Cherries - Prunus avium, Prunus cerasus
 
TAXONOMY

    Cherries are members of the Rosaceae family, subfamily Prunoideae. They occupy the Cerasus subgenus within Prunus, being fairly distinct from their stone fruit relatives plums, apricots, peaches, and almonds. Prunus avium L. is the Sweet Cherry, and Prunus cerasus L. the Sour, Pie, or Tart Cherry.

Sweet Cherry Cultivars
    There are less than 100 sweet cherry cultivars grown in the major production regions around the world today.  'Bing', 'Napoleon' (syn. 'Royal Ann'), ‘Ranier', and 'Lambert' are the most important cultivars in North America. Pollinizers for 'Bing' are often 'Early Burlat', 'Black Tartarian', and 'Van'. There are a few self compatible cultivars such as ‘Stella' and ‘Lapins', but they are of poorer quality than ‘Bing' and others that form the basis of the industry.

Sour Cherry Cultivars
    'Montmorency' is by far the main sour cherry in the USA and Canada, accounting for 99% of all production. In Europe, ‘Schattenmorelle' is a major cultivar.

ORIGIN, HISTORY OF CULTIVATION

Sweet Cherry
    P. avium originated in the area between the Black and Caspian seas of Asia Minor. Birds may have carried it to Europe prior to human civilization. Cultivation probably began with Greeks, and was perpetuated by Romans, where it was believed to be an essential part of the Legionnaire's diet (this lead to the spread throughout Europe). Trees were planted along roadsides and were valued for their timber as well as their fruit. Sweet cherries came to the USA with English Colonists in 1629, and later were introduced to California by Spanish Missionaries. In the 1800's sweet cherries were moved west by pioneers and fur traders to their major sites of production in Washington, Oregon, and California. Cultivars selected at that time still form the base of the industry today.

Sour Cherry
    There is good evidence suggesting that P. cerasus, a tetraploid, arose from a natural cross between P. avium and P. fruticosa (Ground cherry). The geographic ranges of the two species overlap in northern Iran and Turkmenistan, which is the center of origin of sour cherry. From there, sour cherry followed a similar course to Europe as sweet cherry, and ultimately came to North America with English settlers. It is more tolerant of the humid, rainy eastern conditions, and therefore proliferated there more than sweets, where it is still cultivated today in greatest numbers. Low monetary returns make sour cherry a less attractive investment than sweet cherry. Thus, it has been planted in western states only to a limited extent. Michigan, the leading producer, grows sour cherries along the eastern shore of Lake Michigan, where the moderating influence of the lake on winter and spring temperatures is beneficial to production.

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PRODUCTION

World (2004 FAO)

Sweet Cherry - 1,896,522 MT or 4.2 billion pounds. Sweet cherries are produced commercially in 65 countries on over 900,000 acres. Worldwide yield averages just over 4500 lbs/acre.
    
Top 10 countries
(% of world production)
1. Iran (12) 
6. Germany (6)
2. Turkey (12) 7. Russia (6)
3. USA (9) 8. France (4)
4. Italy (7) 9. Romania (4)
5. Spain (6) 
10.Ukraine (4)

Sour cherry - 1,035,650 MT or 2.3 billion pounds. Sour cherries are grown in 27 countries worldwide on 613,000 acres. Yields are 3700 lbs/acre worldwide.
    
Top 10 countries
(% of world production)
1. Russia (24) 6. Serbia & Montenengro (6)
2. Poland (20) 7. Hungary (4)
3. Turkey (12)
8. Belarus (4)
4. Germany (8) 9. USA (3)
5. Iran (6) 
10. Czech Republic (2)

United States (2002 USDA)

Sweet cherry - 253,854 MT or 564 million pounds. The industry value is $436 million. Prices received by growers are 95¢/lb, higher than most other fruit crops.

Sour cherry - 96,800 MT or 213 million pounds, valued at $70.8 million. Returns to growers have improved to 33-45 ¢/lb; previously it was only 10-18 ¢/lb.

Sweet cherry
(% of USA Production)		 Sour cherry
(% of USA Production)
Washington (47) Michigan (70)
California (26) Utah (10)
Oregon (15) Washington (8)

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BOTANICAL DESCRIPTION
Plant

Sweet Cherry. Vigorous tree with strong apical control with an erect-pyramidal canopy shape, capable of reaching 50 ft. In cultivation, sweet cherries are maintained 12-15 ft in height. Leaves are relatively large (largest of cultivated Prunus), elliptic with mildly serrate margins, acute tips, petioled, and strongly veined.

Sour Cherry. Medium sized tree with a rounder, more spreading habit than the erect sweet cherry. Kept <15 ft in cultivation. Leaves elliptic with acute tips, mildly serrate margins, smaller than sweet cherry, with long petioles.

Left, young ‘Bing' sweet cherry trees on semi-dwarfing MxM rootstock (background) or Gisela dwarf stock (foreground). Right, a mature ‘Montmorency' sour cherry orchard in Michigan.

Flowers  

Sweet Cherry. White, with long pedicels, borne in racemose clusters of 2-5 flowers on short spurs with multiple buds at tips; the distal bud is vegetative and continues spur growth.  Spurs are long-lived, producing for 10-12 years. Ovary position is perigynous with a distinct hypanthium, characteristic of stone fruits.

Sour Cherry. Individual flowers are the same as for sweet cherry. Sour cherry inflorescence buds usually produce 2-4 flowers, with long pedicels, as in sweet cherry.  However, many are borne laterally on 1-yr wood, not exclusively on spurs as in sweets. Spurs are shorter-lived on sour than sweet, gradually declining in productivity over 3-5 years. Sour cherries are the latest blooming of the stone fruits.

10.3 left
 10.3 right
Sweet cherry (left) and sour cherry (right) in bloom.

Pollination

Sweet Cherry. Pollination is absolutely essential for production, since sweet cherries are self-incompatible and need a high degree of fruit set (25-50%)  for a commercial crop. In addition to self-incompatibility, there is a high degree of cross-incompatibility. Pollinizers are set every third tree in every third row, or a ratio of 8-9:1. Honey bees are the main pollinator.

Sour Cherry. Sour cherries are self-fertile, and require no pollinizers.

Fruit

Sweet Cherry. A drupe; ½" to 1 1/4", round or heart-shaped, glabrous, with long pedicel attached. The pit is generally smooth, and encloses a single seed. The skin color is generally deep red or purple (often referred to as "black"), yellow, or rarely white. Yellow fruit often have a red cheek. The flesh color varies from white to dark red. Fruit is borne on short spurs that arise from older wood. Sweet cherries require only about 2-3 months for fruit development. Thinning is unnecessary.

Sour Cherry. A drupe; same as for sweet cherry. Sour cherries generally have lower sugars and higher organic acid contents than sweet cherries, giving them their distinct flavor. They are generally bright red in color, and exhibit less color variation than sweets. ‘Montmorency' produces about 2/3 of fruit laterally on longer wood, and 1/3 on spurs. Sour cherries require only about 2-3 months for fruit development. No thinning is required.
Ripe sweet cherries (left) borne on spurs and sour cherries (right) borne laterally on 1-year-old wood.

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GENERAL CULTURE

Soils and Climate
    Deep, well-drained, gravelly to sandy loam soils are best
    Flooded or wet, heavy soils slow growth and reduce productivity.
    Sweet cherry  - cooler, drier climates
    Sour cherries  - cooler, humid climates
    Chilling requirements - about 1000-1500 hr.
    Brown rot is also extremely bad on cherries, and is worsened by high humidity and rainfall near harvest.

Propagation
    Cherries are T-budded onto rootstocks during late summer and forced to grow the next season.

Rootstocks
    In the U.S., most sweet cherries are grown on Mazzard, and most sour cherries on Mahaleb. Both are propagated in nurseries from seed, but clonal selections of both also exist. Hybrids of the two, designated "MxM" are used commercially to a limited extent. A new series of dwarfing rootstocks for cherry known as "Gisela" or the Geissen series, developed in Germany, is now available to growers.

Rootstock Height compared to tree on Mazzard Yield efficiency compared to tree on Mazzard
Gisela 5 45% 210%
Gisela 7 50% 160%
Gisela 12 60% 170%
Gisela 6 70-80% 125%

Planting Design, Training, Pruning

Sweet cherry
   Tree densities -standard rootstocks = 100 trees/acre, Gisela rootstocks = hundreds of trees per acre
   Spacing - 30-35 ft apart in straight rows
   Pollinizers can be dispersed throughout the planting
   Pruning -  central leader or modified central leader, high density systems such as hedgerows, French Axe, or candelabra systems are used to a limited extent with dwarfing stocks. The Spanish Bush system has been used to a limited extent, where several scaffolds originating from near the soil surface are grown out, fruited briefly, and removed or headed back.

Sour Cherry
    Pruning - generally pruned more to stimulate new shoot production, due to the tendency to produce lateral flower buds exclusively on short shoots
    Spacings  - 18x24' rectangular, or up to 25 ft square.
    Training - modified central leader or open center.
 
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HARVEST, POSTHARVEST HANDLING

Maturity
    Traditionally, color change and soluble solids content are used to signal maturity. However, "fruit removal force" has been used more recently, and is more reliable. This is based on the progressive abscission of the fruit from the pedicel starting about 2 weeks before maturity. It is  measured by a pull gauge, which pulls the fruit from the pedicel and registers the force required to remove the fruit.

Harvest Method
    Sweet cherries for fresh consumption are harvested by hand, usually leaving the pedicels intact. They are harvested at firm-mature stage to reduce bruising. Sweets intended for processing are hand harvested also, but without pedicels. Sour cherries intended for processing are shaken from trees when ripe. Ethephon, an ethylene releasing compound, is applied about 2 weeks prior to harvest to reduce fruit removal force, and increase % fruit harvested.





Postharvest Handling
    Both sweet and sour cherries have extremely short shelf lives, and must be handled gently to reduce bruising and oxidation. Sour cherries for processing are dumped into cold water immediately following harvest. They are then transported to processing plants, where they are washed, de-stemmed, pitted, and packed for freezing, all within hours from harvest. Sweet cherries are hydrocooled or dumped into cold water by pickers, and packed in shallow flats after being sorted based on color and size.

Storage
    Shelf life of fresh cherries is only a few days at room temperature, and about 2 weeks at 32°F. Sour cherries canned or frozen can be stored several months. They are subject to the same post-harvest diseases (brown rot, grey mold, blue mold, Rhizopus, Alternaria, etc.) as other stone fruits.

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CONTRIBUTION TO DIET

    Maraschino cherries are made mostly from sweet cherries, but a small proportion of sour cherries are brined for this purpose.  Cherries with clear flesh are picked slightly early, perhaps are de-colorized with SO2, then steeped in Marasca, a liqueur distilled from the fermented juice of wild cherries. Sour cherries are primarily processed into pie fillings. Per capita consumption of cherries is 1.9 lbs/year, divided approximately equally between fresh (sweet) and canned and frozen (sour) cherries.  In 2004, utilization was:

    Sweet:                                                       Sour:
    Fresh - 50-72%                                         Frozen - 52-70% (pie filling)
    Brined (maraschino) - 18-30%                Canned, juice, jam, etc. - 25-38%
    Frozen - 8%                                               Brined (maraschino) - 5-6%
    Canned, juice, wine, brandy, etc. - 5%   Fresh - 1-2%   

Dietary value, per 100 gram edible portion:

 Sweet cherry Sour cherry
Water (%) 80
 84
Calories 70
 58
Protein (%) 1.3
 1.2
Fat (%) 0.3
 0.3
Carbohydrates (%) 17
 14
Crude Fiber (%) < 1 < 1

 % of US RDA*
Vitamin A 2.2
 20
Thiamin, B1 3.6
 3.6
Riboflavin, B2
3.8
 3.8
Niacin 2.2
 2.2
Vitamin C
22.2
 22.2
Calcium 
2.8
 2.8
Phosphorus 2.4
 2.4
Iron 4.0
 4.0
Sodium ---
 ---
Potassium 4.1
 4.1
* Percent of recommended daily allowance set by FDA, assuming a 154 lb male adult, 2700 calories per day.

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