Onion

Where Onion Came From

It is believed that the domestication of onion began more than 4700 years ago in the mountainous regions of Central Asia, specifically in what is now Turkmenistan and northern Iran (Brewster, 2008). It was there, at the crossroads of ancient civilizations (e.g., Sumerian), that it began its journey to our tables.

The closest wild relative of cultivated onion is Allium vavilovii, which can still be found in the Kopet Dag mountains (Turkmenistan) (Brewster, 2008). Another species, Allium pskemense, growing in the Tien Shan mountains, is still sometimes transplanted into gardens by local people, giving us an idea of how domestication occurred. People selected plants with larger bulbs, faster growth, and better taste, gradually turning them into the crop we know today.

The Journey Around the World

From Central Asia, the onion began its triumphant march around the globe:

• It was an important crop in Ancient Egypt, Greece, and Rome. The Egyptians famously used it for food and even included it in religious rituals.
• The Romans played a key role in spreading onion across Europe, bringing it to northern regions (Rubatzky and Yamaguchi, 1997).
• In the 12th–13th centuries, onion reached the territory of modern Russia.
• In the early 17th century, European settlers brought onion to North America. In the 19th century, it reached East Asia (Brewster, 2008).

Two Main Groups

Over thousands of years of cultivation and breeding, two main groups of onion varieties have emerged and are still used around the world:

1. Common Onion Group. This is the backbone of modern onion growing. Plants in this group form a single large bulb. These are the ones we most often see on store shelves. These varieties are typically grown from seed and differ in maturity, storage ability, pungency, and colour (Brewster, 2008).

2. Aggregatum Group (multiplier onion). Varieties in this group form not one but several (a nest) of smaller bulbs. This includes the familiar shallot and potato onion (a relative, but not the common onion). This group is often propagated vegetatively (by bulbs) and is especially valued in regions with short summers and in the tropics, where it allows a quick harvest while avoiding diseases that affect seedlings.

Why Is This Important for the Gardener?

Knowing the origin of onion helps us understand its biology: it developed under conditions of mountain slopes with bright sun and dry air. This explains why onion loves light and cannot tolerate waterlogging. The diversity of variety groups shows that for every climate zone and purpose, there is an ideal variety: some regions prize sweet, salad types, while others prefer pungent, long-storing ones.

The history of onion is the history of its adaptation to humans. In the next chapter, we will look in more detail at how onion is structured from a botanical point of view, so that we can better understand how to care for it in the garden.

Botanical Passport

Common onion (lat. Allium cepa L.) is a species of herbaceous perennial plant, but in cultivation it is most often grown as a biennial or annual. Its systematic position, according to modern data (Friesen et al., 2006), is as follows:

• Class: Monocotyledons (Monocotyledones)
• Order: Asparagales (Asparagales)
• Family: Alliaceae (Alliaceae). In some classifications it is placed in the Amaryllidaceae family (Amaryllidaceae) or even included in the broad Liliaceae family (Liliaceae), but modern molecular studies confirm the separation of Alliums into their own family (Rubatzky and Yamaguchi, 1997).
• Genus: Allium (Allium)
• Species: Common onion (Allium cepa L.)

The genus Allium is one of the largest in its family and includes, according to various estimates, from 750 to 800 species (Rabinowitch and Kamenetsky Goldstein, 2020). This genus also includes garlic, leek, shallot, and ornamental onions. They are united by the characteristic garlic–onion odour, due to the presence of sulfur compounds (cysteine sulfoxides) (Block, 2010).

Intraspecific Diversity

All the economic value of common onion lies in its intraspecific diversity. The entire species Allium cepa is conventionally divided into two main cultivar groups (Brewster, 2008):

1. Common Onion Group.

This is the most widespread and economically important group. Its main feature is the formation of a single large bulb. These are the onions we most often see on shelves. They are propagated by seeds and include thousands of varieties adapted to different climatic conditions (from tropics to subarctic) and purposes (salad, pungent for storage, for processing).

2. Aggregatum Group (multiplier onion).

A characteristic feature of this group is the formation of a nest of several bulbs. It includes two important forms for gardeners:

• Shallot (Allium cepa var. ascalonicum). Forms nests of several elongated, pear‑shaped bulbs. Valued for its delicate, sweetish taste and high flavonoid content (Rubatzky and Yamaguchi, 1997).
• Potato onion (Allium cepa var. aggregatum or solaninum). Produces larger, often flattened bulbs.

These forms are usually propagated vegetatively (by bulbs). They are especially valuable in regions with short summers (Northern Europe) and in hot, humid tropical climates, where they allow a quick harvest before plants are destroyed by diseases (Brewster, 2008).

Close Relatives and Wild Species

To understand the origin and requirements of the crop, it is useful to know about the “relatives” of common onion:

• Wild ancestors: As mentioned, Allium vavilovii and Allium pskemense are considered the closest wild relatives. They grow in the mountains of Central Asia and have high viability.
• Welsh onion (Allium fistulosum). A close species often confused with common onion. It differs in that it does not form a true bulb but produces a thick false stem. Interestingly, it crosses freely with common onion, producing disease‑resistant hybrids (e.g., ‘Beltsville Bunching’) (Brewster, 2008).
• Leek (Allium ampeloprasum var. porrum). This is not just a close relative but a separate species. Unlike common onion, it does not form a bulb; instead, the thickened false stem (stalk) is eaten. Leek is a tetraploid (2n=32), while common onion has a diploid chromosome set (2n=16) (Rubatzky and Yamaguchi, 1997).

Why Is This Important for the Gardener?

1. Choosing “nesting” type: Knowing about the two groups (Common Onion and Aggregatum) lets you make a conscious choice. For large bulbs, you need varieties from the first group. If you want several smaller, but aromatic and early‑maturing bulbs, your choice is shallot or potato onion.

2. Understanding seed production: Most varieties in the Common Onion group are cross‑pollinated, which is important if you want to produce your own seed. This also explains the need for spatial isolation of different varieties.

3. Disease resistance: Knowledge of closely related wild species such as A. fistulosum tells breeders where to look for disease‑resistance genes, and gardeners that there are hybrids with improved hardiness (Brewster, 2008).

In the next chapter, we will move from systematics to “anatomy” – learning what parts an onion consists of and how they are structured. This will help you understand how to plant, water, and harvest for storage.

Root System

Onion roots are fibrous, i.e., there is no main taproot. In an adult plant, the roots are thin, thread‑like, weakly branched outgrowths that emerge from the base of the bulb. They penetrate the soil to a depth of 30–50 cm, but the bulk of the roots are in the topsoil (20–30 cm) (Rubatzky and Yamaguchi, 1997).

Why this matters for the gardener: because of the superficial root system, onion is very sensitive to moisture deficit in the topsoil, especially during the period of active leaf growth and bulb formation. Watering should be regular, but without waterlogging. This also explains why loosening the soil (especially between rows) is so important for onions – the roots need air.

The Bulb: The Main Storage Organ

The bulb is a modified underground shoot. Its structure is the key to understanding how onion stores nutrients and how to harvest it properly.

Main parts of the bulb:

1. Basal plate – a greatly shortened and flattened stem. Roots grow from the basal plate, and buds – the primordia of future bulbs or flower stalks – form on it (Rubatzky and Yamaguchi, 1997).

2. Scales – modified leaves that make up the bulk of the bulb. There are two types of scales:

• Fleshy scales (inner) – thick, meaty, they accumulate water and nutrients (sugars, proteins). This is the edible part of the bulb.
• Dry scales (outer, “tunic”) – thin, papery, they protect the bulb from drying out and the entry of pathogenic microorganisms. Their colour (yellow, white, red, purple) is a varietal trait (Brewster, 2008).
• Neck – the place where the leaves transition into the bulb. This is the narrowest point at the base of the foliage. When the onion matures, the neck softens, the leaves lodge, and the neck closes, preventing moisture and rotting bacteria from entering the bulb during storage.

Why this matters for the gardener: the degree of onion maturity is determined not only by yellowing of the leaves, but also by softening and drying of the neck. A bulb with a tight, well‑closed neck will store for a long time. If the neck remains thick and juicy (so‑called “thick neck”), the onion is underripe and will not keep well (Brewster, 2008). That is why experienced gardeners stop watering 2–3 weeks before harvest to accelerate maturation and drying of the neck.

Leaves (Top)

Onion leaves are tubular, hollow inside, covered with a waxy bloom that protects them from moisture loss and sunburn. They grow from the centre of the bulb, forming a so‑called false stem (pseudostem) from the leaf sheaths.

Important for the gardener: until bulb formation begins, all the plant’s energy goes into leaf growth. Photosynthesis occurs through the leaves, and the more healthy leaf mass, the larger the bulb. Therefore, it is very important not to damage the foliage in the first half of the growing season.

Flower Stalk and Seeds

In the second year (or in the first, if the bulb has been exposed to low temperatures), a flower stalk grows from the centre of the bulb – a hollow stem up to 1.5 m tall, ending in an umbel inflorescence consisting of many small flowers (Rubatzky and Yamaguchi, 1997). The flowers are white, sometimes with a greenish or pinkish tinge, and are cross‑pollinated by insects (mainly bees).

The fruit is a capsule containing seeds (commonly called “black seed” in Russian). The seeds are small (250 to 400 per gram), black, three‑sided, with a hard coat (Brewster, 2008).

Why this matters for the gardener: if you are growing onions for large bulbs, bolting (the appearance of a flower stalk) is undesirable (“going to seed”). It diverts energy from the plant, resulting in small bulbs that store poorly. The cause of bolting is improper storage of planting material (sets) at temperatures between +5 and +15 °C, which stimulates flowering (Rubatzky and Yamaguchi, 1997). Therefore, sets must be stored either below +5 °C (cold storage) or above +20 °C (warm storage). We will discuss how to choose planting material and avoid bolting in the chapter on varieties and cultivation methods.

Life Cycle in Brief

1. Seed germination (or planting sets).

2. Leaf growth. During this period, the foundation for the future bulb is laid.

3. Start of bulb formation. This process is triggered when a certain day length (photoperiod) and temperature are reached. Growth of new leaves slows, and nutrients begin to flow from them into the bulb.

4. Maturation. Leaves turn yellow and lodge, the neck softens and dries.

5. Dormancy (storage). The bulb enters a state of rest that lasts from 4 to 9 weeks. During this time it does not sprout. The duration of dormancy strongly depends on the variety and storage conditions (Rubatzky and Yamaguchi, 1997).

Armed with this knowledge, we can now move on to the next chapter, where we will look at what environmental conditions (light, temperature, moisture, soil) onion needs to reward us with large, healthy bulbs.

Temperature: Cold Hardiness and Heat Requirement

Onion combines remarkable cold hardiness in its early stages with a need for warmth during bulb formation.

• Seedlings and young plants: Onion seeds begin to germinate at soil temperatures as low as +2...4 °C, although the optimum for germination is +18...20 °C (Brewster, 2008). Young seedlings tolerate short‑term frosts down to -2...-3 °C (Rubatzky and Yamaguchi, 1997). This allows onion to be sown very early, as soon as the soil permits.
• Optimum temperature for growth: For leaf growth and root development, temperatures of +15...+20 °C are most favourable. In this range, photosynthesis is most efficient.
• Temperature for bulb formation and maturation: For the bulb to fill and mature, higher temperatures of +20...+25 °C are needed (Rubatzky and Yamaguchi, 1997). Above +30 °C, growth slows, and bulb quality deteriorates (e.g., they may become small or bitter). Temperature fluctuations during maturation are also harmful.

Practical conclusion: In regions with cold, short summers, it is important to choose early‑maturing varieties that have time to form a bulb before autumn cold sets in. In hot climates, water the onion during growth and give it a rest (stop watering) during maturation.

Light: Photoperiod – The Most Critical Factor

This is perhaps the most critical aspect of onion agronomy. Common onion is a long‑day plant. This means that the process of bulb formation is triggered only when the day length exceeds a certain critical value for each variety (Brewster, 2008).

Here is how it works:

• Short‑day varieties (SD): They begin to form bulbs when the day reaches 11–13 hours. They are ideal for southern regions (subtropics, tropics, latitudes up to 35–38°), where the day is relatively short year‑round. If grown in the north, these varieties may “bulb” too early, on tiny plants, producing a small yield (Rubatzky and Yamaguchi, 1997).
• Intermediate‑day varieties (ID): They respond to a day length of 13–14 hours. These are for latitudes between 30° and 38°. They suit regions with mild climates and are often used for autumn and early spring sowings.
• Long‑day varieties (LD): They require a day longer than 14–16 hours to initiate bulb formation. These are typical for temperate and northern latitudes (above 38–40°). They produce the largest and most storable bulbs, but in southern regions with short days they may not form a bulb at all (Rubatzky and Yamaguchi, 1997; Brewster, 2008).

Practical conclusion: Choosing a variety according to photoperiod is a MANDATORY RULE. Planting a long‑day variety in the south risks getting only greens. Conversely, a short‑day variety in the north will form small bulbs. That is why seed catalogues always indicate this parameter.

Important nuance: Temperature also affects the photoperiodic threshold. At low temperatures (around +10 °C), onion may not bulb even under long days. At high temperatures (+25 °C and above), the response to day length is enhanced (Wien and Stützel, 2020).

Moisture: A Delicate Balance

Onion is very sensitive to water regime, but differently at different growth stages.

• During leaf and root growth: The need for moisture is high. The soil should be moist but not waterlogged. Water deficiency at this time will lead to weak plant development and, consequently, small bulbs (Rubatzky and Yamaguchi, 1997).
• During bulb formation and maturation: Watering should be reduced and stopped completely 2–3 weeks before harvest. Excess moisture at this stage delays maturation, causes “thick neck”, and can promote disease and rot during storage (Brewster, 2008).
• Air humidity: Onion prefers dry air. High humidity (above 70–80%) promotes fungal diseases such as downy mildew. In rainy summers, bulbs often fail to mature properly.

Practical conclusion: Water onions generously in the first half of the growing season and stop watering 2–3 weeks before harvest. This is the classic and most reliable approach.

Soil: Loose and Fertile

Onion is very demanding of soil structure and fertility.

• Mechanical composition: The best soils are light and medium loams, sandy loams, and cultivated peatlands. They should be loose, well‑aerated, and well‑drained (Rubatzky and Yamaguchi, 1997). On heavy clay soils, bulbs often grow deformed and store poorly.
• Acidity (pH): Onion prefers a neutral or slightly alkaline reaction (pH 6.0–7.5). On acidic soils, it is depressed, takes up nutrients less well, and often suffers from diseases (Kotov and Adritskaya, 2016). Liming is recommended before planting if the soil is acidic.
• Nutrients: Onion is a “glutton” in the good sense. To produce high yields, it needs all macronutrients. Phosphorus is especially important for root development, and potassium for bulb quality and storage ability. Nitrogen is important in the first half of the growing season, but its excess, especially in the second half, can cause excessive leaf growth at the expense of the bulb and reduce storability (Brewster, 2008).

Practical conclusion: Pay special attention to pre‑planting soil preparation: deep digging, incorporation of well‑rotted compost or manure, and, if necessary, liming. Use balanced compound fertilisers with appropriate N‑P‑K ratios.

In the next chapter, we will follow the plant’s development stage by stage and see how changes in external conditions affect physiological processes, helping you fine‑tune your crop management.

Stage 1: Germination and Seedling Emergence

It all starts with a seed (or set). Germination is the awakening of the embryo.

• Physiology: Upon imbibition, enzymes (especially amylases) become active and break down stored nutrients (proteins, fats, starch) into simple compounds. This provides energy for radicle and cotyledon growth (Rabinowitch and Kamenetsky Goldstein, 2020). Root growth begins at low temperatures (+2...+4 °C), while vigorous shoot growth starts when the soil warms to +15...+20 °C. First, a loop emerges – a curved cotyledon that carries the seed coat to the surface. Then it straightens, and true leaf growth begins.
• Gardener’s tip: Onion seeds germinate slowly – up to two weeks. To speed up the process, use soaked or primed seeds. The key at this stage is soil moisture (it should not dry out) and looseness, so the delicate root can penetrate easily.

Stage 2: Active Leaf Growth (“Vegetative Growth”)

After the first true leaves appear, the most critical phase begins – building green mass.

• Physiology: The plant acts like a pump: roots actively absorb water and minerals, while leaves (tops) photosynthesise intensively, converting carbon dioxide and water into sugars and other organic compounds (Rubatzky and Yamaguchi, 1997). During this period, the basal plate increases in diameter, laying the foundation for the future bulb. Leaf growth rate depends on temperature: it increases with rising temperature up to a certain limit. For leaf growth, onions need nitrogen.
• Gardener’s tip: Until bulb formation begins, maintain optimal soil moisture to provide the plant with “building material”. Regular watering in the first half of the growing season is the key to future yield. Also, do not rush with fertilising in the second half of the cycle, when nitrogen can stimulate leaf growth at the expense of the bulb.

Stage 3: Bulb Initiation (The Critical Moment!)

At some point, plant development changes direction abruptly. Growth of new leaves slows and almost stops. Instead, the plant begins to store reserve nutrients in the bases of the leaves (future fleshy scales) and in the primordia of future buds. This process is called bulb initiation (Wien and Stützel, 2020).

• Physiology: This is the response to day length (photoperiod) and temperature. Upon reaching the critical value (different for different varieties), the plant receives a hormonal signal to prepare for the adverse season – to form an overwintering organ (the bulb). This signal is regulated by hormone‑like substances, notably phytochrome, a light‑sensitive protein (Wien and Stützel, 2020). In response, the flow of assimilates from senescing leaves into the bulb intensifies, and the growth of new leaves is blocked.
• Gardener’s tip: You cannot change day length, but you can influence temperature and nutrition. The closer to the critical point, the more important it is to maintain optimal temperature (+20...+25 °C) and avoid excess nitrogen, which can delay bulbing. The larger the plant at initiation, the larger the bulb will be.

Stage 4: Bulb Growth and Maturation

Once the process is triggered, the bulb begins to grow and fill vigorously.

• Physiology: During this period, sugars, amino acids, and other nutrients are actively translocated from the dying foliage into the fleshy scales. Bulb volume increases through cell expansion in the fleshy scales. Moisture plays a key role: cells must be turgid to accumulate sugars and maintain firmness. When the bulb reaches its maximum size, maturation completes: the neck softens and dries, outer scales dry to form a protective “tunic” (Rubatzky and Yamaguchi, 1997).
• Gardener’s tip: This stage is the most critical for future storability. Stop watering 2–3 weeks before harvest! This accelerates nutrient translocation from leaves to the bulb and drying of the neck. It is also very important to wait for natural lodging and yellowing of most of the foliage – that signals the bulb is mature and ready for harvest and storage.

Stage 5: Dormancy and Rest Period

This is a physiological mechanism that allows onion to survive an unfavourable period (winter or drought).

• Physiology: After harvest, the bulb enters a state of dormancy that can last 4–9 weeks (Rubatzky and Yamaguchi, 1997). During this time, even under favourable conditions, it will not sprout. The bulb synthesises growth inhibitors (particularly abscisic acid) that block cell division in the growing point. Dormancy is a “programmed” state that passes with time (Brewster, 2008). Duration of dormancy is a heritable varietal trait. Long‑day and pungent varieties generally have a longer dormancy period than sweet and early‑maturing ones (Wien and Stützel, 2020).
• Gardener’s tip: Harvest onions only after dormancy has begun (the bulb is mature). If harvested too early, they will store poorly. To extend dormancy and prevent premature sprouting, store onions in cool (0…+4 °C) and dry conditions. For sets that will be planted in spring, on the other hand, too cold storage can provoke bolting (flowering).

Bonus: On Bolting (Going to Seed)

The production of a flower stalk (bolting) is the plant’s attempt to switch to seed reproduction.

• Physiology: To initiate flower buds, onion needs a period of low temperatures (+5 to +10 °C) for 1–2 months. The plant must be sufficiently large and not in dormancy. If sets are stored at temperatures from +5 to +15 °C, flower bud primordia are initiated. When planted, such sets will bolt (Rabinowitch and Kamenetsky Goldstein, 2020).
• Gardener’s tip: To avoid bolting, store sets either below +5 °C (cold storage) or above +20 °C (warm storage). The most reliable method is to warm the sets for 8 hours at +40 °C 1–2 weeks before planting. This kills the flower primordia.

Knowing these five stages, you can consciously influence the growth and development of your onions. In the next chapter, we will answer the main question: for what purpose do we do all this – for flavour, health benefits, and the enormous variety of dishes that can be made with onions. Let’s find out what hides inside their juicy scales.

What Does Onion Contain?

On average, a common onion bulb consists of:

• Water (80–90%). Onion is a juicy product, and water makes up most of its mass. That is why it loses weight so quickly during storage (Rubatzky and Yamaguchi, 1997).
• Dry matter (10–20%). This fraction includes all valuable components: carbohydrates, proteins, vitamins, mineral salts, and aromatic compounds.

Main groups of substances that determine the value of onion:

1. Carbohydrates – Source of Sweetness and Energy

Carbohydrates are the main component of dry matter (up to 60–70%). Onion contains no starch; the main sugars are sucrose, glucose, and fructose, as well as fructan polymers – fructans (inulin) (Rubatzky and Yamaguchi, 1997; Block, 2010). They give onion its sweetish taste. Interestingly, pungent varieties generally contain more sugars (up to 9–12%) than sweet ones (4–8%). But pungent varieties seem less sweet because their pungency masks the sweetness (Brewster, 2008).

Practical conclusion: Sweet, salad varieties (e.g., ‘Exhibition’ or ‘Yalta’) have a lower dry‑matter content and less sugar than pungent ones, but because of the low essential‑oil content, they are perceived as sweeter. However, it is the high sugar and dry‑matter content that makes pungent varieties ideal for storage and caramelisation during frying.

2. Proteins, Fibre, and Minerals

Onion is not rich in protein (about 1.5%), but it contains all essential amino acids. Fibre (0.5–1.5%) stimulates intestinal peristalsis. Onion is a good source of potassium, phosphorus, calcium, magnesium, iron, and trace elements such as zinc, copper, manganese (Rubatzky and Yamaguchi, 1997). It is especially high in potassium, which is necessary for cardiovascular health.

3. Vitamins – Nature’s Recharge

Common onion is a recognised source of vitamins, especially B vitamins (B₁, B₂, B₆, PP) and vitamin C (ascorbic acid). Although onion is inferior to citrus fruits and peppers in vitamin C content, it plays a notable role in the winter‑spring period when fresh vegetables are scarce. In green foliage (leaves), the concentration of vitamins is significantly higher than in the bulbs, especially vitamin C and carotene (provitamin A) (Rubatzky and Yamaguchi, 1997).

Practical conclusion: For maximum vitamin intake, it is best to use fresh onion and especially green tops (forcing for greens). Heat treatment destroys some vitamins, but onion in soups and stews is still beneficial.

4. Flavonoids – Health Protectors

These are powerful natural antioxidants that protect body cells from damage and reduce the risk of cardiovascular diseases and some cancers. The main flavonoid in onion is quercetin and its glycosides (Rubatzky and Yamaguchi, 1997; Block, 2010). Quercetin gives red and yellow onions their characteristic colour. Red varieties have higher quercetin content than yellow or white ones. Quercetin has anti‑inflammatory, antibacterial, and antithrombotic effects.

Practical conclusion: For maximum antioxidant benefit, prefer red and yellow onions. White onion contains fewer flavonoids. Also, the highest flavonoid content is found in the outer, drier layers of the bulb, so do not peel too deeply (Block, 2010).

5. Volatile Sulfur Compounds – Smell, Taste, and Tears

These are the compounds that make onion what it is. They are formed when the bulb is cut or crushed, when the enzyme alliinase comes into contact with precursors – sulfur‑containing amino acids (S‑alk(en)ylcysteine sulfoxides) (Block, 2010; Kamenetsky and Rabinowitch, 2002).

• Cause of tearing: In onion (unlike garlic), the main product of this reaction is thiopropanal S‑oxide (the lachrymatory factor, LF). This volatile substance, when it reaches the eye mucosa, irritates nerve endings and causes copious tearing (Block, 2010; Kamenetsky and Rabinowitch, 2002).
• Cause of pungency and odour: Further transformation of volatile sulfur compounds produces various mono‑ and polysulfides (e.g., dipropyl disulfide), which create the characteristic pungent taste and long‑lasting onion smell (Block, 2010).
• Differences between varieties: Pungent varieties contain more sulfur‑compound precursors and have higher enzyme activity, giving a stronger lachrymatory effect and sharp taste. Sweet, salad varieties have lower levels of these compounds and a milder taste (Block, 2010).

Practical conclusions:

1. How to reduce tears when chopping onion: Chilling the bulb (place in the freezer for 10–15 minutes) or cutting under running water (or near a steam source) helps, because low temperatures slow the reaction, while water and steam dissolve volatile compounds. Using a sharp knife also reduces cell damage, lowering enzyme and precursor release (Block, 2010).

2. How to choose onion for salad: Use sweet (e.g., ‘Exhibition’, ‘Yalta’) or white salad varieties. They are less irritating to the eyes and have a delicate, slightly sweet taste.

3. How to choose onion for frying, soups, and storage: Pungent varieties with yellow and brown tunics are ideal. During frying, they caramelise, giving a golden colour and rich flavour. Moreover, they contain more dry matter and store better.

Comparative Table: Quick Variety Reference

Thus, understanding the chemical composition helps you make an informed choice of variety and how to use onion. Knowing which substances it contains, you can get the most flavour, health benefits, and enjoyment.

In the next chapter, we will systematise all this diversity and look at the main classifications and types of common onion, so you can choose the ideal option for your garden and kitchen.

Excellent, we have come to the most practical section. All the previous theory – botany, ecology, physiology – was necessary so that you could confidently navigate the variety diversity. In this chapter, we will break everything down and see just how different one and the same onion can be.

1. By Growing Method (Life Cycle in Cultivation)

In garden practice, common onion is grown in three main ways, each determining the choice of planting material and harvest timing.

• Annual crop (from seed): Seeds are sown in spring directly into the ground or for seedlings, and in one season a marketable bulb is obtained. This method is economical (no need to store sets) and gives more uniform bulbs. However, in regions with short summers, only early‑maturing varieties are suitable (Brewster, 2008). This method is ideal for the middle belt and southern regions.
• Biennial crop (from sets): In the first year, small bulbs – sets – are grown from seed. In the second year, the sets are planted and produce large marketable bulbs. This is the most reliable method in areas with short summers, where onion does not have time to grow from seed (Rubatzky and Yamaguchi, 1997). It also gives an earlier harvest. However, it requires proper set storage to avoid bolting.
• Perennial crop (vegetative propagation): This method mainly applies to varieties from the Aggregatum group (shallot, potato onion). They are propagated by bulbs (dividing the nest) and can grow in one place for several years. This is a traditional method in northern regions and the tropics, where vegetative material gives a quicker harvest and is more disease‑resistant (Brewster, 2008).
• Forcing for greens (tops): Multi‑germ varieties are specially selected, which produce a lot of greens when planted in the ground, greenhouses, or even at home on a windowsill. For forcing, pungent and semi‑pungent varieties with many germs (e.g., ‘Bessonovsky’ or ‘Arzamassky’) are often used (Brewster, 2008).

2. By Growing Period Length (Maturity Dates)

This is one of the most important classifications for selecting a variety for a particular climate.

• Early‑maturing (early): Growing period 80–100 days from emergence to lodging. They give a harvest in July. Often have a sweet or semi‑pungent taste but generally store poorly (2–3 months). Ideal for fresh consumption and regions with short summers. Examples: ‘Stuttgarter Riesen’, ‘Strigunovsky local’, ‘Zolotnichok’ (Kasynkina and Kudin, 2018).
• Mid‑season: 100–120 days. Harvest in August. Versatile: good both in salads and for storage (3–5 months). This is the largest group. Examples: ‘Odintsovets’, ‘Danilovsky’, ‘Carmen’ (Kasynkina and Kudin, 2018).
• Late‑maturing: More than 120 days. Harvest in late August – September. Distinguished by high storability (6–8 months), dense bulbs, pungent or semi‑pungent taste. Intended for long winter storage and processing. Examples: ‘Bessonovsky’, ‘Tambovsky’ (bred for long storage), ‘Settone’ (Kasynkina and Kudin, 2018).

Practical conclusion: In regions with cold, short summers (North, North‑West, Siberia), the choice should fall on early‑ and mid‑season varieties. In southern regions (Black Earth, Volga region, Kuban, Crimea), you can safely grow late‑maturing varieties, which store best.

3. By Photoperiodic Response (Day Length)

This is not just an academic parameter but a key to successful cultivation. As we discussed in Chapter 4, onion is a long‑day plant, but different varieties have different critical thresholds.

• Short‑day (SD): (11–13 hours). For southern regions (latitude < 35°), tropics and subtropics. Varieties are generally sweet, salad‑type, with short storage life. Examples: ‘Texas Grano’, ‘Yellow Granex’, ‘Red Creole’, ‘Karatal’ (Brewster, 2008).
• Intermediate‑day (ID): (13–14 hours). For temperate latitudes (35–38°). Good for autumn and early spring sowings in mild climates. Often used for very early production. Examples: ‘Candy’, ‘Sterling’.
• Long‑day (LD): (>14–16 hours). For northern regions (latitude > 38°). The most storable, dense, and pungent varieties. These dominate the markets of Russia and Europe. Examples: ‘Stuttgarter Riesen’, ‘Pukekohe Long Keeper’ (the name speaks for itself), ‘Red Baron’, ‘Khalkedon’ (Rubatzky and Yamaguchi, 1997).

Practical conclusion: This is the most important selection criterion. If you live in the south, you need short‑day varieties. In the north – long‑day varieties. Using a long‑day variety in the south may result in it not forming a bulb at all, while using a short‑day variety in the north will lead to small, quickly drying bulbs.

4. By Taste and Essential Oil Content (Pungency)

This classification determines culinary use.

• Pungent varieties: Contain many essential oils and sugars. They have a sharp, biting taste. Bulbs are dense, store well. Ideal for frying, soups, and long storage. Widely represented by long‑day varieties. Examples: ‘Stuttgarter Riesen’, ‘Bessonovsky’.
• Semi‑pungent varieties: Intermediate. Less biting than pungent, but sweeter and juicier. Versatile. Can be used for salads and for storage (3–4 months). Examples: ‘Odintsovets’, ‘Danilovsky’, ‘Zolotnichok’.
• Sweet (salad) varieties: Low in essential oils, so they taste very sweet and juicy, even though they may contain less sugar than pungent varieties. Bulbs are loose, juicy, with thin skin. They practically do not store (1–2 months). Used exclusively fresh (salads, appetisers). This group often includes short‑day varieties. Examples: ‘Exhibition’, ‘Yalta’, ‘Spanish’ (Brewster, 2008; Kasynkina and Kudin, 2018).

5. By Colour of Dry Scales (“Tunic”) and Flesh

This is one of the most noticeable varietal traits and affects chemical composition.

• Yellow onion: The most common. Classic, universal taste, stores well. It is the base for frying, soups, and long storage.
• White onion: Often milder and sweeter than yellow. Traditionally used in salads and sauces. Stores less well than yellow. Widely grown in southern regions (Spain, Mexico) (Rubatzky and Yamaguchi, 1997).
• Red/purple onion (‘Yalta’, ‘Red Baron’): Distinguished by a milder, sweetish taste and bright colour. Rich in anthocyanins (pigments), which are powerful antioxidants. Ideal for fresh salads but stores poorly. Particularly valuable are varieties with a red tunic and white or slightly pinkish flesh, such as the famous Yalta onion (Brewster, 2008; Kasynkina and Kudin, 2018).

6. By Ability to Divide (Nesting)

• Low‑germ varieties: Form one, rarely two bulbs. Give larger and more uniform bulbs. These are most modern varieties for industrial production.
• Medium‑ and multi‑germ varieties: (from 3 to 5 or more germs). Form a nest of several bulbs. This trait is used for forcing greens, as it produces many leaves. For food, such varieties give smaller but denser bulbs. Examples: ‘Bessonovsky’, ‘Arzamassky’, ‘Rostovsky’ (Brewster, 2008).

7. By Purpose and Use

• Salad (for fresh consumption): Sweet, semi‑pungent, juicy varieties with thin skin. Often red or white, with short storage life. Examples: ‘Exhibition’, ‘Yalta’.
• For long storage: Pungent and semi‑pungent, dense varieties with thick dry tunics. Mostly yellow. Examples: ‘Stuttgarter Riesen’, ‘Bessonovsky’.
• For processing and preserving: Varieties with high density and specific dry‑matter content. For example, for onion powder or canning (pickling, brining), white varieties with high density (‘Southport White Globe’) are suitable. For drying, varieties with high dry‑matter content are used (Brewster, 2008).
• For greens (tops): Multi‑germ, pungent varieties that produce a large amount of juicy foliage.

As you can see, variety selection is a compromise between what you want to get (taste, size, storability) and the conditions in which you will grow it (climate, soil). To avoid mistakes, you just need to answer a few questions. That is exactly what we will do in the next, final chapter of this series: “How to Choose a Variety and Growing Method for Your Needs”. There, we will bring all the criteria together and help you find your perfect onion.

Excellent, we have reached the main practical conclusion of our entire article. The previous chapters have given you fundamental knowledge about onion – its history, biology, ecology, and variety diversity. Now it is time to apply this knowledge in practice and answer the most important question: which onion to choose for your garden?

Step 1. Define Your Main Goal: What Do You Want to Get?

Before looking at pretty pictures in a catalogue, honestly answer this question. Your answer will determine about 80% of success.

1. “I need onion for long winter storage”:

• Your choice: Pungent and semi‑pungent varieties. They have a dense structure, thick dry scales (“tunic”), and high dry‑matter content, which ensures their storability (Brewster, 2008). Look at yellow and brown varieties – they are traditionally the most storable.
• Ideal variety: ‘Stuttgarter Riesen’ – a classic, time‑tested. ‘Bessonovsky local’ – reliable, pungent, storable. ‘Penzensky’ – an excellent option for the middle belt. ‘Tervin’ – produces dense, pungent, well‑storing bulbs.
• Growing method: Biennial (from sets). This gives an earlier harvest and denser bulbs that store better.
• Key parameters: Long‑day (LD) variety, late‑maturing, high dry‑matter content, pungent tunic (Rubatzky and Yamaguchi, 1997).

2. “I need onion for salads and fresh use”:

• Your choice: Sweet, semi‑pungent, and salad varieties. They are juicy, with thin skin, less biting, and have a delicate flavour. Red and purple varieties, rich in antioxidants, are especially good (Rubatzky and Yamaguchi, 1997).
• Ideal variety: ‘Exhibition’ – a salad giant, grown through seedlings. ‘Yalta’ – the famous red sweet onion. ‘Karatal’ – an excellent early variety for southern regions. ‘Rosario’ – semi‑pungent, attractive.
• Growing method: Annual (from seed or seedlings). Seeds give more juicy and tender bulbs than sets.
• Key parameters: Short‑day (SD) or intermediate‑day (ID) variety, early‑maturing, high water content, red or white colour.

3. “I need onion for processing and preserving”:

• Your choice: Varieties with high dry‑matter content (for drying, powder) or dense structure for pickling. Often these are white or yellow, dense varieties.
• Ideal variety: ‘Southport White Globe’ – classic for drying. ‘Strigunovsky local’ – good for pickling. ‘Globus’ – universal, semi‑pungent, with round bulbs.
• Growing method: Depending on the region – annual or biennial.
• Key parameters: High dry‑matter content, dense bulb, white or yellow flesh.

4. “I need onion for greens (tops)”:

• Your choice: Multi‑germ varieties that produce many leaves from one planting unit (Brewster, 2008).
• Ideal variety: ‘Bessonovsky’, ‘Arzamassky’, ‘Spassky’ – multi‑germ, give strong tops. Also suitable are Welsh onion and shallot.
• Growing method: Forcing from sets or bulbs (selection). This is the fastest way to get greens.
• Key parameters: Multi‑germ, fast leaf growth.

Step 2. Determine Your Region and Climate

This is the second most important step. It is directly linked to photoperiodic response, which we discussed in Chapter 4.

How to determine your “onion belt”:

• South of Russia (latitude < 45°): Krasnodar Krai, Crimea, Rostov Oblast, Lower Volga, Stavropol.
• Central Russia and Black Earth Region (45°–55° N): Moscow, Vladimir, Voronezh, Tambov regions, Middle Volga.
• North‑West, Siberia, Urals (latitude > 55°): Leningrad Oblast, Novosibirsk Oblast, Sverdlovsk Oblast, Arkhangelsk Oblast.

Correspondence table:

Practical tip: When buying seed, always read the label. Reputable producers always indicate for which region the variety is recommended. Varieties like ‘Stuttgarter Riesen’, ‘Odintsovets’, ‘Bessonovsky’ are long‑day varieties that grow best in the middle belt and further north. Varieties like ‘Texas Grano’, ‘Yellow Granex’ are short‑day, their place is in the south (Brewster, 2008).

Step 3. Consider Your Growing Method

You have already decided what you want (Step 1) and where you live (Step 2). Now decide how you will do it.

• From seed (annual crop):
• Pros: Economical (no need to buy and store sets), healthier crop, more uniform bulbs, ideal for sweet varieties (Brewster, 2008).
• Cons: Requires a longer growing season (only suitable for early‑ and mid‑season varieties), requires more careful early care (weed control, delicate seedlings).
• Suitable for: Southerners and Central residents who want salad varieties. Also suitable for growing for greens.
• From sets (biennial crop):
• Pros: Reliable in regions with short summers (earlier harvest), bulbs are denser and larger, ideal for pungent varieties for storage (Rubatzky and Yamaguchi, 1997).
• Cons: Requires proper set storage (avoid the “golden mean” temperatures – +5…+15 °C – to prevent bolting), more costly.
• Suitable for: Residents of the North and Centre who want onion for long storage (Brewster, 2008).
• For greens (forcing):
• Pros: Very fast way to get a green crop, can be done in greenhouses and even on a windowsill (Kasynkina and Kudin, 2018).
• Cons: Requires multi‑germ varieties, does not produce bulbs.
• Suitable for: Anyone who wants their own greens in early spring or winter.

Practical Examples (How It Works):

• Example 1. A gardener from the Moscow region (55° N). Wants onion for storage for winter. He needs a long‑day (LD), late‑maturing, pungent variety. The best choice is growing from sets. Ideal variety – ‘Stuttgarter Riesen’ or ‘Bessonovsky’.
• Example 2. A gardener from Krasnodar Krai (44° N). Wants to grow sweet salad onion. He needs a short‑day (SD), early‑maturing, sweet variety. The best choice is sowing seeds. Ideal variety – ‘Exhibition’ (through seedlings) or ‘Yalta’ (sowing in the ground).
• Example 3. A resident of Novosibirsk (55° N). Wants early greens. He needs a multi‑germ, fast‑growing variety. The best choice is forcing from sets in a greenhouse. Ideal variety – ‘Bessonovsky’.

Final Top Tips

1. Never ignore photoperiod. This is the most common source of mistakes.

2. Buy planting material from trusted suppliers. This ensures the variety matches the label.

3. Experiment with small batches. In the first year, plant 2–3 different varieties to see which ones best suit your climate and soil.

4. Remember: sweet onion is not for storage, pungent onion is not for salad. These are different categories with different purposes.

Now, armed with this knowledge, you will be able to choose that very variety that will give you a great harvest and delight you all year round!