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Soils and Climate:
Soil - deep, well-drained, loamy soils with pH 6-7.
Climate - Both sweet and sour cherries have relatively high chilling requirements; 500-1600 hrs, mostly about 1000. They also seem to have high post-dormancy heat requirements, since they bloom later than peach, but just prior to or with apples. However, this could be due to insufficient chilling in warmer climates. They are the last of the stone fruits to bloom in a given location, with sweet before sour.
Cherries produce well in Northern Michigan, Ontario, and British Columbia, as well as northern Europe and England; they are among the hardiest of stone fruits. Sour cherries are more cold tolerant than sweet.
Cherries are the earliest maturing of the stone fruits, with most cultivars maturing in 2-3 months after bloom.
Rainfall during harvest is especially harmful, causing a condition known as fruit cracking. For this reason, most sweet cherries are grown in the western US. Sour cherries also are prone to cracking, but do not size well in the west; hence they are grown in the east. Brown rot is also extremely bad on cherries, and is worsened by high humidity and rainfall near harvest.
Intense heat during floral initiation/development causes doubling of ovaries, which results in spurred or double fruit the following year.
T- or chip-budded onto a variety of seedling rootstocks.
There is an age-old controversy over which rootstock is better for both sweet and sour cherries; 'Mazzard' a wild P. avium selection, or 'Mahaleb', P. mahaleb. Mazzard may be the best choice for heavy, wet soils, while mahaleb does best in well-drained soils. Mahaleb is good for sweets on calcareous, droughty soils. In the U.S., most sweets are grown on Mazzard and most sours on Mahaleb. The designation "M x M" stands for Mazzard x Mahaleb hybrids.
A new series of dwarfing rootstocks for sweet cherry known as "Gisela" or the Geissen series, developed in Germany, is now available to growers. These stocks could do for cherries what the Malling series did for apple, i.e., allow production from dwarf trees with high yield efficiency and precocity. Four of the several original stocks have been adopted in the US:
||height compared to tree on Mazzard
||Yield efficiency compared to tree on Mazzard
Orchard design, pruning, training:
Sweet cherry: Sweet cherries often become very large trees, and are spaced 20-32 ft apart. Pollinizers may be dispersed within rows, or in solid alternate rows, with a ratio of 8-9:1. Sweet cherries are trained to central leader or modified central leader, since the growth habit is naturally upright. Young trees are particularly difficult to train due to vigor and strong apical dominance. Trees require minimal pruning since fruit is borne on long-lived spurs, and many fruiting points are needed for full production.
Sour cherry: These trees do not attain the size of sweet cherries, and are generally pruned more to stimulate new shoot production. Hence, closer spacings are used, e.g. 18 x 24 ft. Sour cherries are trained to modified central leader or open center; The trees have more-or-less spherical canopies at maturity, with fruiting heaviest at the periphery. Some selective limb thinning may be necessary to maintain adequate light and spur development inside trees. Trees are headed high to allow room for shaker attachment.
Sweet cherries struggle for survival in the Piedmont of the southeast, and cropping is irregular due to disease, bird predation, frost, and rain cracking. I've seen large, old trees in the North Carolina mountains do fairly well, but sweet cherries should be left out of the backyard. Sour cherries, on the other hand, are better adapted to the eastern US climate, and I've seen these trees do fairly well in the Piedmont. Sours are self-fruitful, later blooming, and more disease and cracking resistant than sweets. Follow the spray schedule for peaches, paying particular attention to brown rot near harvest.
Harvest, Post-harvest Handling.
Traditionally, color change and soluble solids content were the most reliable indices. Soluble solids may approach 23% in ripe sweet cherries. However, fruit removal force has been used more recently, and is more reliable. This is measured by a pull gauge, which pulls the fruit from the pedicel. Fruit acid level is important for sour cherries.
Sweet and sour cherries intended for processing are shaken from trees when ripe. Ethephon at 400-800 ppm is applied about 2 weeks prior to harvest to reduce fruit removal force, and increase % fruit harvested. Tree trunks are often damaged by shaking equipment, if done incorrectly; trees in rapid growth are more prone to cambial injury. Sweet cherries for fresh consumption are harvested by hand, usually leaving the pedicels intact. They are harvested at firm-mature stage to reduce bruising.
Handling and Packing:
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, usually the largest being 15/16 inch or higher.
Sweet cherries are usually shipped immediately, since shelf life is <2 weeks. 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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