Apple

Types of Roots

In the apple root system, several root types are distinguished (Potapov et al., 2000; Trunov and Samoshchenkov, 2012):

1. Skeletal roots. Large, perennial, 2–3 cm or more in thickness. Provide firm anchorage and transport of substances.

2. Semi‑skeletal roots. 1–2 cm thick, branch from skeletal roots, serve for further branching.

3. Feeder roots. Thin, up to 1 cm, subdivided into:

• Growing roots — white, actively elongating, have primary structure, bear root hairs.
• Absorbing roots — fine roots with root hairs that directly absorb water and nutrients. Live for several days or weeks, then die and are replaced by new ones — this process is called "root fall" (Potapov et al., 2000).
• Conducting (lignified) roots — secondary‑structure roots through which water and nutrients move.

Depth and Spread

The depth and spread radius of roots depend on rootstock, variety, soil type, and groundwater level (Westwood, 1993; Potapov et al., 2000):

Important: more than 80–90 % of active absorbing roots are located in the upper 20–60 cm soil layer. This explains why cultivation, mulching, and irrigation of the root zone are so important — nutrients and moisture must be available in this horizon (Potapov et al., 2000; Jackson, 2003).

Growth Patterns of Roots

Apple roots grow continuously during the growing season, but with distinct flushes (Potapov et al., 2000; Trunov and Samoshchenkov, 2012):

• Spring flush — coincides with bud break (April–May in the middle belt).
• Summer flush — after shoot growth ceases (June–July).
• Autumn flush — after harvest (September–October), the most powerful for reserve accumulation.

Practical conclusion: applying fertilizers and irrigation is most effective during periods of active root growth (especially spring and autumn). When planting in autumn, roots continue to grow until soil freezing, so plants have time to establish before winter.

Symbiosis with Microorganisms

Apple roots enter into symbiosis with soil fungi, forming mycorrhiza (Potapov et al., 2000; Westwood, 1993). Mycorrhizal fungi increase the absorbing surface of roots, help assimilate sparingly soluble compounds (especially phosphorus), and improve drought and frost tolerance. Favorable conditions for mycorrhiza are created by adding organic fertilizers and maintaining loose, non‑compacted soil. Deep digging and high rates of mineral fertilizers can suppress mycorrhiza, so in organic farming this factor receives special attention (Phillips, 2005).

Trunk (Stem)

The trunk (stem) is the lower part of the trunk from the root collar to the first large scaffold branch. Its height is determined when the nursery tree is formed (Trunov and Samoshchenkov, 2012; Potapov et al., 2000):

• High‑stem — 1.0–1.2 m (used in ornamental and roadside plantings).
• Medium‑stem — 0.6–0.8 m (main type in home gardens).
• Low‑stem — 0.4–0.5 m (for intensive orchards on dwarfing rootstocks).
• No‑stem — for cover cropping in severe regions.

Stem height affects ease of soil cultivation, winter hardiness (higher stem — less risk of bark damage from snow), and time to bearing (lower stem — earlier bearing) (Westwood, 1993).

Central Leader

The central leader is the continuation of the trunk from the topmost scaffold branch to the crown tip. Its retention determines the crown type:

• Leader crowns — central leader is maintained to the top (apple, pear).
• Non‑leader (vase‑shaped) — leader is removed, forming an open center (often for stone fruits).

In apple, modified‑leader systems are more commonly used, where the leader is retained but limited in height and subordinated to lateral branches (Trunov and Samoshchenkov, 2012).

Scaffold and Semi‑scaffold Branches

Branches of first order — main scaffold branches — arise from the trunk. From them come branches of second order (semi‑scaffold), and so on. A mature tree may have up to 6–8 orders of branching (Potapov et al., 2000).

Branch angles — the angle between a branch and the trunk (or supporting branch). This is a critically important parameter:

• Narrow angles (less than 40°) — branches grow vigorously, but attachment to the trunk is weak. Under fruit or snow load, breakage may occur.
• Optimal angles (40–55°) — provide good union and moderate growth.
• Wide angles (more than 80°) — branch growth is weakened, it quickly shifts to fruiting, but may droop under crop weight.

Practical advice: when forming the crown, choose branches with wide angles of attachment for scaffolds. Narrow forks will later require additional bracing or removal (Jackson, 2003; Phillips, 2005).

Bearing (Fruiting) Wood

These are thin, short twigs located on the scaffold framework — it is on them that the crop is formed. We will discuss their types in detail in Section 3.4.

Shoots

A shoot is the one‑year growth that developed from a bud during one growing season. Distinguish (Potapov et al., 2000; Trunov and Samoshchenkov, 2012):

Extension shoot — a strong terminal growth on the trunk or scaffold branch. Competitors — lateral shoots growing almost vertically and competing with the extension shoot. They should be removed during crown formation (Potapov et al., 2000).

Water sprouts — vigorous vertical shoots, often appearing on old branches, at cut sites, or after damage. They bear little fruit but shade the crown. Remove them or use them for rejuvenation (Trunov and Samoshchenkov, 2012).

Buds

Apple buds are primordia of future shoots or flowers. Distinguish:

1. Vegetative (growth) buds — produce only shoots with leaves. They are smaller and more pointed, tightly pressed to the shoot (Potapov et al., 2000).

2. Generative (flower, fruit) buds — contain flower primordia. In apple they are mixed (one bud contains both flowers and leaf primordia). Such buds are larger, rounder, and more downy than vegetative ones (Westwood, 1993; Potapov et al., 2000).

3. Dormant buds — remain undeveloped for many years. From them, upon pruning or injury, water sprouts appear, allowing the tree to rejuvenate.

Practical skill: in autumn or early spring, it is easy to distinguish a fruit bud from a growth bud: fruit buds are large, rounded, downy, located on fruit structures (spurs, fruit twigs). Growth buds are small, sharp, tight (Trunov and Samoshchenkov, 2012).

Fruit Structures (Bearing Wood)

In apple, several types of fruit structures are distinguished (Potapov et al., 2000; Westwood, 1993):

Fruit cushions — thickenings at the fruit attachment point, bearing marks of fruit stalks. Their presence indicates past fruiting (Potapov et al., 2000).

Fruiting Types by Wood Age

According to the wood on which fruits predominantly form, apple varieties are divided into several groups. This knowledge determines the pruning strategy (Lespinasse, 1977; Phillips, 2005; Trunov and Samoshchenkov, 2012):

Practical conclusion: for Type I varieties, pruning should aim at rejuvenation and thinning of old spurs; for Type IV — at stimulating new long shoots.

Columnar varieties — a separate group where fruits form on short lateral shoots along the trunk, and the tree grows almost without branching (Potapov et al., 2000; Trunov and Samoshchenkov, 2012). They are compact and convenient for small plots.

Flower Structure

Inflorescence

Flowers are grouped in corymbs — 4 to 8 flowers (sometimes up to 12–15) on a short flowering axis. The central flower in the inflorescence is the "king bloom" — opens first, largest, produces the largest fruit (Rieger, 2010; Colavita et al., 2021). Lateral flowers are smaller and open later.

Flowering sequence: the king bloom opens first, then laterals — from bottom to top or simultaneously. Flowering time depends on variety and weather, usually lasting 7–15 days (Westwood, 1993).

Flower Types by Sex

Most apple varieties have bisexual flowers. However, there are:

• Functionally male (staminate) — rare in some wild forms.
• Functionally female — also rare, more common in triploid varieties, where pollen is sterile but stigma functions normally.

Practical conclusion: apple requires cross‑pollination (most varieties are self‑sterile). Even self‑fertile varieties give higher yields with cross‑pollination. Therefore, plant at least 2–3 different varieties flowering at the same time (Westwood, 1993; Jackson, 2003).

Fruit Structure

Seed Structure

Apple seeds are dark brown, shiny, ovoid, 5–7 mm long. Each seed contains an embryo and endosperm. A fruit may have 0 to 10 seeds (average 5–6). The presence of seeds is important for large fruit formation: if seeds are few (less than 3), the fruit often drops or grows small (Rieger, 2010; Westwood, 1993).

Practical significance: when thinning fruit (removing excess fruitlets), leave those with well‑developed seeds — they will grow larger and store better.

Main Fruit Traits (for variety identification)

• Shape: round, flat‑round, conical, cylindrical, flattened (Trunov and Samoshchenkov, 2012).
• Size: from very small (less than 26 g) to very large (more than 200 g). By weight, divided into 5 groups: small (up to 50 g), medium (50–100 g), above average (100–150 g), large (150–200 g), very large (over 200 g) (Potapov et al., 2000).
• Skin color: ground color (yellowish, green, white) and over‑color (red, striped, solid, with pink blush).
• Flesh color: white, cream, yellowish, sometimes with reddish streaks.
• Taste: sweet, sweet‑acid, astringent. Sugar content (average 10–15%), organic acids (0.2–0.8%), vitamin C (4–45 mg%) (Potapov et al., 2000; Colavita et al., 2021).
• Ripening time: summer (August), autumn (September–October), winter (October and later, can store for several months).

Chilling Requirement (Chill Hours)

For normal dormancy completion and uniform spring awakening, the apple needs a certain number of hours at temperatures from 0 to +7 °C (usually below +7 °C). This is called the chilling requirement or chill hours (Westwood, 1993; Jackson, 2003).

Values for different variety groups:

Examples: 'Antonovka' and 'Grushovka Moskovskaya' require about 1200–1500 hours, 'Golden Delicious' — 800–1000, and 'Anna' (Israeli variety) — only 250–350 (Westwood, 1993; Jackson, 2003; Hampson and Kemp, 2003).

Practical conclusions:

• If chilling is insufficient, buds awaken unevenly, flowering is prolonged, and fruit set is reduced. The tree may "oversleep" some buds, leading to bare branches and poor yield.
• With excess chilling in regions with long winters (Siberia, northern USA), choose varieties with high winter hardiness and early ripening so that fruit matures during the short summer.

How to assess your region: if average winter temperatures rarely drop below -5 °C and thaws are frequent, chill hours are likely insufficient for traditional varieties — you need low‑chill varieties. If winters are long with stable frosts, select the most winter‑hardy varieties (see variety chapter).

Winter Hardiness and Frost Resistance

The apple is one of the most frost‑hardy fruit crops. In deep dormancy (mid‑winter), most varieties withstand frosts down to -35…-40 °C, and Siberian forms (M. baccata, some ranetki) — down to -50…-55 °C (Westwood, 1993; Potapov et al., 2000; Trunov and Samoshchenkov, 2012).

However, frost resistance changes with phenophase:

Important: the root system is significantly less frost‑hardy than the above‑ground part. Conducting roots are damaged at -12…-15 °C, and active absorbing rootlets die already at -3…-5 °C. Therefore, in winters with little snow, roots may freeze even if branches survive the frost (Potapov et al., 2000). Snow retention and mulching of the root zone are the best protection against root freezing.

Danger of thaws and spring frosts:

• After a prolonged thaw (above +5 °C for several days), buds lose hardiness, and a frost of -15 °C can damage them, whereas in January the same buds would have withstood -35 °C.
• Spring frosts during flowering — the main cause of crop failure in the middle belt and southern regions. If temperature drops below -2 °C, flowers die. Losses can reach 80–100 % (Westwood, 1993; Rieger, 2010).

How to protect from frost:

• Plant apples on elevated sites with good cold air drainage (see section 4.5).
• Choose late‑flowering varieties for regions with frequent spring frosts.
• Use overhead irrigation during frosts or smoke production (Phillips, 2005).

Heat for Growth and Ripening

Sum of active temperatures (above +10 °C) for different varieties:

For quality fruit, not only total heat matters but also night temperatures: cool nights (15–18 °C) promote good color, while hot nights (above 20 °C) reduce anthocyanin accumulation (Jackson, 2003; Westwood, 1993).

Water Requirement and Critical Periods

On average, an apple needs 500–800 mm of rainfall or irrigation water during the growing season (Rieger, 2010). Most critical periods:

1. Shoot growth and flowering (April–May in N. Hemisphere) — moisture deficit leads to flower drop and small fruitlets.

2. Intensive fruit growth (June–July) — moisture deficit sharply reduces fruit size.

3. Autumn root growth (September–October) — important for reserve accumulation for winter.

Excess moisture (waterlogging) is dangerous: roots suffocate from lack of oxygen, root rot begins, and the tree weakens (Westwood, 1993; Potapov et al., 2000).

Drought Tolerance

The apple is less drought‑tolerant than pear, apricot, or almond. Prolonged drought causes fruitlet drop, reduced fruit size, poor flavor, and premature leaf drop (Potapov et al., 2000).

In arid regions without irrigation, apple does not produce a commercial crop. Irrigation (drip, sprinkler) is mandatory for most commercial orchards worldwide (Washington, South Africa, China) (Jackson, 2003).

Signs of water deficiency:

• Leaves lose turgor, become grey‑green.
• Shoot growth stops.
• Fruits become smaller and drop.
• Poor flower bud initiation for the next year.

Air Humidity

High air humidity (>80 %) promotes fungal diseases — scab, powdery mildew, fruit rots (Montesinos et al., 2000; Jones and Aldwinckle, 2002). Therefore, in humid climates, important measures include:

• Good orchard ventilation (wide spacing, open crowns).
• Resistant varieties (to scab, powdery mildew).
• Regular preventive spraying (see protection chapter).

Mechanical Composition and Depth

• Optimal soils — light and medium loams with humus content 2–4 %, deep (at least 1–2 m for roots).
• Loams provide good water‑air regime and retain nutrients.
• Sandy loams and sands require frequent irrigation and fertilization; trees are smaller and more drought‑sensitive.
• Clay soils drain poorly; with excess moisture, roots suffer from waterlogging.

Groundwater depth should not be shallower than 1.5–2.0 m from the surface, otherwise roots suffocate (Potapov et al., 2000). In northern regions, levels down to 1.0–1.5 m may be acceptable if winters are snowy (roots don't freeze), but summer waterlogging is harmful.

Soil Reaction (pH)

The apple prefers slightly acid to neutral soils with pH 6.0–7.5 (Potapov et al., 2000; Westwood, 1993).

Calcareous (limestone) soils with high CaCO₃ (> 5–10 %) cause lime‑induced chlorosis in apple — yellowing of leaves due to iron deficiency. This is especially typical for southern regions, Crimea, Caucasus (Potapov et al., 2000). Controlled by applying iron chelates, choosing tolerant rootstocks (M.9 and M.26 are more sensitive than MM.106 and MM.111) (Jackson, 2003).

Salinity — another problem. Apple is moderately sensitive to salts. Limiting concentrations of harmful salts: sulphates up to 2 mg‑eq/100 g, chlorides up to 0.3 mg‑eq/100 g (Potapov et al., 2000). Under strong salinization, growth inhibition, marginal leaf scorch, and bark dieback occur.

Fertility and Fertilizers

Main nutrients and their roles (Westwood, 1993; Potapov et al., 2000):

Approximate fertilizer rates (for commercial orchards, see Westwood, 1993; Mandal et al., 2021): per 1 tonne of apple crop, approximately 2.3 kg N, 0.6 kg P₂O₅, 3.0 kg K₂O, 0.8 kg Ca, 0.3 kg Mg are removed. For the home garden, this means replenishing this removal annually with balanced fertilizers, especially during fruit growth.

Role of Topography and Air Drainage

Cold air is heavier than warm and flows into depressions, forming "frost pockets". Even on a flat site, there may be micro‑zones of cold air stagnation (Westwood, 1993; Phillips, 2005).

Rules for choosing topography:

• Ideal site — a gentle south, southwest, or southeast slope (for early warming) or north slope (to delay flowering in areas with late frosts) — depending on region.
• Avoid enclosed hollows, foot slopes, narrow valleys — cold air accumulates there and frosts are strongest.
• Better to plant on the upper or middle part of a gentle slope, where air flows freely.
• Do not plant apples on boggy, flood‑prone sites.
• Remove obstacles to cold air drainage (dense fences, solid hedges lower down the slope).

Effect of site choice: the difference in night temperatures between an ideal slope and a hollow can reach 5–6 °C, sometimes saving flowers from damage.

Wind Regime

Strong winds damage apple trees:

• In winter — desiccate tissues, causing "winter desiccation" (bud and bark damage).
• In spring — hinder bee pollination, blow away pollen.
• In summer — dry out soil and leaves, increasing stress.
• During ripening — cause fruit drop and branch damage.

Protective measures:

• Plant apples in sheltered locations (behind buildings, in shelterbelts).
• Create windbreaks of fast‑growing trees (poplar, birch, spruce) on the windward side, but not closer than 20–30 m from apples to avoid shade and competition for water (Phillips, 2005; Westwood, 1993).
• In open steppe, use hedge plantings of shrubs (lilac, acacia) or fruit trees on vigorous rootstocks to protect more valuable plantings.

What is Dormancy?

Dormancy is an adaptive state that allows the apple to survive winter. Two types are distinguished (Westwood, 1993; Jackson, 2003):

1. Organic (deep) dormancy — sets in autumn, when even under favorable conditions buds do not grow. Caused by internal inhibitors (mainly abscisic acid) accumulating in buds. To exit organic dormancy, chilling is required — a certain number of hours at 0 to +7 °C (chill hours). This is a key mechanism preventing premature awakening during winter thaws.

2. Forced dormancy — occurs after chilling requirement is satisfied, when buds are ready to grow but restrained by external factors (low temperatures). As soon as weather becomes warm, buds start to grow.

Chilling requirement is the number of hours (or units) of low temperature (usually below +7 °C) needed to exit organic dormancy (Westwood, 1993; Jackson, 2003).

Values for apple:

• Most varieties for temperate climates: 800–1600 hours.
• Northern winter‑hardy varieties: 1200–1600 hours or more.
• Low‑chill varieties for southern regions: 200–600 hours.

How this affects the gardener:

• If chilling is insufficient, buds awaken unevenly, flowering is prolonged, fruit set is poor. Some buds may remain dormant, leading to "bare" branches.
• If winter is too long and cold, that is not a problem (for winter‑hardy varieties), but for southern (low‑chill) varieties it is not an issue — they still break dormancy late in spring.
• In regions with mild winters (southern Europe, subtropics), plant only low‑chill varieties, otherwise the tree will grow weakly and produce few fruit.

Winter Hardening and Frost Resistance

The ability of the apple to withstand severe frosts is acquired gradually, through hardening (Westwood, 1993; Potapov et al., 2000). Hardening occurs in two phases:

1. First phase (autumn, with gradual temperature drop to +5…+10 °C and good light): accumulation of sugars, reduction of free water in cells, increase in osmotic pressure. Starch is hydrolyzed to sugars, which protect cells from freezing.

2. Second phase (at onset of the first negative temperatures, about -5…-10 °C): water is frozen out of cells, tissues become more "dry" and dense, preventing cell wall rupture by ice.

Important: maximum frost resistance is reached in mid‑winter (December–January). At this time, most varieties withstand -35…-40 °C. However, after thaws or closer to spring, hardiness is lost, and even -20 °C can cause damage (Westwood, 1993).

What weakens hardening:

• Late nitrogen fertilization (prolongs growth).
• Abundant autumn watering (delays wood ripening).
• Crop overload (tree is exhausted).
• Diseases, leaf damage (reduce photosynthesis and reserve accumulation).

Practical conclusions:

• Stop nitrogen feeding by mid‑July.
• Apply pre‑winter irrigation only in September, not later.
• Harvest in good time so the tree can prepare for winter.

Root Growth (Rhizogenesis)

Apple roots grow continuously during the growing season, but with distinct flushes linked to assimilate availability (Potapov et al., 2000; Westwood, 1993).

Typical root growth rhythm in the middle belt:

1. Spring flush — coincides with bud burst (April–May). Root growth in upper soil layers is supported by reserve nutrients from roots and trunk.

2. Summer flush — after shoot growth ceases (July). Roots actively grow in deeper layers.

3. Autumn flush — after harvest, in September–October. The most powerful and prolonged root growth period, when leaf‑derived assimilates are directed to roots. In autumn, the foundation for next year's crop is laid (reserves for spring growth).

Practical significance:

• Spring feedings and irrigation are best done before flowering, during the onset of root growth.
• Summer irrigation is important to maintain moisture, especially in June–July.
• Autumn irrigation (pre‑winter) and phosphorus‑potassium fertilizers stimulate autumn root growth and increase winter hardiness.

Root depth and activity depend on rootstock, soil, tree age (see Chapter 3).

Shoot Growth

Shoot growth begins in spring from vegetative and mixed buds, using reserves from roots and trunk. Active growth continues 40–60 days, then slows and stops (by late June – early July) (Westwood, 1993; Potapov et al., 2000).

Two types of shoots:

1. Long (extension) — length 20–30 cm to one metre, ensure tree growth and crown formation.

2. Short (fruit) — spurs, spur‑like, fruit twigs (see Chapter 3). They grow only a few millimetres per year and terminate in flower or mixed buds.

Shoot growth intensity depends on:

• Tree age: young trees grow more strongly, old ones weaker.
• Yield: heavy crop load suppresses shoot growth (competition for assimilates).
• Conditions: light, moisture, nutrition.

Optimal annual growth length for a bearing tree is 30–40 cm (for seedling rootstocks) and 20–30 cm (for dwarfing). If growth is less, the tree is weak — improve care. If greater, excess nitrogen and moisture, which may delay bearing and reduce winter hardiness (Phillips, 2005; Westwood, 1993).

Flower Bud Initiation (Previous Year)

Apple flower buds are initiated in the previous season, during June–August (for the middle belt). This is a critical stage determining next year's crop (Potapov et al., 2000; Westwood, 1993).

Bud differentiation passes through several stages:

Conditions favorable for flower bud initiation:

• Good light (at least 30–50 % of full sunlight).
• Moderate moisture (not waterlogged, not drought).
• Balanced nutrition (no excess nitrogen, but sufficient phosphorus and potassium).
• Free light access to inner crown (regular pruning).

What suppresses flower bud initiation:

• Shade (inner crown parts).
• Crop overload (fruit compete for assimilates, suppress flower formation). That is why a heavy crop one year often leads to poor flowering the next — biennial bearing.
• Excess nitrogen in late summer (stimulates vegetative growth at the expense of generative development).
• Drought or conversely waterlogging during differentiation.

Practical conclusion: pruning (thinning) and fruit thinning (removing excess fruitlets) in the current year help initiate quality flower buds for the next.

Flowering

Apple flowering occurs in spring when average daily temperature stably exceeds +5…+8 °C. In the middle belt this is usually mid – late May (Westwood, 1993; Rieger, 2010).

Flowering features:

• Flowers grouped in corymbs of 4–8 flowers.
• The central ("king") bloom opens first — it is the largest and produces the largest fruit.
• Flowering lasts 7–15 days, depending on weather. Cool weather prolongs it, warm weather accelerates it.
• The apple is cross‑pollinated. Most varieties are self‑sterile (need pollen from another variety). Even self‑fertile varieties produce more, larger fruit with more seeds under cross‑pollination.

Pollination and fertilization:

• Main pollinators — bees (entomophily). Pollen is transferred from flower to flower. For good pollination, at least 2–3 varieties flowering at the same time are needed (Westwood, 1993; Jackson, 2003).
• Pollen germinates on the stigma, forms a pollen tube that grows down the style and reaches the ovary in 48–72 hours (in apple). Fertilization occurs 3–5 days after pollination.
• Critical temperature for pollination: below +5 °C pollen hardly germinates; above +25 °C also unfavorable (stigma dries).

What hinders pollination:

• Rain and strong wind — wash off pollen, hinder bees.
• Frost during flowering (flower damage).
• Lack of pollinators (few varieties or few bees in the orchard).
• Varieties flowering at different times (mismatch).

Practical measures:

• Plant at least 2–3 varieties with overlapping flowering times.
• During flowering, do not use insecticides harmful to bees.
• If bees are scarce, place hives (1–2 hives per 100 m²) during flowering.
• For small gardens, hand pollination (with a brush) is possible.

Flower and Fruitlet Drop ("June Drop")

Even after successful fertilization, some fruitlets drop. This is a natural process called "June drop" (physiological drop) (Potapov et al., 2000; Westwood, 1993).

Three drop waves:

1. Drop of unpollinated flowers — immediately after flowering (up to 90–95 % of all flowers).

2. "June drop" (late June – early July) — fruitlets that did not receive enough nutrition (competition among fruit, moisture or nutrient deficiency) drop. At this time, the tree "thins" itself.

3. Pre‑harvest drop — nearly mature fruit drop (wind, disease, over‑ripening).

Causes of June drop:

• Insufficient assimilates (leaves) to support all fruitlets.
• Poor pollination (less than 3 seeds per fruit — such fruit often drops).
• Drought or waterlogging.
• Tree overload.

Practical significance: normal drop is beneficial, as remaining fruit get more resources and grow larger. If drop is excessive, find the cause: improve pollination, irrigation, feeding.

Carbohydrates (Sugars)

The bulk of dry matter (up to 7–15 %) consists of sugars (Westwood, 1993; Potapov et al., 2000). Apples contain three main sugars:

Sugar ratios depend on variety and ripening conditions. In winter varieties, sugar content may increase during storage due to starch hydrolysis (Westwood, 1993). Varietal differences are pronounced: 'Fuji' can accumulate up to 17 % sugars, while 'Granny Smith' only 10–11 % (Hampson and Kemp, 2003; Colavita et al., 2021).

Practical conclusion: if you prefer sweeter apples, choose varieties with genetic predisposition to high sugar content ('Fuji', 'Gala', 'Honeycrisp'). For diabetic diets, varieties with higher acids and fiber are preferable, as they slow sugar absorption.

Organic Acids

Acids give apples freshness and determine the sugar‑acid ratio, the main criterion of flavor (Westwood, 1993; Colavita et al., 2021). The main acid in apples is malic acid (malate), accounting for up to 80–90 % of all acids (Mandal et al., 2021).

Acidity varies greatly among varieties: 'Granny Smith' contains up to 0.7–0.8 % acids, 'Red Delicious' only 0.2–0.3 % (Hampson and Kemp, 2003; Colavita et al., 2021). Acids give the apple its "refreshing" quality, and their combination with sugars creates a unique flavor.

Important: during storage, acids are gradually consumed in respiration, so older apples seem sweeter but lose freshness and aroma.

Fiber (Dietary Fiber)

Apples are one of the best fruit sources of dietary fiber. One medium apple (with skin) contains 2.5–4.5 g fiber, which is 10–15 % of the daily human requirement (USDA, 2017; Colavita et al., 2021).

Fiber composition:

• Pectin (up to 30–50 % of total fiber) — soluble fiber, lowers cholesterol, improves gut function.
• Hemicellulose — promotes peristalsis.
• Cellulose — insoluble fiber, "brush" for the intestines.
• Lignin — partly fermented by microflora, removes toxins.

Practical significance: most pectin is concentrated in the skin and just beneath it. Therefore, apples with skin are more beneficial than peeled ones. For jams and jellies, varieties with high pectin content give a thicker product ('Simirenko', 'Antonovka', 'Borovinka') (Colavita et al., 2021; Potapov et al., 2000).

Vitamins

Important: vitamin C is well preserved in apples during storage (up to 70–80 % over 3–4 months) thanks to natural antioxidants and acidic environment. This compares favorably with many other fruits (Colavita et al., 2021).

Minerals

Apples are rich in potassium (about 100–120 mg per 100 g), which is important for heart function and fluid excretion (USDA, 2017; Colavita et al., 2021).

Interesting fact: apples are among the few fruits with very low sodium and high potassium — ideal for cardiovascular diets and fluid removal (Mandal et al., 2021).

Bioavailability of iron from apples is low (about 5–10 %), but with vitamin C (adequate in acid varieties) absorption improves. For anemia prevention, eat apples with vitamin‑C‑rich foods or choose high‑vitamin C varieties (Colavita et al., 2021).

Essential Oils and Aroma Compounds

Apple aroma is created by a complex blend of volatile compounds (esters, aldehydes, alcohols). Main aroma compounds — ethyl butyrate (gives "apple" smell), amyl acetate (associated with pear), hexanal (green smell), and many others (Westwood, 1993; Jackson, 2003).

Intensity and character of aroma depend on variety, ripeness stage, storage conditions. Summer varieties often lose aroma faster than winter ones. Intensely aromatic varieties ('Cox Orange Pippin', 'Elstar') are prized for rich flavor, though less productive and more disease‑susceptible (Hampson and Kemp, 2003; Jackson, 2003).

Tannins

Tannin content in apples is 0.02–0.12 % (Potapov et al., 2000; Colavita et al., 2021). They give astringency, pucker (especially in wild and acidic varieties). In small amounts, they are beneficial: anti‑inflammatory, antibacterial, promote mucosal healing. In large amounts, they impair flavor and cause dry mouth.

For the gardener: if growing apples for cider or processing, tannin‑rich varieties are prized (special "cider" varieties). For fresh eating, low‑tannin varieties are preferred.

Benzoic Acid (Preservative)

Apples contain benzoic acid (in very small amounts), which has antiseptic properties and slows mold and rot development. Thanks to benzoic acid (and other preservative compounds), apples can store relatively long (Westwood, 1993; Potapov et al., 2000). Benzoic acid content is especially high in acidic varieties and wild apples.

Light

• Intense light stimulates synthesis of sugars (photosynthesis) and anthocyanins (red color).
• In shade, fruit contain less sugar and more acid, because respiration outweighs photosynthesis.
• Pruning (crown thinning) is the best way to improve light and increase sugar content.

Temperature and Humidity

• Warm days and cool nights (+15…+18 °C at night) promote sugar and anthocyanin accumulation. Hot nights (above +20 °C) reduce sugar content and color (Jackson, 2003; Westwood, 1993).
• Moisture deficit (drought) during fruit growth reduces size and water content but may increase sugar concentration (concentration effect). However, severe drought makes fruit small and less juicy.
• Excess moisture (frequent rain or irrigation) leads to watery, less sweet fruit.
• Optimal moisture ensures good sugar‑acid balance.

Nutrition (Fertilizers)

• Nitrogen (N) — in moderate amounts improves growth and fruit size. But excess nitrogen reduces sugar content, worsens color, decreases storage life, and increases storage disease risk. Therefore, nitrogen feeding is restricted in the second half of summer (Westwood, 1993; Colavita et al., 2021).
• Potassium (K) — increases sugar content, improves color, boosts disease resistance and storage life. Potassium deficiency leads to poor fruit color.
• Phosphorus (P) — important for flower bud initiation, root development, and sugar synthesis.
• Calcium (Ca) — critically important for storage life, prevents bitter pit. Calcium is poorly taken up by fruit, so foliar calcium sprays during fruit growth (4–6 weeks after flowering) are especially effective (Colavita et al., 2021; Jackson, 2003).

Practical fertilization recommendations for quality improvement:

• The N:K ratio in fruit should be balanced: excess N, deficit K impair quality and storage.
• To improve storage, give potassium‑phosphorus feeds during fruit growth (especially late summer – early autumn).
• Foliar calcium sprays (calcium chloride or nitrate) in June–July are an effective measure against bitter pit.

Harvest Timing

• Early harvest (unripe fruit) — fruit do not accumulate full sugars, aroma, vitamins. They ripen poorly in storage, becoming dry and tasteless.
• Late harvest (overripe fruit) — may lose firmness, become "mealy", drop. Summer varieties are especially sensitive; winter varieties can be picked 2–3 weeks before consumer ripeness.
• Optimal harvest time is determined by skin color change, flesh firmness, starch disappearance (iodine test) (Colavita et al., 2021; Jackson, 2003).

Spur‑type Varieties (Type I)

Fruits form mainly on spurs and short shoots on 2–3‑year and older wood. Trees are compact, with many fruit buds.

Characteristics:

• Early bearing.
• High yield but prone to biennial bearing (heavy crop alternates with light).
• Require thinning pruning to maintain fruiting (removing old spurs, rejuvenation).

Examples: 'Red Delicious' (spur forms — 'Starkrimson', 'Red Chief'), 'Spur Golden', 'Goldspur'.

Pruning: mainly thinning, less shortening. Keep young spurs, remove old, crowded ones (Phillips, 2005; Potapov et al., 2000).

Type II (Semi‑spur, "Golden Delicious" type)

These varieties fruit on both spurs and short one‑year shoots. They are more flexible than pure spur types.

Characteristics:

• Good balance between vegetative growth and fruiting.
• Less prone to biennial bearing.
• Easier to train.

Examples: 'Golden Delicious', 'Jonagold', 'Elstar', 'McIntosh' (partially).

Pruning: combined — thinning and moderate shortening (Lespinasse, 1977; Trunov and Samoshchenkov, 2012).

Type III ("Cox Orange Pippin" type)

Fruiting occurs on 1–2‑year wood as well as on spurs. Characteristic of many old English and European varieties.

Characteristics:

• Fruit often smallish but high quality.
• Requires regular rejuvenating pruning.
• Does not tolerate heavy pruning.

Examples: 'Cox Orange Pippin', 'Cortland', 'Gala' (partially).

Pruning: retain one‑year growth and rejuvenate old spurs (Lespinasse, 1977; Phillips, 2005).

Type IV (Tip‑bearer, "Rome Beauty" type)

Fruits form at the ends of long one‑year shoots (fruit twigs). Trees tend to become leggy (bare branches).

Characteristics:

• Late bearing.
• Requires regular rejuvenating pruning to stimulate new long shoots.
• Without pruning, fruiting quickly moves to the periphery.

Examples: 'Rome Beauty', 'Granny Smith' (partially), 'Mutsu' ('Crispin') (partially).

Pruning: rejuvenate old branches, stimulate strong one‑year growth (Lespinasse, 1977; Trunov and Samoshchenkov, 2012).

By Vigor (depends on variety and rootstock)

Important: vigor is determined by the interaction of variety and rootstock. The same variety on a vigorous seedling rootstock will be a 6–7 m tree, while on a dwarf (M9) — 2.5–3 m (Jackson, 2003; Westwood, 1993).

Special Crown Forms

Columnar apples — a special group derived from the 'Wijcik' mutation (Trunov and Samoshchenkov, 2012; Potapov et al., 2000). They have practically no side scaffold branches; fruits form on short spurs along the trunk, making the tree look like a column.

Characteristics of columnar varieties:

• Height 2–3 m, crown width 30–50 cm.
• Early bearing (year 2–3).
• Very compact — ideal for small plots (can be planted 0.5–1 m apart in a row).
• Require minimal pruning (only sanitary).
• Give a small but dense crop (up to 10–15 kg per tree).
• Less long‑lived (10–15 years).

Examples of columnar varieties: 'President', 'Ostankino', 'Valyuta', 'Moskovskoye Ozherelye', 'Arbat', 'Gin', 'Triumph' (Russian breeding), 'Teleimon', 'Troyan' (foreign) (Potapov et al., 2000; Trunov and Samoshchenkov, 2012).

Dessert (Table) Varieties

Grown for fresh consumption. They should be tasty, aromatic, attractive, with pleasant texture.

Key requirements:

• Good sugar‑acid balance.
• Pleasant aroma.
• Beautiful color, shape.
• Good storage life (for winter varieties).

Examples: 'Golden Delicious', 'Red Delicious', 'Gala', 'Fuji', 'Jonagold', 'Granny Smith', 'Elstar', 'Cox Orange Pippin', 'Honeycrisp', 'Braeburn'.

Culinary (Processing) Varieties

Grown for processing (jam, jellies, preserves, juices, baking, drying, pickling, cider). They must have specific technological properties.

Key requirements:

• Good gelling (high pectin) — for jams, jellies.
• Holding shape when cooked — for pies.
• High acid, tannin content — for cider.
• Sweet‑acid, pronounced taste (sometimes astringent).

Examples: 'Antonovka', 'Borovinka', 'Korichnoye Polosatoye', 'Streyfling', 'Simirenko' (good both fresh and for processing), 'Bramley' (classic English culinary variety), 'Granny Smith' (good for processing, though also table).

Universal Varieties

Suitable both fresh and for processing, store well. This is the most valuable group for home gardens, offering flexibility in using the crop.

Examples: 'Golden Delicious', 'Jonagold', 'Granny Smith', 'Simirenko', 'Idared', 'Fuji' (excellent fresh and for juices), 'Elstar' (great fresh and for pies).

Cider Varieties

Special varieties grown for cider production. They are characterized by high tannin and acid content, giving cider its characteristic bitterness and astringency. This group is less developed in Russia but very important in Europe (England, France, Spain) (Jackson, 2003; Westwood, 1993).

Examples: 'Kingston Black' (classic English cider variety), 'Foxwhelp', 'Yarlington Mill' (England). In Russia, acidic, astringent varieties are used for cider: 'Antonovka', 'Korichnoye', 'Grushovka Moskovskaya' (though they are not special cider varieties).

Disease Resistance

• Scab‑resistant varieties (Vf gene from Malus floribunda): 'Liberty', 'Freedom', 'GoldRush', 'Sundance', 'Enterprise', 'Florina', 'Prima', 'Scarlet O'Hara', 'Enterprise', 'Williams Pride', 'Priscilla' (Luby, 2003; Hampson and Kemp, 2003).
• Powdery mildew‑resistant varieties: partially 'Golden Delicious', 'Red Delicious' (moderately resistant), 'Liberty', 'Freedom' (also good resistance).
• Fire blight‑resistant varieties (Erwinia amylovora): 'Red Delicious' (moderately resistant), 'Liberty', 'Freedom' (Hampson and Kemp, 2003; Jones and Aldwinckle, 2002).

Important: disease resistance is not absolute, but such varieties are significantly less affected, allowing reduced sprays. For organic home orchards, this is a very valuable trait.

By Winter Hardiness

Note: winter hardiness depends not only on variety but also on rootstock, tree condition, and cultivation practices (Westwood, 1993; Potapov et al., 2000).

By Ploidy

• Diploid varieties (2n = 34) — the majority. Produce good pollen, can serve as pollinizers.
• Triploid varieties (2n = 51) — have sterile pollen. Cannot pollinate other varieties and themselves need a diploid pollinizer. Their fruit are often larger (Westwood, 1993; Hampson and Kemp, 2003).

Examples of triploid varieties: 'Jonagold', 'Baldwin', 'Boskop', 'Cortland', 'Mutsu' ('Crispin'), 'Gloster 69', 'Champagne', 'Welsey' (Westwood, 1993; Hampson and Kemp, 2003; Potapov et al., 2000).

Practical conclusion: if you have a triploid variety in your orchard, plant 1–2 diploid pollinizers nearby that flower at the same time. The triploid itself will not pollinate other apples.

By Self‑fertility

Most apple varieties are self‑sterile (need cross‑pollination), but some are partially self‑fertile.

Practical conclusion: even partially self‑fertile varieties give significantly higher yields with a pollinizer. Therefore, in any orchard, plant at least 2–3 varieties that flower at the same time. This ensures good pollination and large, well‑formed fruit (Westwood, 1993; Jackson, 2003).

What Is Your Winter Like? (Chilling Requirement)

Estimate how many hours in your region temperature stays below +7 °C:

How to determine your chill hours:

• Use online chill calculators for your region (available on weather service websites).
• Ask local growers — which varieties grow and fruit in your area.
• In doubtful cases, choose a variety with lower chilling requirement — the risk is justified, as insufficient chill is worse than excess.

What Is Your Summer Like? (Temperature Sum)

Estimate whether there is enough heat for fruit ripening:

Is There a Threat of Spring Frosts?

• If spring frosts are frequent — choose late‑flowering varieties that open later and escape damage ('Antonovka', 'Korichnoye Polosatoye', 'Welsey', 'Borovinka').
• If frosts are rare or mild — any varieties.

Practical conclusion: in regions with unstable climate, plant 2–3 varieties with different flowering times to minimize risk of total crop loss from frost.

Soil

Topography and Microclimate

How Much Space Are You Willing to Allocate?

For the Beginner (1–3 trees on a homestead)

• Choose reliable, low‑maintenance varieties that forgive errors in care.
• Best choices: 'Golden Delicious' (universal, partially self‑fertile, grows almost everywhere), 'Antonovka' (very hardy, undemanding), 'Gala' (tasty, early bearing).
• Rootstock: MM.106 (semi‑vigorous) or M.9 (compact) depending on space.
• Plant 2 varieties for pollination (e.g., 'Golden Delicious' + 'Gala').

For the Organic (Chemical‑Free) Gardener

• Main criterion — disease resistance. Choose genetically scab‑resistant varieties ('Liberty', 'GoldRush', 'Enterprise', 'Florina').
• Rootstock: MM.106 or seedling (for greater hardiness and longevity).
• Look for partially self‑fertile varieties to reduce dependence on pollinating insects.

For Small Plots (up to 30 m²)

• Use dwarf rootstocks (M.9, M.26), columnar varieties, or train palmettes.
• Ideal varieties: 'Gala' (compact, early bearing), 'Elstar' (tasty, moderate growth), 'Golden Delicious' (on M9), 'Liberty' (resistant).
• Consider multi‑variety trees (several varieties on one rootstock) — saves space and ensures pollination.

For Northern Regions (Siberia, Urals, northern USA/Canada)

• Only the hardiest varieties — 'Altayskoye Bagryanoye', 'Altayskiy Golubok', 'Uralskoye Nalivnoye', 'Skala', 'Novosibirsky Krasny', 'McIntosh', 'Northern Spy' (in southern parts of the zone).
• Rootstock: seedling or M.7 (more winter‑hardy than M.9 and M.26) (Jackson, 2003; Westwood, 1993).
• Plant on south slopes, with snow retention.
• Choose early and early‑autumn varieties — so fruit can mature in the short summer.

For Southern Regions (southern Russia, subtropics, warm zones)

• If winters are very mild — low‑chill varieties: 'Anna', 'Dorsett Golden', 'Maayan'.
• If winters are moderately mild — 'Granny Smith', 'Fuji', 'Gala', 'Pink Lady'.
• Rootstock: M.9, M.26 (under irrigation) or MM.106 (on drier soils).
• Irrigation is mandatory — without it, apples do not produce quality crops in the south.
• Protect against fruit sunburn (kaolin spraying, shade nets).