You don’t need more than one avocado tree to get fruit production, but having two trees and allowing for cross pollination can never hurt. And there are some studies showing increased yield when two different avocado varieties are growing in proximity.

The idea of avocado cross pollination makes so much sense on paper. Some avocado varieties have female flowers in the morning (called “A types”) while other avocado varieties have male flowers in the morning (called “B types”). You get a bee to fly from one tree’s male flower to a nearby tree’s female flower and voila!

(Learn more about avocado flowers here.)

The reality outside is more fluid, however. Sometimes a single tree will have both male and female flowers at the same time, and sometimes two different A types will have slightly different flowering schedules such that for an hour or so one day each tree will have many opposite-sex flowers. Because of this there are many examples of groves of thousands of avocado trees of only one variety that set heavy crops, or lone avocado trees in a yard with no other avocado trees in the neighborhood that fruit well, at least in most years.

These GEM avocados were set without any non-GEM trees nearby.

Cross pollination increases average yields

Nevertheless, having two trees of different types allows for the most cross-pollination opportunities. And this probably explains the studies that show increased fruit yield when different types are growing next to each other.

Here is a study by Bob Bergh and Don Gustafson from 1958 which focuses on the Fuerte variety, a “notoriously erratic bearer,” interplanted with Hass and Topa Topa. Bergh and Gustafson report, “Fuerte trees which adjoin Topas set about two-and-one-half times as many fruits as Fuerte trees one row or more removed from Topa interplants.” And then, the Fuerte trees that were isolated “had set an average of 99.3 fruits per tree, while four rows of Fuerte trees which have Hass interplants had set 157.6 fruits on the average.”

Conclusion: Fuertes average more fruit production when interplanted with complementary varieties, at least in this particular grove in San Diego County.

Fuerte avocados on a tree near Hass and Gwen avocado trees in Fallbrook.

Another study, this one focusing on Hass instead of Fuerte, was done by University of California researchers in 2002 to 2005. Part of the summary reads: ” . . . the presence of pollinizer varieties in close proximity enhance the total number of fruit harvested from ‘Hass’. The influence of pollinizers on yield diminishes as the distance from the pollinizer variety increases.”

Fruitset on Hass tree near multiple B-type varieties in my yard.

Proximity of pollenizer

All of the studies report this last finding — that the benefits of cross pollination are at their highest when the two varieties have branches that are very close, so close that they touch. They suggest a few different ways of achieving this: grafting two varieties on one trunk; planting two trees only a couple feet apart and growing them up like a multi-trunked, single-unit tree; or planting two trees close enough so that their canopies will touch or nearly touch when they reach their mature sizes.

Commercial growers only use this last option. Many decades ago, they found multi-graft trees too difficult to maintain; one of the varieties always ended up overtaking and shading out its partner. They seem to have settled on mere interplanting because it doesn’t require skilled labor to maintain nor to harvest.

I have tried all of the options in my yard. I agree that giving each variety its own trunk is easiest to maintain.

In this video, I show a Hass tree that I have provided with extreme cross-pollination opportunities. I planted four different B-type avocados (Hass is an A type) beside it.

Hot or cold weather

It seems that avocado trees need cross-pollination opportunities most when the weather is not ideal. Nights in the 50s or 60s and days in the 70s or 80s are ideal for avocado pollination in California. (See my post, “What are the best avocado pollination conditions?”)

Researchers in Israel have found that during high heat, avocado flowers that were cross pollinated become harvestable fruit more often than flowers that were self pollinated. (See, “The Israeli Ways.”)

During the cool spring of 2023, I saw that trees with cross-pollination opportunities had better fruitset than those without, in most locations. For example, in this video, I show the influence that a Bacon avocado tree (B type) has had on nearby GEM avocado trees (A types) in a commercial grove.

So while lone avocado trees or groves of a single variety can set lots of fruit in some years, it is during years of stressful conditions or difficult weather that cross-pollination opportunities reveal their benefits.

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