Self-sterile fruit trees must have a source of pollen within 500 m. The pollen source must be a tree of the same species but of a different cultivar, and which blooms at about the same time. This is especially important for the various plums and cherry cultivars. Self-sterile trees that are not pollinated, or poorly pollinated, will not produce any fruit. Weather Weather conditions can markedly affect tree fruit production.
High temperatures can decrease flower bud development.
Winter thaws followed by cold weather can kill flower buds. Frost during blossoming can damage flowers, and cool temperatures can decrease the viability of the pollen. Excessive rainfall in late-summer and early fall followed by freezing temperatures can damage flower buds that have not developed adequate winter hardiness. Finally, a large variety of insect pests and diseases can affect fruit trees. Poor fruit production can result from the direct effects of insects and diseases on growing and mature fruit.