Deep-freezing weather in mid-January affected some native and non-native plants - but only time will tell if any saguaros or other desert dwellers will die from cold damage.
"The more tropical introductions such as Indian fig (similar to prickly pear cacti) were shattering all over town" as a result of the freeze, said Mark Dimmitt, a plant expert and former director of natural history at the Arizona-Sonora Desert Museum.
Overnight lows dropped well below freezing for several days in Tucson - including a record low of 17 degrees Jan. 15.
"I had 11 degrees in my carport, and 7 in the drainage at the bottom of my property" at one point during the cold snap, Dimmitt said. "That's 6 degrees colder than ever before in the 33 years I've been here. There may be increased saguaro mortality after this freeze."
Don Swann, a biologist at Saguaro National Park, said there was no immediate sign of freeze damage, but he added that "some saguaro mortality or damage" could show up.
NATURE OF THE FREEZE
Plant experts say this year's big chill, while severe for a desert region, might prove to be less deadly to plants than another period of severe freezing in February 2011.
Swann reported last year that the 2011 freeze killed some saguaros - especially older, more vulnerable plants. Other researchers found that the saguaro bloom was vastly reduced after the freeze.
This year, biologists say, was different.
"The difference is that we had one day in February 2011 that did not rise above freezing in many parts of Tucson during the day," Swann said. During this month's freeze, "the daytime temperatures, while cool, seem to have been generally above freezing."
Swann said research has shown that the greatest damage to saguaros comes when there is a prolonged period - 15 to 20 hours - below freezing.
"This would typically be when there is a freezing night, followed by a freezing day and then another freezing night, as we had in 2011, but not in 2013," he said.
That doesn't mean that saguaros are out of the woods, or the desert, in terms of freeze damage this year.
"We had some very low nighttime temperatures, and several cool days, so it seems possible that in some areas of the saguaro's range in the Tucson area - for example, at higher elevations or in localized shaded areas - there might have been some saguaro mortality or damage as a result," Swann said.
ABOUT YOUR PLANTS
Michael Chamberland, director of horticulture at the Tucson Botanical Gardens, had an encouraging word for people concerned about plants in their yards or gardens.
"Any plants that survived for you in 2011 will probably get through this recent freeze as well," Chamberland said.
He said that's because this month's conditions were "comparable but not quite as severe" as those in 2011.
"We had very strong winds with that freeze in 2011, and those winds had a devastating effect. We did not have the winds this year, and the daytimes rose well above freezing."
save your plantS
The Tucson Botanical Gardens website offers advice for care of plants affected by freezing weather. Go to tucsonbotanical.org and look under the "Gardening" heading for "Guidelines for Care of Frost-Damaged Plants."
Contact reporter Doug Kreutz at firstname.lastname@example.org or at 573-4192. On Twitter: @DouglasKreutz