{"id":12911,"date":"2021-06-18T21:28:46","date_gmt":"2021-06-19T04:28:46","guid":{"rendered":"https:\/\/gregalder.com\/yardposts\/?p=12911"},"modified":"2021-06-23T14:02:21","modified_gmt":"2021-06-23T21:02:21","slug":"overhead-watering-for-evaporative-cooling-on-avocado-trees","status":"publish","type":"post","link":"https:\/\/gregalder.com\/yardposts\/overhead-watering-for-evaporative-cooling-on-avocado-trees\/","title":{"rendered":"Overhead watering for evaporative cooling on avocado trees"},"content":{"rendered":"\n

\u201cDoes not the spraying of the foliage of the trees protect them to some extent in hot weather?\u201d asked J.B. McLaughlin, rhetorically. He had seen the effects of this practice for mitigating heat when he tried it during the devastating heat wave of more than a century ago, on June 14-17 of 1916<\/a>: \u201cI have 23 varieties of which only 4 were injured. I sprayed the foliage during the hot spell and only the bark on exposed trunks and limbs was injured on a few trees; the rest were not injured.\u201d<\/p>\n\n\n\n

Watering an avocado tree\u2019s canopy for evaporative cooling is not a new idea, and its benefits are undeniable. We could even guess that it works before trying it, as we know how much our own bodies are cooled down by jumping into a pool on a hot summer day.<\/p>\n\n\n\n

In 1962 an experiment was conducted to quantify these benefits, in terms of how many degrees the temperature could be reduced. Miller, Turrell, and Austin wrote in \u201cCooling Avocado Trees by Sprinkling\u201d<\/a> that \u201ctemperature reductions up to 5 and 7 degrees were obtained.\u201d<\/p>\n\n\n\n

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Fuerte avocado leaves wilting at about 112 degrees on September 5, 2020.<\/figcaption><\/figure><\/div>\n\n\n\n
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Same leaves perked up, stress relieved — as if it’s cooler outside — ten minutes after being sprayed with water.<\/figcaption><\/figure><\/div>\n\n\n\n

The goal of their experiment was to see if using overhead sprinklers for evaporative cooling could reduce the temperature sufficiently in order to prevent fruit drop from hot weather. Contemporary avocado growers using this method in their commercial orchards have reported that it can indeed totally prevent the loss of fruit during high heat. A commercial avocado grower named Matt Nelson of Temecula employed overhead sprinklers to cool his grove during the heat wave of early September 2020 and reported zero fruit drop while other avocado groves in the area had losses. (See the interview with Nelson in this video by Index Fresh<\/a>.)<\/p>\n\n\n\n

In this post I\u2019ll describe the way some commercial growers like Nelson use overhead watering, but I\u2019ll focus on how home growers can make use of it too. I\u2019ve been trying to achieve evaporative cooling in various ways on my own avocado trees ever since I first encountered the idea in Reuben Hofshi\u2019s paper from 1998 titled, \u201cDreaming in Reality.\u201d<\/a> I\u2019ve tried out some new designs in the last few years that I\u2019d like to share.<\/p>\n\n\n\n

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Four methods of overhead watering<\/strong><\/p>\n\n\n\n

For home growers, the best way to get water all over the canopies of our avocado trees in order to cool them is likely to be through holding a hose in our hands — the simplest method. When I do this, I prefer to use a shut-off valve at the end of the hose so I can adjust the volume, droplet size, and distance that the water sprays.<\/p>\n\n\n\n

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Shutoff valve for hose.<\/figcaption><\/figure><\/div>\n\n\n\n

Farmers can’t walk around with a hose spraying down hundreds of trees though. They mount sprinklers on posts between trees. Some use high volume sprinklers that shoot water far, and because of that they only need a handful of sprinklers to cover an acre of trees.<\/p>\n\n\n\n

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High volume sprinklers on risers on old Silent Ranch avocado grove in Glendora, Los Angeles County.<\/figcaption><\/figure><\/div>\n\n\n\n

Others use low volume (micro) sprinklers that only throw water up to about 30 feet so they need more sprinklers by comparison.<\/p>\n\n\n\n

I\u2019m a home grower, and most of my avocado trees are arranged in pairs or rows, not blocks. So I\u2019ve had to come up with other ways to use overhead sprinklers efficiently to cool my trees. Over the past couple years, I have been experimenting with two main ways so that I don\u2019t have to run around spraying trees with a hose.<\/p>\n\n\n\n

First, if the tree is short, less than approximately 10 feet tall, then I mount a micro-sprinkler on a post within the tree\u2019s canopy. The post might be the same one that served as a training stake when the tree was planted. Here is a Nabal avocado tree with one such setup:<\/p>\n\n\n\n

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Second, if the tree is taller, then I hang a micro-sprinkler on a branch high up in the canopy. The sprinkler is suspended at a height only a few inches above the highest leaves.<\/p>\n\n\n\n

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Sprinkler hung on branch high in canopy of Hass avocado tree.<\/figcaption><\/figure><\/div>\n\n\n\n

I got this second idea from John Rowley of Nelson Irrigation up in Washington, where such overhead sprinklers are used for cooling apples, pears, and cherries. Rowley made a video showing how to make and hang such a sprinkler, and he shows the video at 2 hours 14 minutes into the presentation here at Index Fresh Seminar 23<\/a>.<\/p>\n\n\n\n

I’ve made a few modifications from Rowley\u2019s design. One is to add a shutoff (adjustment) valve into the line that feeds the overhead sprinkler. This is for two important reasons. I can control the diameter of the sprinkler\u2019s throw, and I can turn the sprinkler off when I’m not using it. This way I can use my overhead sprinklers on the same irrigation lines as my under-tree sprinklers — I don’t have to lay a second set of pipe just for the overhead sprinklers.<\/p>\n\n\n\n

Here is what one of my designs looks like before it goes up into a tree:<\/p>\n\n\n\n

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Overhead sprinkler ready to be hung on a high branch.<\/figcaption><\/figure><\/div>\n\n\n\n

I am still refining my design and use of these sprinklers hung in large trees as well as those mounted on posts, but I\u2019ve been pleased with their performance in 2020\u2019s September extreme heat as well as in this minor heat wave that just passed last week. Here is a short video showing the two methods in use in my yard:<\/p>\n\n\n\n

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