No, you don’t need two avocado trees to get fruit. Before I explain how I know this, let me say where I think this myth originates: avocado flowers are strange.
They are dichogamous, it’s called by botanists. The standard description of avocado flower behavior can be found here. Suffice it to say that the conclusion drawn from this standard description is that any single avocado tree has very little opportunity for its flowers to be pollinated, especially in California’s climate, and therefore it’s best to plant two trees of different, complementary flower types in order to get fruit.
But the standard description is oversimplified and this conclusion is mistaken. Rather than get into the complex reality of avocado flower behavior, have a look at the reality that is before my eyes in my yard at this moment:
This is a photo of fruit that has just set on a Lamb avocado tree in my yard.
The only other avocado trees in the yard that flowered this year were a Reed and a Hass. All three of these varieties are “A” types in their flowering behavior. In other words, according to the standard description, they’re not supposed to be able to cross-pollinate because they’re all male at the same time or female at the same time, and are therefore of no use to one another. Moreover, there are no “B” type avocado trees in the yards of my neighbors that could have contributed to this fruitset.
How was my Lamb tree pollinated then? I don’t know for sure. A female flower could’ve received pollen from the male part on the same flower, or from the male part on another flower on the Lamb tree, or it could’ve received pollen from the male part on a flower on the Reed or Hass. I don’t know. And it doesn’t really matter. What I do know from the evidence of the fruit hanging on their limbs is that you certainly don’t need avocado trees of different flower types to get fruit.
There is another question of whether you’ll get more fruit if you have an “A” and a “B” type in proximity. But that’s another question. If you’re interested in reading about that issue, then read my post called “Cross pollination of avocados, or why I planted a Hass next to a Fuerte.”
I’ve seen so many single avocado trees in different parts of Southern California bearing plenty of fruit over the years, but let me note the fruitset on a couple of single trees in my own yard over the last couple years. The Lamb in the photo above held around 40 avocados for eating in 2016. The Reed held about 35, and the Hass held 73. Again, I’ll call these “single” trees because they had no “B” flower-type avocado trees nearby to pollenize them.
It is now August, 2017, and the Lamb tree has no fruit. Zero. It didn’t flower this year, unfortunately. So that’s not a pollenization issue; it’s a flowering issue, or what is called “alternate bearing.” On the other hand, fortunately, the Reed has 126 fruits, and the Hass has 154. Again, I consider these “single” trees because they have no “B” flower-type avocados nearby. Note that these are the Reed and Hass varieties, and some other varieties don’t bear as well when they are single trees.