Cherry Tree Propagation and Pollination
Cherry Tree Propagation
As in many popular fruit trees, the cherry tree is propagated by grafting. Cherries can also be propagated by seeds, but it is usually not recommended for many reasons. Generally, 1-2 years old seedlings (sown during fall) are used as subjects for grafted trees. Trees that start from seeds typically take 10 years to produce fruits. For this reason, growers prefer to use the grafting method. Professional cherry growers benefit from a tree that combines two different plant tissues, the rootstock and the scion (a healthy cutting from the main cultivar, up to 0.5-1 in or 1.3-2.5 cm in diameter). Especially in temperate climates, in plant nurseries, cherry trees are grafted by applying bench grafting or a specialized type of grafting called chip budding. The scion will develop the upper plant parts (the tree trunk, branches, leaves, and fruits). On the other hand, the rootstock will give the root system of the grafted cherry tree. The rootstock variety should help the main variety (scion) cope with soil stresses (resistant to soil-born pathogens, water-logging, etc.).
Some growers/nurseries may use wild cherry trees or mahaleb tree as rootstocks. The average cherry tree with wild cherry rootstock is usually taller than the average cherry tree and normally starts production 6-8 years after grafting. It is frost tolerant and can produce fruits for 50 years. On the contrary, cherry trees with mahaleb rootstock start production 3-4 years after grafting. They can tolerate frost and drought but are sensitive to high humidity. They usually produce fruits for about 25 years. Finally, it is common among growers to graft cherry trees in the so-called dwarf rootstocks. Some common sweet cherry rootstocks are:
- Mazzard (P. avium). Its good compatibility with almost all commercial sweet cherry varieties and is cold-hardy.
- Mahaleb (P. mahaleb). It is usually chosen due to its drought-tolerance.
- Gisela 5, Gisela 6 (P. cerasus x P. canescens), Gisela 12 (P. cerasus x P. canescens). All 3 give small cherry trees up to 8 feet tall. There may need support, especially in areas exposed to very strong winds. Sweet cherry varieties grafted on Gisela 5 and 6 rootstock can start yielding already from the 3rd year. They are a bit less tolerant to bacterial canker than Mazzard, while they present various levels of tolerance to Prune dwarf virus (PDV) and prunus necrotic ringspot virus (PNRSV).
- Colt (P. avium x P. pseudocerasus). It is best for standard-density orchards. It gives vigorous trees that need irrigation since they are relatively sensitive to droughty soils and cold winter temperatures. However, it is preferred in California due to its resistance to cherry stem pitting virus disease, Phytophthora root rot, and bacterial canker.
- F 12/1 (P. avium). Sometimes used instead of Mazzard because it is more resistant to bacterial canker.
- Maxma 14 (P. mahaleb x P. avium). It is widely used in France, resilient to calcareous soils and iron deficiency. It is not very suitable for super high-density plantations.
- Krymsk 5 or VSL 2 (P. fruticosa x P. lannesiana), semi-dwarfing rootstock, adapted to a wide range of soils (even in heavy soils) and cold climates
- Krymsk 6 or LC 52 ((P. cerasus x (P. cerasus x P. maackii)). It has the advantages of the previous one but gives a tree 75-80% smaller in size. Both Krymsk is sensitive to the PDV and PNRSV viruses.
Cherry Tree Pollination
Pollination is one of the most critical procedures in cherry production. It is essential for good quality cherries. A good cherry production can be achieved when 21-32% of the tree flowers are fertilized and produce fruits. Since most popular sweet cherry varieties are not self-fertile, cross-pollination is required between compatible varieties with the help of pollinators (e.g., honeybees). On the other hand, most sour or tart cherry varieties are self-fertile (e.g., North Star, Balaton, Meteor, Montmorency, English Morello, Early Richmond, Nanking, and Hansen Bush Cherry). Experienced cherry growers claim that bees are the best insects for this because they can facilitate the cross-pollination of cherry trees.
Cherry trees usually bloom in spring, and the flowering period can last several weeks. As a general rule, flowering depends greatly on weather conditions; the average flowering period could be up to 25 days, but each flower remains open for 7-8 days. As mentioned earlier, growers often plant one row of trees of the pollen-donating variety (pollinizer) for every three rows of the main variety. If the pollinizer variety can also be commercially exploited, it can be planted in greater numbers in the cherry orchard.
- Cross-unfruitful (incompatible varieties) of sweet cherries are: Bing, Lambert, Royal Ann/Napoleon.
- Self-fruitful sweet cherry varieties (universal pollinator) are: Index, Lapins, Skeena, Sweetheart, Sonata, Symphony, Sunburst, BlackGold, WhiteGold, Stella, Van, Rainier, and Bing. When Stella and Bing were combined, some problems (reduced fertilization success) were recorded.
Due to the unsynchronised flowering, one pollinating variety usually doesn’t ensure cross-pollination. Therefore, it is always recommended to take blooming time into consideration and use two pollinating varieties (usually one early flowering and one late flowering variety). As a result, these two varieties’ flowering stages will cross the main variety’s flowering stage. Therefore, this will normally ensure cross-pollination.
Most cherry growers depend greatly on strong and healthy honeybee colonies (collaboration with beekeepers), which ensure the best possible cross-pollination. A big population of bees is usually required (5-7 strong colonies per hectare) inside the orchard. Except for common honey bees, other native/wild bee species can serve as pollinators of cherries (e.g., Blue Orchard mason bee (Osmia lignaria), Horn-faced bee (Osmia cornifrons)). According to growers, bees will not only visit different flowers of the same tree but also transfer the pollen to another tree of a different variety.
Furthermore, growers should support the cross-pollination activity of bees by removing all competing blooming weeds from the field during the cherry flowering period. Otherwise, bees will be distracted and probably visit the blooming weeds. Finally, it is vital to avoid using pesticides during flowering when bees are present in the orchard. The cherry grower is advised to inform the neighbors when having bee colonies inside its orchard and ask them not to spray during the day or/and with strong winds because the product (droplets) can easily be transferred. Finally, heavy rainfalls and strong winds will shorten the flowering period and deteriorate the cross-pollination and, consequently, the fruit production of cherry trees. Similar problems will arise when there are high temperatures during blooming.
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Soil requirements, preparation, and planting of cherry trees
Cherry Tree Water Requirements
Cherry Tree Propagation and Pollination
Cherry Tree Training, Pruning, and Fruit Thinning
Cherry Tree Fertilization
Cherry Tree Pests and Diseases
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