecke, 1989). The larger the umbel, the more potential seeds.

Structure of an individual flower (Brewster, 2008; Nonnecke, 1989):

• Perianth — six white or greenish‑white petals.
• Stamens — six (arranged in two whorls).
• Pistil — one, with a superior ovary (with three locules, each containing two ovules, thus up to six seeds in one capsule‑fruit).
• Nectaries — located at the base of the stamens, readily accessible to insects.

Key feature: onion flowers are protandrous. This means that the anthers mature and release pollen before the stigma of the same flower becomes receptive (Brewster, 2008; Balashev and Zeman, 1981). That is, the male organs of the flower function earlier than the female ones.

Why this matters: protandry is a mechanism that promotes cross‑pollination. The flower’s own pollen cannot pollinate its own flower because the stigma becomes ready to receive pollen only a few days after the anthers have shed. This is a biological safeguard against self‑pollination, ensuring genetic diversity in the offspring (Brewster, 2008).

How Does Pollination Occur?

Who pollinates onion?

• The main pollinators are bees and flies (Brewster, 2008; Nonnecke, 1989).
• Onion pollen is heavy and sticky; it is not carried by wind over significant distances (Nonnecke, 1989; Autko et al., 2012).
• Nectar attracts insects: it contains sugars (mainly glucose and fructose) and has a fluorescent glow in ultraviolet light, which is easily visible to bees (Brewster, 2008).

How pollen transfer happens:

1. An insect visiting a flower touches mature anthers and picks up pollen on its body (hairs, legs).

2. Flying to another flower (or to a neighbouring plant), the insect touches the stigma, which by then has matured, and deposits pollen on it.

3. Pollen germinates on the stigma, and the pollen tube grows down the style to the ovary, where fertilisation of ovules occurs.

Flowering time:

• Flowering of one umbel lasts from 10–15 days (in southern regions) to 25–45 days or more in cool weather (Autko et al., 2012; Balashev and Zeman, 1981).
• Flowers in the umbel do not open simultaneously but in several tiers—the upper ones earlier, the lower ones later. As a result, seed maturation is also spread over time, which complicates harvesting (see next chapter) (Brewster, 2008).
• In hot weather (above +30°C), flowering intensity decreases: flowers may open only in the morning and evening hours (Balashev and Zeman, 1981).

Weather Risks and Their Influence on Pollination

Favourable conditions:

• Warm, dry, sunny weather without strong winds.
• Daytime temperature +20…+27°C (Brewster, 2008).
• Relative humidity below 70% — this favours better pollen shedding (Nonnecke, 1989; Brewster, 2008).

Unfavourable factors:

1. Rain and moisture. Water washes pollen off flowers, making it sticky and unsuitable for pollination. Moreover, high humidity promotes downy mildew (Brewster, 2008; Autko et al., 2012).

2. Extreme heat (above +30°C). At high temperatures, nectaries produce less nectar, pollen loses viability, and insects are less active. Furthermore, fertilisation itself may not occur at temperatures above +35°C (Brewster, 2008; Nonnecke, 1989).

3. Cold and frost. Flowers and young ovaries are damaged even by brief frosts down to –1°C (Autko et al., 2012). Therefore, it is important that flowering occurs after the danger of spring frosts has passed and before autumn cold sets in.

4. Lack of pollinating insects. If there is no apiary nearby or no natural population of wild bees and flies, pollination may be poor. In this case, artificial pollination must be used (Brewster, 2008).

How to Help Pollination on Your Plot

For the amateur gardener, the following techniques are available:

1. Attracting pollinating insects.

• Sow honey plants near the onions (phacelia, buckwheat, sweet clover, clover)—they attract bees (Nonnecke, 1989).
• Do not apply insecticides during flowering—they kill bees.
• If possible, place 3–4 bee hives at the edge of the plot (at a rate of 3–4 bee colonies per hectare). For a small garden, one hive can be placed, positioned so that the distance to the furthest plants does not exceed 500 m (Autko et al., 2012).

2. Artificial (hand) pollination.

• Method 1: In dry, sunny weather, gently shake the inflorescences so that pollen falls and lands on the stigmas of neighbouring flowers.
• Method 2: Use a soft brush or cotton swab—carefully transfer pollen from flower to flower, first touching mature anthers (yellow pollen sacs) and then the stigma (the small sticky style in the centre of the flower).
• Hand pollination is especially useful if flowering occurs in bad weather (cloudy, rainy), when insects are less active.

3. Temporal isolation for variety purity. If you want to obtain pure‑variety seeds and at the same time protect the umbels from unwanted cross‑pollination, cover them with muslin bags before flowering begins. You can place a few captured bees inside the bag or carry out hand pollination during the flowering period (Brewster, 2008; Nonnecke, 1989).

What Happens After Pollination

After pollen has landed on the stigma and fertilisation has occurred:

• The ovary begins to grow—forming a capsule fruit.
• In each capsule, up to 6 seeds can mature (two in each locule), but in practice usually 3–4 (Brewster, 2008; Nonnecke, 1989).
• Unfertilised flowers wilt and dry up without producing seeds.
• The initial stage of seed development (from pollination to filling) takes about 3–4 weeks (Brewster, 2008).

How to assess whether pollination was good:

• If most flowers in the umbel have set ovaries (small green spheres), pollination was successful.
• If there are many wilted and dried flowers without ovaries, pollination was insufficient.

Summary

Flowering and pollination are the critical stages at which the seed yield is set. Provide plants with access to insects, protect them from adverse weather, and if necessary, carry out hand pollination. This will significantly increase seed yield and quality.

Signs of Maturity: When Seeds Are Ready

Onion seeds mature in dry three‑celled capsules. Each capsule (with full fertilisation) contains up to 6 seeds—2 in each locule (Nonnecke, 1989; Balashev and Zeman, 1981). However, in reality, a capsule often contains 3–4 seeds (Brewster, 2008).

How to know that seeds are ripe:

1. Colour and condition of capsules. Ripe seeds have capsules that become dry, taking on a straw‑yellow or brownish tint. They begin to split open along the edges (Brewster, 2008; Autko et al., 2012). This sign—the beginning of splitting—is the main signal for harvest.

2. Colour and hardness of seeds. Fully mature onion seeds are black, three‑sided, wrinkled, and hard to the touch (Nonnecke, 1989; Kasynkina and Kudin, 2018). If seeds are still greenish or brown and soft, they are immature.

3. Time from pollination. From flowering to full seed maturity in onion takes about 45 days (Brewster, 2008). In terms of thermal time (sum of active temperatures), this is about 810 degree‑days above 0 °C (Brewster, 2008). This is a good guideline: if you know the date of mass flowering, add 45–50 days to get the expected maturity time.

4. Condition of the stalk. On a ripening plant, the stalk gradually dries out and loses its firmness. However, do not wait for the entire stalk to dry completely—seeds may start shedding earlier (Balashev and Zeman, 1981).

Non‑uniform Ripening: The Main Complication

Flowers in the umbel do not open simultaneously but in tiers (in three stages). Therefore, seeds also mature at different times (Brewster, 2008; Nonnecke, 1989). Upper capsules (from flowers that opened first) mature earlier than lower ones. If you wait until all seeds in the umbel are mature, the earliest ones will have already fallen to the ground.

How to solve this problem in a home garden:

• Selective harvesting. When the first capsules begin to split in the umbel (usually on the upper part and edges of the inflorescence), it is a signal to start harvest. The umbel is cut whole, even if the lower seeds are still green. They can be ripened during drying (Balashev and Zeman, 1981; Autko et al., 2012).

• Harvesting in 2–3 stages. If you have many umbels, you can collect the most mature umbels first, and then—after 5–7 days—the rest when they ripen. This increases the yield of sound seeds.

Important: do not allow widespread splitting of capsules on the plant—losses can be very high. Onion seeds are small and easily shed at the slightest disturbance (Brewster, 2008).

Harvesting Times in Different Regions

The time of seed ripening depends on climate and weather conditions of the year.

• In southern regions (Central Asia, the Caucasus, southern Russia, the Mediterranean), seeds usually ripen in late June – early July (Balashev and Zeman, 1981).
• In temperate climates (central Russia, Europe, northern USA) — in late July – early August (Autko et al., 2012; Nonnecke, 1989).
• In colder regions (the north, Siberia), ripening may be delayed until late August – early September. Here it is especially important to plant mother bulbs early and use early‑maturing varieties (Nonnecke, 1989).

Danger of autumn frosts: if seeds have not ripened before the first autumn frosts, even a light frost (–1°C) damages immature capsules, and the seeds become non‑viable (Autko et al., 2012). Therefore, in cold regions, either accelerate ripening (stop watering, use desiccants—but this is not relevant for gardeners) or use covers or move cut umbels to a warm place for after‑ripening (Balashev and Zeman, 1981).

Harvesting Technique: How to Cut Umbels Correctly

When to cut: in the morning, after the dew has dried. Wet umbels dry poorly and may become mouldy. Choose a dry, sunny day (Balashev and Zeman, 1981).

How to cut:

• Cut the umbel together with a portion of stalk 15–25 cm long (Nonnecke, 1989; Autko et al., 2012). This facilitates drying and subsequent threshing—the “tail” makes it easy to hold the umbel.
• Cut umbels that already have split capsules, but where most capsules are still dry and yellow.
• Carefully place the cut umbels in a basket or bucket, trying not to shake them so that mature seeds do not fall out. You can immediately put them in paper bags or muslin bags in the field (if you isolated the umbels for purity, continue drying in the same bags).

Drying and After‑ripening

Cut umbels must be dried and after‑ripened for 7–10 days (Balashev and Zeman, 1981; Autko et al., 2012). During this time, seeds in immature capsules finally fill out and mature using nutrients flowing from the cut stalk portion.

Conditions for drying:

• A bright, warm, dry, well‑ventilated place. Ideally—an attic, shed, veranda. Umbels are spread in a single layer on a dry, clean surface (paper, burlap, wooden boards) or hung in bunches with the inflorescences downwards (Nonnecke, 1989).
• Temperature: not above +30°C. At higher temperatures, seeds may lose germination.
• Periodically turn the umbels (gently) for even drying and to prevent mould.

After 7–10 days, the umbels should become brittle, and capsules should split easily when pressed. This signals that it is time for threshing.

Threshing and Seed Separation

Threshing is the process of separating seeds from dry capsules, receptacles, and other impurities.

Threshing methods for the gardener:

1. Hand threshing. The simplest way: take a dry umbel and gently rub it in your hands (preferably over a clean sheet of paper or a basin). The seeds will fall out, while large impurities (stalks, empty capsules) remain. Then separate the seeds from small debris—you can use wind (winnowing) or simply pour from a height in a breeze (light impurities blow away, heavy seeds fall) (Balashev and Zeman, 1981; Nonnecke, 1989).

2. Threshing on a floor. If you have many umbels, spread a tarpaulin or thick cloth, place the umbels on it, and walk over them (e.g., with a stick) or tread with soft footwear. Then gather the heap and winnow.

3. Washing with water. Onion seeds sink in water, while empty capsules, husks, and debris float. This method is used for final cleaning (Balashev and Zeman, 1981). Pour water over the seeds, stir, and let settle. Collect the floating debris, and carefully pour off the seeds at the bottom through a fine sieve, then dry (mandatory!).

Important: do not rub the umbels too hard to avoid damaging the hard seed coat. Damaged seeds lose germination (Nonnecke, 1989).

Sorting and Quality Assessment

After threshing and cleaning, it is necessary to calibrate the seeds—separate the fullest and heaviest from the shrivelled ones. This can be done by:

• Winnowing in a light breeze or in front of a fan.
• Sifting through a sieve with a suitable mesh size (for onions, about 2 mm).
• Testing germination (optional but recommended): take a sample of seeds and germinate them on moist cloth at 20°C—good seeds should give at least 80% germination (Kasynkina and Kudin, 2018).

The 1000‑seed weight for onions should be 2.7–4.0 g (Autko et al., 2012; Kasynkina and Kudin, 2018). Seeds smaller in weight are usually weak, with reduced germination.

Final Harvesting Recommendations

1. Start harvesting when the first split capsules appear.

2. Cut umbels with a portion of stalk (15–25 cm) in dry weather.

3. Dry umbels in a warm, ventilated place for 7–10 days.

4. Thresh when umbels become brittle.

5. Clean seeds from impurities (winnowing, water washing).

6. Finally dry to a free‑flowing state (moisture content no more than 11%) (Autko et al., 2012).

7. Store in a dry, cool place in paper or fabric bags.

Drying: Why It Is Critically Important

Seed moisture content is the main factor affecting their longevity. The higher the moisture content, the faster seeds lose germination, become infected with mould, and rot (Brewster, 2008; Autko et al., 2012).

Optimal moisture content for storage: no more than 11% (Autko et al., 2012). At this moisture level, seeds are in a state of deep dormancy, their respiration is minimal, and they can maintain germination for several years.

How to tell if seeds are sufficiently dry:

• Seeds should be free‑flowing, easy to pour.
• When squeezed in a fist, they should not stick together.
• Visually—black, dull, with a hard seed coat.

How to dry correctly:

1. After threshing, spread the seeds in a thin layer (1–2 cm) on a dry, clean surface—paper, cloth, plywood sheet. Do not use newspapers—printer ink may contain toxic substances.

2. Dry in a warm, dry, well‑ventilated place (attic, veranda, shed) at a temperature of +25…+30°C (Brewster, 2008).

3. Stir the seeds periodically (1–2 times a day) for even drying.

4. Do not dry in direct sunlight—direct sun can overheat the seeds and reduce germination (Nonnecke, 1989).

5. Continue drying until the seeds become completely free‑flowing. This usually takes 5–10 days depending on air humidity and temperature (Balashev and Zeman, 1981).

Important scientific fact: Onion seeds are so‑called “orthodox” seeds—they can tolerate deep dehydration without loss of viability. Maximum longevity is achieved at moisture around 3.5% (“ultra‑dry” storage), but for home conditions, reducing moisture to 10–11% is sufficient (Brewster, 2008; Ellis et al., 1990).

Cleaning: How to Separate Seeds from Impurities

Even after careful threshing, the bulk contains much foreign material:

• Empty capsules and their valves.
• Fragments of stems and flower stalks.
• Weed seeds, sand, dust.
• Shrivelled, unfilled seeds.

Cleaning is important not only for appearance—impurities increase moisture (especially organic residues) and can serve as a source of mould and pests during storage (Nonnecke, 1989).

Cleaning methods for the gardener:

1. Winnowing (air separation). The simplest and most effective method for home conditions.

• Take two buckets or basins. Pour seeds from one to the other from a height of 30–50 cm on a windy day or in front of a fan (set to low power).
• Light impurities (empty capsules, husks) will blow further away, while heavy seeds will fall into the bucket.
• Repeat 2–3 times for better cleaning (Balashev and Zeman, 1981).

2. Density sorting (water washing).

• Sound onion seeds are heavier than water, while empty and light impurities float.
• Cover the seeds with room‑temperature water, stir, and let settle for 1–2 minutes.
• Collect floating debris, and carefully pour off the seeds through a fine sieve (Nonnecke, 1989; Balashev and Zeman, 1981).
• After washing, be sure to dry the seeds to a free‑flowing state (see previous section)!
• This method is good for small quantities of seeds.

3. Manual sorting. The most labour‑intensive but reliable method—manually select the largest, fullest, typically coloured seeds. This is ideal for obtaining the highest‑quality seeds for your own sowing.

4. Using sieves. If you have sieves with different mesh sizes, you can separate seeds by fractions. For onions, a sieve with about 2 mm mesh is usually used—small shrivelled seeds pass through, while larger ones remain (Kasynkina and Kudin, 2018).

Quality assessment after cleaning:

• 1000‑seed weight. For onions, a good indicator is 2.7–4.0 g (Autko et al., 2012). Seeds with lower mass give weaker seedlings.
• Germination. You can conduct a germination test: soak 10–20 seeds between layers of moist cloth at +20°C. After 7–10 days, count how many have germinated. For a good crop, germination of at least 80% is needed (Kasynkina and Kudin, 2018).

Storing Seeds: How to Maintain Germination

Onion seeds are among the most “finicky” in terms of longevity. Under improper storage, they quickly lose germination. This is due to the seed coat containing essential oils that can oxidise, and high sensitivity to moisture and temperature (Brewster, 2008; Ellis and Roberts, 1980a).

Optimal storage conditions:

1. Temperature. Ideally—a cold but not freezing place: +2…+5°C (Brewster, 2008). At this temperature, seed ageing processes are slowed down as much as possible. At home, suitable storage places include:

• Refrigerator (lower shelf, vegetable drawer).
• A dry basement with a constant temperature.
• An unheated pantry.
• Important: do not store seeds at room temperature (+20°C) for a long time—they quickly lose germination. According to studies, at +20°C onion germination noticeably declines within 1–2 years (Ellis and Roberts, 1980a).

2. Humidity of air and seeds. Seed moisture should be no higher than 10–11%. Air humidity in the storage place — no more than 60–65% (Autko et al., 2012; Nonnecke, 1989). If the air is too humid, seeds become damp, mouldy, and lose germination. If too dry, seeds may become overly dry and brittle, but for “orthodox” seeds this is not critical (Brewster, 2008).

3. Containers for storage.

• Paper bags or pouches (kraft paper, cloth)—they allow seeds to “breathe” and prevent excess moisture.
• Glass jars with tight lids—if the seeds are well dried, this provides airtightness and protection from pests. But make sure the seeds are absolutely dry—otherwise condensation will form in the jar.
• Do not store in plastic bags! They create a greenhouse effect; seeds “suffocate”, may become mouldy or lose germination due to increased humidity (Nonnecke, 1989).

4. Protection from pests. Dry seeds are not infested by all pests, but if conditions are violated (increased humidity), seed mites or other insects may appear. Prevention:

• Store seeds in cleanliness.
• Periodically check them.
• You can add dry mint leaves, lavender, or a few cloves of garlic to the bag to repel pests (folk method).

5. Labelling. Be sure to label each seed lot: variety name, collection date (year), quantity of seeds. Without labelling, in a year or two you will not remember which variety is in the packet. Use a permanent marker or stickers (Autko et al., 2012).

How Long Do Onion Seeds Keep?

Onion seeds retain satisfactory germination for 2–3 years (Autko et al., 2012; Kasynkina and Kudin, 2018). Under optimal conditions (cold, dry) they can be stored longer—up to 4–5 years, but germination declines each year.

How germination changes with seed age (approximate):

• 1st year (fresh) — 90–95% germination.
• 2nd year — 80–85%.
• 3rd year — 60–70% (for sowing, it is already advisable to increase the seeding rate).
• 4th year and older — germination drops to 30–50%; such seeds are better not used for sowing (Ellis and Roberts, 1980a; Brewster, 2008).

Important: onion seeds age quickly, so try to use fresh seeds—those collected in the previous season or, at most, two years ago (Nonnecke, 1989).

Checking Germination Before Sowing

If you have stored seeds for more than one year, be sure to check their germination before sowing—this will save you time and effort (Kasynkina and Kudin, 2018).

Quick test:

1. Take 20–30 seeds.

2. Place them on moist cloth (preferably filter paper or cotton pads) in a plastic container with a lid (to maintain moisture).

3. Put in a warm place (+20…+22°C).

4. After 7–10 days, count the germinated seeds.

5. If germination is below 70%, sow the seeds more thickly than usual, or replace the batch with fresh seeds.

Final Checklist: From Harvest to Storage

1. Harvest: cut umbels with a portion of stalk when the first split capsules appear.

2. Drying: 7–10 days in a dry, warm, ventilated place (until umbels become brittle).

3. Threshing: separate seeds from capsules (rubbing, beating).

4. Cleaning: winnow, wash with water (if necessary), dry.

5. Final drying: to moisture <11% (free‑flowing, not sticky).

6. Packaging: place in paper bags or glass jars.

7. Labelling: indicate variety and year of collection.

8. Storage: in a dry, cool place (+2…+5°C), air humidity no more than 60–65%.

Problem 1. Bulbs Did Not Bolt

Causes:

1. Did not undergo vernalization. This is the main and most common cause. The bulbs did not receive the necessary cold stimulus during storage (Brewster, 2008).

• What went wrong: storage at temperatures above +12…+15°C throughout the winter. At such temperatures, vernalization does not occur, and the bulb remains vegetative.
• What to do: ensure mother bulbs are kept at a stable temperature of +2…+6°C for 2–3 months over winter (Nonnecke, 1989).

2. Bulbs were too small. For the transition to flowering, the bulb must reach a certain critical size (Brewster, 2008). This threshold varies among varieties, but on average a bulb of at least 4–5 cm in diameter is needed for bolting.

• What to do: leave only large, well‑ripened bulbs (5–8 cm) for seed.

3. Variety is not prone to bolting. Some modern hybrids and varieties are specifically bred to bolt very little (especially F1 hybrids for food purposes). This is convenient for producing bulbs but bad for seed production (Nonnecke, 1989).

• What to do: for seed production, choose varieties that are known in your region as “prone to bolting” or traditional open‑pollinated varieties (e.g., ‘Stuttgarter Riesen’, ‘Strigunovsky’, ‘Bessonovsky’). F1 hybrids do not preserve varietal traits in their seeds (Nonnecke, 1989).

4. Variety is not adapted to your region. Some varieties require a longer or, conversely, shorter cold period for vernalization (Brewster, 2008; Nonnecke, 1989). For example, southern‑type varieties (sweet, intermediate‑day) may not bolt under conditions of a long cold winter.

• What to do: use regionalised varieties recommended for your climatic zone.

Problem 2. Stalks Emerged, but Seeds Are Few or Shrivelled

Causes:

1. Poor pollination. Onion is pollinated by insects, mainly bees and flies (Brewster, 2008; Nonnecke, 1989). If during flowering there was rainy, windy, or too hot weather, insects were less active, and pollination was incomplete.

• What to do: attract insects (plant honey plants near the seed onions), do not use insecticides during flowering. If necessary, carry out hand pollination (transfer pollen from flower to flower with a soft brush) (Brewster, 2008).

2. Nutrient deficiency. Seed plants need more phosphorus and potassium than ordinary onions grown for bulbs (Autko et al., 2012; Balashev and Zeman, 1981). If you did not apply phosphorus‑potassium fertilisers, seeds may be small and shrivelled.

• What to do: be sure to apply fertilisers: nitrogen at the beginning of growth, phosphorus‑potassium before flowering and during seed filling.

3. Moisture deficiency during flowering and seed filling. The onion root system is weak, and even a short drought during critical periods reduces seed set (Brewster, 2008; Balashev and Zeman, 1981).

• What to do: maintain soil moisture at 75–80% of field capacity throughout the growth and flowering period. Stop watering only 2–3 weeks before seed harvest.

4. Damage by diseases or pests. Downy mildew, Fusarium, onion fly, thrips—all weaken plants and reduce seed productivity (Autko et al., 2012; Nonnecke, 1989).

• What to do: observe crop rotation, remove diseased plants, apply preventive treatments (fungicides, insecticides) as needed, strictly observing pre‑harvest intervals.

Problem 3. Seeds Ripened but Are Non‑viable

Causes:

1. Harvested too early (immature). Seeds collected at the milk stage do not ripen during drying and produce weak seedlings or fail to germinate at all (Brewster, 2008).

• What to do: wait for the capsules to begin splitting on the umbel. If you cut umbels earlier, allow them to after‑ripen for 7–10 days in a warm, dry place.

2. Overheating during drying. Drying at temperatures above +35°C can “cook” the seed embryo (Brewster, 2008).

• What to do: dry seeds at +25…+30°C in a ventilated place, out of direct sunlight.

3. Improper storage. Onion seeds quickly lose germination when stored in warmth (Brewster, 2008; Ellis and Roberts, 1980a).

• What to do: store seeds in a dry, cool place (+2…+5°C), in paper or fabric bags, with seed moisture not above 11%.

4. Seeds affected by fungal diseases during storage. If seeds were moist before storage, mould may develop, killing the embryo (Nonnecke, 1989).

• What to do: thoroughly dry seeds before packaging. Store in a dry place with good ventilation. If mould is found, immediately sort and re‑dry.

5. Seeds are too old. Even under ideal storage, onion germination declines every year (Ellis and Roberts, 1980a).

• What to do: use fresh seeds (1–2 years old). If seeds are 3 years or older, be sure to test germination before sowing and increase the seeding rate.

Problem 4. Seeds Were Obtained, but the Crop Does Not Match the Variety

Causes:

1. Cross‑pollination with other varieties. Onion is cross‑pollinated, and pollen from other varieties (or even related species) can reach your seed plants if they grow within 2 km (Brewster, 2008; Nonnecke, 1989). Progeny from such crossing loses varietal traits.

• What to do: on a small plot, either isolate inflorescences with muslin bags before flowering, or grow only one variety for seed in a given season.

2. Using F1 hybrids for seed production. First‑generation hybrids segregate in progeny—the crop will be heterogeneous, with loss of valuable traits (Nonnecke, 1989).

• What to do: for seed production, use only open‑pollinated varieties, not F1 hybrids.

Problem 5. Bulbs Rotted During Storage

Causes:

1. Too high humidity during storage (>80%). This provokes neck rot (Botrytis allii) and other fungi (Autko et al., 2012; Brewster, 2008).

• What to do: store mother bulbs at 70–80% humidity, in a dry, ventilated place. Regularly check and remove rotting specimens.

2. Bulbs were poorly dried before storage. Wet bulbs inevitably rot in storage (Nonnecke, 1989).

• What to do: dry the harvest until the dry scales rustle before storing.

3. Diseased or damaged bulbs were selected. Even a tiny wound is an entry point for infection.

• What to do: during autumn selection, discard all bulbs with suspicious signs. In spring, carry out a second sorting.

Checklist: Quick Diagnosis of Problems

Final Conclusion

Growing your own onion seeds is a fascinating and rewarding endeavour, but it requires attention to detail and an understanding of plant biology. Failures are not a reason to be upset, but an opportunity to analyse mistakes and achieve excellent results in the next season.

The most important thing is to remember the three pillars of onion seed production:

1. Vernalization — proper cold storage (without it, there will be no stalks!).

2. Nutrition — phosphorus and potassium for flowering and seeds.

3. Pollination — insects and good weather.

If you take these principles into account and are attentive at every stage, within a couple of seasons you will have your own reliable source of high‑quality nigella, adapted to your climate and soil.

Good luck with your seed‑growing experiment!