Pollination
Apples are self-incompatible and must be cross-pollinated to develop fruit. Pollination management is an important component of apple culture. Before planting, it is important to arrange for pollenizers, cultivars of apple or crab apple that provide plentiful, viable and compatible pollen. Orchard blocks may alternate rows of compatible cultivars, or may have periodic crab apple trees, or grafted-on limbs of crab apple. Some cultivars produce very little pollen, or the pollen is sterile, so these are not good pollenizers. Quality nurseries have pollenizer compatibility lists.
Growers with old orchard blocks of single cultivars sometimes provide bouquets of crab apple blossoms in drums or pails in the orchard for pollenizers. Home growers with a single tree, and no other cultivars in the neighbourhood can do the same on a smaller scale.
During the flowering each season, apple growers usually provide pollinators to carry the pollen. Honeybee hives are most commonly used, and arrangements may be made with a commercial beekeeper who supplies hives for a fee. Orchard mason bees are also used as supplemental pollinators in commercial orchards. Home growers may find these more acceptable in suburban locations because they do not sting. Some wild bees such as carpenter bees and other solitary bees may help. Bumble bee queens are sometimes present in orchards, but not usually in enough quantity to be significant pollinators.
Symptoms of inadequate pollination are excessive fruit drop (when marble sized), small and misshapen apples, slowness to ripen, and low seed count. Well pollinated apples are the best quality, and will have 7 to 10 seeds. Apples having fewer than 3 seeds will usually not mature and will drop from the trees in the early summer. Inadequate pollination can result from either a lack of pollinators or pollenizers, or from poor pollinating weather at flowering time. It generally requires multiple bee visits to deliver sufficient grains of pollen to accomplish complete pollination.
A common problem is a late frost that destroys the delicate outer structures of the flower. It is best to plant apples on a slope for air drainage, but not on a south facing slope (in the northern hemisphere) as this will encourage early flowering and increase susceptibility to frost. If the frost is not too severe, the tree can be wetted with water spray before the morning sun hits the flowers, and it may save them. Frost damage can be evaluated 24 hours after the frost. If the pistil has turned black, the flower is ruined and will not produce fruit.
Growing apples near a body of water can give an advantage by slowing spring warm up, which retards flowering until frost is less likely. In some areas of the USA, such as the eastern shore of Lake Michigan, the southern shore of Lake Ontario, and around some smaller lakes, this cooling effect of water, combined with good, well-drained soils, has made apple growing concentrations possible. However, the cool, humid spring weather in such locations can also increase problems with fungal diseases, notably apple scab; many of the most important apple-growing regions (e.g. northern China, central Turkey, and eastern Washington in the USA) have climates more like the species' native region well away from the sea or any lakes, with cold winters leading to a short, but warm spring with low risk of frost.
Home growers may not have a body of water to help, but can utilise north slopes or other geographical features to retard spring flowering. Apples (or any fruit) planted on a south facing slope in the northern hemisphere (or north facing in the southern hemisphere), will flower early and be particularly vulnerable to spring frost.
posted by Serg @ 7:57 AM
