It's so hot in Arizona's capital that not even the cactuses are surviving.
Chief Science Officer Kimberlie McCue with the Desert Botanical Garden in Phoenix says this record-breaking stretch of heat is breaking cactuses all over the state.
People think, "Oh these are desert plants so they should be just fine," McCue says. "But cactus are living things."
Like all plants, saguaro cactuses use photosynthesis but they perform their essential functions at night when it's supposed to be cooler.
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Phoenix has had a record streak of 110-degree or more days and 90-degree or more nights. On Thursday morning, the temperature in Phoenix finally dipped below 90 degrees for the first time since July 9th.
The lack of a nighttime cooldown makes it difficult for the cactuses to recover. Instead, they're "roasting."
"They literally can't function," McCue says. "The way I describe it is they start to suffocate."
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At what temperature do cactuses die?
Plant physiologists at the Desert Botanical Garden are studying how much heat cactuses can take. Until recently, the assumption was that cactuses were perfectly adapted to withstand desert conditions.
"At a certain temperature or certain length of time, they just can't do it anymore," McCue says.
Sun scorch is a warning sign that the plant is starting to shut down. You'll notice yellowing on the epidermis. If it's noticed early and shading is applied, it may be reversed.
The garden can try to throw shade cloths over them but they can be 20-30 feet tall. Once they're in bad shape, there isn't much that can be done.
Severe sunburn will cause death of the outer epidermis, which will brown and may crack, resulting in a bark-like scarring, as outlined by the University of Arizona. The wounding caused by the sunburn can be an entry point for bacteria.
Do cactuses die in the cold?
While some cactuses will survive in cold areas with temperatures as low as -20F, others cannot tolerate anything below freezing.
If a cactus plant is exposed to temperatures that are too cold for its species, it can suffer damage. The most common type of damage is called “frost scald.” This occurs when the water inside the plant’s cells freezes, expands, and bursts the cell walls.
What are other signs that a cactus is dying?
Firmness is a good sign. If it's soft or squishy that is an indicator that it's in bad shape and likely won't be able to hold itself up much longer.
If it has started to tilt, that probably means it's on its way to falling over.
"If that plant is really starting to shut down, it doesn't matter how much water you pour on them," McCue says. "They won't be able to take it up and do anything with it."
