Given that a tree is healthy and making lots of flowers, there are three main external conditions that create ideal avocado pollination potential: warm weather, lots of bees, and different varieties blooming near each other.
While I’ve seen these elements work together for good avocado fruitset in my yard and elsewhere, below I note snippets of more robust evidence from others. Click the reference links for the full stories.
High mean (average of daily high and nightly low): “Ordinarily, the higher the temperature mean, the more favorable the set prognosis. This explains why most of our set is usually toward the end of the blooming period.” Bob Bergh in 1967
How high? “Daily means above 60° are necessary before much fruit will set; and means above 65° give the best fruit set.” Len Francis in 1974
B types need it warmer than A types: Shepherd (B) needs five degrees F higher than Hass (A) for “potentially favourable fruit-set.” Birdie Carr of Australia in 2019
What to do? We have no control the weather! True, but by growing the most suitable varieties for our location we can achieve results as if we have some control. For example, since B type avocado varieties require warmer weather than A types, if you live right on the beach where spring days don’t warm up or at the bottom of an inland valley where spring nights dip down low you can grow an A instead of a B to increase your pollination chances.
Lots of bees
Need for bees: “The evidence from our caging experiments indicates the following. Practically every avocado fruit set means that a honey bee transferred pollen to that flower, from some other flower.” Bob Bergh in 1967
More bees the better: ” . . . an average count of 40 bees per medium size tree is a good number.” This is research from Gad Ish-Am as presented by Reuben Hofshi.
Not only honeybees: Other effective pollinators observed include bumblebees, numerous species of stingless bees, and even wasps and flies. Pollinators of Avocado by Ish-Am et al.
What to do? To bring in more bees you can install a bee hive or simply provide food for them, as I explain how I’ve done in my post, “Growing a Bee Garden”
Different varieties together
Different varieties: “The data from the various groves observed show that trees of a given variety frequently set more fruit when located proximate to a second variety than when located farther removed from the other variety.” Bob Bergh in 1964
Varieties of different flower types even better: “Interplanting an A and a B variety, provided that their blooming season overlaps adequately, thus provides maximum opportunity for cross-pollination. We have thereby obtained yield increases up to 150% in individual years, with 50% increases frequent.” Bob Bergh in 1967
Closer together the better: “Close watching showed that bees have a strong preference for sticking to one avocado tree at a time . . . But as can be observed bees do cross freely when the foliage of two varieties interlace, with no open space between.” Orange Clark in 1922
What to do? Plant a companion for your avocado tree. Or if space is at a premium, then you can plant two trees in one hole (see examples of this in my post, “How far apart to plant avocado trees”) or graft in a pollenizer branch (see my post, “Grafting a pollenizer branch into your fruit tree”). For a list of the flower types of avocado varieties, see this one from the Orange County chapter of the California Rare Fruit Growers.
Here’s a two-minute video version of the ideas in this post, showing trees in my yard:
Having warm weather during bloom, seeing lots of bees visiting female flowers, and different varieties of avocado trees growing near each other don’t guarantee fruit. And cooler weather, few bees, and a lone avocado tree can still end up with a decent crop. But the presence of these three ingredients is almost always correlated with higher pollination and fruitset in avocado trees.
Interested in learning more about avocado pollination? Check out these papers, including their references:
“The Avocado Flower and the Pollination-Fruitset Process: Ideas from a California Perspective” by Mary Lu Arpaia and Reuben Hofshi
“Finding the Best Polliniser for ‘Hass’ Avocado and the Effect of Honeybees as Pollinators” by Bezuidenhout et al.
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