Cherry

Wild Ancestors and Native Land of the Cherry

The cherry is one of the oldest fruit crops, known to humanity since prehistoric times. Archaeological evidence shows that fruits of wild cherry forms were consumed as food as early as the Neolithic era, around 4000–5000 BC (Brown et al., 1996; Webster, 1996). Fossilized cherry stones dating from the Neolithic to the Bronze Age have been found in caves in Switzerland, France, Italy, and Hungary (Faust and Suranyi, 1997).

Wild cherry forms originate from two main centers:

• Sweet cherry (wild cherry) — Prunus avium — originated in the Caspian and Black Sea region, from where it spread throughout Europe (Hedrick et al., 1915; Webster, 1996). Its spread was aided by birds that ate the fruits and dispersed the seeds.
• Sour cherry (tart cherry) — Prunus cerasus — formed through natural hybridization between sweet cherry and steppe cherry (Prunus fruticosa) in regions of Eastern Europe and Asia Minor, where the ranges of these species overlapped (Olden and Nybom, 1968; Iezzoni et al., 1990).

The Path to Cultivation

Ancient Period

The first peoples to cultivate cherries were the ancient Greeks. The Greek historian Theophrastus (around 300 BC) mentioned cherries under the name kerasos (Hedrick et al., 1915). However, the widespread cultivation of the crop in Europe is associated with the Romans.

According to historical sources, the Roman general Lucullus brought cherry trees from the city of Cerasunt (modern-day Black Sea coast, Turkey) to Rome in 74–66 BC (Pliny, 1793). However, modern historians believe that cherries were already known in Italy before Lucullus, and he likely introduced new, improved varieties (Webster, 1996). Within a hundred years of this, at least ten different cherry varieties were being cultivated in the Roman Empire.

Middle Ages and Early Modern Period

With the fall of the Roman Empire, many varieties were lost, but cherry orchards were preserved in monasteries and princely estates. In the 8th century, Emperor Charlemagne, in his decree Capitulare de Villis, ordered cherries to be planted in royal gardens (Roach, 1985).

In Britain, cherries appeared during the Roman conquest (1st–4th centuries AD), but were reintroduced from Europe in the 16th century during the reign of King Henry VIII (Webster, 1996). In Germany and Central Europe, cherry orchards became widespread in the 15th–16th centuries.

Development of Table Varieties

Until the 19th century, variety improvement occurred mainly through the selection of the best seedlings from local populations. Systematic breeding work began only in the 19th century.

In 1819, Baron von Truchess-Heim in Germany classified 75 cherry varieties, laying the foundations for the taxonomy and breeding of the crop (Webster, 1996).

The first targeted crossings and development of new varieties began:

• In England — Thomas Knight in the early 19th century
• In the USA — Seth Lewelling developed the famous 'Bing' variety in Oregon in 1875 (Hedrick et al., 1915)
• In Russia — I. V. Michurin in the late 19th – early 20th century

Spread Around the World

Europe remains the traditional center of cherry cultivation. The largest producers of sweet and sour cherries in Europe are:

• Sweet cherries: Turkey, Italy, Spain, Ukraine, Poland
• Sour cherries: Turkey, Poland, Ukraine, Russia, Serbia, Hungary

The Americas. Cherries were introduced to North America by European settlers in the 17th–18th centuries. In the US, sweet cherry production is concentrated in Washington, California, and Oregon, while sour cherries are mainly grown in Michigan (Quero-García et al., 2017). In Canada, the main areas are in British Columbia and Ontario.

Asia. Cherry has been known in China since ancient times; however, rapid production growth has occurred only in recent decades. China has become a major producer of both sweet cherries (more than 141,000 ha) and traditional local species (Quero-García et al., 2017).

Southern Hemisphere. Chile is one of the world's leading exporters of sweet cherries, supplying products to China and the US. Australia and New Zealand are also developing export production.

Table 1 — Largest producers of sweet and sour cherries in the world

Note: Data may vary slightly from year to year.

Source: Quero-García et al. (2017), Webster and Looney (1996).

Two Main Cultivated Species

In global fruit growing, two main species are cultivated — sweet cherry (Prunus avium) and sour cherry (Prunus cerasus):

Thanks to breeding achievements, today there are over 1,000 varieties of sweet and sour cherries, adapted to various climatic conditions — from temperate cold regions to subtropics (Quero-García et al., 2017).

Systematic Position

Understanding which genus and species cherry belongs to helps the gardener understand its biological features, growing requirements, and graft compatibility.

Brief taxonomy:

According to modern classification, all "true" cherries belong to the genus Prunus and subgenus Cerasus (Rehder, 1974; Potter et al., 2007). Previously they were sometimes separated into the genus Cerasus, but most modern botanists consider such division outdated (Webster, 1996).

Main Cultivated Species

Two main species, as well as their hybrids, are cultivated in global fruit growing.

Intraspecific Groups of Sour Cherry

In practical horticulture, varieties of sour cherry are conventionally divided into two main groups, differing in fruit juice color and morphological features (Hedrick, 1915; Schuster et al., 2017).

Dukes — Hybrids of Sweet and Sour Cherry

Dukes (from English duke cherries) are natural or artificial hybrids between sweet cherry and sour cherry (Prunus × gondouinii Rehd.). They:

• Have intermediate traits between parents
• Often more winter-hardy than sweet cherry
• Fruits larger than sour cherry, but more tart than sweet cherry
• Can be self-fertile or partially self-fertile

The most famous duke variety is 'May Duke', known since the 18th century (Webster, 1996). In modern breeding, dukes are used to create winter-hardy sweet cherry varieties.

Related Wild Species and Their Significance

For the gardener, it is useful to know about several wild species that are used as rootstocks or as sources of valuable genes for breeding.

Important for the gardener: graft compatibility is generally high within the subgenus Cerasus. The most common rootstocks for sour and sweet cherries are seedlings of sweet cherry (wild form), mahaleb, as well as clonal rootstocks such as 'Colt', 'Gisela', 'VSL-2' (Webster and Schmidt, 1996; Quero-García et al., 2017).

Why Should a Gardener Know This?

1. Choice of rootstock. Understanding relatedness helps select a compatible rootstock for grafting the desired variety.

2. Resistance to conditions. Species with different genetic origins vary in their tolerance to frost, drought, and calcareous soils.

3. Type of fruiting. Different cherry groups bear fruit on different types of branches — this determines the pruning system.

4. Pollination. Most sweet cherry varieties are self-sterile and require pollinator varieties, while many sour cherry varieties are self-fertile (Iezzoni et al., 1990).

3.1. Life Form and General Appearance

Cherry is a perennial deciduous tree or shrub. Depending on the species and variety, it can take different forms (Kurennoi et al., 1985; Mikheev and Revyakina, 2004):

Longevity. Tree-like cherries can live 50–70 years or more, while bush-like ones live 20–30 years. In commercial orchards, the economically viable lifespan is 15–25 years. Sweet cherry under favorable conditions lives up to 80–100 years (Trunov et al., 2012).

3.2. Structure of the Above-Ground Part

The above-ground system of cherry consists of the trunk (lower part of the stem up to the first skeletal branches), central leader, skeletal and semi-skeletal branches, and fruiting wood on which the crop is formed.

Important for the gardener: in bush-like forms, the trunk is weakly expressed or absent, and the crown is formed from several equal trunks. This affects the method of pruning and shaping.

Shoots of cherry are classified by length and purpose (Potapov et al., 2000):

• Vegetative (long) — 30–50 cm or more, bear mainly vegetative (growth) buds. The skeleton of the crown is formed from them.
• Fruiting — shorter (10–30 cm), bear flower buds and form the crop.
• Bouquet spurs — very short (0.5–3 cm) formations, characteristic of sweet cherry and tree-like sour cherries; at the top is a growth bud, and on the sides are 4 to 10 flower buds (Trunov et al., 2012; Webster, 1996).

3.3. Buds: Vegetative and Generative

In sour and sweet cherries, buds are of two types (Kurennoi et al., 1985; Mikheev and Revyakina, 2004):

• Vegetative (growth) buds — form shoots and leaves.
• Generative (flower) buds — produce only flowers and fruits; after fruiting they die, and the branch becomes bare in that area.

Important feature: in sour cherries, flower buds are most often simple (i.e., forming only a flower), whereas in apples and pears, buds are mixed (producing both shoot and flowers simultaneously). Therefore, in cherries, after fruiting, the shoot does not continue growing from this bud — it dies.

Group arrangement of buds. At one node of a cherry shoot, 2–3 buds can develop: the central one is growth, and the side ones are flower buds. This is typical for bush-like varieties. In tree-like forms and sweet cherries, single buds usually predominate (Trunov et al., 2012).

3.4. Types of Fruiting

According to the nature of fruiting, all cherry varieties are divided into two groups (Mikheev and Revyakina, 2004; Potapov et al., 2000):

3.5. Root System

The root system of cherry is mostly superficial (Mikheev and Revyakina, 2004; Trunov et al., 2012):

• Horizontal roots lie at a depth of 20–40 cm and extend far beyond the crown projection.
• Vertical roots penetrate to 1.5–2 m, but the bulk of absorbing rootlets are concentrated in the upper layer.
• The root system is sensitive to soil compaction, waterlogging, and drought.

Root suckers. Sour cherry (especially bush-like varieties and own-root plants) abundantly produces root suckers — shoots growing from adventitious buds on roots. Sweet cherry and cherries grafted on clonal rootstocks produce few or no suckers (Trunov et al., 2012).

3.6. Leaves and Flowers

Leaves of cherry are simple, oval or obovate, with serrated or doubly serrated edges. In sweet cherry, leaves are larger and have characteristic reddish glands at the base of the blade (on the petiole). Color varies from light green to dark green; in autumn, many varieties turn yellow or reddish.

Cherry flowers:

• Gathered in inflorescences — umbels (in sweet cherry usually 2–4 flowers, in sour cherry up to 5–7).
• Flowers white or pale pink, bisexual.
• Most sour cherry varieties are self-fertile (capable of setting fruit from their own pollen). Sweet cherries, conversely, are predominantly self-sterile and require a pollinator variety (Iezzoni et al., 1990).

Flowering time: cherries bloom earlier than apples, but later than apricots and peaches. In the temperate zone — usually in May, in southern regions — in April. Flowers are sensitive to spring frosts: buds are damaged at –4…–5 °C, flowers at –2…–3 °C, and ovaries already at –1…–2 °C (Krivko et al., 2014).

3.7. Fruit — a Drupe

The cherry fruit is a drupe, consisting of:

• Outer layer (exocarp) — thin skin (color from yellow to dark red or almost black).
• Middle layer (mesocarp) — fleshy pulp (light in amarelles, dark-colored in morellos).
• Inner layer (endocarp) — lignified stone protecting the seed.

Fruit size varies from 1.5 to 2.5 cm in diameter for sour cherry and up to 3 cm or more for sweet cherry. Fruit weight in different varieties — from 2–3 g (sour cherry) to 6–10 g (large-fruited sweet cherry varieties).

Practical significance:

• In varieties with tender pulp, fruits transport and store poorly; in bigarreau (sweet cherry with firm flesh), storage and transportability are higher.
• Varieties with dry fruit-stem separation are convenient for mechanical harvesting, which is important for processing.

3.8. Growth and Fruiting Features in the Annual Cycle

For proper care, it is important to know the key developmental phases of cherry (Tarasov et al., 1981; Potapov et al., 2000):

1. Dormancy (autumn — early spring). During this time, the necessary chilling hours pass for normal bud development.

2. Bud swelling and bursting — start of vegetation; determined by temperature and completion of dormancy period.

3. Flowering (lasts 7–14 days depending on weather). Important: presence of pollinators and absence of frost.

4. Shoot growth and fruit formation. Simultaneously, flower buds for the future crop are laid (in most varieties — in June–July).

5. Fruit ripening — in sour cherry usually 45–60 days after flowering, in sweet cherry — 50–70 days.

6. End of vegetation and preparation for winter — growth slows, leaf fall, accumulation of reserves.

What Does This Knowledge Give the Gardener?

4.1. Climatic Zones and Winter Hardiness

Sour and sweet cherries originate from temperate climate regions, but their relationship to frost differs significantly (Krivko et al., 2014; Westwood, 1993).

Winter hardiness of species in descending order:

Practical conclusion: in regions with severe winters (Siberia, Urals, northern European Russia), sour cherry is preferred over sweet cherry. Sweet cherry is optimal for southern regions with mild winters (Krasnodar Krai, Crimea, southern Ukraine, Mediterranean countries).

Winter damage. In cherries, the following most often suffer:

• Flower buds (damaged at –25…–30 °C for sour cherry and –24…–25 °C for sweet cherry).
• Trunk and bases of skeletal branches (sunburn and frost cracks — longitudinal bark cracks, especially on the south side).
• Root system (in the absence of snow cover and soil temperatures below –12…–15 °C).

Winter-kill (heaving). In regions with frequent thaws and heavy snowfall (Non-Black Earth region, northwest), the danger is not so much frost as root collar rot — bark rot when under snow for a long time on wet, unfrozen soil (Krivko et al., 2014; Mikheev and Revyakina, 2004). This is especially relevant for bush-like varieties.

4.2. Chilling Requirement (Chill Hours)

For normal development and subsequent flowering, cherries need a period of winter dormancy with a certain sum of low positive temperatures (Westwood, 1993; Webster, 1996).

What are "chill hours"?

This is the number of hours (or days) with temperature below +7.2 °C that the plant must "accumulate" over winter for normal spring awakening. If chill hours are insufficient, buds open unevenly, flowering is prolonged, and yield is reduced.

Approximate chill requirements:

• Sour cherry — 800–1200 hours (depending on variety)
• Sweet cherry — 900–1200 hours (except for low-chill varieties for subtropics)

In regions with warm winters (southern US, North Africa, parts of the Mediterranean), special low-chill varieties of sour and sweet cherry are selected, requiring 300–600 chill hours (Westwood, 1993).

Important: in areas with unstable snow cover and frequent thaws, chill hours are "lost," which prolongs dormancy and may delay flowering.

4.3. Temperature Requirements by Season

Cherry is a temperate zone crop, and its growth directly depends on air and soil temperatures (Trunov et al., 2012; Krivko et al., 2014).

Accumulated active temperatures. For normal fruit ripening, sour cherry requires about 2000–2500 °C of active temperatures (above +10 °C), sweet cherry — 2600–2800 °C (Krivko et al., 2014). This explains why sweet cherry is more heat-loving and does not succeed in northern regions.

For the gardener: in cold regions, choose early-ripening varieties and varieties resistant to return frosts. Sour cherries with such properties include 'Molodyozhnaya', 'North Star', 'Volochaevka' (Mikheev and Revyakina, 2004).

4.4. Moisture Requirements

Cherry is a crop with moderate drought tolerance (Kurennoi et al., 1985; Westwood, 1993). It tolerates drought worse than apricot or almond, but better than plum and apple.

Critical water consumption periods (Trunov et al., 2012):

1. Flowering and fruit set. Moisture deficiency at this time leads to massive ovary drop.

2. Fruit growth (3–4 weeks after flowering). With water deficiency, fruits become smaller, yield drops.

3. Autumn (August–September). Excessive watering at this time prolongs growth and reduces winter hardiness.

Optimal soil moisture: 70–80 % of field capacity. Excess moisture is dangerous — cherry roots are sensitive to anaerobic conditions.

Tolerance to excess moisture. Sour cherry tolerates short-term waterlogging better than sweet cherry, but prolonged flooding (more than 10–15 days during the growing season) leads to death of absorbing roots and subsequent tree death (Fernández-Escobar, 1996).

Recommendation: in arid regions without irrigation, cherry grows poorly. In the temperate zone with precipitation of 500–600 mm/year, cherry survives without irrigation, but yield and fruit quality are higher with watering.

Air humidity. Cherry prefers moderate humidity. Excessive humidity during flowering hinders pollination and promotes fungal diseases (moniliosis, coccomycosis). Strong wind combined with dry air increases evaporation, which can cause leaf scorch and gummosis (Agustí, 2010).

4.5. Light Requirements

Cherry is a light-demanding crop. Its need for light is among the highest of fruit crops (Krivko et al., 2014; Trunov et al., 2012).

Consequences of light deficiency:

• Shoots become elongated, thin, and weak.
• Flower bud set decreases.
• Fruits become smaller and less colored.
• Inner parts of the crown become bare, fruiting shifts to the periphery.

Practical conclusions:

• Plant cherries in well-lit areas, away from tall trees and buildings.
• Avoid crowding — between trees should be at least 3–4 m (for vigorous varieties — 5–6 m).
• Carry out regular thinning pruning to illuminate the inner parts of the crown.

4.6. Soil Requirements

Cherry is a crop with fairly high soil requirements (Agustí, 2010; Fernández-Escobar, 1996; Westwood, 1993).

Mechanical composition. Light and medium loams are optimal — loose, well-aerated, and water-permeable.

Acidity (pH). Optimal range — pH 6.0–7.5 (slightly acidic or neutral soils).

• On acidic soils (pH < 5.5), cherry suffers, growth slows, signs of calcium and magnesium deficiency appear.
• On strongly alkaline soils (pH > 7.5), chlorosis develops — yellowing of leaves due to iron inaccessibility.

Calcium and lime. Cherry is quite sensitive to active lime in the soil. Limit of 10–12 % calcium carbonates (active lime) — for most varieties. Steppe cherry and some hybrids are more lime-tolerant (Fernández-Escobar, 1996).

Recommendation: before planting, test soil pH and calcium content. If necessary, add gypsum for acidic soils or organic matter to improve structure.

Soil layer depth. For normal development, cherry requires at least 0.7–1.0 m of loose fertile layer. Roots penetrate deeper, but the bulk of roots are in the 20–50 cm horizon (Kurennoi et al., 1985).

Saline soils. Cherry does not tolerate salinization (Agustí, 2010; Fernández-Escobar, 1996). In regions with saline soils (southern Russia, Central Asia), choose varieties on more salt-tolerant rootstocks (e.g., mahaleb) or avoid cultivation.

4.7. Topography and Microclimate

Proper placement in the orchard is important for cherry (Trunov et al., 2012).

• Slope. Northern, northeastern, or northwestern slopes are preferred in southern regions — they warm less in winter, delaying flowering and reducing spring frost risk. In the temperate zone, southern slopes are also suitable — they warm earlier in spring.
• Wind protection. Cold northern and eastern winds in winter intensify freezing, and in spring hinder bee activity. Natural or artificial protection is desirable (windbreaks, fences, buildings).
• Frost pockets. Do not plant cherries in lowlands and depressions — cold air flows there, increasing the risk of flower damage by spring frosts (Agustí, 2010).

Summary Table — Cherry Ecological Requirements

Summary for the Gardener

1. For survival: sour cherry is more winter-hardy than sweet cherry; for harsh regions choose sour cherry or winter-hardy sweet cherry varieties on hardy rootstocks.

2. For yield: always consider spring frosts — plant on elevated, well-ventilated sites.

3. For growth: soil should be loose, with no water stagnation, neutral reaction.

4. For fruiting: cherries need sun — do not plant in shade or overcrowd.

5. In arid regions without irrigation, yields will be poor — plan for irrigation.

5.1. Annual Development Cycle

Like all deciduous fruit plants of temperate zones, cherry passes through a successive change of physiological phases during the year (Tarasov et al., 1981; Potapov et al., 2000).

Main phases of the annual cycle:

5.2. Features of the Dormancy Period

Deep dormancy (endodormancy) is the internal state of the plant in which it is unable to resume growth even under favorable conditions (Agustí, 2010). This is an evolutionary mechanism protecting buds from premature opening during winter thaws.

What happens during dormancy?

• Respiration and all metabolic processes slow down.
• Content of growth inhibitors (primarily abscisic acid — ABA) increases in buds.
• Starch in storage tissues hydrolyzes to soluble sugars, which serve as cryoprotectants — protecting cells from ice damage.
• Water content in tissues decreases, increasing frost resistance.

Exiting dormancy occurs only after accumulating the required number of chill hours (temperature below +7.2 °C). After that, ABA content decreases, and the concentration of growth stimulators (gibberellins and cytokinins) increases (Potapov et al., 2000).

For the gardener: if the winter was warm and the cherry did not accumulate sufficient chill hours, flowering will be weak, prolonged, and yield reduced. In such conditions, choose varieties with lower chill requirements (low-chill) (Westwood, 1993).

Important distinction between sour and sweet cherry: sour cherry has deeper dormancy than sweet cherry. Therefore, sweet cherry more often suffers from premature bud opening during winter thaws and from spring frosts (Krivko et al., 2014).

5.3. Root Growth

The root system of cherry grows not continuously, but in waves — several waves of active root growth occur during the growing season (Kurennoi et al., 1985; Potapov et al., 2000).

Typical root growth dynamics in the temperate zone:

1. Spring wave (late April – early June) — most intensive. Roots begin to grow when soil warms to +5…+8 °C, before leaf emergence. This wave provides the tree with water and nutrients during flowering and initial shoot growth.

2. Summer slowdown — root growth slows in June–July, when most assimilates are directed to shoot and fruit growth.

3. Autumn wave (late August – October) — renewed root growth after harvest, when carbohydrates begin to flow to roots and accumulate as winter reserves.

Root depth distribution depends on region and soil (Krivko et al., 2014):

• Northern zone (Non-Black Earth) — bulk of roots at 20–40 cm depth.
• Middle zone — up to 50–75 cm.
• Southern zone — up to 1.0–1.2 m.

Practical conclusion: fertilizing, irrigation, and cultivation should be timed to the beginning of root growth waves (early spring and autumn). Deep cultivation (on a spade) in the root zone is undesirable — it can damage fine absorbing roots.

5.4. Shoot Growth

Cherry shoots grow mainly in one or two waves per season (Mikheev and Revyakina, 2004; Trunov et al., 2012).

• First wave — immediately after flowering (May – early June). This is the most intensive growth, determining the future crown and fruit bud initiation.
• Second wave (July–August) — in young trees and with excess nitrogen. The second wave is dangerous because shoots do not have time to ripen before winter and may freeze.

Connection between shoot growth and fruiting. In bush-like cherries, the crop is laid on previous year's growth. Therefore, if the annual growth is less than 20–30 cm, then few flower buds are set, and next year's yield decreases (Potapov et al., 2000).

Practical conclusion: for stable cherry fruiting, annual stimulation of strong shoots 30–40 cm long is needed. This is achieved by moderate pruning, fertilizing, and maintaining optimal soil moisture.

In tree-like sour cherries and sweet cherries, fruiting is concentrated on perennial bouquet spurs. Therefore, the main task here is not to allow bareness of old branches and to preserve productive fruiting formations (Trunov et al., 2012).

5.5. Flowering and Pollination

Flowering is one of the most critical phases determining the future harvest. In sour and sweet cherries, it begins early in spring, often before leaves emerge (in sweet cherry, flowering coincides with leaf emergence; in sour cherry, slightly earlier) (Kurennoi et al., 1985).

Flowering sequence of different species (Agustí, 2010; Webster, 1996):

Self-fertility and cross-pollination (Iezzoni et al., 1990; Quero-García et al., 2017):

• Most sour cherry varieties — self-fertile (capable of setting fruit from pollination by their own pollen). This is an important advantage for small gardens and home plots.
• Most sweet cherry varieties — self-sterile. They definitely need a pollinator variety flowering at the same time and compatible in incompatibility groups (S-alleles). Without a pollinator, there will be no crop or it will be negligible.

Critical temperatures for flowers (Krivko et al., 2014):

Practical conclusion: in regions with frequent spring frosts, choose late-flowering sour cherry varieties. Their buds open later, and the risk of flower damage is lower. Sweet cherry has fewer such varieties, so it is recommended for warmer regions.

5.6. Fruit Formation and Growth

The cherry fruit goes through several stages of development from fertilization to full ripeness (Agustí, 2010; Potapov et al., 2000):

1. Cell division (first 2–3 weeks after fertilization). Active cell division in the ovary. Fruits are still small, green. During this period, the potential size of the fruit is determined. Lack of moisture or nutrients at this stage results in small fruits, even if conditions improve later.

2. Cell expansion growth (next 3–5 weeks). Cells enlarge, accumulating water and sugars. At this stage, fruits grow rapidly — this is the period of maximum water consumption.

3. Ripening (final phase). Accumulation of sugars, anthocyanins (color), reduction of acidity. In sour cherry, ripening takes 45–60 days from flowering; in sweet cherry — 50–70 days (depending on variety and region).

Role of seeds (stones). Forming seeds secrete hormones (auxins, gibberellins) that stimulate fruit flesh growth (Agustí, 2010). Therefore, varieties with underdeveloped seeds (parthenocarpic) form small fruits.

Double ripening. Some cherry varieties show uneven ripening of fruits on one tree: fruits on well-lit peripheral branches ripen first, then those in the inner parts of the crown. This extends the harvest period, which is sometimes convenient for a hobby garden, but for commercial plantings, varieties with uniform ripening are preferred (Mikheev and Revyakina, 2004).

5.7. Flower Bud Initiation

One of the key physiological processes determining next year's yield is initiation and differentiation of flower buds (Potapov et al., 2000; Trunov et al., 2012).

When does this happen?

• In most cherry varieties, flower bud initiation begins in June, immediately after active shoot growth ends, and continues until August–September.
• In sweet cherry — similarly, but slightly later.

Stages of differentiation (Tarasov et al., 1981):

1. Initiation start — the bud growth cone becomes convex, flower primordia form.

2. Flower tubercle formation — primordia of individual flowers separate.

3. Sepal and petal formation — perianth elements are laid down.

4. Stamen and pistil initiation — spore-bearing organs form (occurs in autumn, before leaf fall).

5. Final development — pollen and embryo sac formation completes in spring, before flowering.

Conditions for full bud initiation (Agustí, 2010):

• Adequate light (at least 50–70 % of full sunlight).
• Moderate water and nitrogen supply. Excess nitrogen prolongs shoot growth and delays differentiation.
• Healthy leaf apparatus, actively photosynthesizing.
• Presence in the crown of "growth points" — young shoots on which future flower buds are laid.

For the gardener: if in June–July trees suffer from drought or leaf diseases (coccomycosis, moniliosis), flower bud initiation is disrupted. Therefore, protecting leaves from diseases and maintaining moisture during this period is the key to next year's harvest.

5.8. Physiological Disorders and Their Causes

It is useful for the gardener to know the main physiological disorders found in cherry (Agustí, 2010; Mikheev and Revyakina, 2004):

Summary for the Gardener

1. Dormancy period is important. If winter was warm — do not expect friendly flowering. Choose low-chill varieties for southern regions.

2. In spring, the main task is to protect flowers from frost. Use smoking, covering with non-woven material, or choose late-flowering varieties.

3. Roots grow in two waves — in spring and autumn. These are good times for fertilizing and watering.

4. Flower bud initiation — in June–July. Avoid drought and leaf diseases at this time, otherwise there will be no harvest next year.

5. Sour and sweet cherries have different fruiting strategies. Bush-like varieties need strong annual growth (30–40 cm), tree-like varieties need preservation of bouquet spurs. Accordingly, pruning differs.

6.1. Why Cherry Is a Valuable Food Product

Cherry fruits are a true natural concentrate of biologically active substances. They contain (Mikheev and Revyakina, 2004; Trunov et al., 2012):

• Sugars — from 7 to 14 % (depending on variety and conditions)
• Organic acids — 0.8–2.6 %
• Vitamins — C, B₁, B₂, B₆, B₉ (folic acid), PP, E, carotenoids (provitamin A)
• Mineral elements — potassium, calcium, magnesium, phosphorus, iron, copper, manganese
• Phenolic compounds — anthocyanins, flavonoids, coumarins
• Pectin substances — 0.2–1.2 %
• Tannins and coloring substances — impart astringency and color

In terms of calorie content, cherry is second only to grapes, surpassing apples, pears, apricots, peaches, currants, raspberries, and strawberries (Mikheev and Revyakina, 2004).

6.2. Sugars and Organic Acids: The Basis of Taste

The taste of cherries is determined by the ratio of sugars and organic acids. It is this ratio that creates the characteristic tart-sweet range for which this berry is valued.

Sugar composition (Mikheev and Revyakina, 2004):

Organic acids (Trunov et al., 2012):

• Malic acid — predominant (up to 2.0 %)
• Citric acid — 0.2–0.8 %
• Succinic, quinic, oxalic — in smaller amounts

Important: in ripe cherry fruits, sucrose usually predominates (up to 75 % of all sugars), while in unripe fruits, glucose and fructose predominate. Therefore, fruits should be picked fully ripe — they will be sweeter than those picked early (Mikheev and Revyakina, 2004).

Difference between sour and sweet cherry (Mikheev and Revyakina, 2004; Webster, 1996):

Sweet cherry is significantly sweeter precisely because it has less acid. Sour cherry has pronounced acidity, making it ideal for processing, but for fresh consumption, choose sweet varieties or those with high sugar content.

6.3. Vitamin Composition: Nature's Pharmacy

Cherry is a rich source of vitamins, especially important for maintaining health (Mikheev and Revyakina, 2004; Trunov et al., 2012).

Folic acid deserves special attention. In fresh ripe fruits, its content is 0.05–0.15 mg/100 g, and in beginning to overripe fruits, the content increases to 0.25–0.5 mg/100 g (Mikheev and Revyakina, 2004). The daily human requirement for folic acid is 0.5–1.0 mg. This means that 100–200 g of overripe fruits can cover the daily requirement.

Interesting fact: cherry contains simultaneously two substances involved in hematopoiesis — iron and folic acid. This is a rather rare combination, making cherry valuable for the prevention of anemia (Mikheev and Revyakina, 2004).

6.4. Mineral Composition: Trace Elements for Health

Cherry fruits contain a wide range of mineral elements essential for humans (Trunov et al., 2012; Krivko et al., 2014).

Cherry is twice as rich in iron as apples (Mikheev and Revyakina, 2004). Iron content ranges from 1 to 2 mg per 100 g of fruit. For comparison: the daily requirement for an adult is 10–15 mg of iron (for women — up to 18–20 mg).

6.5. Biologically Active Substances

Coumarins — a special group of substances worth paying attention to (Mikheev and Revyakina, 2004; Trunov et al., 2012).

• Cherry fruits contain 0.8–1.2 % coumarins and hydroxycoumarins.
• These substances reduce blood clotting and prevent thrombus formation.
• Among garden crops, cherry is second only to red currant, black raspberry, and pomegranate in coumarin content.
• Coumarins are well preserved when fruits are dried, so dried cherries (like prunes) are a valuable product for thrombosis prevention.

Anthocyanins — pigments that give cherries their dark red color (Agustí, 2010; Quero-García et al., 2017).

• Have anti-inflammatory and antioxidant effects.
• The intensity of juice coloring (in morellos) directly correlates with anthocyanin content.
• Varieties with colorless juice (amarelles) have significantly fewer anthocyanins.

Pectin substances (Trunov et al., 2012):

• Content in cherry fruits — 0.2–1.2 % (on fresh weight basis).
• Have the ability to remove heavy metals and toxins from the body.
• Determine the gelling ability of juice — important for jam, jelly, marmalade production.

Tannins (Trunov et al., 2012):

• Impart astringency to fruits, which in some varieties can be strongly expressed.
• Have astringent and anti-inflammatory effects.

6.6. Chemical Composition Depending on Variety and Ripeness

Composition change during ripening (Agustí, 2010; Mikheev and Revyakina, 2004):

Practical conclusion: for fresh consumption, pick fruits at consumer ripeness — they are then most sweet and aromatic. For processing (jam, juices), fruits picked at technical ripeness can be used — they contain more pectin and gel better.

Varietal differences (Mikheev and Revyakina, 2004; Quero-García et al., 2017):

• Amarelle varieties (light juice) have fewer anthocyanins but more organic acids.
• Morello varieties (dark juice) are richer in anthocyanins and coumarins.
• Sweet varieties (dessert) have more sugars and fewer acids — eaten fresh.
• Processing varieties are characterized by high dry matter and acid content — they store better and are used for juices, jams, and dried fruits.

6.7. How Cherry Is Beneficial for Health — Brief Summary

Important: the greatest benefit comes from fresh fruits at consumer ripeness. During heat treatment (jam, compote), some vitamins are destroyed, but coumarins, anthocyanins, pectins, and minerals are well preserved (Mikheev and Revyakina, 2004).

6.8. Uses of Cherry Fruits

Drying. To obtain 1 ton of dried cherries, 4–4.5 tons of fresh fruits are required. Dried cherries (like prunes) are a valuable product for long-term storage, preserving coumarins and trace elements (Trunov et al., 2012).

Summary for the Gardener

1. For taste and health. Cherry is not just a tasty berry, but also a valuable source of vitamins, iron, coumarins, and pectins. It is beneficial for the heart, blood, and digestion.

2. Sweetness depends on variety and picking time. Pick fruits at full ripeness — they are significantly sweeter. For fresh consumption, choose sweet varieties and sweet cherries; for processing — tart-sweet ones.

3. Different varieties for different purposes. Amarelles (light juice) are good for compotes and jams, morellos (dark juice) — for juices, wines, and as medicinal raw material.

4. Don't be afraid of overripening. Overripe fruits have higher folic acid content, useful for anemia prevention.

5. Freezing and drying preserve beneficial properties. If you can't eat all the harvest fresh, freeze or dry the berries — they almost don't lose coumarins and anthocyanins.

7.1. Classification by Species Affiliation

Let's recall the main division of cultivated cherries (see Chapter 2). In horticulture, three main groups are used (Webster, 1996; Quero-García et al., 2017):

In hobby gardening, Nanking cherry (Prunus tomentosa) is also sometimes grown — it belongs to a different subgenus and does not cross with common cherry, but its fruits are edible and the bushes are very winter-hardy (Mikheev and Revyakina, 2004).

7.2. Classification of Sour Cherry by Main Characteristics

The diversity of sour cherry varieties can be systematized by several practically important traits.

7.3. Features of Sweet Cherry Varieties

Sweet cherries are generally larger, sweeter, and more heat-loving than sour cherries. Their varieties are also divided by ripening time, color (from yellow to almost black), and flesh consistency (Trunov et al., 2012; Webster, 1996).

By flesh consistency:

• Guignes — tender, juicy flesh; fruits spoil quickly, not transportable. For local consumption.
• Bigarreaux — firm, crunchy flesh; fruits tolerate transport and storage well. Main commercial varieties.

Important: sweet cherry varieties with firm flesh (bigarreaux) are better for long storage and transport. Varieties with tender flesh (guignes) are tastier, but should be eaten on the day of harvest.

7.4. Dukes — Hybrids of Sour and Sweet Cherry

Dukes occupy an intermediate position (Webster, 1996; Quero-García et al., 2017).

Advantages: larger than sour cherry, sweeter than sour cherry, hardier than sweet cherry, many are self-fertile, often disease-resistant.

Disadvantages: yield may be lower than the best sour cherry varieties, some varieties have small fruits, demanding on soil.

Examples of dukes: 'May Duke' — oldest, known since the 18th century; 'Chudo-vishnya' — popular large-fruited, winter-hardy; 'Shpanka' (different forms) — often considered a duke; 'North Star' — sometimes considered a duke due to origin; new varieties from breeding programs.

7.5. Nanking Cherry — A Separate Crop

Sometimes gardeners grow Nanking cherry (Prunus tomentosa). It does not belong to the subgenus Cerasus and does not cross with common cherry (Mikheev and Revyakina, 2004).

Differences:

• Shrub up to 3 m, very winter-hardy (down to –40 °C).
• Fruits on short stalks, pubescent, tart-sweet, ripen early.
• Does not produce root suckers.
• Blooms abundantly, ornamental.

For the temperate zone and north, it can be an alternative to common sour cherry, but its fruits are smaller and tarter, usually used for processing.

7.6. Rootstocks for Sour and Sweet Cherry

Choosing a rootstock is no less important than choosing a variety. The rootstock determines tree vigor, winter hardiness, soil adaptation, and time to bearing (Webster and Schmidt, 1996; Quero-García et al., 2017).

Main rootstock types:

For the hobbyist: on low-vigor rootstocks ('Gisela 5', 'VSL-2'), trees begin bearing in year 2–3, are easy to cover for winter and treat for diseases. On vigorous rootstocks (seedlings), trees live longer and tolerate drought better, but come into bearing later.

7.7. Brief Overview of Popular Varieties for Different Regions

For the temperate zone of Russia (Non-Black Earth, Moscow region):

• Sour cherry: 'Vladimirskaya', 'Lyubskaya', 'Molodyozhnaya', 'Turgenevka', 'Zhukovskaya', 'Volochaevka', 'North Star'.
• Sweet cherry: (only in protected locations and with winter-hardy varieties) — 'Bryanskaya rozovaya', 'Iput', 'Revna', 'Fatezh'.
• Dukes: 'Chudo-vishnya', 'Shpanka' (some forms).

For southern Russia (Krasnodar Krai, Crimea, Rostov region):

• Sour cherry: 'Anadolskaya', 'Shpanka', 'Griot melitopolskiy', 'Krasnodarskaya sladkaya', 'Chernokorka'.
• Sweet cherry: 'Bing', 'Napoleon', 'Daibera chernaya', 'Valery Chkalov', 'Drogana zheltaya', 'Krupnoplodnaya', 'Regina'.

For Siberia and the Urals (harsh winters):

• Sour cherry: only winter-hardy varieties of steppe origin — 'Altayskaya lastochka', 'Bolotovskaya', 'Rubinovaya', 'Subbotinskaya', 'Shchedraya' (northern forms), 'Maksimovskaya'.
• Sweet cherry — not recommended.
• Dukes — not all are winter-hardy; can try 'Chudo-vishnya' only in the most protected locations.

For European countries and the USA (temperate and mild climates):

• In Europe, popular varieties include 'Schattenmorelle' (processing), 'Montmorency' (light juice), 'Griot Ostheim', and new sweet cherry varieties (Kordia, Regina, Sweetheart, Lapins).
• In the USA (Michigan) — 'Montmorency' (main processing variety), 'Balaton' (Hungarian large-fruited).
• For warm climates (California, Chile) — 'Bing', 'Lapins', 'Sweet Anne', 'Brooks'.

7.8. How to Choose Between Sour Cherry, Sweet Cherry, and Duke

7.9. Bridge to the Next Chapter: How Not to Make a Mistake in Choice

So, we've covered what varieties exist and by what traits they are classified. But how, among this diversity, to choose exactly what suits your garden?

The answer depends on four main factors:

1. Your climate (winter hardiness, heat sum, risk of spring frosts).

2. Site size (is there room for 2–3 trees, do you need a dwarf tree).

3. Your goals (fresh consumption, processing, or both).

4. How much time you are willing to spend on care (intensive pruning or minimal care).

In the next chapter, we will provide a step-by-step guide on how to choose a sour or sweet cherry variety for your specific conditions, so that the tree brings joy with harvest rather than trouble.

8.1. Step One: Assess Your Climate

Climate is the most stringent limiting factor. If a variety does not suit your winters and spring conditions, no amount of care will fix it. Start by answering three questions.

8.2. Step Two: Decide What You Are Growing Cherries For

The answer to this question will determine what taste, size, and color of fruit you need.

8.3. Step Three: Assess Space and Desired Tree Size

The size of your plot and your preferences determine the rootstock and training system. This is the second most important choice after climate.

8.4. Step Four: Determine Fruiting Type — Bush-like or Tree-like

As we discussed in Chapter 3, the type of fruiting determines pruning. If you are not ready for annual intensive pruning, choose tree-like varieties; if you are — bush-like varieties give higher yields in favorable years.

Note: in bush-like varieties, the crop forms on one-year shoots, so if shoots are weak (shorter than 20–30 cm) — there will be almost no yield (Potapov et al., 2000). This requires annual growth monitoring and pruning.

8.5. Step Five: Self-fertility — Solitary or Companions?

If you have space for only one tree or you don't want to bother with pollinators — choose self-fertile sour cherry varieties.

8.6. Step Six: Choosing Between Sour Cherry, Sweet Cherry, and Duke — Summary Table

Now let's put all factors into one table for quick comparison (Krivko et al., 2014; Trunov et al., 2012; Mikheev and Revyakina, 2004).

8.7. Step-by-Step Selection Algorithm for Your Garden

1. Determine your climatic limits. If you live north of Voronezh and Tambov — sour cherry (and possibly dukes) is your choice, sweet cherry is a risk. For sweet cherry, choose only winter-hardy varieties ('Bryanskaya rozovaya', 'Iput', 'Revna', 'Fatezh') and plant in protected locations.

2. Decide what is more important: yield, taste, or minimal care. If you want maximum yield with minimal hassle — take a self-fertile sour cherry of bush type on a medium-vigor rootstock ('Vladimirskaya', 'Lyubskaya', 'Molodyozhnaya'). If you are a gourmet and ready to care for the tree — plant sweet cherry, but not one, but a couple of different varieties.

3. Assess plot size. For small plots, choose low-vigor rootstocks (Gisela 5, VSL-2) — they produce compact trees, bear early, and are easy to cover.

4. Think about processing. If you plan to prepare jam, juices, compotes, and freeze berries — sour cherry with dark juice (morellos) will be ideal. If you want to eat fresh berries all summer — plant 2–3 varieties with different ripening times (early, mid, late) to extend the season.

5. Check compatibility and pollination. For sweet cherry, be sure to check whether the chosen pollinator variety is suitable (by flowering time and genetic compatibility). For most sour cherries, a pollinator is not needed, but several varieties nearby always give higher yields.

6. When purchasing a seedling, check: rootstock (indicated on the label or in the catalog), age (1–2-year-old seedlings establish better than 3–4-year-olds), root condition, and certificate (virus-free planting material is much more durable).

8.8. Examples of "Ready Solutions" for Different Cases

8.9. Final Advice: Don't Chase "Fashionable" Varieties

Beginning gardeners often choose varieties based on a beautiful catalog description or because they are popular in another climatic zone. This is a mistake.

Main principle: choose varieties regionalized in your region. They have passed trials in local conditions; their winter hardiness, flowering times, and disease resistance are confirmed by practice.

• For the temperate zone of Russia — choose varieties from the State Register of Breeding Achievements recommended for your region.
• For southern regions — rely on local nurseries and neighbor experience.
• For cold regions — don't risk with sweet cherry, prefer winter-hardy sour cherries.
• If you live outside Russia — consult the local agricultural service or university — they have lists of recommended varieties for your climate.

Good luck with your choice! A properly selected variety with minimal care will delight you with harvests for 15–25 years, or even longer.