Avocados on the Ground After a Heat Wave: What Hot Days Do to the Crop
Why are there so many avocados on the ground? Because it has been hot. After a run of very hot days here in Southern California, a lot of fruit came off our trees — fruit we would love to have sold, and that we will now just have to eat ourselves.
It is not a pleasant walk, stepping around avocados that should have been in someone’s box. But heat-driven fruit drop is something every avocado grower in this part of the state deals with sooner or later.
Why does heat make avocado trees drop fruit?
An avocado tree under heat stress is trying to hold on to water. On a very hot day the leaves lose moisture faster than the roots can replace it, and the tree responds by cutting its losses. Some of the fruit it is carrying gets let go, because keeping every avocado on the branch costs water the tree does not have to spare. Water also keeps the leaves cool as it evaporates through their pores, and Avocado Production in California: A Cultural Handbook for Growers, Book Two, notes that an overheated leaf will usually shut down photosynthesis and may burn.
The UC Cooperative Extension growers’ handbook, Avocado Production in California, puts numbers on it. Avocados start to drop fruit when summer brings prolonged spells over 100°F, and temperatures over 105°F in late May or June have been known to drop almost the entire crop of young fruit that had just set. It is one reason avocados are not grown in the desert. Hot, dry Santa Ana winds can do the same thing on exposed slopes, sometimes causing almost complete fruit drop.
Avocados are particularly exposed to this. Their feeder roots sit shallow, with 80 to 90 percent of their length in the top 8 to 10 inches of soil, where the soil dries out first when temperatures climb, and they have few root hairs, which makes them relatively inefficient at taking up water. Fruit can also scorch, worst on the south and southwest sides of the tree, and trees that cannot take up enough water are the most susceptible to sunburn. We have written about how avocados shrivel and sunburn when summer gets rough.
Why can’t we sell the fruit that fell?
Once an avocado hits the ground it cannot go to market. That is a food safety rule, not a quality judgment — plenty of the fruit is perfectly fine to eat — and we explain the reasoning in why ground-dropped fruit can’t be sold. So what falls in a heat wave is simply lost as income. Our kitchen does well out of it, at least.
What can a grower do?
You cannot stop a heat wave, but you can go into one with the trees in the best shape possible. For us that mostly means water: making sure the soil is properly wet before the heat arrives rather than scrambling once it is here (without waterlogging it; avocado roots start to die after about 48 hours in flooded soil), and keeping an eye on the grove during and after. The handbook’s irrigation chapter warns that missing irrigations for one to two weeks can set off fruit drop and ruin a year’s production, and because weather-based watering schedules look back at the previous seven days, a sudden hot or windy spell may mean watering again sooner than planned. Our notes on managing late-season fruit and summer heat go into more of that.
For a home grower, the same principles apply on a smaller scale: deep watering ahead of forecast heat, mulch over the roots to keep the surface cooler (but check the soil before watering, because mulched trees are easy to over-water), and not panicking when a few avocados come down. Some drop in a heat spike is normal. If a tree sheds most of its crop, check your watering, but do not assume you failed: extreme heat on its own, especially above 105°F in late spring, can take nearly all of the young fruit.
A cost you cannot plan for
Weather is the part of farming you do not get a vote on. A few days of heat can take fruit off the trees that took a year to grow, and all we can do is learn from it and water smarter next time.
The fruit that stays on the tree is the fruit that ships. Our 4lb Hass box and 6lb Hass box are picked from the branch the week they go out and ship free — and between harvests, the waitlist on either page will let you know when we are picking again. Until the trees are picking again, the avocado scoop, the Hawaiian shirt and our hats ship year-round.
This post is part of our guide to growing avocado trees.
