Extreme heat in Phoenix is destroying the famous saguaro with no end in sight
After recording the warmest average monthly temperature of any U.S. city ever in July, Phoenix returned to dangerously high temperatures on Wednesday. This could mean trouble not only for people but for some plants as well.
Residents across the sprawling metro are finding that prolonged extreme heat has fried plants, and have been sharing photos and videos of damaged cacti with the Desert Botanical Garden. Nurseries and landscapers are inundated with requests for help dealing with saguaros or fruit trees that are losing their leaves.
Phones are “ringing nonstop” about everything from a cactus to a citrus tree or ficus, said Sophia Booth, a landscape designer at Moon Valley Nursery, which has nearly a dozen locations in suburban Phoenix.
“A lot of people call and say their cactus is turning really yellow, or they fell over or their arms broke, or something like that,” Booth said. “Twenty-year-old trees lose all their leaves, or they turn brittle brown.”
She advises people to give water and specialized fertilizers to the struggling tree or plant every two days and not to prune it.
Take precautions: Caring for your plants in extreme heat: When to water, and how to prevent sunburn
At the Desert Botanical Garden, three of the prized institution’s more than 1,000 saguaro cactus plants fell or lost a limb last week, a rate that officials there say is highly unusual.
These saguaros, a towering trademark of the Sonoran Desert landscape, were already stressed by record-breaking heat three years ago, and it turns out that this summer’s historic heat — the average temperature in Phoenix last month was 102.7 degrees Fahrenheit — was a cactus needle that… Break the camel’s back.
“Since 2020, we have seen higher mortality rates in our saguaro population compared to pre-2020 mortality rates,” said Kimberly McCue, the park’s chief scientific officer. “So part of our thinking is that there are still saguaros today who are at risk from what they went through in 2020. And that this may push them over the edge.”
The saguaro can live up to 200 years and reach up to 40 feet in length. Some at the Desert Botanical Garden date back to after it opened 85 years ago, and the largest is about 30 feet tall, according to McCue.
People often assume that cactus plants are made to withstand scorching heat, but even these plants can have their limitations, McCue said.
It wasn’t just the string of 31-day highs this summer of 110 degrees Fahrenheit or more, but also the multiple nights in which the low never dipped below 90 degrees. She explained that night time is when the cactus opens its pores to get rid of retained water and absorb carbon dioxide.
“With the loss of water, if they become dehydrated, it can compromise the structural integrity of their tissues,” McCue said.
The size of a cactus can also affect its susceptibility, and larger plants with more mass are more vulnerable to the effects of heat and drought, said Kevin Holten, the park’s research director.
“Larger (and older) plants have more arms and thus tend to be the first to start losing structural integrity,” Hultin said via email. “The first sign of heat-related stress in populations is shoots falling off large plants. Eventually, the entire plant may fall due to stress.”
There is hope that the arrival of thunderstorms during the monsoon, which traditionally begins on June 15, will bring more late-stage moisture that will help struggling plants. The American monsoon is characterized by a shift in wind patterns that pulls moisture from the tropical coast of Mexico. It is prepared differently in other parts of the world. In Arizona, nearly half of the year’s precipitation comes during the monsoon.
It can be a mixed bag – cooling sweltering cities like Las Vegas and Phoenix, but bringing the risk of flooding to mountain cities and low-lying deserts alike. It holds the promise of rain but does not always deliver. Even when this happens, the moisture is not evenly shared across the four-corner area and beyond. The last two seasons have been impressive, and the previous two were largely failures.
The Sonoran Desert Living Outdoor Museum in Tucson, which has already seen some monsoon activity, doesn’t have the same problems with its succulents, McCue said.
“We have the double whammy of this heat dome that seems to have decided to sit on top of Phoenix. We also have this widely spread space with freeways and parking lots,” McCoy said. However, “the story is not yet complete.”
Booth, of Moon Valley Nurseries, agrees that rain may prevent some plants and trees from reaching the point of no return. Meanwhile, nursery staff are bracing for temperatures to rise again this week.
“We’re taking a lot of precautions, especially for our farmers and people who don’t just work in the office,” Booth said. “Our yard crew, they wear long sleeves. They wear their straw hats. We make sure we have bottled water in the refrigerator at all times. We haven’t had any heat stress yet outside of this (site).”
The National Weather Service reported Wednesday that there will be no rain anytime soon. After two days of slight decline, high temperatures reached 111 degrees, and are expected to reach 110 degrees or more over the next 10 days.
There is some seasonal activity in southern and northern Arizona, but Phoenix is ”stuck in the middle,” meteorologist Matt Salerno said.
“There is still hope that the monsoon will become more active again in the middle of this month,” Salerno said.
However, there will likely be some record breaking numbers before then. The weather service plans to issue an extreme heat warning Friday through Monday, when maximum temperatures will range between 111 and 117.
Meanwhile, the Desert Botanical Garden is propagating cacti that appear better able to withstand scorching conditions after staff noticed that 2020’s heat was more challenging for some plants than others. Some seem to have a genetic makeup that allows them to thrive.
“We want to try to capture that and grow more saguaros from seed here to add to our population in the park with the idea that over time, that will bring more resilience to our population here,” McCoy said.