Avocado (Persea americana) trees are popular in the home garden in U.S. Department of Agriculture plant hardiness zones 9b to 11, because they are easy to grow and they produce both shade and food. Avocado trees have male and female flowers on the same tree, and many gardeners assume they are self-pollinating. However, both male and female flowers are never open at the same time on the same tree.
Avocado flowers are both male and female. Each distinctive part opens at different times of the day and on different days. All of the parts for one gender in the flower open at the same time and then close before the opposite gender parts open the next day. The trees are classified as group A or B, based on their flower opening schedule.
Group A avocado trees open the female parts of the flowers first. Generally, they open in the morning of their blossom day. They close that night, and then the next day, in the afternoon, all of the male parts of the flowers open. Since there are no female flower parts open at that time, the males cannot pollinate the females on the same tree.
Group B avocado trees bloom in a similar way but with important differences. The female flower parts open in the late afternoon of the first day, while the male flower parts open in the morning of the second day.
By combining the bloom schedule from groups A and B, you can ensure successful pollination for your avocado tree. By planting one from each group of trees near each other, you're able to take advantage of the flower opening schedule overlap. Some of the male flower parts will still be open on group B when the females from group A open, and vice versa.