{"id":5750,"date":"2023-07-10T07:46:41","date_gmt":"2023-07-10T14:46:41","guid":{"rendered":"http:\/\/gregalder.com\/yardposts\/?p=5750"},"modified":"2026-03-21T08:13:00","modified_gmt":"2026-03-21T15:13:00","slug":"protecting-avocado-trees-from-heat","status":"publish","type":"post","link":"https:\/\/gregalder.com\/yardposts\/protecting-avocado-trees-from-heat\/","title":{"rendered":"Protecting avocado trees from heat"},"content":{"rendered":"\n

If the air temperature is comfortable for you, then it is comfortable for your avocado tree.<\/p>\n\n\n\n

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Optimum temperature for avocado trees<\/strong><\/p>\n\n\n\n

It\u2019s tempting to think of avocados as loving heat because they originated in the tropics, but we must remember that they come from high elevations where temperatures are surprisingly cool. (The avocado varieties that perform well in California do anyway.) Plant explorer Wilson Popenoe once estimated that California\u2019s avocado-growing climate corresponds closely to the climates he experienced in Guatemala at between 6,000 and 7,000 feet in elevation. (\u201cExploring Guatemala for Desirable New Avocados\u201d in the California Avocado Society Yearbook 1917.)<\/p>\n\n\n\n

Getting more specific, one pair of researchers at the University of California estimated that avocados grow best at between 68 and 75 degrees. (See details in this paper.)<\/a> Now, is that not about where you\u2019d like your daytime thermostat set?<\/p>\n\n\n\n

So yes indeed, avocados grow beautifully in Carpinteria, where summertime temperatures are near optimum.<\/p>\n\n\n\n

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Old avocado tree in Carpinteria getting no dedicated irrigation but still looking great and full of fruit.<\/figcaption><\/figure>\n\n\n\n
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How hot is too hot for avocado trees? Protect them when over 75 degrees?<\/strong><\/p>\n\n\n\n

Fortunately, avocado trees can thrive in heat well above 75 degrees as long as they\u2019re watered sufficiently. But there does come a point on the thermometer at which an avocado tree suffers regardless of how much moisture is in the soil. <\/p>\n\n\n\n

Apparently, above roughly 90 degrees avocado trees begin to function poorly. Specifically, the holes in their leaves (called stomata or stomates), which sort of breathe for the tree, begin to close above about 90. (Read more on that here<\/a> and here<\/a>.)<\/p>\n\n\n\n

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Protect an avocado tree when it’s over 90 degrees?<\/strong><\/p>\n\n\n\n

Does this mean we must come to the rescue of our avocado trees when temperatures break the 90-degree barrier? Maybe, maybe not. Depends on the tree and where it\u2019s growing, in addition to how much attention you\u2019re interested in giving it and how much you care about its appearance.<\/p>\n\n\n\n

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Watering sufficiently is defense number one<\/strong><\/p>\n\n\n\n

Watering enough is absolutely the most important thing you can do to help an avocado tree cope with heat above its comfort zone.<\/p>\n\n\n\n

Here is one avocado tree, a young Sharwil, that was slightly damaged by a 103-degree day:<\/p>\n\n\n\n

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Do you even notice the damage? Some leaves are bleached.<\/p>\n\n\n\n

An interpretation might be that if the temperature is just over 100 for a few days, a young tree that is healthy overall and watered well should only get some bleaching on a few leaves. That\u2019s not real damage. Because of that, my rule of thumb is that unless it\u2019s over 105 degrees, protection beyond good watering is unnecessary to prevent a healthy avocado tree from real damage<\/em><\/strong>. <\/p>\n\n\n\n

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Shading young trees<\/strong><\/p>\n\n\n\n

But what if you don\u2019t like bleached leaves? I don\u2019t. So I shaded most of my other young avocado trees while I was away. Here is another young Sharwil tree that had been shaded with a piece of 60-percent shade cloth overhead:<\/p>\n\n\n\n

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Unbleached foliage because of the midday protection from the shade cloth. The way I use shade cloth for my young trees when I\u2019m home (not on vacation) is usually to place some over the top if the temperature gets around 95 degrees or over.<\/em><\/strong> I use clothespins to fasten it to the top of a cage.<\/p>\n\n\n\n

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Sometimes though, I leave the shade cloth in place for most of a baby tree\u2019s entire first summer, as I live in a relatively hot part of Southern California (Ramona) where the average daily high temperature in summer is about 90. I\u2019ve found that if the cage holds the shade cloth high enough above the top of the tree, then the 60-percent shade in the middle of every day is enough and not too much. But if the shade cloth is closer to the tree or wrapping the sides at all, you want no more than 30 percent or else you’re shading it more than necessary and slowing down growth.<\/p>\n\n\n\n

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Shade can help a young tree get through the worst of Southern California heatwaves. Remember July 2018? The nearby weather station for the National Weather Service registered 118 degrees while my shaded front porch was still 113 degrees two days in a row. Some young avocado trees out in the yard would have been cooked without shade, but I doubled up 60-percent shade cloth over them in the middle of the day and they didn\u2019t show a bit of stress. (Other unshaded avocado trees nearby were sunburned so badly that entire branches died.)<\/p>\n\n\n\n

Other methods of providing shade to young trees include setting up a beach umbrella for the day or posting four stakes around the tree and stretching burlap across.<\/p>\n\n\n\n

A grower in Riverside erected this shade structure over his young avocados, and it has helped his trees get through high heat:<\/p>\n\n\n\n

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The shade cloth can be slid out of the way when not needed.<\/figcaption><\/figure>\n\n\n\n

A commercial grower in the Central Valley built a shade structure over four acres of avocados. (See my tour of his grove here<\/a>.)<\/p>\n\n\n\n

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Avocado grove of Tarcisio Ruiz under 30% shade cloth in California’s Central Valley.<\/figcaption><\/figure>\n\n\n\n
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Painting young trees<\/strong><\/p>\n\n\n\n

One more thing that is most relevant to protecting a young avocado tree from heat is painting its branches and trunk. <\/p>\n\n\n\n

I noticed a young Hass avocado tree while I was in Carpinteria that had a bare branch exposed to the western sun but was barely bronzed.<\/p>\n\n\n\n

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That branch would be blackened and cracking if it had gone through the 100-degree days in my yard. If you live in a climate like Carpinteria, you can get away with leaving such a branch unprotected. But if you live inland, you\u2019d be wise to paint such a branch on a young tree lest it get sunburned and possibly die in the long run. Young trees often don\u2019t have the mass of canopy to protect themselves like older trees do, and they need our sunscreen to help.<\/p>\n\n\n\n

Painting branches is also often called \u201cwhitewashing,\u201d and many materials are used to get the effect. I use white latex paint mixed with one part water.<\/p>\n\n\n\n

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Trunk painted on newly planted avocado tree.<\/figcaption><\/figure>\n\n\n\n

Some people also use a kaolin clay product called \u201cSurround\u201d<\/a>. It can even be sprayed on leaves to protect them from sunburn. <\/p>\n\n\n\n

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Surround sprayed on avocado leaf.<\/figcaption><\/figure>\n\n\n\n

But I’m not sure how effective Surround is in protecting avocado foliage in high heat. During the September 5 and 6, 2020 heat wave, where my yard reached 115 degrees, I sprayed some trees with Surround. On my Nimlioh avocado tree in particular, I sprayed only the tip of one branch with new growth to see if it would fare better than the unsprayed branches nearby. I didn’t notice any difference. Do you?<\/p>\n\n\n\n

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For more on avocado sunburn, see my post \u201cAvocado trees get sunburned — what to do?\u201d<\/a> <\/p>\n\n\n\n

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Mulching or growing companion plants<\/strong><\/p>\n\n\n\n

Avocado roots like to grow right at the surface of the soil if they can. If it\u2019s hot there, they can\u2019t. Mulch keeps that level of the soil comfortably cool and hospitable to avocado roots. The more roots a tree has, the more water it can draw up into its canopy to cool itself.  I like to use wood chips around my avocado trees. <\/p>\n\n\n\n

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Scrape back the wood chips to find white avocado roots comfortable just underneath.<\/figcaption><\/figure>\n\n\n\n

One day it was in the mid-90s and I felt the wood chips and then felt the bare dirt near the wood chips. The bare dirt was noticeably hotter, and it was so hot that I couldn\u2019t keep my hand pressed down for long. That kind of temperature fries avocado roots. I\u2019ve seen it happen where my chickens have scratched the mulch away in a spot. The revealed roots brown and shrivel rapidly.<\/p>\n\n\n\n

Wood chips are not the only option for cooling the soil surface around an avocado tree. I often grow a vine or two on the ground near a young avocado tree, and one reason is to reduce the heat and increase the humidity in that immediate environment.<\/p>\n\n\n\n

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Spaghetti squash vine beside young avocado tree.<\/figcaption><\/figure>\n\n\n\n
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Sprinkling during heatwaves<\/strong><\/p>\n\n\n\n

Usually, in Southern California, when it\u2019s over 100 degrees the humidity is very low. This makes it even harder for an avocado tree to manage the heat. Think of how much more thirsty you get when there\u2019s a spell of Santa Anas and the relative humidity is less than 20 percent.<\/p>\n\n\n\n

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Pulsing sprinklers<\/strong><\/p>\n\n\n\n

During such heat, I run the micro-sprinklers under my trees for 15-30 minutes in the middle of the day — sometimes once every hour or two throughout the afternoon — in order to raise the humidity under the tree and within its canopy. I\u2019ve seen a tree with wilting leaves perk up after such a pulse, indicating that it has given the tree welcome relief. <\/p>\n\n\n\n

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Micro-sprinkler running under avocado tree.<\/figcaption><\/figure>\n\n\n\n

I usually only run these pulses if it\u2019s around 105 or higher.<\/p>\n\n\n\n

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Spraying for evaporative cooling<\/strong><\/p>\n\n\n\n

I also sometimes spray a tree’s leaves if it’s 105 or higher. This works to cool a tree even better. The tree shows relief almost instantly if the leaves have wilted: within minutes they become turgid and look normal again.<\/p>\n\n\n\n

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Fuerte avocado leaves wilting during heat of about 110 degrees. <\/figcaption><\/figure>\n\n\n\n
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Same leaves 15 minutes after I sprayed them down with a hose.<\/figcaption><\/figure>\n\n\n\n

This evaporative cooling method has been used on avocados for over a hundred years, and it was formally studied back in the 1960s, and a report was published in the 1963 California Avocado Society Yearbook called \u201cCooling Avocado Trees by Sprinkling.\u201d<\/a> The report says, \u201cTemperature reductions up to 5 and 7 degrees were obtained.\u201d<\/p>\n\n\n\n

It\u2019s clear that wetting down a tree cools it; the challenge is how to do it economically. Spraying trees with a hose takes time and effort, and you have to be with your trees during the heat of the day (what if you’re away at work?).<\/p>\n\n\n\n

In an old avocado grove, I found these Rain Bird sprinklers atop tall risers that can be used to wet down the trees during high heat:<\/p>\n\n\n\n

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Using these old Rain Birds as inspiration, along with some advice from growers of apples and pears up in Washington, I’ve been experimenting with different designs.<\/p>\n\n\n\n

Here is one of my early attempts on a young Nabal tree:<\/p>\n\n\n\n

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See more about this method of cooling in my post, “Overhead watering for evaporative cooling of avocado trees.”<\/a><\/p>\n\n\n\n

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Video<\/strong><\/p>\n\n\n\n

Here’s a video that shows how I protect my avocado trees from heat:<\/p>\n\n\n\n