Excessive Heat Wave

I was nervous about going on a two week vacation and leaving my precious plants to be hand watered by a kind neighbor during the hottest month of the year. Our cisterns and water barrels had long since run out of rainwater. In preparation for the trip, I started deep watering all the plants a few days ahead.  Dan had read that when the temperture is over 80 degrees that plants can't transpire, so they don't take in water. Since we don't have a drip system, I had to wait until it cooled off in the evening or early morning. I used that time to gather my Zero Waste assessories for our road trip.

For our deep watering we use a method recommended by a local arborist. Dan had drilled two small holes in five gallon buckets.  We use three buckets of water on each of our three jujube trees. It takes 20 minutes for each bucket to drain. Luckily, we have three buckets or I would have been there all night. I did that same process with our moringa, pomegranate, fig, and curry plants. The day before we left, I even watered our cactus garden, agaves, and an acacia that hadn't started to leaf yet. On the night before we left, I used the hose to slow water our Mexican Honeysuckle that usually get our sink rinse water everyday.

Meanwhile, I took pictures of our plants to include in the directions for our neighbor (which included filling the bird bath.) I didn't get much sleep that night worrying about my plants and all that water!  I guess you can call me a parachute plant parent. And I still had to plant my sweet potato slip in the morning! 

After a lovely family vacation, I finally got the nerve to text our neighbor to see how things were doing. She said the plants were doing well. She enjoyed two tasty cherry tomatos. Whew! 

When we got home three days later, I was shocked to find that Tucson was under an excessive heat warning! 

One of the tomato plants was looking pretty sad (despite having several tomatoes on it.) Our mint plant that was struggling before the trip was now dead along with some tomato volunteers. (Mint never makes it in our yard... Go figure...) Some of the leaves on our sunchokes were a little crispy.  Oddly, our moringa had flowers. Usually they get flowers after they are really big. And one of them was really struggling.

After 12 hours on the road, I stayed up late watering my emaciated plants. 

I was actually surprised to find that the sweet potato plant was flourishing with new leaves (in the compost under the bird netting cage.)

And the curry and some of the tomatoes were doing just fine. Thanks to my kind neighbor! Of course our native plants were doing great. The acacia now has leaves, and the mesquite has lots of pods. I was surprised to see how well the jujubes were doing. All three have lots of little fruit! Maybe those shiny leaves make it durable?  

Since I got home I've been kind of sleep deprived, staying up late and getting up early trying to water the plants in my garden before it reaches 80 degrees.  It was 78 degrees at 5:30 this morning! When am I supposed to water them?!! We haven't even washed our dirty clothes from the trip yet because the greywater irrigates the fig and pomegranate and we don't want to waste that water if they aren't taking it in. 

When I decided to write this blog, I figured I'd reach out to some gardening experts on Facebook.  

I heard that plants can't take in water after the temperature reaches 80 degrees. With this extreme heat way into the night, how are you watering your plants? Also, are there some plants (heritage figs and pomegranate or native trees maybe) that have adapted to take in water after 80 degrees?

Jared Kitty Katt McKinley from Spade Foot Nursury gave the best reply: 

That is an overstatement. And it’s a dangerous one because it leads people to making bad choices. One must water plants when it’s hot and dry. Plants most certainly take in water above 80°. It’s kind of ludicrous to suggest otherwise. Especially native plants that evolved with monsoon. Sometimes institutions take research done in other places and extrapolate. I would pay that advice no heed as it really doesn’t apply to our climate. Plants cool themselves off by taking in water and letting the water evaporate from their leaves. If they weren’t taking in water after 80° they would die. One can always expect some wilting and visual struggle in some plants, particularly new plants in summer. But as someone who has started countless plants in summer, I’m here to tell you that so long as you water consistently and correctly, your plant (given it’s appropriate for our climate and properly planted) will make it. For whatever it’s worth, I think it’s best to water in the morning in summer if only because you don’t want a plant to spend it’s driest hours during a hot part of the day.

Thanks, Jared! So what did I learn from all this?  That I should check with our local desert plant experts before getting sleep deprived. I think it's best to water early in the morning or late at night so the water doesn't all evaporate.  We need to get those other two cisterns installed before the big monsoon rains start! And hook up a string of clay ollas to them so they can be self watering! I'm so grateful to have native mesquites and drought adapted jujubes that do great on just the water that sinks into their catchment basins - and palo verde volunteers that shade our little garden.  

I plan to finally get a good nights sleep... well... as soon as I water the moringas. 

Larger considerations:

Planning for Urban Heat Resilience

PAS REPORT 600 BY LADD KEITH, SARA MEEROW