Heat waves make me a worried gardener. What can I do to help my plants? Should I water again? How much?
This summer of 2017 has started off with a blast of multiple heat waves for Southern California’s valleys (the beach has been spared by the presence of a marine layer). In my yard, twenty miles from the ocean in San Diego County, it was over 95 for six days June 16 through 21, and then again for three days June 25 through 27. A couple days reached over 100.
But my vegetables and fruit trees came through pretty well, save some sunburned apricots:
I believe it’s because I’ve settled on a two-part watering routine that helps the plants cope with heat waves. Here’s what I do:
First, I make a pre-emptive attack. I’m convinced that this is the most important thing to do. When a heat wave is predicted, I pre-irrigate, heavily. I learned this from Reuben Hofshi, an avocado farmer. The day before a heat wave is forecast to start, I water with enough to give all plants full moisture in the soil of their root zone, and then I add about 50% or more. So, for example, I gave my avocado and citrus trees a normal round of irrigation of three hours and 18 minutes, and then I applied an extra 50% of one hour and 39 minutes.
The idea is to make sure the trees have access to all the moisture their roots can touch. They’re totally prepared to pull up maximum amounts of water to supply their transpiring leaves in the stressful heat.
Second, I replenish the water used by some plants each day during the heat wave. I feel the need to do this for avocados and vegetables. I’ve noticed that they stress if I don’t. On the other hand, citrus and deciduous fruit trees (apricot, peach, pomegranate, plum, apple, etc.) don’t need such coddling. I don’t water them daily through a heat wave.
But for avocados and vegetables, I estimate how much water they’re using each day and replace it each day. For example, I gave my avocados 42 minutes each afternoon.
Meanwhile, for my vegetables, before the heat waves I had been watering my vegetables for 25 minutes every three days, which had been working well, and which is equal to about eight minutes per day. During the heat wave, I ran the drip lines on my vegetables for 12 minutes each day; that was my estimate of how much they needed. I came up with that time by taking the daily eight minutes and adding 50% (four minutes) since it was hotter than usual, which gave me 12 minutes.
To sum up, I pre-irrigate with at least 150% of what I think the plants need the day before the heat hits in order to be fully saturated, and then I irrigate every day during the heat with about 150% of what avocados and vegetables normally need each day in the summer.
Let me mention some factors about my specific situation and why they might make things work differently for you. My soil is sandy loam. If yours is clay, you shouldn’t need to water anything daily even in a heat wave. Also, I irrigate my vegetables with drip lines. When I used to irrigate with overhead sprinklers, I could get through heat waves without watering my vegetables daily. The sprinklers gave them larger root zones and therefore made for tougher plants.
I have always watered my deciduous fruit trees every ten days to two weeks in the summer. It is when a heat wave occurs that I’ll water every ten days; otherwise, during normal summer temperatures, it’s every two weeks. Deciduous fruit trees (and grapes) never stop surprising me by how little and infrequently they need water — while still producing oodles of great fruit. That’s why I keep planting more of them!
P.S. Apologies for the pretentious “nota bene,” but whatever, I’ll leave it in there.
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