I believe they need to cross-pollinate.
I sure as heck don’t know.....having trouble enough to get the mini-tree to grow! :0)
Avocado trees are actually perfect, meaning they have both male and female reproductive organs. Thus, avocado trees are theoretically able to self-pollinate by producing both male and female flowers, albeit on different days, and at different times of the day. Wind and bees may help to accomplish the task.
A second avocado tree of the same type A or B will help to increase the odds that both male and female blooms will cross-pollinate.
Type A flowers open their female parts during the morning of the first day and their male parts on the second day's afternoon. Type B flowers wait until the afternoon of the first day to open the female parts and open their male parts the following morning.
And now you know the rest of the story...
Actually, all avocado trees are hermaphrodites, meaning their flowers will be male one day, they will close, then open up the next day and be female. So, technically, they can self-pollinate, but that's a little hit or miss.
There are two varieties of avocado trees, A and B. The A-variety include, Haas, Gwen, (dwarf) Reed, etc. The B-variety include Fuerte, Bacon, etc.
What makes an avocado and A or B is A varieties open as female on the morning of the first day. The flower closes in late morning or early afternoon. The flower will remain closed until the afternoon of the second day when it opens as male. B varieties open as female on the afternoon of the first day, close in late afternoon and re-open in the male phase the following morning.
Usually growers will grow both A and B to enhance chances of pollinating.
Also, avocado trees grown from a seed rarely produce fruit. If they do, it'll take at least 5 years for that to happen. Fruiting trees are usually grafted from already mature, fruit producing trees. Avocado trees usually flower in January-February. If it's too cold, they won't flower and if they don't flower they won't produce fruit.
I live in Southern California and have three Avocado trees -- Haas, Fuerte and a Gwen. The Haas is in the ground and the Fuerte and Gwen are in pots. All three flowered, and set fruit. All the fruit dropped off when they were very small except for one Haas. Since this is the first year I've had them this isn't too surprising. Once they get more established, I expect them to produce fruit next year.