There can be many reasons for the failure of a citrus tree to bear a crop in any year. Lack of water can affect fruit production. Very dry conditions during the bloom period can cause flowers and tiny fruit to drop. Although established citrus trees are fairly drought tolerant, some irrigation, especially during the hot and dry late spring and early fall seasons, can be beneficial. Generally irrigation would not be needed more than once a week during hot, dry weather and less often during cooler periods, such as most of the winter.

For the best fruit production, citrus trees usually require some fertilization. Three fertilizations per year using a granular fertilizer, such as an 8-0-8 or similar analysis, are adequate.

Some citrus hybrids, primarily some of the tangelos and other varieties that include tangerines in the parentage, do not set fruit well without cross-pollination by a compatible variety. More information about varieties that need cross-pollination and compatible varieties can be found here: http://edis.ifas.ufl.edu/ch082

Sometimes a fugal disease called post-bloom fruit drop can attack the flowers and tiny fruit on citrus trees, reducing or nearly eliminating the crop. Since wet conditions on the flowers tends to encourage this disease, avoid using overhead irrigation during the bloom period to reduce this problem.

Of course, keep in mind that even completely healthy citrus trees sometime experience “off” years in fruit production. Such years are more likely to follow years when there have been very heavy crops of fruit.