Avocados trees self-pollinate, but they have evolved in such a way that they are much more likely to fruit when cross-pollinated. This evolutionary trait helps to ensure diversity in the avocado gene pool. Avocado trees produce both male and female flowers, but the flowers open up at different times to discourage cross-pollination. A few avocado varieties, however, are known to reliably self-pollinate and produce exceptional yields without the help of a second tree.
Though it originates from one of the warmest parts of the country, "Taylor" is an exceptionally cold-hardy cultivar that may be grown successively in areas where other avocado trees do not fare well. Despite its adaptation to the cold, the shape of the tree — tall and slender — makes it less desirable than others. The shape makes it less aesthetically pleasing and less practical for harvesting, as fruits may be somewhat inaccessible. It provides fruit from January through March.
The "Lula" cultivar is another reliable self-pollinator that for a time was the primary commercially grown variety of avocado in southern Florida. This variety is also somewhat cold-tolerant, though not as much so as Taylor. The tree provides exceptional yields of fruit between October and December. One unique and desirable trait of Lula is that its seed can remain viable for planting for up to five months, whereas most other avocado seeds are viable for only a month or less.
"Waldin" avocados are grown commercially in southern and central Florida. The fruit itself is somewhat more rounded relative than other avocados, almost resembling an unripened mango. Waldin seed is frequently used to provide rootstock to grow other avocado varieties. The tree expends large amounts of energy providing huge yields of fruit, then dies back and goes into dormancy. Fruit is harvested between August and November.
Self-Pollination vs. Cross-Pollination
Taylor, Lula and Waldin are the most reliable self-pollinators among avocado tree species, but all varieties are capable of self-pollination.
"New evidence indicates avocado flowers may be both self- and cross-pollinated under Florida conditions," the University of Florida IFAS Extension explains. "Self-pollination occurs during the second flower opening when pollen from the anthers is transferred to the stigma of the female flower parts. Cross-pollination may occur when female and male flowers from A and B type varieties open simultaneously. Self-pollination appears to be primarily caused by wind, whereas cross-pollination is caused by large flying insects such as bees and wasps."