Pollination is the transfer of pollen from the male part of the flower (stamen) to the female part of the flower (pistil). Pollen is transferred by wind, rain, and by pollinators such as bees, butterflies, moths, and birds. Fruit trees are primarily pollinated by bees, making the placement of compatible cultivars crucial for cross-pollination. Fruit trees that require cross-pollination should be planted no farther than 50-60 yards from each other to ensure the pollinators visit each type of flower. Flower types are also important; a flower from a peach tree will not pollinate a flower on an apple tree, etc. Pesticides or other chemicals should never be applied during flowering stages, as many will be detrimental to the beneficial insects pollinating your trees.
Pears require a pollinizer, but most varieties are compatible. Cherries benefit from companion planting, which results in more bee activity and thus more pollen movement. Sweet cherries require two, or preferably more, cultivars to be planted together for proper pollination. Sour cherries, however, are self-fertile and do not require pollination. Apple trees require cross-pollination from two compatible cultivars and although some cultivars may be considered self-pollinating, they will benefit from cross-pollination.
Strawberries, raspberries, and blackberries are self-pollinating. Blueberry cultivars are typically self-pollinating but will benefit from having different varieties close by.